Density is a fundamental physical property that can be used in conjunction with other properties to characterize crude oil sand other substances present in crude oil emulsions. It is useful when the hydrodynamics of emulsion droplets are discussed and can also help to investigate impact of particle collisions. Digital density analyzer was used to measure the densities in this study according to ASTM D5002. The density is measured with a U-shaped hollow glass tube, which is put into oscillation. The oscillation frequency of the tube filled with the sample is measured. The higher weight of the sample the lower the frequency. The density is calculated with the measured frequency. The density values of the crude oil, castor oil, fresh water, and two brine solutions (20 and 40 g/L) were obtained at room temperature, 50 and 70°C. Viscous force is an important phenomenon that prevents emulsion droplets from falling free when suspended in fluids. Standard method ASTM D445 was used to measure the viscosity of the crude oil. The EV 1000 instrument was used and it is based on a simple and reliable electromagnetic concept. Two coils move the piston back and forth magnetically at a constant force which could be likened to the movement of emulsion droplets under hydrodynamic and gravitational forces.

#### **3.5. Refractive index and interfacial tension measurements**

Dissolution of salts (e.g. NaCl) in water involves a process whereby Na+ and Cl− break free from the crystal-lattice structure of the solid. This process can be captured by examining the optical density of the aqueous solution. The index of refraction value of a material is a number that indicates the number of times slower that a light wave would be in that material than it is in a vacuum. A vacuum is given an *n* value of 1.0000. The *n* values of other materials are calculated from Eq. (4):

$$m\_{material} = \frac{3.00 \ast 10^8 \, m/s}{V\_{material}} \tag{4}$$

Refractometer with the aid of a light-emitting diode, a sapphire prism and a high-resolution optical sensor is used to measure the refractive index. The sample is put on the prism and the measurement started. From a certain angle of incidence—the so-called critical angle—the ray no longer penetrates the sample but is fully reflected from its surface and is detected by the optical sensor. The refractive index is calculated from this critical angle. Emulsification is affected by interfacial tension and the separating potential between two or more phases. Interfacial tension is the work done to expand the interface between two non-mixing adjacent phases. At the separating boundary, the sum of cohesive forces is greater than the adhesive forces between the two phases. Accordingly, molecules at the interface have fewer attractive interacting partners than in the bulk phase. The phases therefore form the smallest possible interface without the action of external force.

Work must be done to expand the interface. Hence, cohesive and adhesive forces are critical to interfacial tension. The interfacial tension (IFT) of the crude oil in fresh water and the prepared brine solutions was determined using the spinning drop tensiometer. A horizontal capillary filled with a bulk phase and a drop phase is set in rotation. The diameter of the drop which is elongated by centrifugal force correlates with the interfacial tension. When a heavy bulk phase and a light drop phase are situated in a horizontal, rotating capillary, the drop radius perpendicular to the axis of rotation depends on the interfacial tension γ between the phases, the angular frequency ω of the rotation and the density difference Δρ. Thus, with a given speed of rotation and with known densities of the two phases, the interfacial tension can be calculated from the measured drop diameter d (=2r) in accordance with Vonnegut's equation:

$$\gamma = -\frac{r^3 \omega^2 \Delta \rho}{4} \tag{5}$$

#### **3.6. Emulsion samples preparation**

Asphaltene was removed by diluting the crude oil with n-heptane using a standard method prescribed in ASTM D3279 since asphaltenes are insoluble in liquid paraffins. The remaining components, saturates, aromatics and resins collectively known as maltenes are separated by polarities using ASTM D6591. The maltene with heptane was pumped through a chromatographic packed column of Agilent 1260 Infinity equipment for separation. The column contains silica and amine which have more affinity to more polar components. Resins which are the most polar of the maltenes are adsorbed on the column earlier thereby limiting heptane from pushing them through. Both the saturates and aromatics are pushed through the column by heptane but saturates would flow pass quicker due to their less polar nature. Thus, saturates are detected by the Refractive Index Detector (RID) of the equipment at a shorter time (retention time) than the aromatics which are more polar. The eluent (heptane) was replaced with Dichloromethane (DCM) to push out the resins using back flush since the resins are stuck near the top end of the column. Ultraviolet (UV) signals also record retention time for UV active components. In this

case, only the aromatics are UV active and UV will only confirm the results of RID.

**3.5. Refractive index and interfacial tension measurements**

*nmaterial* = 3.00 ∗ 10 \_\_\_\_\_\_\_\_\_\_\_ 8 *m*/*s*

Dissolution of salts (e.g. NaCl) in water involves a process whereby Na+

from the crystal-lattice structure of the solid. This process can be captured by examining the optical density of the aqueous solution. The index of refraction value of a material is a number that indicates the number of times slower that a light wave would be in that material than it is in a vacuum. A vacuum is given an *n* value of 1.0000. The *n* values of other materials are

Refractometer with the aid of a light-emitting diode, a sapphire prism and a high-resolution optical sensor is used to measure the refractive index. The sample is put on the prism and

*Vmaterial*

and Cl−

break free

(4)

Density is a fundamental physical property that can be used in conjunction with other properties to characterize crude oil sand other substances present in crude oil emulsions. It is useful when the hydrodynamics of emulsion droplets are discussed and can also help to investigate impact of particle collisions. Digital density analyzer was used to measure the densities in this study according to ASTM D5002. The density is measured with a U-shaped hollow glass tube, which is put into oscillation. The oscillation frequency of the tube filled with the sample is measured. The higher weight of the sample the lower the frequency. The density is calculated with the measured frequency. The density values of the crude oil, castor oil, fresh water, and two brine solutions (20 and 40 g/L) were obtained at room temperature, 50 and 70°C. Viscous force is an important phenomenon that prevents emulsion droplets from falling free when suspended in fluids. Standard method ASTM D445 was used to measure the viscosity of the crude oil. The EV 1000 instrument was used and it is based on a simple and reliable electromagnetic concept. Two coils move the piston back and forth magnetically at a constant force which could be likened to the movement of emulsion droplets under hydrodynamic and gravitational forces.

**3.4. Density measurement**

88 Science and Technology Behind Nanoemulsions

calculated from Eq. (4):

The kinetics of emulsion stability involves considerations on droplets interactions in the crude oil. The intra-actions within the droplets that are responsible for the droplets' momentum are also important. Thus, fresh water and brine solution formed droplets were examined in this study. Water-in-oil emulsions were prepared by mixing crude oil with fresh water and synthetic brine solutions in turn (volume/volume). Two brine solutions were prepared by diluting 20 grams and 40 grams of NaCl in a liter of distilled water to make 20 and 40 g/L aqueous solutions respectively. 20, 40 and 50 ml of fresh water were mixed with 80, 60 and 50 ml of crude oil respectively to make 20, 40 and 50% fresh water-in-crude oil emulsions. Similarly, 20, 40 and 50% brinein-crude oil emulsions were prepared. These water cuts were chosen to capture the significance of droplets interactions in the crude oil since lower water cuts might defy resolution with the about-to-be tested demulsifiers. The two phases were homogenized using Hamilton constant mixer. No external emulsifier was used since the aim was to achieve natural emulsifier-stabilized emulsions. Agitation was allowed to take place for 5 minutes to achieve stable emulsions. About 100 ml of emulsion was prepared at a time for uniformity and repeatability purpose.

#### **3.7. Emulsion stability measurement**

Measuring the ability of a solution to conduct electric current is a crucial step in determining the presence of interfacial films especially when the phases involved have non-similar electrical conductivity values. Sulaimon and Bamikole [34] used the Turbiscan classic MA 2000 to investigate the effect of stability on the aging of water-in-oil (w/o) emulsions for proper characterization and resolution. They concluded that the Turbiscan is a robust, accurate and automatic multiple light scattering technique for characterizing w/o emulsion stability. Through this method, the concentration of ions in brine solutions can be determined. The presence of interfacial films can easily be noted since crude oil does not conduct electricity. The effect of temperature on the conductivity of materials is significant. Conductivity measurements are taken at 25°C since the ionic activity increases with temperature. The electrical conductivity of the fresh water, two brine solutions, crude oil and the resulting emulsions were measured an electrical conductivity meter.

overcome to do so. Perhaps, all the particles in the crude oil responded uniformly to tempera-

**SAL-0 SAL-1 SAL-2 CRO**

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water molecules. Water molecules possess low kinetic energy and therefore prevented the salt ions from fully responding to temperature change. The ions, therefore, assumed the kinetic

There was a corresponding decrease in viscosity with temperature due to easier movement of particles at elevated temperature. At low temperature, the particles are closely-packed, and their movement is restricted. Some components of the crude oil such as waxes are dissolved back into the bulk crude oil at higher temperature than their cloud points and thereby leaving other components which are resistant to heat such as asphaltene particles to move more freely. This phenomenon brings about easy flow of fluid and any other particle such as water droplets, introduced into the crude oil would move more freely and interact with the asphaltene particles. The SARA content of the crude oil is presented in **Table 2**. The crude oil

Interfacial tension (IFT) of the crude oils SAL-0, SAL-1 and SAL-2 are presented in **Table 3**. Obviously, IFT decreases with temperature and it is highest in SAL-0 and lowest in SAL-1. Theoretically, IFT is a function of pressure, temperature and composition. The pressure exerted on the interfacial films was highest in SAL-1 and lowest in SAL-0 due to salt particles solvation forces acting in the aqueous solutions. The pressure is reduced in SAL-2 due to less collision impacts of the particles caused by incomplete solvation. Hence, the work required to break the interfacial films encapsulating resulting emulsion droplets would be highest for

and Cl−

in

91

ture change. Dissociation of sodium chloride in water leads to encapsulation of Na+

1 25 0.99704 1.0138 1.0258 0.9079 2 50 0.98803 1.0048 1.0163 0.8909 3 70 0.97776 0.9972 1.0083 0.8767

**C) Density (g/cc)**

**4.2. Effects of** *SMES* **on the intermolecular interactions and emulsion stability**

energy of the water molecules.

**S/N Temperature (o**

**Table 1.** Sample density.

contained 2.09% asphaltenes and 26.3% resins.

SAL-0 and least for SAL-1 droplets.

**Table 2.** SARA content of the crude oil.

**Component Amount (%)**

Asphaltene 2.09 Resin 26.30 Saturate 53.21 Aromatics 18.40

Measuring cylinders, 10 ml, were filled with emulsions and incubated in an oven at 25, 50 and 70°C for 5 days. Thereafter, the cylinders were removed, and the amount of separated water was recorded. This test was carried out using emulsions with all salinities and water cuts. Turbiscan classic MA 2000 was used to monitor the rate of sedimentation, flocculation and coalescence to determine the degree of stability of each emulsion composition formed. The testing tube was filled with 10 ml of emulsion and 10 acquisitions were made at room temperature. The autoscan was set to obtain a scan acquisition at every 2 minutes. Subsequently, the emulsions were heated to 50 and 70°C for 6 hours in a water bath and 10 acquisitions were also made at 2 minutes interval for comparison. Understanding the impact of collisions among emulsion droplets is important to study the destabilization of crude oil emulsions. Rotational viscometer was used to measure the deformation of the emulsion droplets under shearing forces. Rotational rheometry is most suited to very low shear rate / viscosity measurement, determining changes in structural properties via low amplitude and controlled strain oscillatory measurements. Double-gap plate was used since it has highest sensitivity for low viscous samples, lower inertia compared to other plates, nearly no impact on loading errors. The rheology was measured at 25, 50 and 70°C and the shear rate was varied from 1 to 1000 per second.

## **4. Results and discussion**

#### **4.1. Density and SARA analysis**

The crude oil originally contained 0.2% water. This shows that the crude oil was within the specified limit of BS&W. Removing this intrinsic water content is difficult and may not be achieved with current dehydration techniques. Then, the crude oil (CO) was considered dry. The crude oil was then mixed with fresh water (SAL-0), 20,000 ppm aqueous solution of NaCl (SAL-1) and 40,000 ppm aqueous solution of NaCl (SAL-2) for this work. There exists a proportionate increase in density according to salt content in water as shown in **Table 1** since total pressure corresponds to the amount or number of particles present in the system. Solvation of NaCl crystal in water produced Na+ and Cl− (ions) surrounded by water molecules and the ions gained energy to move more freely. An increase in the number of salt particles led to more frequent collisions in the system. Obviously, fresh water has the lowest density while 40,000 ppm brine has the highest density. This observation can be explained by the amount of the average kinetic energy possessed by the particles in the liquids [35]. The particles in the crude oil gained more kinetic energy to move faster since there is no difficult barrier to

**Table 1.** Sample density.

investigate the effect of stability on the aging of water-in-oil (w/o) emulsions for proper characterization and resolution. They concluded that the Turbiscan is a robust, accurate and automatic multiple light scattering technique for characterizing w/o emulsion stability. Through this method, the concentration of ions in brine solutions can be determined. The presence of interfacial films can easily be noted since crude oil does not conduct electricity. The effect of temperature on the conductivity of materials is significant. Conductivity measurements are taken at 25°C since the ionic activity increases with temperature. The electrical conductivity of the fresh water, two brine solutions, crude oil and the resulting emulsions were measured

Measuring cylinders, 10 ml, were filled with emulsions and incubated in an oven at 25, 50 and 70°C for 5 days. Thereafter, the cylinders were removed, and the amount of separated water was recorded. This test was carried out using emulsions with all salinities and water cuts. Turbiscan classic MA 2000 was used to monitor the rate of sedimentation, flocculation and coalescence to determine the degree of stability of each emulsion composition formed. The testing tube was filled with 10 ml of emulsion and 10 acquisitions were made at room temperature. The autoscan was set to obtain a scan acquisition at every 2 minutes. Subsequently, the emulsions were heated to 50 and 70°C for 6 hours in a water bath and 10 acquisitions were also made at 2 minutes interval for comparison. Understanding the impact of collisions among emulsion droplets is important to study the destabilization of crude oil emulsions. Rotational viscometer was used to measure the deformation of the emulsion droplets under shearing forces. Rotational rheometry is most suited to very low shear rate / viscosity measurement, determining changes in structural properties via low amplitude and controlled strain oscillatory measurements. Double-gap plate was used since it has highest sensitivity for low viscous samples, lower inertia compared to other plates, nearly no impact on loading errors. The rheology was measured at 25, 50 and 70°C and the shear rate was varied from 1 to 1000 per second.

The crude oil originally contained 0.2% water. This shows that the crude oil was within the specified limit of BS&W. Removing this intrinsic water content is difficult and may not be achieved with current dehydration techniques. Then, the crude oil (CO) was considered dry. The crude oil was then mixed with fresh water (SAL-0), 20,000 ppm aqueous solution of NaCl (SAL-1) and 40,000 ppm aqueous solution of NaCl (SAL-2) for this work. There exists a proportionate increase in density according to salt content in water as shown in **Table 1** since total pressure corresponds to the amount or number of particles present in the system. Solvation

and Cl−

ions gained energy to move more freely. An increase in the number of salt particles led to more frequent collisions in the system. Obviously, fresh water has the lowest density while 40,000 ppm brine has the highest density. This observation can be explained by the amount of the average kinetic energy possessed by the particles in the liquids [35]. The particles in the crude oil gained more kinetic energy to move faster since there is no difficult barrier to

(ions) surrounded by water molecules and the

an electrical conductivity meter.

90 Science and Technology Behind Nanoemulsions

**4. Results and discussion**

**4.1. Density and SARA analysis**

of NaCl crystal in water produced Na+

overcome to do so. Perhaps, all the particles in the crude oil responded uniformly to temperature change. Dissociation of sodium chloride in water leads to encapsulation of Na+ and Cl− in water molecules. Water molecules possess low kinetic energy and therefore prevented the salt ions from fully responding to temperature change. The ions, therefore, assumed the kinetic energy of the water molecules.

There was a corresponding decrease in viscosity with temperature due to easier movement of particles at elevated temperature. At low temperature, the particles are closely-packed, and their movement is restricted. Some components of the crude oil such as waxes are dissolved back into the bulk crude oil at higher temperature than their cloud points and thereby leaving other components which are resistant to heat such as asphaltene particles to move more freely. This phenomenon brings about easy flow of fluid and any other particle such as water droplets, introduced into the crude oil would move more freely and interact with the asphaltene particles. The SARA content of the crude oil is presented in **Table 2**. The crude oil contained 2.09% asphaltenes and 26.3% resins.

#### **4.2. Effects of** *SMES* **on the intermolecular interactions and emulsion stability**

Interfacial tension (IFT) of the crude oils SAL-0, SAL-1 and SAL-2 are presented in **Table 3**. Obviously, IFT decreases with temperature and it is highest in SAL-0 and lowest in SAL-1. Theoretically, IFT is a function of pressure, temperature and composition. The pressure exerted on the interfacial films was highest in SAL-1 and lowest in SAL-0 due to salt particles solvation forces acting in the aqueous solutions. The pressure is reduced in SAL-2 due to less collision impacts of the particles caused by incomplete solvation. Hence, the work required to break the interfacial films encapsulating resulting emulsion droplets would be highest for SAL-0 and least for SAL-1 droplets.

**Table 2.** SARA content of the crude oil.

**Table 3.** Interfacial tension of the crude oil.

The cohesive forces among molecules of fresh water are strong since there is no presence foreign material present. Fresh water tends to maintain a surface area that is as small as possible when in contact with crude oil due to their immiscibility and an interfacial tension will be maintained between the two liquids. Owing to the presence of the "surface active" component (asphaltenes) in the crude oil, its molecules will tend to be oriented between the two faces with the polar ends in the polar phase and the non-polar ends in the non-polar phase, which will lower interfacial tension.

The cohesion between the water molecules reduces when NaCl is introduced due to the solvation process. Both Na+ and Cl− are surrounded by water molecules and thereby causing the molecules to move faster and collide more freely with the wall of the container. The pressure generated due to collisions leads to the tendency of SAL-1 maintaining lower IFT than fresh water. However, increase the salinity leads to higher adhesive forces among the particles of the salt and water molecules. The molecules are more packed in SAL-2 due to more NaCl molecules compared to the particles in SAL-1. Thus, more particles led to closer packing and lesser particle movement and collision since the particles tend towards the water molecules for solvation. Lesser pressure is therefore mounted on the wall of the container which resulted in higher IFT for SAL-2 as against that of SAL-1. Meanwhile, the IFT of SAL-0 is the highest since the cohesive forces in SAL-0 is greater than the adhesive forces in both SAL-1 and SAL-2. There was a great reduction in the IFT's when 50,000 and 150,000 ppm of Sodium Methyl-Ester Sulfonate (*SMES*) were added to the crude oil. However, SAL-1 droplets had higher IFT than SAL-2. At 50000 ppm shown in **Figure 3**, higher temperature (70°C) led to higher IFT of the mix in SAL-0 and SAL-2. This phenomenon was reversed when 150,000 ppm of *SMES* was added to the crude oil (**Figure 4**). The IFT of the crude in SAL-1 became higher at 70°C.

in SAL-1 due to agitation and thereby leading to higher IFT at 70°C since the interfacial film was made up of more polar components in the crude oil. The critical micelle concentration is

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93

Three important properties of the emulsions formed were determined to gain insight into their behavior under different conditions. They are described in the following subsections. **Table 4** presents the electrical conductivities of the crude oil, SAL-0, SAL-1, SAL-2 and those of the resulting emulsions. The results show that electrical conductivity increased with salinity. The zero conductivity of the emulsions is an indication that the electrode of the conductivity meter could only contact the continuous phase and thereby giving the electrical conductivity of the crude oil as that of the emulsions. Hence, the SAL-0, SAL-1 and SAL-2 droplets were encapsulated by the natural emulsifiers in the crude oil. Interfacial films were

The kinetics of emulsion stability was studied by monitoring the behavior of the emulsions under the three different destabilization mechanisms: coalescence, flocculation, sedimentation. The following sub-subsections describe the results. Bottle tests gave no visible phase

therefore, confirmed to be present and all the emulsions formed were water-in-oil.

approximately 60,000 ppm irrespective of salinity and temperature.

**Figure 3.** Critical micelle concentration of *SMES* at 50°C.

**Figure 4.** Critical micelle concentration of *SMES* at 70°C.

*SMES* preferentially migrated to the interface and caused lower IFT since it has more affinity to water molecules than the polar components of the crude oil. This follows the work of [36] where it was confirmed that demulsifiers are interfacially active and thus, replace weakly adsorbed natural emulsifiers. Subsequently, the droplets gained energy and interacted with the particles in the crude oil when the temperature was raised. The *SMES* molecules exhausted and thereby supported by the polar components of the crude oil. The effect of temperature was significant in SAL-1 since its initial momentum allowed it used up all the *SMES* molecules and attracted the polar components. Therefore, temperature effect dominated the events at 70°C. Increase in the concentration of *SMES* in the system prevented the polar components from taking significant impact in the interactions. However, dissolution of *SMES* was faster Effects of Interfacial Tension Alteration on the Destabilization of Water-Oil Emulsions http://dx.doi.org/10.5772/intechopen.74769 93

**Figure 3.** Critical micelle concentration of *SMES* at 50°C.

The cohesive forces among molecules of fresh water are strong since there is no presence foreign material present. Fresh water tends to maintain a surface area that is as small as possible when in contact with crude oil due to their immiscibility and an interfacial tension will be maintained between the two liquids. Owing to the presence of the "surface active" component (asphaltenes) in the crude oil, its molecules will tend to be oriented between the two faces with the polar ends in the polar phase and the non-polar ends in the non-polar phase,

50 13.9248 9.3770 11.6847 70 9.2829 5.3807 8.7446

**Crude oil SAL-0 SAL-1 SAL-2**

The cohesion between the water molecules reduces when NaCl is introduced due to the solva-

molecules to move faster and collide more freely with the wall of the container. The pressure generated due to collisions leads to the tendency of SAL-1 maintaining lower IFT than fresh water. However, increase the salinity leads to higher adhesive forces among the particles of the salt and water molecules. The molecules are more packed in SAL-2 due to more NaCl molecules compared to the particles in SAL-1. Thus, more particles led to closer packing and lesser particle movement and collision since the particles tend towards the water molecules for solvation. Lesser pressure is therefore mounted on the wall of the container which resulted in higher IFT for SAL-2 as against that of SAL-1. Meanwhile, the IFT of SAL-0 is the highest since the cohesive forces in SAL-0 is greater than the adhesive forces in both SAL-1 and SAL-2. There was a great reduction in the IFT's when 50,000 and 150,000 ppm of Sodium Methyl-Ester Sulfonate (*SMES*) were added to the crude oil. However, SAL-1 droplets had higher IFT than SAL-2. At 50000 ppm shown in **Figure 3**, higher temperature (70°C) led to higher IFT of the mix in SAL-0 and SAL-2. This phenomenon was reversed when 150,000 ppm of *SMES* was added to the crude oil (**Figure 4**). The IFT of the crude in SAL-1 became higher at 70°C. *SMES* preferentially migrated to the interface and caused lower IFT since it has more affinity to water molecules than the polar components of the crude oil. This follows the work of [36] where it was confirmed that demulsifiers are interfacially active and thus, replace weakly adsorbed natural emulsifiers. Subsequently, the droplets gained energy and interacted with the particles in the crude oil when the temperature was raised. The *SMES* molecules exhausted and thereby supported by the polar components of the crude oil. The effect of temperature was significant in SAL-1 since its initial momentum allowed it used up all the *SMES* molecules and attracted the polar components. Therefore, temperature effect dominated the events at 70°C. Increase in the concentration of *SMES* in the system prevented the polar components from taking significant impact in the interactions. However, dissolution of *SMES* was faster

are surrounded by water molecules and thereby causing the

which will lower interfacial tension.

**Temp (°C) IFT (mN/m)**

92 Science and Technology Behind Nanoemulsions

**Table 3.** Interfacial tension of the crude oil.

and Cl−

tion process. Both Na+

**Figure 4.** Critical micelle concentration of *SMES* at 70°C.

in SAL-1 due to agitation and thereby leading to higher IFT at 70°C since the interfacial film was made up of more polar components in the crude oil. The critical micelle concentration is approximately 60,000 ppm irrespective of salinity and temperature.

Three important properties of the emulsions formed were determined to gain insight into their behavior under different conditions. They are described in the following subsections. **Table 4** presents the electrical conductivities of the crude oil, SAL-0, SAL-1, SAL-2 and those of the resulting emulsions. The results show that electrical conductivity increased with salinity. The zero conductivity of the emulsions is an indication that the electrode of the conductivity meter could only contact the continuous phase and thereby giving the electrical conductivity of the crude oil as that of the emulsions. Hence, the SAL-0, SAL-1 and SAL-2 droplets were encapsulated by the natural emulsifiers in the crude oil. Interfacial films were therefore, confirmed to be present and all the emulsions formed were water-in-oil.

The kinetics of emulsion stability was studied by monitoring the behavior of the emulsions under the three different destabilization mechanisms: coalescence, flocculation, sedimentation. The following sub-subsections describe the results. Bottle tests gave no visible phase

**Table 4.** Electrical conductivity.

separation after the test period (5 days). Opacity was the only justification possible from the bottle tests to show that no coalescence occurred. This observation was common to all the emulsions formed and tested. While it was correct to ascertain that the emulsions were all stable due to absence of coalescence, there was no evidence to show there was no sedimentation and flocculation of the droplets. There was zero percent transmission for the entire column of the testing tube occupied by the emulsions. Zero transmission was an indication of opacity of the emulsions which confirmed the results obtained from the bottle tests. Back scattering profiles were then used for stability analysis.

The stability profiles of the emulsions were obtained for water-in-crude oil emulsions formed with SAL-0, SAL-1 and SAL-2 at 20, 40 and 50% water cuts i.e. SAL-0E20, SAL-0E40, SAL-0E50, SAL-1E20, SAL-1E40, SAL-1E50, SAL-2E20, SAL-2E40 and SAL-E50. All the emulsions were kinetically stable since the droplets remained highly dispersed and no appreciable change over an extended period. The droplets dispersed in an equilibrium manner. Thus, the repulsive forces impeding the aggregation of the emulsion droplets were sufficiently high. Elevated temperature reduced the continuous phase viscosity and enhanced force of gravity to dominate the stability process through sedimentation. The attractive forces between emulsion droplets might lead to constantly structured arrangement with stable phase. There was no observed cohesion of droplets (flocculation) in the tested emulsions. Flocculation might lead to bigger droplets which would facilitate sedimentation and disrupt phase stability leading to subsequent coalescence. Hence, aggregative stability was observed due to the ability of the emulsions to maintain the dispersion and segregation of the droplets. In aggregates, despite mobility alteration, the droplets probably remained as such for a period after which they could fuse extemporaneously with weakening phase interfacial capacity if destabilization techniques are applied. The Coalescence, that is, merging of droplets never occurred in any of the emulsions tested.

Crude oil is a Newtonian fluid as shown in the measured shear stress against shear rate. Approximately, its viscosity decreases with temperature but remains constant with shear rate. **Figures 5**–**7** show the rheology profiles of the crude oil (CRO) and effects of water cuts on the rheological behavior of the crude oil. It is shown that the water cuts change the rheological properties of crude oil by deviating from Newtonian fluid to non-Newtonian depending on the amount of water present in it. Emulsions are pseudo plastic or shear-thinning fluids. They have lower apparent viscosity at higher shear rates. According to Chhabra [37], pseudo plastic fluid is generally supposed that the large molecular chains tumble at random and affect large

volumes of fluid under low shear, but that they gradually align themselves in the direction of

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The effect of salinity on the rheological behavior exhibited by the emulsions is shown in **Figures 8**–**10**. Shear stress became highest on the emulsions of SAL-1 at higher water cuts. This behavior can be explained by considering the impact of droplet collisions with the emulsions.

increasing shear and produce less resistance.

**Figure 7.** Rheological profile of brine (40 g/L salinity)-crude oil emulsions at 25°C.

**Figure 6.** Rheological profile of brine (20 g/L salinity)-crude oil emulsions at 25°C.

**Figure 5.** Rheological profile of fresh water-crude oil emulsions at 25°C.

Effects of Interfacial Tension Alteration on the Destabilization of Water-Oil Emulsions http://dx.doi.org/10.5772/intechopen.74769 95

**Figure 5.** Rheological profile of fresh water-crude oil emulsions at 25°C.

separation after the test period (5 days). Opacity was the only justification possible from the bottle tests to show that no coalescence occurred. This observation was common to all the emulsions formed and tested. While it was correct to ascertain that the emulsions were all stable due to absence of coalescence, there was no evidence to show there was no sedimentation and flocculation of the droplets. There was zero percent transmission for the entire column of the testing tube occupied by the emulsions. Zero transmission was an indication of opacity of the emulsions which confirmed the results obtained from the bottle tests. Back scattering

The stability profiles of the emulsions were obtained for water-in-crude oil emulsions formed with SAL-0, SAL-1 and SAL-2 at 20, 40 and 50% water cuts i.e. SAL-0E20, SAL-0E40, SAL-0E50, SAL-1E20, SAL-1E40, SAL-1E50, SAL-2E20, SAL-2E40 and SAL-E50. All the emulsions were kinetically stable since the droplets remained highly dispersed and no appreciable change over an extended period. The droplets dispersed in an equilibrium manner. Thus, the repulsive forces impeding the aggregation of the emulsion droplets were sufficiently high. Elevated temperature reduced the continuous phase viscosity and enhanced force of gravity to dominate the stability process through sedimentation. The attractive forces between emulsion droplets might lead to constantly structured arrangement with stable phase. There was no observed cohesion of droplets (flocculation) in the tested emulsions. Flocculation might lead to bigger droplets which would facilitate sedimentation and disrupt phase stability leading to subsequent coalescence. Hence, aggregative stability was observed due to the ability of the emulsions to maintain the dispersion and segregation of the droplets. In aggregates, despite mobility alteration, the droplets probably remained as such for a period after which they could fuse extemporaneously with weakening phase interfacial capacity if destabilization techniques are applied. The

Coalescence, that is, merging of droplets never occurred in any of the emulsions tested.

Crude oil is a Newtonian fluid as shown in the measured shear stress against shear rate. Approximately, its viscosity decreases with temperature but remains constant with shear rate. **Figures 5**–**7** show the rheology profiles of the crude oil (CRO) and effects of water cuts on the rheological behavior of the crude oil. It is shown that the water cuts change the rheological properties of crude oil by deviating from Newtonian fluid to non-Newtonian depending on the amount of water present in it. Emulsions are pseudo plastic or shear-thinning fluids. They have lower apparent viscosity at higher shear rates. According to Chhabra [37], pseudo plastic fluid is generally supposed that the large molecular chains tumble at random and affect large

profiles were then used for stability analysis.

**Material Electrical conductivity (μS/cm)**

Crude oil 0 SAL-0 0.23 SAL-1 844 SAL-2 1665 All emulsions 0

94 Science and Technology Behind Nanoemulsions

**Table 4.** Electrical conductivity.

**Figure 6.** Rheological profile of brine (20 g/L salinity)-crude oil emulsions at 25°C.

**Figure 7.** Rheological profile of brine (40 g/L salinity)-crude oil emulsions at 25°C.

volumes of fluid under low shear, but that they gradually align themselves in the direction of increasing shear and produce less resistance.

The effect of salinity on the rheological behavior exhibited by the emulsions is shown in **Figures 8**–**10**. Shear stress became highest on the emulsions of SAL-1 at higher water cuts. This behavior can be explained by considering the impact of droplet collisions with the emulsions.

**Figure 8.** Rheological behavior of emulsions with 20% water cut at 25°C.

temperature irrespective of salinity. Obviously, SAL-2E20was most viscous but the viscosity dropped fastest with shear rate. Droplets of SAL-2E20contained ions that were more closely packed than those in SAL-1 droplets and required more work to break them. Also, SAL-0 droplets possess greater cohesive forces than the adhesive forces of SAL-1. Corresponding amount of energy was required to overcome these binding forces within the emulsion droplets. At increased shear rate, the frequency at which the droplets collided with each other and with the wall of their container increased. Denser droplets broke more often than less dense ones due to the intensity of the collision impact. The slopes of the rheology profile assumed approximately equal and constant values at elevated temperature since all droplets had reached the minimum size that could be broken by the shearing forces. Thus, the emulsions tend to assume the

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The frequency of droplet collisions increased at 40% water cut due to a reduction in the distance between the droplets and therefore, leading to greater impact. The closeness of the droplets was responsible for the higher amount of shearing force required to overcome the resistance to flow of the emulsions. Hence, all the emulsions became more viscous than the emulsions at 20% water cut as shown in **Figure 12**. Droplet breakage occurred according to the molecular packing of the salt particles and water molecules. Droplets of SAL-2E40 broke fastest at lesser force due to highest density and collision impact. However, the slope of SAL-1E40 plot was higher due to high rate of deformation since the first collision impact. Emulsions with SAL-0E40 and SAL-2E40 required equal amount of energy to flow at the beginning of the shearing process. They had equal viscosity of 1630 cP each at 52500001/s due to similar collision intensity. However, they had unequal slope which eventually led to different but close viscosity values of 742 cP and 756 cP at 1000 1/s respectively. SAL-2E40 droplets broke down quicker since the product of the binding forces within SAL-2E40 was lesser that that in SAL-0E40. The droplets continued to break until the critical breaking size was achieved and the shearing force equaled to that required by the original crude oil. Thus, the emulsions tend to assume Newtonian

The viscosity versus shear rate profiles of the emulsions at 50% water cut at the three test temperatures are shown in **Figure 13**. Increased water cut led to reduction in the distance between the droplets and thus, required greater shearing force. Further reduction in the

Newtonian behavior of the continuous phase.

**Figure 11.** Rheological behavior of emulsions with 20% water cut at 70°C.

behavior with shear rate and temperature.

**Figure 9.** Rheological behavior of emulsions with 40% water cut at 25°C.

**Figure 10.** Rheological behavior of emulsions with 50% water cut at 25°C.

The amount of shear stress developed was dependent on the average kinetic energy of such droplets. At higher water cuts (40 and 50%), SAL-1 emulsions contained freer droplets that collide faster with higher impact due to shorter distance between the droplets. At lower water cut (20%), the viscous force within the continuous phase restricted the collision impact.

**Figure 11** shows the changes in viscosity with shear rate at 70°C and different temperature and brine salinity for emulsions with 20% water cut. All the emulsions were non-Newtonian at room Effects of Interfacial Tension Alteration on the Destabilization of Water-Oil Emulsions http://dx.doi.org/10.5772/intechopen.74769 97

**Figure 11.** Rheological behavior of emulsions with 20% water cut at 70°C.

The amount of shear stress developed was dependent on the average kinetic energy of such droplets. At higher water cuts (40 and 50%), SAL-1 emulsions contained freer droplets that collide faster with higher impact due to shorter distance between the droplets. At lower water cut (20%), the viscous force within the continuous phase restricted the collision impact.

**Figure 8.** Rheological behavior of emulsions with 20% water cut at 25°C.

96 Science and Technology Behind Nanoemulsions

**Figure 9.** Rheological behavior of emulsions with 40% water cut at 25°C.

**Figure 10.** Rheological behavior of emulsions with 50% water cut at 25°C.

**Figure 11** shows the changes in viscosity with shear rate at 70°C and different temperature and brine salinity for emulsions with 20% water cut. All the emulsions were non-Newtonian at room temperature irrespective of salinity. Obviously, SAL-2E20was most viscous but the viscosity dropped fastest with shear rate. Droplets of SAL-2E20contained ions that were more closely packed than those in SAL-1 droplets and required more work to break them. Also, SAL-0 droplets possess greater cohesive forces than the adhesive forces of SAL-1. Corresponding amount of energy was required to overcome these binding forces within the emulsion droplets. At increased shear rate, the frequency at which the droplets collided with each other and with the wall of their container increased. Denser droplets broke more often than less dense ones due to the intensity of the collision impact. The slopes of the rheology profile assumed approximately equal and constant values at elevated temperature since all droplets had reached the minimum size that could be broken by the shearing forces. Thus, the emulsions tend to assume the Newtonian behavior of the continuous phase.

The frequency of droplet collisions increased at 40% water cut due to a reduction in the distance between the droplets and therefore, leading to greater impact. The closeness of the droplets was responsible for the higher amount of shearing force required to overcome the resistance to flow of the emulsions. Hence, all the emulsions became more viscous than the emulsions at 20% water cut as shown in **Figure 12**. Droplet breakage occurred according to the molecular packing of the salt particles and water molecules. Droplets of SAL-2E40 broke fastest at lesser force due to highest density and collision impact. However, the slope of SAL-1E40 plot was higher due to high rate of deformation since the first collision impact. Emulsions with SAL-0E40 and SAL-2E40 required equal amount of energy to flow at the beginning of the shearing process. They had equal viscosity of 1630 cP each at 52500001/s due to similar collision intensity. However, they had unequal slope which eventually led to different but close viscosity values of 742 cP and 756 cP at 1000 1/s respectively. SAL-2E40 droplets broke down quicker since the product of the binding forces within SAL-2E40 was lesser that that in SAL-0E40. The droplets continued to break until the critical breaking size was achieved and the shearing force equaled to that required by the original crude oil. Thus, the emulsions tend to assume Newtonian behavior with shear rate and temperature.

The viscosity versus shear rate profiles of the emulsions at 50% water cut at the three test temperatures are shown in **Figure 13**. Increased water cut led to reduction in the distance between the droplets and thus, required greater shearing force. Further reduction in the

(100% water separation at 4 hours) and least in SAL-0E50 (100% at 96 hours) as shown in **Figure 14**. Increasing *SMES* dose to 150,000 ppm led to significant improvement in demulsification of SAL-1E50 and SAL-0E50 by shifting the time required to achieve 100% water separation to 2 hours and 6 hours respectively (**Figure 15**). Force of gravity dominated the demulsification process due to density difference. At 250000 ppm dose of *SMES*, 100% water separation was obtained in SAL-0E50 and SAL-2E50 within the first hour of testing but no significant increase in SAL-1E50 (**Figure 16**). Perhaps, the interfacial films of SAL-1E50 droplets became more elastic due to lower IFT and therefore, had quicker surface

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reconstruction after deformation.

**Figure 14.** Phase separation at 50 g/L of S*MES* in emulsions with 50% water cut.

**Figure 15.** Phase separation at 150 g/L of *SMES* in emulsions with 50% water cut.

**Figure 12.** Rheological behavior of emulsions with 40% water cut at 70°C.

**Figure 13.** Rheological behavior of emulsions with 50% water cut at 70°C.

distance between droplets (derby length) brought about significant decrease in the collision intensity. At 25°C, SAL-0E50 droplets were able to break easier than those of SAL-2E50 due to lesser steric repulsion between the droplets. The collision impact was weaker and rupturing of the droplets might be dominant. SAL-1E50 maintained the same behavior as SAL-1E40, but required higher shearing force due to the closeness of the droplets at this level. The droplets became more agitated at elevated temperature and the collision intensity increased. Thus, SAL-2E50 droplets became easier to break and thereby assuming lesser viscosity profile than SAL-0E50.

#### **4.3. Equal amount of emulsion phases**

**Figures 18**–**20** show the respective amount of water separation with time at three doses (50,000, 150,000 and 250,000 ppm) of *SMES* at 70°C. Demulsification obtained at 50000 ppm of *SMES* was faster in SAL-2E50 (100% water separation at 2 hours) followed by SAL-1E50 (100% water separation at 4 hours) and least in SAL-0E50 (100% at 96 hours) as shown in **Figure 14**. Increasing *SMES* dose to 150,000 ppm led to significant improvement in demulsification of SAL-1E50 and SAL-0E50 by shifting the time required to achieve 100% water separation to 2 hours and 6 hours respectively (**Figure 15**). Force of gravity dominated the demulsification process due to density difference. At 250000 ppm dose of *SMES*, 100% water separation was obtained in SAL-0E50 and SAL-2E50 within the first hour of testing but no significant increase in SAL-1E50 (**Figure 16**). Perhaps, the interfacial films of SAL-1E50 droplets became more elastic due to lower IFT and therefore, had quicker surface reconstruction after deformation.

**Figure 14.** Phase separation at 50 g/L of S*MES* in emulsions with 50% water cut.

distance between droplets (derby length) brought about significant decrease in the collision intensity. At 25°C, SAL-0E50 droplets were able to break easier than those of SAL-2E50 due to lesser steric repulsion between the droplets. The collision impact was weaker and rupturing of the droplets might be dominant. SAL-1E50 maintained the same behavior as SAL-1E40, but required higher shearing force due to the closeness of the droplets at this level. The droplets became more agitated at elevated temperature and the collision intensity increased. Thus, SAL-2E50 droplets became easier to break and thereby assuming lesser

**Figures 18**–**20** show the respective amount of water separation with time at three doses (50,000, 150,000 and 250,000 ppm) of *SMES* at 70°C. Demulsification obtained at 50000 ppm of *SMES* was faster in SAL-2E50 (100% water separation at 2 hours) followed by SAL-1E50

viscosity profile than SAL-0E50.

**4.3. Equal amount of emulsion phases**

**Figure 13.** Rheological behavior of emulsions with 50% water cut at 70°C.

**Figure 12.** Rheological behavior of emulsions with 40% water cut at 70°C.

98 Science and Technology Behind Nanoemulsions

**Figure 15.** Phase separation at 150 g/L of *SMES* in emulsions with 50% water cut.

**Figure 16.** Phase separation at 250 g/L of *SMES* in emulsions with 50% water cut.

#### **4.4. Demulsification of emulsions with lower water content**

The respective phase separation profiles of SAL-0E40, SAL-1E40 and SAL-2E40 at 50000, 150,000 and 250,000 ppm of *SMES* are shown in **Figures 21**–**23**. Obviously, the electrostatic repulsion in SAL-1E40 was higher at 50000 ppm *SMES* dose due to dipole-dipole interactions between the salt ions present in SAL-1E40 and the Na+ external to the emulsion droplets. This led to the least demulsification obtained in SAL-1E40 as shown in **Figure 17**. However, gravitational force was dominant in SAL-2E40 system and thereby leading to 100% water separation in 2 hours.

the repulsion presented by the ions present in the dispersed phase. Full phase separation occurred within 1 hour, 3 hours and 8 hours in SAL-2E40, SAL-0E40 and SAL-1E40 respectively. Subsequent increase in dosage to 250,000 ppm *SMES* led to 100% water separation

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The distance (Derby length) between the emulsions droplets was longer at 20% water cut. The droplets required adequate momentum to overcome the Derby length. Demulsification proceeded fastest in SAL-1E40 at 50000 ppm *SMES* (**Figure 20**) since it possessed highest momentum. Increase in dosage to 150,000 and 250,000 ppm brought about 100% phase separation in all the emulsions since adequate quantity of *SMES* was available to destabilize the droplets as

within 1 hour in SAL-0E40 and 3 hours in SAL-1E40 (**Figure 19**).

**Figure 19.** Phase separation at 250 g/L of *SMES* in emulsions with 40% water cut.

**Figure 18.** Phase separation at 150 g/L of *SMES* in emulsions with 40% water cut.

depicted in **Figures 21** and **22**.

More *SMES* molecules as made available by 150,000 ppm dose improved resolution of the emulsions significantly (**Figure 18**). London van der Waals forces dominated the demulsification process in SAL-1E40 through the ability of the Na+ external to droplets to overcome

**Figure 17.** Phase separation at 50 g/L of *SMES* in emulsions with 40% water cut.

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**Figure 18.** Phase separation at 150 g/L of *SMES* in emulsions with 40% water cut.

**4.4. Demulsification of emulsions with lower water content**

**Figure 16.** Phase separation at 250 g/L of *SMES* in emulsions with 50% water cut.

between the salt ions present in SAL-1E40 and the Na+

fication process in SAL-1E40 through the ability of the Na+

**Figure 17.** Phase separation at 50 g/L of *SMES* in emulsions with 40% water cut.

separation in 2 hours.

100 Science and Technology Behind Nanoemulsions

The respective phase separation profiles of SAL-0E40, SAL-1E40 and SAL-2E40 at 50000, 150,000 and 250,000 ppm of *SMES* are shown in **Figures 21**–**23**. Obviously, the electrostatic repulsion in SAL-1E40 was higher at 50000 ppm *SMES* dose due to dipole-dipole interactions

This led to the least demulsification obtained in SAL-1E40 as shown in **Figure 17**. However, gravitational force was dominant in SAL-2E40 system and thereby leading to 100% water

More *SMES* molecules as made available by 150,000 ppm dose improved resolution of the emulsions significantly (**Figure 18**). London van der Waals forces dominated the demulsi-

external to the emulsion droplets.

external to droplets to overcome

the repulsion presented by the ions present in the dispersed phase. Full phase separation occurred within 1 hour, 3 hours and 8 hours in SAL-2E40, SAL-0E40 and SAL-1E40 respectively. Subsequent increase in dosage to 250,000 ppm *SMES* led to 100% water separation within 1 hour in SAL-0E40 and 3 hours in SAL-1E40 (**Figure 19**).

The distance (Derby length) between the emulsions droplets was longer at 20% water cut. The droplets required adequate momentum to overcome the Derby length. Demulsification proceeded fastest in SAL-1E40 at 50000 ppm *SMES* (**Figure 20**) since it possessed highest momentum. Increase in dosage to 150,000 and 250,000 ppm brought about 100% phase separation in all the emulsions since adequate quantity of *SMES* was available to destabilize the droplets as depicted in **Figures 21** and **22**.

**Figure 19.** Phase separation at 250 g/L of *SMES* in emulsions with 40% water cut.

**Figure 20.** Phase separation at 50 g/L of *SMES* in emulsions with 20% water cut.

When added to emulsions, *SMES* dissociates into its anion and sodium salt action. It is adsorbed to the interface between the droplets and the crude oil with some preferential orientation according to the relative polarity of the interfacial film. Adsorption of surfactants is a dynamic occurrence which is prevented by another process that is responsible for surfactant transfer into the bulk phase. This phenomenon occurs rapidly. Consequently, equilibrium is attained after certain period depending on the concentration of the surfactant in the bulk phase. According to Salager [25], the free energy of the absorbed molecules of surfactants is lower compared to the

freer molecules in the bulk phase. Hence, the equilibrium is very much displaced towards the adsorbed state. Subsequently, a monolayer of the surfactant rapidly occupies the interface and the molecular arrangement of the surfactant depends its structural and geometrical properties. In the presence of *SMES*, the cohesion between the droplets is substantially modified since this force action is very short, compared to the accumulating rate of the surfactant monolayer. The hydrophobic tail of the surfactant is adsorbed at the nonpolar phase leaving the hydrophilic head in the bulk phase. The anions are fixed to the interface, while the cations (Na+) are subjected to random molecular motion. There is uniform distribution of the cations in the system and there exists a Coulomb attractive force between the adsorbed anions and the wandering cations. The Coulomb force prevents the cations from separating far away from the interface making them to form a layer located near to the interface. The stable dispersion experience in the emulsions with 20 percent water cut even in the presence of demulsifier was due to large Derby length that prevented the short-range forces from acting on the droplets. Increasing the concentration of electrolytes in the system will shorten the Derby length, especially the polyvalent electrolytes. Reducing the Debye length will lead to a shorter distance of potential overlapping, and thereby encouraging the short-range forces (cohesion and adhesion) to disrupt the emulsions. The steric repulsion among asphaltenes and resins (respon-

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**Figure 22.** Phase separation at 250 g/L of *SMES* in emulsions with 20% water cut.

There was a corresponding increase in pressure with water content and consequently, higher shearing force was required to make emulsions flow. Comparison of emulsion rheology profiles with shear rate shows the progressive increase in viscosity according to water content.

sible for emulsion stability) is broken by this process.

**5. Conclusion**

**Figure 21.** Phase separation at 150 g/L of *SMES* in emulsions with 20% water cut.

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**Figure 22.** Phase separation at 250 g/L of *SMES* in emulsions with 20% water cut.

freer molecules in the bulk phase. Hence, the equilibrium is very much displaced towards the adsorbed state. Subsequently, a monolayer of the surfactant rapidly occupies the interface and the molecular arrangement of the surfactant depends its structural and geometrical properties.

In the presence of *SMES*, the cohesion between the droplets is substantially modified since this force action is very short, compared to the accumulating rate of the surfactant monolayer. The hydrophobic tail of the surfactant is adsorbed at the nonpolar phase leaving the hydrophilic head in the bulk phase. The anions are fixed to the interface, while the cations (Na+) are subjected to random molecular motion. There is uniform distribution of the cations in the system and there exists a Coulomb attractive force between the adsorbed anions and the wandering cations. The Coulomb force prevents the cations from separating far away from the interface making them to form a layer located near to the interface. The stable dispersion experience in the emulsions with 20 percent water cut even in the presence of demulsifier was due to large Derby length that prevented the short-range forces from acting on the droplets. Increasing the concentration of electrolytes in the system will shorten the Derby length, especially the polyvalent electrolytes. Reducing the Debye length will lead to a shorter distance of potential overlapping, and thereby encouraging the short-range forces (cohesion and adhesion) to disrupt the emulsions. The steric repulsion among asphaltenes and resins (responsible for emulsion stability) is broken by this process.

#### **5. Conclusion**

When added to emulsions, *SMES* dissociates into its anion and sodium salt action. It is adsorbed to the interface between the droplets and the crude oil with some preferential orientation according to the relative polarity of the interfacial film. Adsorption of surfactants is a dynamic occurrence which is prevented by another process that is responsible for surfactant transfer into the bulk phase. This phenomenon occurs rapidly. Consequently, equilibrium is attained after certain period depending on the concentration of the surfactant in the bulk phase. According to Salager [25], the free energy of the absorbed molecules of surfactants is lower compared to the

**Figure 20.** Phase separation at 50 g/L of *SMES* in emulsions with 20% water cut.

102 Science and Technology Behind Nanoemulsions

**Figure 21.** Phase separation at 150 g/L of *SMES* in emulsions with 20% water cut.

There was a corresponding increase in pressure with water content and consequently, higher shearing force was required to make emulsions flow. Comparison of emulsion rheology profiles with shear rate shows the progressive increase in viscosity according to water content. Collision impact, especially at elevated temperature was high enough to break the droplets but unable to destroy the interfacial film and, flocculation of the droplets was therefore impossible. The films encapsulating the emulsion droplets possess elastic properties that facilitated surface reconstruction of the interfacial films to compensate for "dimples" created after droplet deformation. Thus, it has been established that the interactions of the constituents of the crude oil system, the produced water system and the emulsion system play major roles in characterizing water-in-crude oil emulsions. The presence of interfacial films and the deviation of the emulsions from being Newtonian towards pseudo plastic behavior with respect to water cut and salinity suggest the breakage of emulsion droplets due to shear stress. Meanwhile, interfacial films possess surface reconstruction capability which ensures dimples coverage after collision impact. It was shown that the ease or difficulty with which droplets break depend largely on water cut and salinity. Hence, the stability of water-in-crude oil emulsions is related to the viscous force presented by the continuous phase, water cut and salinity.

ASTM D5002 standard test method for density and relative density of crude oils by digi-

ASTM D6591 standard test method for determination of aromatic hydrocarbon types in

ASTM D93 standard test methods for flash point by Pensky-Martens closed cup tester

middle distillates-high performance liquid chromatography method with

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tal density analyzer

DBSA dodecylbenzene sulfonic acids

HLB hydrophilic-lipophilic balance

DCM dichloromethane

IFT interfacial tension

NaCl sodium chloride NIR near infrared RI refractive index

MLS multiple light scattering

RID refractive index detector

SAL-0E20 20% SAL-0 cut-in-crude oil emulsion SAL-0E40 40% SAL-0 cut-in-crude oil emulsion SAL-0E50 50% SAL-0 cut-in-crude oil emulsion SAL-1 brine solution (20000 ppm salinity) SAL-1E20 20% SAL-1 cut-in-crude oil emulsion SAL-1E40 40% SAL-1 cut-in-crude oil emulsion SAL-1E50 50% SAL-1 cut-in-crude oil emulsion SAL-2 brine solution (40000 ppm salinity) SAL-2E20 20% SAL-2 cut-in-crude oil emulsion SAL-2E40 40% SAL-2 cut-in-crude oil emulsion SAL-2E50 50% SAL-2 cut-in-crude oil emulsion

SARA saturates, aromatics, resins and asphaltenes

S&W sediment and water

SAL-0 fresh water

K-F Karl Fischer

refractive index detection

DLVO Derjaguin, Landau, Verwey and Overbeek GCMS gas chromatography mass spectrometry

HPLC high performance liquid chromatography

## **Acknowledgements**

The authors would like to thank the University Technology PETRONAS (UTP) for providing the grant used for this study and the permission to present the research findings.

## **Nomenclature**

Collision impact, especially at elevated temperature was high enough to break the droplets but unable to destroy the interfacial film and, flocculation of the droplets was therefore impossible. The films encapsulating the emulsion droplets possess elastic properties that facilitated surface reconstruction of the interfacial films to compensate for "dimples" created after droplet deformation. Thus, it has been established that the interactions of the constituents of the crude oil system, the produced water system and the emulsion system play major roles in characterizing water-in-crude oil emulsions. The presence of interfacial films and the deviation of the emulsions from being Newtonian towards pseudo plastic behavior with respect to water cut and salinity suggest the breakage of emulsion droplets due to shear stress. Meanwhile, interfacial films possess surface reconstruction capability which ensures dimples coverage after collision impact. It was shown that the ease or difficulty with which droplets break depend largely on water cut and salinity. Hence, the stability of water-in-crude oil emulsions is related

The authors would like to thank the University Technology PETRONAS (UTP) for providing

BS 4708 method for determination of viscosity of transparent and opaque liquids

ASTM D445 standard test method for kinematic viscosity of transparent and opaque

ASTM D4928 standard test method for water in crude oils by Coulometric Karl Fischer

(kinematic and dynamic viscosities)

ASTM D2500 standard test method for cloud point of petroleum product

liquids (and calculation of dynamic viscosity

ASTM D3279 standard test method for n-heptane insolubles

to the viscous force presented by the continuous phase, water cut and salinity.

the grant used for this study and the permission to present the research findings.

**Acknowledgements**

104 Science and Technology Behind Nanoemulsions

**Nomenclature**

API America petroleum institute Ast transformed resin content, %

BO butylene oxide

BS back scattering

Ca capillary number

CRO crude oil

BS & W basic sediment and water

CII colloidal instability index

Titration

liquid dynamic viscosity

W summation of water separation

Aliyu Adebayo Sulaimon\* and Bamikole Joshua Adeyemi

\*Address all correspondence to<EMAIL_ADDRESS>
Universiti Teknologi PETRONAS, Seri Iskandar, Perak, Malaysia

[1] Kaiser A. Environmentally Friendly Emulsion Breakers: Vision or Reality? SPE International Symposium on Oilfield Chemistry. Woodlands, Texas, USA: Socienty of

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[2] Oriji A, Appah D. Suitability of local demulsifier as an emulsion treating agent in oil and gas production. Paper SPE 162989 presented at the SPE Nigeria Annual international

[3] Abdel-Aal H, Aggour M, Fahim M. Petroleum and Gas Field Processing. New York,

[4] Kokal S. Crude Oil Emulsions. Petroleum Engineering Handbook – General Engineering.

[5] Becker J. Crude Oil Waxes, Emulsions, and Asphaltenes. Tulsa, Oklahoma: PennWell

[6] Othman A. Study on Emulsion Stability and Chemical Demulsification Characteristics.

[7] Stewart M, Arnold K. Emulsions and Oil Treating Equipment: Selection, Sizing and

[8] Zhou H, Dismuke K, Lett N, Penny G. Development of more environmentally friendly demulsifiers. In: I SPE 151852 Presented at the SPE International Symposium and Exhibition on Formation Damage Control. Kuala Lumpur, Malaysia: Society of Petro-

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tion processes. Chemistry and Technology of Fuels and Oils. 2000;**36**(2)

conference and exhibition (NAICE). Abuja, FCT, Nigeria; August 6-8 2012

Vol. 1. Texas, USA: Society of Petroleum Engineers; 2006. pp. 533-570

Bachelor Degree Thesis. Pahang: Universiti Malaysia Pahang; 2009

Troubleshooting. New York: Gulf Publishing, Elsevier; 2009

leum Engineers, Inc; February 15-17 2012

o viscosity of a medium

Petroleum Engineers Inc.; 2013

BASEL: Marcel Dekker, Inc.; 2003

B Boltzmann constant

**Author details**

**References**

Books; 1997

## **Author details**

SG specific gravity

106 Science and Technology Behind Nanoemulsions

∆p pressure change ∆ρ density difference

1/s per second Å angstrom Cl− chlorine ion cP centipoise

UV ultra-violet

*SMES* sodium methyl ester sulfonate

μS/cm micro-Siemens per centimeter

1/k extension of double layer

ɛo relative permittivity

g asymmetry factor

n refractive index

C degree Celsius

Qs scattering efficiency

, Rb,1, Rb,2 radius of curvature T absolute temperature

x particle diameter

Zi valency of the ions γ interfacial tension

ω angular frequency

\* photon transport mean free path

ϕ concentration

ẏ shear rate

Na+ sodium ion nm nanometer

o

Ra

ɛr permittivity of free space

g/cc, g/cm3 gram per cubic centimeter

no number of ions per unit volume of each type present in bulk solution

Visc untransformed natural logarithm of viscosity

VDWL Van Der Waals London

Aliyu Adebayo Sulaimon\* and Bamikole Joshua Adeyemi

\*Address all correspondence to<EMAIL_ADDRESS>
Universiti Teknologi PETRONAS, Seri Iskandar, Perak, Malaysia

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Petroleum Science and Engineering. 1993;**9**(1):1-8

mists' Society (Yukagaku). 1994;**43**(7):551-555

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Stability. Boca Raton: CRC Press and Taylor & Francis Group; 2006

Ester Sulphonates. Journal of Oil Palm Research. 2004;**16**(1):39-44

pp. 305-326

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Ingenieria Quimica; 1994

[24] Claesson PM, Blomberg E, Poptoshev E. Surface Forces and Emulsion Stability. Encyclopedic Handbook of Emulsion Technology. New York: Marcel Dekker, Inc.; 2001; pp. 305-326

[10] Stout C, Nicksic S. Separation and gel permeation analysis of natural emulsion stabilizers. In: SPE 42nd Annual Fall Meeting. Vol. 243. Houston, Texas: American Istitute of Mining, Metallurgical, and Petroleum Engineers, Inc; October 1-4 1967. pp. 253-259 [11] Nghiem L, Hassam M, Nutakki R, George A. Efficient Modelling of Asphaltene Precipitation. Paper SPE 26642 presented at the SPE Annual Technical Conference and

[12] Sjoblom J, Urdahl O, Borve K, Mingyuan L, Saeten J, Christy A, et al. Stabilization and destabilization of water-in-crude oil emulsion from the Norwegian continental shelf. Correlation with model systems. Advances in Colloid and Interface Science.

[13] Fingas MF. Water-In-Oil Emulsions: Formation and Prediction. Handbook of Oil Spill

[14] Fingas M, Fieldhouse B. A review of knowledge on water-in-oil emulsions. AMOP.

[15] Tadros TF. Emulsion Formation, Stability, and Rheology. Applied Surfactants. Germany:

[16] Eley D, Hey M, Symonds J. Emulsions of water in asphaltene-containing oils 1. Droplet size distribution and emulsification rates. Colloids and Surfaces. 1988;**32**:87-101

[17] Gurkov TD, Basheva ES. Hydrodynamic Behaviour and Stability of Approaching Deformable Drops, "Encyclopedia of Surface and Colloid Science". New York: Marcel

[18] Yarranton HW, Alboudwarej H, Jakher R. Investigation of Asphaltene association with vapor pressure Osmometry and interfacial tension measurements. Industrial and Engi-

[19] McLean JD, Kilpatrick PK. Effects of Asphaltene solvency on stabibility of water-incrude-oil emulsions. Journal of Colloid and Interface Science. 1997;**189**:242-253

[20] Al-Jarrah M, Al-Dujaih A. Characterization of some Iraqi asphalts II. New findings on physical nature of asphaltenes. Fuel Science and Technology International. 1989;**7**(1):69-88

[21] Sztukowski D, Jafari M, Alboudwarej H, Yarranton H. Asphaltene self-association and water-in-hydrocarbon emulsions. Journal of Colloid and Interface Science. 2003;

[22] Jamalluddin A, Nazarko T, Hills S, Fuhr B. Deasphalted oil: A natural asphaltene solvent. Journal of SPE Production & Facilities. Paper SPE 28994 presented at the 1995 SPE International Symposium on Oilfield Chemistry held in San Antonio, Feb. 14-17. Texas,

[23] Sato T, Ruch R. Stabilization of Colloidal Dispersions by Polymer Adsorption. New York:

USA: SPE International Symposium on Oilfield Chemistry; 1996

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Marcel Dekker Inc.; 1980

**Chapter 7**

**Provisional chapter**

**An SVM-Based Classification and Stability Analysis of**

Emulsions are metastable systems typically formed in the presence of surfactant molecules, amphiphilic polymers, or solid particles, as a mixture of two mutually immiscible liquids, one of which is dispersed as very small droplets in the other. These dispersions are unwanted occurrences in some areas, like those formed during crude oil production, but are also put into many other useful applications in the oil and gas industry, food industry, and construction industry, among others. These emulsions form when two immiscible liquids come together in the presence of an emulsifying agent and sufficient agitation strong enough to disperse one of the liquids in the other. Thermodynamically, these emulsions are unstable and thus would separate into their individual phases when left alone. To be stabilized, surface-active agents (surfactants) or solids (that act in so many ways like surfactants) ought to be used. Like many commercially available products, several pharmaceutical products are usually supplied in the form of emulsions that must be stabilized before they are being administered. Pharmaceutical emulsions used for oral administration either as medications themselves or as carriers come in form of stable emulsions. Either water-in-oil (w/o) or oil-in-water (o/w), these emulsions after formulation must be classified, majorly as stable or unstable. Only formulations that give stable emulsions are used, and the unstable ones reformulated or discarded. Classifying such emulsions using results obtained by visual observation in most cases can be very tedious and inaccurate. This necessitates the use of a more scientific and intelligent method of classification. The objective of this study is to employ support vector machine (SVM) as a new technique to classify synthetic emulsions. The study will assess the effects of nonionic surfactant (sodium monooleate) and Laponite clay (LC) on the stability of synthetic emulsions prepared using a response surface methodology (RSM) based on a Box-Behnken design. The stability of the emulsions was measured using batch test and TurbiScan, and the SVM was used to classify the emulsions into stable, moderately stable and unstable emulsions.

**An SVM-Based Classification and Stability Analysis**

**of Synthetic Emulsions Co-Stabilized by a Nonionic**

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.75707

**Synthetic Emulsions Co-Stabilized by a Nonionic**

**Surfactant and Laponite Clay**

**Surfactant and Laponite Clay**

Abubakar A. Umar, Ismail M. Saaid and

Abubakar A. Umar, Ismail M. Saaid and

http://dx.doi.org/10.5772/intechopen.75707

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Aliyu A. Sulaimon

**Abstract**

Aliyu A. Sulaimon

#### **An SVM-Based Classification and Stability Analysis of Synthetic Emulsions Co-Stabilized by a Nonionic Surfactant and Laponite Clay An SVM-Based Classification and Stability Analysis of Synthetic Emulsions Co-Stabilized by a Nonionic Surfactant and Laponite Clay**

DOI: 10.5772/intechopen.75707

Abubakar A. Umar, Ismail M. Saaid and Aliyu A. Sulaimon Abubakar A. Umar, Ismail M. Saaid and Aliyu A. Sulaimon

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.75707

#### **Abstract**

Emulsions are metastable systems typically formed in the presence of surfactant molecules, amphiphilic polymers, or solid particles, as a mixture of two mutually immiscible liquids, one of which is dispersed as very small droplets in the other. These dispersions are unwanted occurrences in some areas, like those formed during crude oil production, but are also put into many other useful applications in the oil and gas industry, food industry, and construction industry, among others. These emulsions form when two immiscible liquids come together in the presence of an emulsifying agent and sufficient agitation strong enough to disperse one of the liquids in the other. Thermodynamically, these emulsions are unstable and thus would separate into their individual phases when left alone. To be stabilized, surface-active agents (surfactants) or solids (that act in so many ways like surfactants) ought to be used. Like many commercially available products, several pharmaceutical products are usually supplied in the form of emulsions that must be stabilized before they are being administered. Pharmaceutical emulsions used for oral administration either as medications themselves or as carriers come in form of stable emulsions. Either water-in-oil (w/o) or oil-in-water (o/w), these emulsions after formulation must be classified, majorly as stable or unstable. Only formulations that give stable emulsions are used, and the unstable ones reformulated or discarded. Classifying such emulsions using results obtained by visual observation in most cases can be very tedious and inaccurate. This necessitates the use of a more scientific and intelligent method of classification. The objective of this study is to employ support vector machine (SVM) as a new technique to classify synthetic emulsions. The study will assess the effects of nonionic surfactant (sodium monooleate) and Laponite clay (LC) on the stability of synthetic emulsions prepared using a response surface methodology (RSM) based on a Box-Behnken design. The stability of the emulsions was measured using batch test and TurbiScan, and the SVM was used to classify the emulsions into stable, moderately stable and unstable emulsions.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The study showed that an increase in surfactant concentration in the presence of moderate to high concentrations of LC can provide a stable emulsion. Also, a clear classification of the emulsion samples was provided by the SVM, with high accuracy and reduced misclassifications due to human error. A higher accuracy in classification would reduce the risk of using the wrong formulation for any pharmaceutical product.

of fine drops of one liquid in another liquid. However, Roberts [9] defined emulsion as a system containing two liquid phases, one of which is dispersed as globules in the other. Other researchers [10–12] defined emulsion as a mixture of two mutually immiscible liquids, one of which is dispersed as very small droplets in the other, and is stabilized by an emulsifying agent. According to Leal-Calderon and Schmitt [13], emulsions are metastable systems typically formed in the presence of surfactant molecules, amphiphilic polymers or solid particles. The relative balance of the hydrophilic and lipophilic properties of these emulsifiers is known to be the most important parameter dictating the emulsion type: oil-in-water (O/W) emulsions are preferentially obtained with molecules which are rather hydrophilic whereas water-in-oil (W/O) emulsions are produced in the presence of hydrophobic molecules. A close look at all the definitions provided above indicates that there is a common understanding and belief that emulsions are thermodynamically unstable [11]. By thermodynamic instability, it means that the contact between the oil and water molecules is unfavorable, and so they will always break down over time, leading to decrease in free energy. Based on the sizes of their dispersed droplets, these dispersions can either fall under macroemulsions or microemulsions. Macroemulsions are liquid-in-liquid dispersions with droplet size ranging usually from 1 to 100 μm (and can sometimes be extended down to 0.5 or up to 500 μm). This range of droplet sizes is in general large enough to allow settling due to gravity influence. Microemulsions are single-phase systems that are thermodynamically stable. According to Nielloud [14], many microemulsions would not qualify to be called dispersions of very small droplets, but reasonably as percolated or bicontinuous structures in which there is no dispersed nor continuous phase, and no probability of dilution as in normal emulsions. According to Lambert et al. [15], microemulsions can be defined as thermodynamically stable, isotropically clear dispersion of two immiscible liquids, like oil and water, stabilized by an interfacial film of surfactant molecules. The microemulsion has a mean droplet diameter of less than 200 nm, in general

An SVM-Based Classification and Stability Analysis of Synthetic Emulsions Co-Stabilized by…

http://dx.doi.org/10.5772/intechopen.75707

113

For emulsions to form, three conditions must be satisfied [17]: (1) the two liquids forming the emulsion must be immiscible; (2) there must be sufficient agitation to disperse one liquid as droplets in the other, and (3) the presence of an emulsifying agent. Lecithin from egg yolks or soybeans is a commonly used surfactant [15]. Pharmaceutical products can be stabilized by the addition of various amphiphilic molecules, including anionic, nonionic, cationic, and zwitterionic surfactants. The amphiphilic molecules in addition comprise of surfactants such as ascorbyl-6-palmitate, stearylamine, sucrose fatty acid esters, various vitamin E derivatives, and so on. One or a combination of these surfactants can be used to stabilize the emulsion, and excipients are added to render the emulsion more biocompatible, stable and less toxic [15]. In addition to surfactants, solids have been widely used as stabilizers of emulsions, a process

These colloidal particles perform in several ways like surfactant molecules, mostly if adsorbed to a fluid-fluid interface [16]. The same way a surfactant's oil or water-liking tendency is defined by the hydrophilic-lipophilic balance (HLB) [18], so are spherical particles defined

There exists some important dissimilarities between these two types of surface-active solids, partially as a result of how they are held at the oil-water interface [4, 18, 19]. Hydrophilic particles

with respect to their wettability via contact angle, as shown in **Figure 1**.

between 10 and 50 nm.

called Pickering Stabilization [5].

**Keywords:** water-in-oil emulsions, oil-in-water emulsions, multiple emulsions, Pickering emulsions, support vector machine, response surface methodology

## **1. Introduction**

Several processes that involve choice of materials and operational decisions are required in the formation of an emulsified system. One is tasked with selecting the type of emulsion that is needed (whether a water-in-oil or an oil-in-water), what types of surface-active-agents and how much of them are required to form the emulsion, what level of stability is required and so on. These are, no doubt, some of the most important operational decisions required when handling an emulsified system.

The process via which emulsion droplets are stabilized is achievable either by small molecular weight surfactants that reduce the interfacial tension between the two fluids or amphiphilic macromolecules (like proteins and polysaccharides) by the formation of steric elastic film as well as the reduction of interfacial tension. The process by which these surfactants stabilize emulsions has been widely studied. Surfactants form a unique class of chemical compounds, and their widespread applications in emulsification and other industrial processes have advanced a wealth of published literature [1]. Lecithin from egg yolk and various proteins from milk are some naturally occurring surfactants used in the food industry for the preparation of food products like mayonnaise, salad creams and so on [2]. Most of these compounds, like short-chain fatty acids, have a part of them with affinity for the nonpolar hydrocarbon chain and one the other part that has its affinity for polar group such as water. These compounds are referred to as amphiphilic or amphipathic. The most satisfactory orientation these molecules can assume is at the interface, so that each part of the molecule can stay in the phase (polar or non-polar) which it has the greatest affinity [3].

Apart from natural or artificial surfactants, dispersed colloidal particles were discovered to function as emulsion stabilizers in a fundamentally unique way, and this concept was formally recognized since the publication of Pickering. The knowledge that fine solid powders can stabilize emulsions dates to centuries ago. Clayton [4] reported that emulsions of oil and water were prepared with North-African argillaceous sand in 1898, and in 1903, Ramsden [5] concluded that the stability of many emulsions could be attributed, in part, to "the presence of solid or highly viscous matter at the interfaces of the two liquids." Pickering performed the first extensive experimental study in 1907 [6] in connection with plant sprays [7].

The word "emulsion" is used very frequently in identifying both microemulsions and macroemulsions. The term has been defined severally by experts in different areas of its application. Emulsion according to Manning and Thompson [8] was defined as a quasi-stable suspension of fine drops of one liquid in another liquid. However, Roberts [9] defined emulsion as a system containing two liquid phases, one of which is dispersed as globules in the other. Other researchers [10–12] defined emulsion as a mixture of two mutually immiscible liquids, one of which is dispersed as very small droplets in the other, and is stabilized by an emulsifying agent. According to Leal-Calderon and Schmitt [13], emulsions are metastable systems typically formed in the presence of surfactant molecules, amphiphilic polymers or solid particles. The relative balance of the hydrophilic and lipophilic properties of these emulsifiers is known to be the most important parameter dictating the emulsion type: oil-in-water (O/W) emulsions are preferentially obtained with molecules which are rather hydrophilic whereas water-in-oil (W/O) emulsions are produced in the presence of hydrophobic molecules. A close look at all the definitions provided above indicates that there is a common understanding and belief that emulsions are thermodynamically unstable [11]. By thermodynamic instability, it means that the contact between the oil and water molecules is unfavorable, and so they will always break down over time, leading to decrease in free energy. Based on the sizes of their dispersed droplets, these dispersions can either fall under macroemulsions or microemulsions. Macroemulsions are liquid-in-liquid dispersions with droplet size ranging usually from 1 to 100 μm (and can sometimes be extended down to 0.5 or up to 500 μm). This range of droplet sizes is in general large enough to allow settling due to gravity influence. Microemulsions are single-phase systems that are thermodynamically stable. According to Nielloud [14], many microemulsions would not qualify to be called dispersions of very small droplets, but reasonably as percolated or bicontinuous structures in which there is no dispersed nor continuous phase, and no probability of dilution as in normal emulsions. According to Lambert et al. [15], microemulsions can be defined as thermodynamically stable, isotropically clear dispersion of two immiscible liquids, like oil and water, stabilized by an interfacial film of surfactant molecules. The microemulsion has a mean droplet diameter of less than 200 nm, in general between 10 and 50 nm.

The study showed that an increase in surfactant concentration in the presence of moderate to high concentrations of LC can provide a stable emulsion. Also, a clear classification of the emulsion samples was provided by the SVM, with high accuracy and reduced misclassifications due to human error. A higher accuracy in classification would reduce the risk

Several processes that involve choice of materials and operational decisions are required in the formation of an emulsified system. One is tasked with selecting the type of emulsion that is needed (whether a water-in-oil or an oil-in-water), what types of surface-active-agents and how much of them are required to form the emulsion, what level of stability is required and so on. These are, no doubt, some of the most important operational decisions required when

The process via which emulsion droplets are stabilized is achievable either by small molecular weight surfactants that reduce the interfacial tension between the two fluids or amphiphilic macromolecules (like proteins and polysaccharides) by the formation of steric elastic film as well as the reduction of interfacial tension. The process by which these surfactants stabilize emulsions has been widely studied. Surfactants form a unique class of chemical compounds, and their widespread applications in emulsification and other industrial processes have advanced a wealth of published literature [1]. Lecithin from egg yolk and various proteins from milk are some naturally occurring surfactants used in the food industry for the preparation of food products like mayonnaise, salad creams and so on [2]. Most of these compounds, like short-chain fatty acids, have a part of them with affinity for the nonpolar hydrocarbon chain and one the other part that has its affinity for polar group such as water. These compounds are referred to as amphiphilic or amphipathic. The most satisfactory orientation these molecules can assume is at the interface, so that each part of the molecule can stay in the phase (polar or non-polar) which it has the greatest affinity [3].

Apart from natural or artificial surfactants, dispersed colloidal particles were discovered to function as emulsion stabilizers in a fundamentally unique way, and this concept was formally recognized since the publication of Pickering. The knowledge that fine solid powders can stabilize emulsions dates to centuries ago. Clayton [4] reported that emulsions of oil and water were prepared with North-African argillaceous sand in 1898, and in 1903, Ramsden [5] concluded that the stability of many emulsions could be attributed, in part, to "the presence of solid or highly viscous matter at the interfaces of the two liquids." Pickering performed the

The word "emulsion" is used very frequently in identifying both microemulsions and macroemulsions. The term has been defined severally by experts in different areas of its application. Emulsion according to Manning and Thompson [8] was defined as a quasi-stable suspension

first extensive experimental study in 1907 [6] in connection with plant sprays [7].

**Keywords:** water-in-oil emulsions, oil-in-water emulsions, multiple emulsions, Pickering emulsions, support vector machine, response surface methodology

of using the wrong formulation for any pharmaceutical product.

**1. Introduction**

handling an emulsified system.

112 Science and Technology Behind Nanoemulsions

For emulsions to form, three conditions must be satisfied [17]: (1) the two liquids forming the emulsion must be immiscible; (2) there must be sufficient agitation to disperse one liquid as droplets in the other, and (3) the presence of an emulsifying agent. Lecithin from egg yolks or soybeans is a commonly used surfactant [15]. Pharmaceutical products can be stabilized by the addition of various amphiphilic molecules, including anionic, nonionic, cationic, and zwitterionic surfactants. The amphiphilic molecules in addition comprise of surfactants such as ascorbyl-6-palmitate, stearylamine, sucrose fatty acid esters, various vitamin E derivatives, and so on. One or a combination of these surfactants can be used to stabilize the emulsion, and excipients are added to render the emulsion more biocompatible, stable and less toxic [15]. In addition to surfactants, solids have been widely used as stabilizers of emulsions, a process called Pickering Stabilization [5].

These colloidal particles perform in several ways like surfactant molecules, mostly if adsorbed to a fluid-fluid interface [16]. The same way a surfactant's oil or water-liking tendency is defined by the hydrophilic-lipophilic balance (HLB) [18], so are spherical particles defined with respect to their wettability via contact angle, as shown in **Figure 1**.

There exists some important dissimilarities between these two types of surface-active solids, partially as a result of how they are held at the oil-water interface [4, 18, 19]. Hydrophilic particles

**Figure 1.** Position of a small spherical particle at w/o interface [16].

have the tendency of forming oil-in-water (o/w) emulsions while hydrophobic particles form water-in-oil (w/o) emulsions. Many of the properties can be attributed to the very large free energy of adsorption for particles of intermediate wettability (contact angle at the oil-water interface, say, between 50 and 130°) [19]. This adsorption of solids at the fluids interface is efficiently irreversible and leads to extreme stability for certain emulsions.

The support vectors defined as *WT* + *W*0 = ±1 are the training vectors that are the closest to the

An SVM-Based Classification and Stability Analysis of Synthetic Emulsions Co-Stabilized by…

http://dx.doi.org/10.5772/intechopen.75707

115

**Figure 2.** A depiction of the decision boundary showing the maximum margin m and other parameters [27].

Support vector machines, Bayes point machines, kernel principal component analysis and other Kernel-based techniques represent a key advancement in machine learning algorithms. Support vector machines (SVM) are a group of supervised learning methods that can be used in classification or regression [28]. Industrial processes that require classifications have utilized the emergence of rapid development in artificial intelligence like neural networks to solve classification problems [20]. As in many industries, pharmaceutical emulsions require accurate classification in order to avoid waste of materials during formulation or using an

To accomplish the set objectives of this study, Castor oil supplied by Merck Malaysia in its pure form (99%) was used as the oleic phase, while deionized water obtained from a PureLab Flex 3 purifier as the internal phase. Laponite clay and Sorbitan monooleate were used as emulsifiers, in the form they were supplied by Avantis Chemicals Bhd Malaysia. The batch of the Laponite clay used in this study is the 9/4156 batch, with chemical compositions expressed

used to measure the droplet size of the emulsions prepared. The CPM provides us a unique window into the internal structure of crystals and at the same time is esthetically pleasing due

; 59.6 and MgO; 27.4. A cross polarized microscopy was

linear classifier, and they constitute the critical elements of the training set.

unstable emulsion where a stable one is required.

**2. Methodology**

as wt%: Li2

**2.1. Materials and methods**

O; 0.8, Na2

to the colors and shapes of the crystals.

O; 28, SiO2

In this study, the effects of Laponite clay (a colloidal particle) and a nonionic surfactant (sorbitan monooleate) on the stability of synthetic emulsions were investigated. The synthetic emulsions were further classified using a kind of typical machine learning method, support vector machine (SVM), designed and developed to classify the synthetic emulsions formulated based on the response surface methodology (RSM). According to Hu et al. [20], the novel SVM algorithm has its origin from Vapnik [21]. Together with Cortes, Vapnik suggested the modified maximum margin idea that allows for mislabeled examples [22]. Support vector machine (SVM) is a supervised machine learning algorithm used both in classification and regression-related challenges, though it has higher applications in classification problems. In an SVM algorithm, each data item is plotted as a point in n-dimensional space (n- representing the number of features to be classified) with the value of each feature being the value of a particular coordinate. Then, classification is performed by finding the hyper-plane that differentiates the two classes very well [23]. The primary focus while drawing the hyperplane is on maximizing the distance from hyperplane to the nearest data point of either class. The drawn hyperplane called as a maximum-margin hyperplane [21, 24]. For linearly separable data, two parallel hyperplanes that separate the two classes of data are chosen, so that distance between both the lines is the maximum. The region between these two hyperplanes is known as "margin" and the maximum margin hyperplane is the one that lies in the middle of them, as shown in **Figure 2**. Details of the algorithm and derivations are beyond the scope of this paper. For those interested in understanding the details, the following references would suffice [21, 22, 25, 26].

An SVM-Based Classification and Stability Analysis of Synthetic Emulsions Co-Stabilized by… http://dx.doi.org/10.5772/intechopen.75707 115

**Figure 2.** A depiction of the decision boundary showing the maximum margin m and other parameters [27].

The support vectors defined as *WT* + *W*0 = ±1 are the training vectors that are the closest to the linear classifier, and they constitute the critical elements of the training set.

Support vector machines, Bayes point machines, kernel principal component analysis and other Kernel-based techniques represent a key advancement in machine learning algorithms. Support vector machines (SVM) are a group of supervised learning methods that can be used in classification or regression [28]. Industrial processes that require classifications have utilized the emergence of rapid development in artificial intelligence like neural networks to solve classification problems [20]. As in many industries, pharmaceutical emulsions require accurate classification in order to avoid waste of materials during formulation or using an unstable emulsion where a stable one is required.

#### **2. Methodology**

have the tendency of forming oil-in-water (o/w) emulsions while hydrophobic particles form water-in-oil (w/o) emulsions. Many of the properties can be attributed to the very large free energy of adsorption for particles of intermediate wettability (contact angle at the oil-water interface, say, between 50 and 130°) [19]. This adsorption of solids at the fluids interface is

In this study, the effects of Laponite clay (a colloidal particle) and a nonionic surfactant (sorbitan monooleate) on the stability of synthetic emulsions were investigated. The synthetic emulsions were further classified using a kind of typical machine learning method, support vector machine (SVM), designed and developed to classify the synthetic emulsions formulated based on the response surface methodology (RSM). According to Hu et al. [20], the novel SVM algorithm has its origin from Vapnik [21]. Together with Cortes, Vapnik suggested the modified maximum margin idea that allows for mislabeled examples [22]. Support vector machine (SVM) is a supervised machine learning algorithm used both in classification and regression-related challenges, though it has higher applications in classification problems. In an SVM algorithm, each data item is plotted as a point in n-dimensional space (n- representing the number of features to be classified) with the value of each feature being the value of a particular coordinate. Then, classification is performed by finding the hyper-plane that differentiates the two classes very well [23]. The primary focus while drawing the hyperplane is on maximizing the distance from hyperplane to the nearest data point of either class. The drawn hyperplane called as a maximum-margin hyperplane [21, 24]. For linearly separable data, two parallel hyperplanes that separate the two classes of data are chosen, so that distance between both the lines is the maximum. The region between these two hyperplanes is known as "margin" and the maximum margin hyperplane is the one that lies in the middle of them, as shown in **Figure 2**. Details of the algorithm and derivations are beyond the scope of this paper. For those interested in understanding the details, the following references would

efficiently irreversible and leads to extreme stability for certain emulsions.

**Figure 1.** Position of a small spherical particle at w/o interface [16].

114 Science and Technology Behind Nanoemulsions

suffice [21, 22, 25, 26].

#### **2.1. Materials and methods**

To accomplish the set objectives of this study, Castor oil supplied by Merck Malaysia in its pure form (99%) was used as the oleic phase, while deionized water obtained from a PureLab Flex 3 purifier as the internal phase. Laponite clay and Sorbitan monooleate were used as emulsifiers, in the form they were supplied by Avantis Chemicals Bhd Malaysia. The batch of the Laponite clay used in this study is the 9/4156 batch, with chemical compositions expressed as wt%: Li2 O; 0.8, Na2 O; 28, SiO2 ; 59.6 and MgO; 27.4. A cross polarized microscopy was used to measure the droplet size of the emulsions prepared. The CPM provides us a unique window into the internal structure of crystals and at the same time is esthetically pleasing due to the colors and shapes of the crystals.

#### **2.2. Surface response methodology based on box: Behnken design**

Response surface methodology is a collection of statistical and mathematical methods that are useful for modeling and analyzing engineering problems. In this technique, the main objective is to optimize the response surface that is influenced by various process parameters [29]. It is indispensable that experimental design methodology is a cost-effective way for mining the maximum amount of multifaceted data, a weighty experimental time saving factor and likewise, it saves the material used for analyses and personal costs as well [29–31]. An experiment is a series of tests in which the input variables are changed according to a given rule in order to identify the reasons for the changes in the output response [32]. Such tasks that require investigating the effects of different variables on one or more outputs can be tedious and may be accompanied with different kinds of errors.

Assuming that the variation of Y (STABILITY) obeys an eight parameter, second-order equa-

**Variables Symbol Actual variable levels**

An SVM-Based Classification and Stability Analysis of Synthetic Emulsions Co-Stabilized by…

Weight concentration of Laponite clay (%) X1 0.1 0.0 0.3 Volume concentration of Span80 (v/v) X2 0.5 0.0 1.5

are linear, quadratic and interaction regression coefficients, respectively. The competence of the models was determined using model analysis; lack-of fit test and coefficient of determina-

of a response model. The corresponding variables will be more significant (p < 0.05), if the absolute t value becomes larger and the p-value becomes smaller [33]. For all terms statistically found non-significant (p > 0.05), they would be dropped from the initial models and the experimental data refitted only to significant (p < 0.05) independent variable effects in order

Emulsions used in this study were prepared using a w/o ratio of 30/70 (v/v). Deionized water was used as the aqueous phase and castor oil was used as the oleic phase. For every 28 mL of the oil phase, an equivalent 12 mL of the aqueous phase was added, into a 50 mL plastic centrifuge bottle with a Wheaton adjustable pipet. Before the two phases were mixed, different wt% and v/v% concentrations of the Laponite clay (LC) and sorbitan monooleate (Span80) were dispersed in the oil phase with a homogenizer for 1 min. The oil-phase which now contains the LC and Span80, and the deionized water was then mixed with a Virtis Virtishear Cyclone IQ Homogenizer. The homogenization was performed at 15,000 rpm for 5 min. All the

The emulsions prepared were investigated of the percent water released, and based on that were preliminarily classified into stable, moderate stable and unstable emulsions. This scheme is applied for the optimization of the sparse coefficient matrix. In each case, there was a repetition of the analysis over all the training set where one sample was left out for testing. The training group was used in building the SVM classifier while the performance of the classifier was calculated by the testing group. The important terms used to evaluate the performance of the classifier are accuracy, sensitivity and specificity. A confusion matrix, which comprises

2 + *βij xi xj* (1)

should be at least 0.80 for a good fitness

is an offset value; *βi*

**Low Center High**

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, *βii* , *βij* 117

tion of the following type:

to obtain the final reduced model.

**2.3. Preparations of synthetic emulsions**

**2.4. Support vector machine classification**

tion (R2

*STABILITY* = *β*0 + ∑*βi xi* + ∑*βii xi*

**Table 2.** The level of variables chosen for the Box-Behnken design.

) analysis. Joglekar [31] recommended that R2

15 emulsion samples were prepared based on the RSM design.

where Y (STABILITY) is the response value predicted by the model; *β*0

This experiment was designed using a Statgraphic Centurion XVII a flagship data analysis and visualization software. It encloses 32 statistical procedures and significant upgrades to 20 other existing procedures. As shown in **Tables 1** and **2**, 15 castor oil synthetic emulsions were prepared using different compositions of Laponite clay (0.1–0.3% w/w), Span80 (0.5–1.5% v/v), and deionized water. The emulsifier compositions were prepared based on Box-Behnken design for the estimation of emulsion stability (as amount of water released from the emulsions). Analysis of variance (ANOVA) and regression surface analysis were conducted to determine the statistical significance of model terms and fit a regression relationship relating the experimental data to the independent variable.

**Table 1.** Box-Behnken design with actual values for three size fractions and results.

**Table 2.** The level of variables chosen for the Box-Behnken design.

**2.2. Surface response methodology based on box: Behnken design**

116 Science and Technology Behind Nanoemulsions

and may be accompanied with different kinds of errors.

the experimental data to the independent variable.

**Runs Clay% (w/w) Span80% (v/v)**

1 0.2 1.0 2 0.3 1.0 3 0.2 0.5 4 0.1 1.0 5 0.2 1.5 6 0.3 0.5 7 0.2 1.5 8 0.1 1.5 9 0.2 1.0 10 0.3 1.0 11 0.2 1.0 12 0.3 1.5 13 0.2 0.5 14 0.1 0.5 15 0.1 1.0

**Table 1.** Box-Behnken design with actual values for three size fractions and results.

Response surface methodology is a collection of statistical and mathematical methods that are useful for modeling and analyzing engineering problems. In this technique, the main objective is to optimize the response surface that is influenced by various process parameters [29]. It is indispensable that experimental design methodology is a cost-effective way for mining the maximum amount of multifaceted data, a weighty experimental time saving factor and likewise, it saves the material used for analyses and personal costs as well [29–31]. An experiment is a series of tests in which the input variables are changed according to a given rule in order to identify the reasons for the changes in the output response [32]. Such tasks that require investigating the effects of different variables on one or more outputs can be tedious

This experiment was designed using a Statgraphic Centurion XVII a flagship data analysis and visualization software. It encloses 32 statistical procedures and significant upgrades to 20 other existing procedures. As shown in **Tables 1** and **2**, 15 castor oil synthetic emulsions were prepared using different compositions of Laponite clay (0.1–0.3% w/w), Span80 (0.5–1.5% v/v), and deionized water. The emulsifier compositions were prepared based on Box-Behnken design for the estimation of emulsion stability (as amount of water released from the emulsions). Analysis of variance (ANOVA) and regression surface analysis were conducted to determine the statistical significance of model terms and fit a regression relationship relating Assuming that the variation of Y (STABILITY) obeys an eight parameter, second-order equation of the following type:

$$\text{STABIITY} = \beta\_0 + \sum \beta\_i \mathbf{x}\_i + \sum \beta\_{\bar{u}} \mathbf{x}\_i^2 + \beta\_{\bar{y}} \mathbf{x}\_i \mathbf{x}\_i \tag{1}$$

where Y (STABILITY) is the response value predicted by the model; *β*0 is an offset value; *βi* , *βii* , *βij* are linear, quadratic and interaction regression coefficients, respectively. The competence of the models was determined using model analysis; lack-of fit test and coefficient of determination (R2 ) analysis. Joglekar [31] recommended that R2 should be at least 0.80 for a good fitness of a response model. The corresponding variables will be more significant (p < 0.05), if the absolute t value becomes larger and the p-value becomes smaller [33]. For all terms statistically found non-significant (p > 0.05), they would be dropped from the initial models and the experimental data refitted only to significant (p < 0.05) independent variable effects in order to obtain the final reduced model.

#### **2.3. Preparations of synthetic emulsions**

Emulsions used in this study were prepared using a w/o ratio of 30/70 (v/v). Deionized water was used as the aqueous phase and castor oil was used as the oleic phase. For every 28 mL of the oil phase, an equivalent 12 mL of the aqueous phase was added, into a 50 mL plastic centrifuge bottle with a Wheaton adjustable pipet. Before the two phases were mixed, different wt% and v/v% concentrations of the Laponite clay (LC) and sorbitan monooleate (Span80) were dispersed in the oil phase with a homogenizer for 1 min. The oil-phase which now contains the LC and Span80, and the deionized water was then mixed with a Virtis Virtishear Cyclone IQ Homogenizer. The homogenization was performed at 15,000 rpm for 5 min. All the 15 emulsion samples were prepared based on the RSM design.

#### **2.4. Support vector machine classification**

The emulsions prepared were investigated of the percent water released, and based on that were preliminarily classified into stable, moderate stable and unstable emulsions. This scheme is applied for the optimization of the sparse coefficient matrix. In each case, there was a repetition of the analysis over all the training set where one sample was left out for testing. The training group was used in building the SVM classifier while the performance of the classifier was calculated by the testing group. The important terms used to evaluate the performance of the classifier are accuracy, sensitivity and specificity. A confusion matrix, which comprises of actual and predicted classifications, is usually used in the performance evaluation. The different components of a confusion matrix that are used in the performance evaluation are: true positive (TP), true negative (TN), false positive (FP) and false negative (FN). Another important parameter used in the performance evaluation and also to select the optimum model is the area under the curve (AUC), also called the receiver operating characteristics (ROC). It is obtained by plotting the TPR against the FPR at different settings. Another commonly used metric is the rate of detection (RoD) also known as the Sensitivity or Recall. Equal error rate (EER) or crossover rate (COR) is the percentage of misclassified frames when the acceptance and rejection errors are equal, that is, FPR = FNR.

## **3. Results and discussions**

#### **3.1. Emulsion stability measurements: bottle test**

Emulsion stability measurement by bottle test is the most popular technique employed in determining the stability of emulsions. It measures the amount of water resolved from the emulsion over time. In this study, it is employed to assess the stability of the prepared emulsions at 60°C. This phenomenon is controlled by the gravity separation, where the amount of water released is being observed with time, and used as a measure of the stability. All prepared emulsions were kept in a graduated plastic centrifuge bottle in a water bath of 60°C, and aged for 60 h. The percentage of water separated was calculated, and plotted against time (**Tables 1** and **2**). The results are as shown in **Figures 3** and **4**.

This is evident from Emulsion B which though has the same concentration of Span80, but a lower LC concentration of 0.2 wt% indicated a wide range of difference between water released by the two emulsions under comparison. This trend also applies to Emulsion C, which has equal concentration of LC as Emulsion B, but lower Span80 concentration, and subsequently lower stability with the highest water release of almost 70% within the time under study.

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**Figure 4.** Water separation percent for emulsions G to L observed at 60°C for 48 h.

The Laponite clay discs are believed to play a critical role in the nucleation stage of the Pickering emulsion polymerization process. The use of increasing amounts leads to smaller average particle sizes but inflicts longer nucleation periods [34]. This same trend observed in **Figure 1** applies through **Figure 4**. Emulsion L in **Figure 4** indicates the most stable emulsion, having released 0% throughout the study time. This is due to the high concentrations of both Span80 and LC used in its preparation. Emulsions H and K exhibit somewhat similar behavior. As observed, Emulsion H released around 70% of its emulsified water in 12 h, and there was no visible increase till the end of this study. This is similar to what obtains in Emulsion K; where it released around 50% of its emulsified water within 5 h with no further increase in release. In both cases, higher concentrations of Span80 were used with relatively lower concentrations of LC. This could be as a result of the irreversible nature of particle adsorption at oil/water interfaces, where it is rapid at the beginning and ceases completely over a long

In this section, we present the estimated regression coefficients for the response variable (Y-

Y was evaluated as a function of main, cubic and interaction effects of Laponite clay (X1or A), Span80 (X2 or B) and time taken for separation to occur (X3 or C). The individual significance F-value and p-value of independent variables are presented in **Table 3**. The ANOVA table segregates the variability in STABILITY into separate pieces for each of the effects. It further tests the statistical significance of each effect by comparing the mean square against an estimate of the experimental error. In this case, three effects have P-values less than 0.05, indicating that they are significantly different from zero at the 95.0% confidence level. The R-Squared statistic

, F-value and p-value of lack of fit. The response,

period of time [35].

**3.2. Design data analysis**

Stability) together with the corresponding R2

From **Figures 3**–**7**, the trend observed is that of varying water separation percent over the entire period of this study. **Figure 3** indicates that Emulsion B with 0.3 wt% of LC and 1.0 v/v% of Span80 is the most stable, having released barely 10% of its emulsified water over the entire study period. As the Span80 and LC concentrations increase, the extent of emulsified water release decreases and the dispersed droplet size correspondingly decreases. Although sorbitan monooleate (Span80), a nonionic oil soluble surfactant has the ability to stabilize emulsions on its own, a synergy between the two emulsifiers has shown a higher stability being achieved.

**Figure 3.** Water separation percent for emulsions A to F observed at 60°C for 48 h.

**Figure 4.** Water separation percent for emulsions G to L observed at 60°C for 48 h.

This is evident from Emulsion B which though has the same concentration of Span80, but a lower LC concentration of 0.2 wt% indicated a wide range of difference between water released by the two emulsions under comparison. This trend also applies to Emulsion C, which has equal concentration of LC as Emulsion B, but lower Span80 concentration, and subsequently lower stability with the highest water release of almost 70% within the time under study.

The Laponite clay discs are believed to play a critical role in the nucleation stage of the Pickering emulsion polymerization process. The use of increasing amounts leads to smaller average particle sizes but inflicts longer nucleation periods [34]. This same trend observed in **Figure 1** applies through **Figure 4**. Emulsion L in **Figure 4** indicates the most stable emulsion, having released 0% throughout the study time. This is due to the high concentrations of both Span80 and LC used in its preparation. Emulsions H and K exhibit somewhat similar behavior. As observed, Emulsion H released around 70% of its emulsified water in 12 h, and there was no visible increase till the end of this study. This is similar to what obtains in Emulsion K; where it released around 50% of its emulsified water within 5 h with no further increase in release. In both cases, higher concentrations of Span80 were used with relatively lower concentrations of LC. This could be as a result of the irreversible nature of particle adsorption at oil/water interfaces, where it is rapid at the beginning and ceases completely over a long period of time [35].

#### **3.2. Design data analysis**

of actual and predicted classifications, is usually used in the performance evaluation. The different components of a confusion matrix that are used in the performance evaluation are: true positive (TP), true negative (TN), false positive (FP) and false negative (FN). Another important parameter used in the performance evaluation and also to select the optimum model is the area under the curve (AUC), also called the receiver operating characteristics (ROC). It is obtained by plotting the TPR against the FPR at different settings. Another commonly used metric is the rate of detection (RoD) also known as the Sensitivity or Recall. Equal error rate (EER) or crossover rate (COR) is the percentage of misclassified frames when the acceptance

Emulsion stability measurement by bottle test is the most popular technique employed in determining the stability of emulsions. It measures the amount of water resolved from the emulsion over time. In this study, it is employed to assess the stability of the prepared emulsions at 60°C. This phenomenon is controlled by the gravity separation, where the amount of water released is being observed with time, and used as a measure of the stability. All prepared emulsions were kept in a graduated plastic centrifuge bottle in a water bath of 60°C, and aged for 60 h. The percentage of water separated was calculated, and plotted against time

From **Figures 3**–**7**, the trend observed is that of varying water separation percent over the entire period of this study. **Figure 3** indicates that Emulsion B with 0.3 wt% of LC and 1.0 v/v% of Span80 is the most stable, having released barely 10% of its emulsified water over the entire study period. As the Span80 and LC concentrations increase, the extent of emulsified water release decreases and the dispersed droplet size correspondingly decreases. Although sorbitan monooleate (Span80), a nonionic oil soluble surfactant has the ability to stabilize emulsions on its own, a synergy between the two emulsifiers has shown a higher stability being achieved.

and rejection errors are equal, that is, FPR = FNR.

**3.1. Emulsion stability measurements: bottle test**

(**Tables 1** and **2**). The results are as shown in **Figures 3** and **4**.

**Figure 3.** Water separation percent for emulsions A to F observed at 60°C for 48 h.

**3. Results and discussions**

118 Science and Technology Behind Nanoemulsions

In this section, we present the estimated regression coefficients for the response variable (Y-Stability) together with the corresponding R2 , F-value and p-value of lack of fit. The response, Y was evaluated as a function of main, cubic and interaction effects of Laponite clay (X1or A), Span80 (X2 or B) and time taken for separation to occur (X3 or C). The individual significance F-value and p-value of independent variables are presented in **Table 3**. The ANOVA table segregates the variability in STABILITY into separate pieces for each of the effects. It further tests the statistical significance of each effect by comparing the mean square against an estimate of the experimental error. In this case, three effects have P-values less than 0.05, indicating that they are significantly different from zero at the 95.0% confidence level. The R-Squared statistic

**Table 3.** Analysis of variance for stability index.

indicates that the model as fitted demonstrates 44.0204% of the variability in STABILITY INDEX. The adjusted R-squared statistic, which is more suitable for comparing models with different numbers of independent variables, is 40.3958%. The standard error of the estimate shows the standard deviation of the residuals to be 0.195919. The mean absolute error (MAE) of 0.147747 is the average value of the residuals.

the horizontal bars on the pareto Chart, the higher the significance. This is again confirmed in **Table 3**. For all terms statistically found significant, their p-values should be less than 0.05. All

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From **7A**, an increase in the concentrations of span80 and LC leads to an increase in the stability index. The effects of both LC and Span80 with time on stability index were shown on **Figure 7B** and **C**. Both response plots indicate that there is a concentration value for both emulsifiers that may tend to decrease the stability index, indicated by the curved surface on the plot. Also, the longer the time the studied emulsions stay, the more water release from

terms with p > 0.05 are statistically non-significant.

**Figure 6.** Pareto chart showing all the factors in the modified model.

**Figure 5.** Pareto chart showing all the factors in the initial model.

them, also indicated by the curved surface on the response plot.

The Durbin-Watson (DW) statistic tests the residuals to determine if there is any significant correlation based on the order in which they occur in your data file. Since the P-value is less than 5.0%, there is an indication of possible serial correlation at the 5.0% significance level. Plot the residuals versus row order to see if there is any pattern that can be seen. **Figure 5** shows the Pareto chart displaying all the variables of the general model. Pareto analysis is a statistical procedure that seeks to discover from an analysis of defect reports or customer complaints which "critical few" causes are responsible for most of the reported problems. The old adage states that 80% of reported problems can usually be traced to 20% of the various underlying causes [29, 31, 33].

From **Figure 5**, it shows that all the variables in the study have significance on emulsion stability index, albeit at different level. The time it takes the emulsions to release their emulsified water has the highest effect on the stability index, then followed by the square of its value, Span80, a mixture of span80 and Laponite clay and finally Laponite clay. Those parameters with standardized effect below 2 are AB, AA, AC and BC. These are statistically ineffective on this model and therefore are removed and the pareto chart recomputed, as shown in **Figure 6**.