(a) SEM images of pollutant-charged MOF-DP (b) EDX images of pollutant-charged MOF-DP Fig. 21. SEM investigation of MOF-DP charged with pollutants - case of depollution of water coming from medicine industry (VEGA II LMU SEM microscope)

Fig. 22. Integral yield and efficiency of the depollution of water coming from medicine industry in the presence of 67.4 grams of MOF-DP ((a) – integral yield of depollution; (b) - relative yield of acetonil dimethylcarbinol)

functionality and the integral depollution potential. This implies the existence of specific differentiated reticular mechanisms, which take place in the composite nanostructures, leading to the selective separation of pollutants, depending on the specific chemical

reactivity and on the achieved density of functional groups on MOF-DP microsurfaces.

(a) SEM images of pollutant-charged MOF-DP (b) EDX images of pollutant-charged MOF-DP Fig. 21. SEM investigation of MOF-DP charged with pollutants - case of depollution of water

Total yield

 of depollution (a)

coming from medicine industry (VEGA II LMU SEM microscope)

0 50 100 150 200

Fig. 22. Integral yield and efficiency of the depollution of water coming from medicine industry in the presence of 67.4 grams of MOF-DP ((a) – integral yield of depollution;

2x108

3x108

4x108

5x108

Relative abundance

6x108

7x108

8x108 Acetonyl

 dimtehylcarbinol (b)

0 50 100 150 200

cm3

cm3

8.0x109

(b) - relative yield of acetonil dimethylcarbinol)

1.6x1010

2.4x1010

Relative abundance

3.2x1010

4.0x1010

Fig. 23. Relative variation of microelements in the depth and on the surface of MOF-DP (according to tab.6)

The separation investigations of the pollutants found in waters coming from medicine industry shows the manifestation of the dynamic degradation phenomenon of the pollutants. This is demonstrated by the analytical behaviour of the depollution curves of the valeric acid, 3,5-dihydroxy-2,4-dimethyl-lactones (fig.20b), the partially decelable pollutant CAS 4376-20-3 (fig.20f) and acetonyl dimethylcarbinol (fig.22b), which, after reaching the saturation point of the functionality of MOF-DP, have growth rates that exceed by far the originally detected values. This indicates the presence of a pollutant in the contaminated water, which, following the reticulation processes, degrades and generates chemical structures that cannot be reticulated, or that are partially reticulated by the composite. All pollutants entering the structure of the integral spectrum, sensitized by pollution, of the investigated waters, have lower or higher separation rates. Thus, the lack of the reticulation potential, in relation to the degenerated pollutants listed above, is due, most likely, to: a. the saturation of MOF-DP with the previously existing fractions of pollutants; b. large quantities of pollutants present in depolluted water, which quickly saturate the functionality of MOF-DP; the degeneration of the separated pollutants in the depth of MOF-DP. Moreover, the morphostructural (agglomeration, compactness) and morphochemical (functionality saturation processes, masking, chemical degradation processes of reticulated pollutants) degeneration processes were emphasized in all investigated depollution cases. The effects of pollutant charging are also showed in the case of polluted waters coming from medicine industry. In this sense, the processed data presented in figure 15 (tab.6) indicate a significant increase in the quantity of chemical microelements, specific to the structures and organic pollutants (C, N). This is indirectly confirmed by morphostructural investigations (fig.21, fig.21b), indicating the increase of the agglomeration and compactness degree of the composite, as well as its degeneration under the action of separated organic pollutants.

New Methods and New Types of

7842-7, Amsterdam

8, Enfield (NH), Jersey, Plymouth

Enfield (NH), New York

Boston, London

York, Oxford

550-559, ISSN 1454-4164

U.S.A.

York, Basel

**7. References**

Functionalised Nanocomposites Intended for the Ecological Depollution of Waters 143

Lu, A. H.; Zhao, D. & Wan, Y. (2010). *Nanocasting - A Versatile Strategy for Creating*

Cheremisinoff, N. P. (2002). *Handbook of water and wastewater treatment technologies*,

Tolgyessy, J. (2003). *Water, air and soil - Fundamental sources of the biosphere*, In: Chemistry and

Bayliss, C. R. & Langley, K. F. (2003). *Nuclear Decommissioning, Waste Management, and Environmental Site Remediation*, Elsevier, ISBN 978-0-7506-7744-8, Amsterdam Socolow, R. H.; Andrews, C.; Berkhout, F. & Thoma, V. (2003). *Industrial ecology and global change*, Cambridge University Press, ISBN 0-521-47197-4, New York

Lal, R. & Shukla, M. (2005). *Principles of soil physics*, Marcel Dekker, ISBN 0-8247-5324-0, New

Haider, K. & Shäffer, M. (2009). *Soil Biochemistry*, Science Publishers, ISBN 978-1-57808-579-

Asano, T.; Burton, F. L.; Leverenz, H. L.; Tsuchihashi, R. & Tchobanoglous, G. (2007). *Water*

Cheremisinoff, N. P. (2003). *Handbook of solid waste management and waste minimization*

Cheremisinoff, N. P. & Cheremisinoff, P. N. (1995). *Hazardous materials and waste*

Hester, R. E. & Harrison, R. M. (2002). *Environmental and health impact of solid waste*

Baud, I.; Post, J. & Furedy, C. (2004). *Solid waste management and recycling*, Kluwer Academic, ISBN 1-4020-1975-0, New York, Boston, Dordrecht, London, Moscow Yu, T. R. & Wang, E. J. (1997). *Chemistry of variable charge soils, In: Chemistry of variable charge*

Ojovan, M. I. & Lee, W. E. (2005). *An introduction to nuclear waste immobilisation*, Elsevier,

Iordache, P. Z.; Lungu, R. M.; Epure, G.; Mureşan, M.; Petre, R.; Petrea, N.; Pretorian, A.;

*management activities*, RS•C, ISBN 0-85404-285-7, Manchester

ISBN 0-080-44462-8, Amsterdam, Boston, Heidelberg

*Reuse - Issues, Technologies, and Applications*, McGrow-Hill, ISBN 978-0-07-145927-3,

*technologies*, Butterworth-Heinemann, ISBN 0-7506-7507-1 (alk. paper), Amsterdam,

*management*, Noyes Publications, ISBN 0-8155-1372-0, Park Ridge, New Jersey,

*soils*, T. R. Yu, (Ed.), 309-338, Oxford University Press, ISBN 0-19-509745-9, New

Dionezie, B.; Mutihac, L. & Ordeanu, V. (2011). The determination of the nanostructurated materials' morphology, by applying the statistics of the structural element maps, *Journal of Optoelectronics and Advanced Materials*, Vol. 13, No. 5, pp.

Elsevier, ISBN 0-444-98798-3, Amsterdam-London-New York-Tokyo Evanghelou, V. P. (1998). *Environmental soil and water chemistry - Principles and applications*, John Wiley & Sons, ISBN 0-471-16515-8 (cloth: alk. paper), New York Rosenfeld, P. E. & Feng, L. G. H. (2011). *Risks of Hazardous Wastes*, Elsevier, ISBN 978-1-4377-

biology of water, air and soil - Environmental Aspects, J. Tolgyessy, (Ed.), 3-13,

*Nanostructured Porous Materials*, RS•C, ISBN 978-0-85404-188-6

Butterworth-Heinemann, ISBN 0-7506-7498-9, Boston

#### **5. Conclusions**

In this chapter we have presented and investigated the specific mechanisms underlying the reticulation, separation and encapsulation processes of organic pollutants. Specific depollution mechanisms, as well as the main depollution parameters (yield, efficiency), have been investigated by testing a polyfunctionalized nanocomposite material (MOF-DP) on three types of water charged with organic pollutants. The polluted waters on which the depollution features of MOF-DP have been investigated came from various pollution sources: milk processing industry, medicine industry, sewage waters. The investigations' secondary aim was to determine the effects of organic pollutants on the morphological and morphochemical structure of the obtained MOF-DP, as well as to determine how they influence the depollution parameters. It was intended, in particular, to check the range of pollutants that MOF-DP is able to separate, in order to determine the type of chemical functionality of pollutants capable to establish reticulation relations with the functional structure of the composite. The reticulated functionalities are a direct measure of the depollution efficiency of the obtained material, by defining the range of separated pollutants and the extent to which the depollution was carried out. The investigation processes included various analytical techniques, in order to confirm, through complementarity (SEM, TEM, EDX, FTIR, GC-MS), the depollution parameters and the morphostructural characteristics of MOF-DP, both before the testing and after its completion. The investigation results confirm the reticulation, encapsulation and degradation mechanisms of the pollutants that the authors proposed in chapters "New methods and new types of functionalised nanocomposites intended for the ecological depollution of waters" and "Nanocomposite materials with oriented functionalized structure". The acquired experimental data have shown that the obtained MOF-DP presents high pollutant separation yield and efficiency. The concentrations of most decelated pollutants and of those partially decelated in depolluted water were below the detection limit, showing the applicative potential of this type of materials. The aim of the investigations of the morphological and morphochemical structure which we have carried out was to identify and quantify the critical parameters that influence the processes of encapsulation and degradation of pollutants. The acquired experimental data indicate that MOF-DP is able to reduce the level of organic pollution in surface waters by up to two orders of magnitude (the observed typical values have a separation factor of 20 ÷ 50 x). The oxide materials with a functionalised mixed structure represent a viable solution for the removal of organic pollutants in surface waters, having the most favourable applicative potential in terms of economy, depollution yield and efficiency.

#### **6. Acknowledgements**

The authors are grateful for the financial support granted by the CNMP (National Research, Development and Innovation Plan II - Program 4) inside project 32-165/2008, as well as for the logistic support granted by the Scientifical Research Center for CBRN Defence and Ecology. Also, for their contribution to the obtaining of results, we are grateful to Dionesie Bojin, Filipescu Laurenţiu, Toader Constantin and Mihaela Muraşan. For her contributions to text editing and translating, we are grateful to Loredana Iordache.

#### **7. References**

142 Nanomaterials

In this chapter we have presented and investigated the specific mechanisms underlying the reticulation, separation and encapsulation processes of organic pollutants. Specific depollution mechanisms, as well as the main depollution parameters (yield, efficiency), have been investigated by testing a polyfunctionalized nanocomposite material (MOF-DP) on three types of water charged with organic pollutants. The polluted waters on which the depollution features of MOF-DP have been investigated came from various pollution sources: milk processing industry, medicine industry, sewage waters. The investigations' secondary aim was to determine the effects of organic pollutants on the morphological and morphochemical structure of the obtained MOF-DP, as well as to determine how they influence the depollution parameters. It was intended, in particular, to check the range of pollutants that MOF-DP is able to separate, in order to determine the type of chemical functionality of pollutants capable to establish reticulation relations with the functional structure of the composite. The reticulated functionalities are a direct measure of the depollution efficiency of the obtained material, by defining the range of separated pollutants and the extent to which the depollution was carried out. The investigation processes included various analytical techniques, in order to confirm, through complementarity (SEM, TEM, EDX, FTIR, GC-MS), the depollution parameters and the morphostructural characteristics of MOF-DP, both before the testing and after its completion. The investigation results confirm the reticulation, encapsulation and degradation mechanisms of the pollutants that the authors proposed in chapters "New methods and new types of functionalised nanocomposites intended for the ecological depollution of waters" and "Nanocomposite materials with oriented functionalized structure". The acquired experimental data have shown that the obtained MOF-DP presents high pollutant separation yield and efficiency. The concentrations of most decelated pollutants and of those partially decelated in depolluted water were below the detection limit, showing the applicative potential of this type of materials. The aim of the investigations of the morphological and morphochemical structure which we have carried out was to identify and quantify the critical parameters that influence the processes of encapsulation and degradation of pollutants. The acquired experimental data indicate that MOF-DP is able to reduce the level of organic pollution in surface waters by up to two orders of magnitude (the observed typical values have a separation factor of 20 ÷ 50 x). The oxide materials with a functionalised mixed structure represent a viable solution for the removal of organic pollutants in surface waters, having the most favourable applicative potential in terms of economy, depollution

The authors are grateful for the financial support granted by the CNMP (National Research, Development and Innovation Plan II - Program 4) inside project 32-165/2008, as well as for the logistic support granted by the Scientifical Research Center for CBRN Defence and Ecology. Also, for their contribution to the obtaining of results, we are grateful to Dionesie Bojin, Filipescu Laurenţiu, Toader Constantin and Mihaela Muraşan. For her contributions to text editing and translating, we are grateful to Loredana

**5. Conclusions**

yield and efficiency.

Iordache.

**6. Acknowledgements**

**1. Introduction**

any physical importance.

seen as the solution of this issue.

**Review of Nanocomposite Thin**

Commonly it is assumed that the nanocrystalline materials are composed of elements like grains, crystallites, layers, e.g., of a size of ca. 100 nm. (more typically less than 50 nm; often less than 10 nm – in the case of superhard nanocomposite, materials for optoelectronic applications, etc.) at least in one direction. The definition give above limits the size of the structure elements, however it has to be seen only as a theoretical value and doesn't have

Thin films and coatings are applied to structural bulk materials in order to improve the desired properties of the surface, such as corrosion resistance, wear resistance, hardness, friction or required colour, e.g., golden, black or a polished brass-like. The research issues concerning the production of coatings are one of the more important directions of surface engineering development, ensuring the obtainment of coatings of high utility properties in the scope of mechanical characteristics and wear resistance. Giving new utility characteristics to commonly known materials is frequently obtained by laying simple monolayer, multilayer or gradient coatings using PVD methods (Dobrzanski et al., 2005; Lukaszkowicz & Dobrzanski, 2008). While selecting the coating material, we encounter a barrier caused by the fact that numerous properties expected from an ideal coating are impossible to be obtained simultaneously. The application of the nanostructure coatings is

Nanostructure and particularly nanocomposite coatings deposited by physical vapour deposition or chemical vapour deposition, have gained considerable attention due to their unique physical and chemical properties, e.g. extremely high indentation hardness (40-80 GPa) (Veprek et al., 2006, 2000; Zou et al., 2010), corrosion resistance (Audronis et al., 2008; Lukaszkowicz et al., 2010), excellent high temperature oxidization resistance (Vaz et al., 2000; Voevodin & Zabinski, 2005), as well high abrasion and erosion resistance (Cheng et al.,

In the present work, the emphasis is put on current practices and future trends for nanocomposite thin films and coatings deposited by physical vapour deposition (PVD) and chemical vapour deposition (CVD) techniques. This review will not be so exhaustive as to cover all aspects of such coatings, but the main objective is to give a general sense of what

2010; Polychronopoulou et al., 2009; Veprek & Veprek-Heijman, 2008).

has so far been accomplished and where the field is going.

**Films and Coatings Deposited**

**by PVD and CVD Technology**

Krzysztof Lukaszkowicz *Silesian University of Technology*

*Poland*

Jain, A. K. (1989). *Fundamentals of digital image processing*, Prentice-Hall, ISBN 0-13-336165-9, New Jersey **7**

### **Review of Nanocomposite Thin Films and Coatings Deposited by PVD and CVD Technology**

Krzysztof Lukaszkowicz *Silesian University of Technology Poland*

#### **1. Introduction**

144 Nanomaterials

Jain, A. K. (1989). *Fundamentals of digital image processing*, Prentice-Hall, ISBN 0-13-336165-9,

Commonly it is assumed that the nanocrystalline materials are composed of elements like grains, crystallites, layers, e.g., of a size of ca. 100 nm. (more typically less than 50 nm; often less than 10 nm – in the case of superhard nanocomposite, materials for optoelectronic applications, etc.) at least in one direction. The definition give above limits the size of the structure elements, however it has to be seen only as a theoretical value and doesn't have any physical importance.

Thin films and coatings are applied to structural bulk materials in order to improve the desired properties of the surface, such as corrosion resistance, wear resistance, hardness, friction or required colour, e.g., golden, black or a polished brass-like. The research issues concerning the production of coatings are one of the more important directions of surface engineering development, ensuring the obtainment of coatings of high utility properties in the scope of mechanical characteristics and wear resistance. Giving new utility characteristics to commonly known materials is frequently obtained by laying simple monolayer, multilayer or gradient coatings using PVD methods (Dobrzanski et al., 2005; Lukaszkowicz & Dobrzanski, 2008). While selecting the coating material, we encounter a barrier caused by the fact that numerous properties expected from an ideal coating are impossible to be obtained simultaneously. The application of the nanostructure coatings is seen as the solution of this issue.

Nanostructure and particularly nanocomposite coatings deposited by physical vapour deposition or chemical vapour deposition, have gained considerable attention due to their unique physical and chemical properties, e.g. extremely high indentation hardness (40-80 GPa) (Veprek et al., 2006, 2000; Zou et al., 2010), corrosion resistance (Audronis et al., 2008; Lukaszkowicz et al., 2010), excellent high temperature oxidization resistance (Vaz et al., 2000; Voevodin & Zabinski, 2005), as well high abrasion and erosion resistance (Cheng et al., 2010; Polychronopoulou et al., 2009; Veprek & Veprek-Heijman, 2008).

In the present work, the emphasis is put on current practices and future trends for nanocomposite thin films and coatings deposited by physical vapour deposition (PVD) and chemical vapour deposition (CVD) techniques. This review will not be so exhaustive as to cover all aspects of such coatings, but the main objective is to give a general sense of what has so far been accomplished and where the field is going.

Review of Nanocomposite Thin Films and Coatings Deposited by PVD and CVD Technology 147

The main concept for achieving of high hardness of nanostructure coatings and good mechanical properties and high strength related to it, particularly in case of nanocomposite coatings is the restriction of the origination and the movement of dislocations. High hardness and strength of the nanocomposite coatings are due to the fact that the movement of dislocations is suppressed at small grains and in the spaces between them, which causes the appearance of incoherent deformations. When the grain size is reduced to that of nanometers, the activity of dislocations as the source of the material ductility is restricted. This type of coatings is also characterized with a large number grain boundaries with a crystalline/amorphous transition across grain-matrix interfaces, restricting the forming and development of cracks. Such mechanism explains the resistance to fragile cracking of nanocomposite coatings. Simultaneously, the equiaxial grain shapes, high angle grain boundaries, low surface energy and the presence of the amorphous boundary phase facilitating the slide along the grain boundaries cause high plasticity of the nanocomposite

According to the model proposed by Veprek (Veprek & Reiprech, 1995;Veprek, 1997, Veprek et al., 1998) nanocomposite coatings comprise at least two phases, a nanocrystalline phase and a matrix phase, where the matrix can be either nanocrystalline or amorphous phase. In this design, the nanocrystalline grains must be 3÷10 nm in size and separated by

Fig. 2. Model and TEM image of nanocomposite structure (Source: PLATIT AG).

Nanocomposite coatings are usually formed from ternary or quaternary system with nanocrystalline (nc-) grains of hard transition metal-nitrides (e.g. TiN, TiAlN, CrN, BN, VN, ZrN, W2N, etc.), carbides (e.g. TiC, VC, WC, etc.), borides (e.g. TiB2, TiB, CrB2, etc.), oxides (e.g. Al2O3, TiO2, B2O3, SiO2, etc.), or silicides (e.g. TiSi2, CrSi2, ZrSi2, etc.) surrounded by amorphous (a-) matrices (e.g. Si3N4, BN, C, etc.) (Moore et al., 2007). There are many different nanocrystalline grain/amorphous matrix (nc-/a-) systems, such as: nc-TiN/a-Si3N4, nc-TiN/a-Si3N4/a-&nc-TiSi2, nc-CrN/a-Si3N4, nc-W2N/a-Si3N4, nc-TiAlN/a-Si3N4, nc-TiN/a-BN, nc-TiC/a-C, nc-WC/a-C (Moore et al., 2007, Voevodin et al., 2005; Zhang et al., 2007). The synthesis of such nanocomposite coatings depends on the ability to co-deposit

Various analyses revealed that the synthesized TiAlSiN coatings exhibited nanostructured composite microstructures consisting of solid-solution (Ti,Al,Si)N crystallites and amorphous Si3N4. The Si addition caused the grain refinement of (Ti,Al,Si)N crystallites and its uniform distribution with percolation phenomenon of amorphous silicon nitride. The (Ti,Al)N crystallites became finer with a uniform distribution as the Si content was

coatings (Rafaja et al., 2006; Voevodin et al., 2005).

1÷2 nm within an amorphous phase as shown in Fig. 2.

both phases.

#### **2. Synthesis of nanocomposite films and coatings**

In conventional bulk materials, refining grain size is one of the possibilities for hardness increase. The same is true for nanocomposite films or coatings. Looking for coating materials with high hardness, higher then the hardness of traditional polycrystalline coatings, there are founding materials with unique nanometric structure properties. With a decrease in grain size, the multiplication and mobility of the dislocations are hindered, and the hardness of materials increase according to the Hall-Petch relationship. This effect is especially prominent for grain size down to tens of nanometers. However, dislocation movement, which determines the hardness in conventional materials, has little effect when the grain size is less than approximately 10 nm. There is a critical value of the grain size at which a maximum hardness can be achieved (Fig. 1). For grains with diameters less than the critical value the material should be "softened" due to the action of a new deformation mechanism. i.e., the Hall-Petch relation is inverted (Koch et al., 2007; Voevodin et al., 2005; Zhang et al., 2007).

Fig. 1. Schematic illustration of materials hardness versus grain size (Zhang et al., 2007).

According to the Hall-Petch equation, the strength properties of the material rise along with the reduction of the grain size. In case of the coatings deposited by the PVD and CVD processes, the structures obtained, with grain size ~10 nm results with the maximum mechanical properties. Coatings of such structure present very high hardness >40 GPa, ductility, stability at high temperatures, etc.(Tjong et al., 2004; Veprek et al., 2006).

The known dependency between the hardness and abrasion resistance became the basis for the development of harder and harder coating materials. The progress in the field of producing coatings by the physical vapour deposition and/or chemical vapour deposition process enables the obtainment of coatings of nanocrystal structure presenting high mechanical and usable properties. The coatings of such structure are able to maintain a low friction coefficient (self-lubricating coatings) in numerous working environments, maintaining high hardness and increased resistance (Donnet & Erdemir, 2004; Voevodin & Zabinski, 2005).

In conventional bulk materials, refining grain size is one of the possibilities for hardness increase. The same is true for nanocomposite films or coatings. Looking for coating materials with high hardness, higher then the hardness of traditional polycrystalline coatings, there are founding materials with unique nanometric structure properties. With a decrease in grain size, the multiplication and mobility of the dislocations are hindered, and the hardness of materials increase according to the Hall-Petch relationship. This effect is especially prominent for grain size down to tens of nanometers. However, dislocation movement, which determines the hardness in conventional materials, has little effect when the grain size is less than approximately 10 nm. There is a critical value of the grain size at which a maximum hardness can be achieved (Fig. 1). For grains with diameters less than the critical value the material should be "softened" due to the action of a new deformation mechanism. i.e., the Hall-Petch relation is inverted (Koch et al., 2007; Voevodin et al., 2005;

> **1 nm 10 nm 100 nm 10 m 100 m Grain size**

Fig. 1. Schematic illustration of materials hardness versus grain size (Zhang et al., 2007).

ductility, stability at high temperatures, etc.(Tjong et al., 2004; Veprek et al., 2006).

According to the Hall-Petch equation, the strength properties of the material rise along with the reduction of the grain size. In case of the coatings deposited by the PVD and CVD processes, the structures obtained, with grain size ~10 nm results with the maximum mechanical properties. Coatings of such structure present very high hardness >40 GPa,

The known dependency between the hardness and abrasion resistance became the basis for the development of harder and harder coating materials. The progress in the field of producing coatings by the physical vapour deposition and/or chemical vapour deposition process enables the obtainment of coatings of nanocrystal structure presenting high mechanical and usable properties. The coatings of such structure are able to maintain a low friction coefficient (self-lubricating coatings) in numerous working environments, maintaining high hardness and increased resistance (Donnet & Erdemir, 2004; Voevodin &

**Nanomaterials**

**Optimum grain size**

**Conventional grain size material**

**2. Synthesis of nanocomposite films and coatings**

Zhang et al., 2007).

Zabinski, 2005).

**Hardness**

**Amorphous**

The main concept for achieving of high hardness of nanostructure coatings and good mechanical properties and high strength related to it, particularly in case of nanocomposite coatings is the restriction of the origination and the movement of dislocations. High hardness and strength of the nanocomposite coatings are due to the fact that the movement of dislocations is suppressed at small grains and in the spaces between them, which causes the appearance of incoherent deformations. When the grain size is reduced to that of nanometers, the activity of dislocations as the source of the material ductility is restricted. This type of coatings is also characterized with a large number grain boundaries with a crystalline/amorphous transition across grain-matrix interfaces, restricting the forming and development of cracks. Such mechanism explains the resistance to fragile cracking of nanocomposite coatings. Simultaneously, the equiaxial grain shapes, high angle grain boundaries, low surface energy and the presence of the amorphous boundary phase facilitating the slide along the grain boundaries cause high plasticity of the nanocomposite coatings (Rafaja et al., 2006; Voevodin et al., 2005).

According to the model proposed by Veprek (Veprek & Reiprech, 1995;Veprek, 1997, Veprek et al., 1998) nanocomposite coatings comprise at least two phases, a nanocrystalline phase and a matrix phase, where the matrix can be either nanocrystalline or amorphous phase. In this design, the nanocrystalline grains must be 3÷10 nm in size and separated by 1÷2 nm within an amorphous phase as shown in Fig. 2.

Fig. 2. Model and TEM image of nanocomposite structure (Source: PLATIT AG).

Nanocomposite coatings are usually formed from ternary or quaternary system with nanocrystalline (nc-) grains of hard transition metal-nitrides (e.g. TiN, TiAlN, CrN, BN, VN, ZrN, W2N, etc.), carbides (e.g. TiC, VC, WC, etc.), borides (e.g. TiB2, TiB, CrB2, etc.), oxides (e.g. Al2O3, TiO2, B2O3, SiO2, etc.), or silicides (e.g. TiSi2, CrSi2, ZrSi2, etc.) surrounded by amorphous (a-) matrices (e.g. Si3N4, BN, C, etc.) (Moore et al., 2007). There are many different nanocrystalline grain/amorphous matrix (nc-/a-) systems, such as: nc-TiN/a-Si3N4, nc-TiN/a-Si3N4/a-&nc-TiSi2, nc-CrN/a-Si3N4, nc-W2N/a-Si3N4, nc-TiAlN/a-Si3N4, nc-TiN/a-BN, nc-TiC/a-C, nc-WC/a-C (Moore et al., 2007, Voevodin et al., 2005; Zhang et al., 2007). The synthesis of such nanocomposite coatings depends on the ability to co-deposit both phases.

Various analyses revealed that the synthesized TiAlSiN coatings exhibited nanostructured composite microstructures consisting of solid-solution (Ti,Al,Si)N crystallites and amorphous Si3N4. The Si addition caused the grain refinement of (Ti,Al,Si)N crystallites and its uniform distribution with percolation phenomenon of amorphous silicon nitride. The (Ti,Al)N crystallites became finer with a uniform distribution as the Si content was

Review of Nanocomposite Thin Films and Coatings Deposited by PVD and CVD Technology 149

system. This adaptation was found in crystallization and reorientation of initially nanocrystalline and randomly oriented WS2 grains, graphitization of the initially amorphous DLC matrix, reversible regulation of the composition of the transfer film between WS2 and graphite with environmental cycling from dry to humid air, and a possible DLC/WS2 synergistic effect, providing friction reduction in oxidizing environments

A scheme of a "chameleon" coating of the YSZ/Au/DLC/MoS2 type as well the WC/DLC/WS2 type, where the amorphous matrix and hard nanocrystalline phases (YSZ or

Fig. 4. Schematic conceptual design of a nanocomposite tribological coating with chameleon-

Carrying out investigations over nanocomposite coatings it was found, that the creation mechanisms of such structures have a form of spinodal transformation. During deposition of nanocomposite coatings using physical vapor deposition methods a spinodal character of the segregation of the crystallized phase (e.g. TiN) and amorphous (np. Si3N4) was observed during production of nanocomposite coating of the nc-TiN/a-Si3N4 type. Such layer is composed of nanocrystalline TiN structure of 3÷4 nm in diameter, positioned in amorphous

During deposition of nanocomposite coatings in the PVD process the spinodal decomposition occurs when following conditions are fulfilled (Zhang & Veprek, 2006): appropriate temperature occurs making possible a complete segregation of phases

sufficiently high nitrogen pressure, for achieving of stechiometric nitride phases by a

Different techniques are available for the preparation of nanocomposite coatings. The most promising methods are plasma assisted chemical vapour deposition (PACVD), thermallyinduced chemical vapour deposition (TCVD), magnetron sputtering, vacuum arc evaporation, laser ablation and hybrid techniques consisting of a combination of these. Other techniques, such as ion beam deposition, electrodeposition are also used (Table 1).

during the deposition process of coatings by controlled diffusion;

like surface adaptive behaviour (Voevodin et al., 2005).

WC) were used for achieving optimal mechanical properties are presented in Fig. 4.

(Voevodin & Zabinski, 2000).

silicon nitride Si3N4.

given coating deposition rate.

increased. Si addition changes microstructure from columnar to isotropic (Fig. 3). Grain size decreases with an increase in Si content (Park et al., 2003; Yu et al., 2009).

Fig. 3. Cross sectional morphology of TiAlSiN coatings with different Si content (Yu et al., 2009).

Phase size decrease occurred in the nanocomposite coatings to a value of few nanometers, offered an unique possibility to design smart tribological coatings called "chameleon", for their ability to decrease wear and friction by changing surface chemical composition and microstructure according to the applied load and environmental changes – like a chameleon changes the colour in case of emergence (Voevodin & Zabinski, 2000).

Nanocomposite coatings make it possible to achieve a combination of several layers with opposite properties, such as: high hardness, strength, plasticity or low friction coefficient in the single layer. First "chameleon" coatings were produced using mixtures of oxides and disulphides (PbO/MoS2, Sb2O3/MoS2, ZnO/WS2), which were applicable in a wide range of temperatures (Zabinski et al., 1992; Zabinski et al., 1993).

It was the next steep to create the advanced multilayer coatings, where the previously achieved nanocomposite layers were put together with layers in form of diffusion barrier and as a result a self adapting surface was achieved, resistant against cyclic temperature changes. In the following new materials were developed, which are wear resistant, they were developed as a combination of nanocrystall based carbides (TiC, WC), ceramics (YSZ i AlON), bisulphites (MoS2 i WS2) and amorphous DLC for achieving the nanocomposite structure of the coating (Voevodin et al., 2001; 2002). An example of "chameleon" coatings is the composite coating produced within the W-C-S system, which consist of 1÷2 nm WC and 5÷10 nm WS2 grains embedded in the amorphous DLC matrix. The WC/DLC/WS2 nanocomposite exhibits self-adaptation to tribological conditions that occur in aerospace

increased. Si addition changes microstructure from columnar to isotropic (Fig. 3). Grain size

decreases with an increase in Si content (Park et al., 2003; Yu et al., 2009).

Fig. 3. Cross sectional morphology of TiAlSiN coatings with different

changes the colour in case of emergence (Voevodin & Zabinski, 2000).

temperatures (Zabinski et al., 1992; Zabinski et al., 1993).

Phase size decrease occurred in the nanocomposite coatings to a value of few nanometers, offered an unique possibility to design smart tribological coatings called "chameleon", for their ability to decrease wear and friction by changing surface chemical composition and microstructure according to the applied load and environmental changes – like a chameleon

Nanocomposite coatings make it possible to achieve a combination of several layers with opposite properties, such as: high hardness, strength, plasticity or low friction coefficient in the single layer. First "chameleon" coatings were produced using mixtures of oxides and disulphides (PbO/MoS2, Sb2O3/MoS2, ZnO/WS2), which were applicable in a wide range of

It was the next steep to create the advanced multilayer coatings, where the previously achieved nanocomposite layers were put together with layers in form of diffusion barrier and as a result a self adapting surface was achieved, resistant against cyclic temperature changes. In the following new materials were developed, which are wear resistant, they were developed as a combination of nanocrystall based carbides (TiC, WC), ceramics (YSZ i AlON), bisulphites (MoS2 i WS2) and amorphous DLC for achieving the nanocomposite structure of the coating (Voevodin et al., 2001; 2002). An example of "chameleon" coatings is the composite coating produced within the W-C-S system, which consist of 1÷2 nm WC and 5÷10 nm WS2 grains embedded in the amorphous DLC matrix. The WC/DLC/WS2 nanocomposite exhibits self-adaptation to tribological conditions that occur in aerospace

Si content (Yu et al., 2009).

system. This adaptation was found in crystallization and reorientation of initially nanocrystalline and randomly oriented WS2 grains, graphitization of the initially amorphous DLC matrix, reversible regulation of the composition of the transfer film between WS2 and graphite with environmental cycling from dry to humid air, and a possible DLC/WS2 synergistic effect, providing friction reduction in oxidizing environments (Voevodin & Zabinski, 2000).

A scheme of a "chameleon" coating of the YSZ/Au/DLC/MoS2 type as well the WC/DLC/WS2 type, where the amorphous matrix and hard nanocrystalline phases (YSZ or WC) were used for achieving optimal mechanical properties are presented in Fig. 4.

Fig. 4. Schematic conceptual design of a nanocomposite tribological coating with chameleonlike surface adaptive behaviour (Voevodin et al., 2005).

Carrying out investigations over nanocomposite coatings it was found, that the creation mechanisms of such structures have a form of spinodal transformation. During deposition of nanocomposite coatings using physical vapor deposition methods a spinodal character of the segregation of the crystallized phase (e.g. TiN) and amorphous (np. Si3N4) was observed during production of nanocomposite coating of the nc-TiN/a-Si3N4 type. Such layer is composed of nanocrystalline TiN structure of 3÷4 nm in diameter, positioned in amorphous silicon nitride Si3N4.

During deposition of nanocomposite coatings in the PVD process the spinodal decomposition occurs when following conditions are fulfilled (Zhang & Veprek, 2006):

Different techniques are available for the preparation of nanocomposite coatings. The most promising methods are plasma assisted chemical vapour deposition (PACVD), thermallyinduced chemical vapour deposition (TCVD), magnetron sputtering, vacuum arc evaporation, laser ablation and hybrid techniques consisting of a combination of these. Other techniques, such as ion beam deposition, electrodeposition are also used (Table 1).

Review of Nanocomposite Thin Films and Coatings Deposited by PVD and CVD Technology 151

Fig. 5. Coating equipment with the LARC Technology (Lateral Rotating Arc-Cathodes)

 Fig. 6. Schematic of deposition arrangements to produce DLC and CNx coatings by (a) pulsed laser deposition and (b) filtered cathodic arc deposition. A Ti magnetron was used to grow a functionally graded Ti–TiC–C interface by either a hybrid of laser ablation and magnetron sputtering (a) or a hybrid of filtered cathodic arc and magnetron sputtering (b)

fullerene-like carbon nitride (CNx) (Voevodin et al., 2005).

To enhance the strong points of above mentioned technologies and avoid their weakness the hybrid deposition techniques are used. Yu and co-workers have used hybrid physical vapour deposition system, which combine ion plating and sputter plating in order to modify the properties of coatings, and to enhance controllability of the ion energy and the manageable coatings component (Yu et al., 2009). Voevodin and co-workers used the pulsed laser ablation (PLD) of graphite in combination with magnetron sputtering of titanium and filtered cathodic arc deposition (FCAD) of graphite with magnetron sputtering of titanium (Fig. 6) in order to prepare the unhydrogenated amorphous diamond-like carbon (DLC) and

(Cselle et al., 2002).

(Voevodin et al., 2005).

Uniform deposition for complicated geometries and high deposition rate are the advantages of the CVD method. However, the main concern for the CVD process is that the precursor gases, TiCl4, SiCl4 or SiH4, may pose problems in deposition because they are a fire hazard and corrosive. In conventional thermally activated CVD heating provides sufficient high temperature for the dissociation of gaseous species. In case of TiCl4 at low temperatures the chemical equilibrium is one the side of the chlorides, high temperatures (~1000ºC) are needed to shift the equilibrium towards TiN and HCl.

$$\text{TiCl}\_4 + 2\text{H}\_2 + 0.5\text{N}\_2 \rightarrow \text{TiN} + 4\text{HCl} \tag{1}$$

For most applications (e.g. high speed steel, hot work tool steel, etc.) the low deposition temperature is required to prevent substrate distortion and loss of mechanical properties. It precludes the use of substrates having melting points or tempering temperature much lower than the reaction temperature. Plasma assisted CVD exhibit a distinct advantages over thermal CVD owing to its lower deposition temperature (Koch et al., 2007; Tjong, 2007).

Vacuum arc evaporation technology has high ionization (≥90 %) but limited material. Magnetron sputtering is a low temperature technology, which can deposit various materials, but its ionization is low. In magnetron sputtering process the energetic ion (several hundred to a few thousand electronovolts) bombardment is used to vaporize the target. During magnetron sputtering process, the sputtered atoms carry more energy than the evaporated atoms, therefore sputter-grown films usually have higher density. Moreover, ion bombardment of the growing film can restrict the grain growth and permit the formation of nanocrystalline. In arc evaporation process atoms are removed from source by thermal or electron means. Thermal evaporation has a limitation in multicomponent materials since one of the metallic elements typically evaporates before the other. The advantages of deposition of coatings by means of vacuum arc are the high deposition rate and fully ionized plasma. The disadvantages are the emission of droplets of molten metal from the cathodic spot and the uncontrolled movement of the cathodic spot over the surface. Nowadays one of the commonly used coating equipment for large-scale industrial production is the LARC Technology (Fig. 5). The most important advantages on the LARC Technology come from the rotating cathodes and their lateral position. The cathodes are in permanent rotation; the magnetic field is generated by coils and permanent magnets controlled both vertically and radially (Cselle et al., 2002; Koch et al., 2007).

Sputter deposition Magnetron sputtering

Arc vapour deposition Vacuum arc deposition

Ion implantation Ion beam deposition (IBD)

((ECR-CVD)

Pulsed laser deposition (PLD) Electron beam deposition (EB-PVD)

Plasma enhanced CVD (PECVD) Plasma assistant CVD (PACVD) Electron cyclotron resonance CVD

Ion beam sputtering

Filtered arc deposition

Group Sub-group Methods

Table 1. Main preparation methods for nanocomposite thin films (Zhang et al., 2007).

needed to shift the equilibrium towards TiN and HCl.

Uniform deposition for complicated geometries and high deposition rate are the advantages of the CVD method. However, the main concern for the CVD process is that the precursor gases, TiCl4, SiCl4 or SiH4, may pose problems in deposition because they are a fire hazard and corrosive. In conventional thermally activated CVD heating provides sufficient high temperature for the dissociation of gaseous species. In case of TiCl4 at low temperatures the chemical equilibrium is one the side of the chlorides, high temperatures (~1000ºC) are

 TiCl4 + 2H2 + 0.5N2 TiN + 4HCl (1) For most applications (e.g. high speed steel, hot work tool steel, etc.) the low deposition temperature is required to prevent substrate distortion and loss of mechanical properties. It precludes the use of substrates having melting points or tempering temperature much lower than the reaction temperature. Plasma assisted CVD exhibit a distinct advantages over thermal CVD owing to its lower deposition temperature (Koch et al., 2007; Tjong, 2007). Vacuum arc evaporation technology has high ionization (≥90 %) but limited material. Magnetron sputtering is a low temperature technology, which can deposit various materials, but its ionization is low. In magnetron sputtering process the energetic ion (several hundred to a few thousand electronovolts) bombardment is used to vaporize the target. During magnetron sputtering process, the sputtered atoms carry more energy than the evaporated atoms, therefore sputter-grown films usually have higher density. Moreover, ion bombardment of the growing film can restrict the grain growth and permit the formation of nanocrystalline. In arc evaporation process atoms are removed from source by thermal or electron means. Thermal evaporation has a limitation in multicomponent materials since one of the metallic elements typically evaporates before the other. The advantages of deposition of coatings by means of vacuum arc are the high deposition rate and fully ionized plasma. The disadvantages are the emission of droplets of molten metal from the cathodic spot and the uncontrolled movement of the cathodic spot over the surface. Nowadays one of the commonly used coating equipment for large-scale industrial production is the LARC Technology (Fig. 5). The most important advantages on the LARC Technology come from the rotating cathodes and their lateral position. The cathodes are in permanent rotation; the magnetic field is generated by coils and permanent magnets

controlled both vertically and radially (Cselle et al., 2002; Koch et al., 2007).

Thermal evaporation (TE)

Physical vapour deposition (PVD)

Chemical vapour deposition (CVD)

Fig. 5. Coating equipment with the LARC Technology (Lateral Rotating Arc-Cathodes) (Cselle et al., 2002).

To enhance the strong points of above mentioned technologies and avoid their weakness the hybrid deposition techniques are used. Yu and co-workers have used hybrid physical vapour deposition system, which combine ion plating and sputter plating in order to modify the properties of coatings, and to enhance controllability of the ion energy and the manageable coatings component (Yu et al., 2009). Voevodin and co-workers used the pulsed laser ablation (PLD) of graphite in combination with magnetron sputtering of titanium and filtered cathodic arc deposition (FCAD) of graphite with magnetron sputtering of titanium (Fig. 6) in order to prepare the unhydrogenated amorphous diamond-like carbon (DLC) and fullerene-like carbon nitride (CNx) (Voevodin et al., 2005).

Fig. 6. Schematic of deposition arrangements to produce DLC and CNx coatings by (a) pulsed laser deposition and (b) filtered cathodic arc deposition. A Ti magnetron was used to grow a functionally graded Ti–TiC–C interface by either a hybrid of laser ablation and magnetron sputtering (a) or a hybrid of filtered cathodic arc and magnetron sputtering (b) (Voevodin et al., 2005).

Review of Nanocomposite Thin Films and Coatings Deposited by PVD and CVD Technology 153

attachments create a more powerful tool for the study of qualitative and quantitative chemical analysis, for example X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), energy dispersive X-ray emission (EDX), wavelength dispersive X-ray

Fig. 7. Schematic view of the different signals generated after an electron beam interacts

X-ray photoelectron spectroscopy is the most useful analysis technique used to obtain chemical information about different elements at sample surfaces. In XPS the sample is placed in a high vacuum environment and the beam of low-energy X-rays (or electron) irradiates the sample and produce photo-ionisation. The energy of the ejected photoelectrons is a function of its binding energy (which is the energy required to remove the electron from its atom) and is characteristic of the element from which it was emitted.

 EB=hυ- EK-W (2) where EB is binding energy of the electron from a particular energy level, hυ is the incident X-ray photon (or electron) energy, EK is the kinetic energy of the ejected photoelectron, W is

From the binding energy we can obtain some important information about the samples (Fig. 8) under investigation: the relative quantity of each element, the elements from which it

is made, the chemical state of the elements present, depth distribution (Zhang, 2007).

Fig. 8. Typical XPS core-level spectra of (a) Si 2p and (b) N 1s from several Ti–Si–N lms

emission (WDX), electron back-scattered diffraction (EBSD) (Smith, 2005).

with a bulk specimen (Materials Evaluation and Engineering, Inc., 2010).

The equation which describes the energy of the photo-ionisation process is:

the spectrometer work function (Clarke & Eberhardt, 2002).

(Jiang et al., 2004).

**3.3 X-ray photoelectron spectroscopy (XPS)**

#### **3. Characterization of nanocomposite films**

Film characterization is the inevitable and important step for ensuring of high-quality film for the intended application. Different characterization techniques can be used to identify nanocomposite coatings.

#### **3.1 High resolution transmission electron microscope (HRTEM)**

Since nanoscale irregularities have the enormous inuence on bulk behavior, the high resolution transmission electron microscope has become a powerful and indispensable tool for characterizing nanostructured materials. HRTEM is a powerful technique due to its high imaging spatial resolution (~0.1 nm). Using correct operating conditions and well-prepared samples (specimen materials must be specially prepared to thickness which allow electrons to be transmitted through), high-resolution image characteristics are interpretable directly in terms of projections of individual atomic positions. As the wavelength of electrons is much smaller than that of light, the optimal resolution of transmission electron microscope images is many orders of magnitude better than that of a light microscope. Imaging with the HRTEM enables individual atomic columns to be resolved in most inorganic materials, making it possible to determine the atomic-scale microstructure of lattice defects and other inhomogeneities. Structural features of interest include planar faults such as grain boundaries, interfaces and crystallographic shear planes, linear faults such as dislocations and nanowires, as well as point defects, nanosized particles and local surface morphology. Additional information can be obtained from high-resolution studies, including unique insights into the controlling inuence of structural discontinuities on a range of physical and chemical processes such as phase transformations, oxidation reactions, epitaxial growth and catalysis (Materials Evaluation and Engineering, Inc., 2010; Smith, 2005).

#### **3.2 Scanning electron microscope (SEM)**

Scanning electron microscopy is a very useful technique in the characterization of thin films and undoubtedly the most widely used of all electron beam instruments. SEM is a method for high-resolution imaging of surfaces. Scanning electron microscopy provides magnified images by using electrons instead of light waves (in case of conventional light microscopes). The advantages of SEM over light microscopy include much higher magnification (> 1,000,000×) and greater depth of field up to 100 times. The resolution of modern scanning electron microscopes is typically <10 nm (image resolution of about 0.5 nm can be now achieved in the most recent generation field-emission-gun SEM), so in principle SEM could be used to measure nanocrystalline grain size. The problem is obtaining the appropriate surface contrast for grain sizes in the nanoscale regime. To create the SEM image, the incident electron beam is scanned in a raster pattern across the sample's surface. When an electron beam interacts with a bulk specimen, a variety of signals can be generated. Figure 7 shows the various types of electrons and electromagnetic radiation produced when a high energy electron beam interacts with a bulk specimen (Liu, 2005).

The popularity of the SEM can be attributed to many factors: the versatility of its various modes of imaging, the excellent spatial resolution, the very modest regarding sample preparation, the relatively straightforward interpretation of the acquired images, the accessibility of associated spectroscopy and diffraction techniques. Most electron microscopes have extra attachments to allow them to generate and analyse X-rays or generate and analyse the energy spectra of the secondary emission electrons. These attachments create a more powerful tool for the study of qualitative and quantitative chemical analysis, for example X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), energy dispersive X-ray emission (EDX), wavelength dispersive X-ray emission (WDX), electron back-scattered diffraction (EBSD) (Smith, 2005).

Fig. 7. Schematic view of the different signals generated after an electron beam interacts with a bulk specimen (Materials Evaluation and Engineering, Inc., 2010).

#### **3.3 X-ray photoelectron spectroscopy (XPS)**

152 Nanomaterials

Film characterization is the inevitable and important step for ensuring of high-quality film for the intended application. Different characterization techniques can be used to identify

Since nanoscale irregularities have the enormous inuence on bulk behavior, the high resolution transmission electron microscope has become a powerful and indispensable tool for characterizing nanostructured materials. HRTEM is a powerful technique due to its high imaging spatial resolution (~0.1 nm). Using correct operating conditions and well-prepared samples (specimen materials must be specially prepared to thickness which allow electrons to be transmitted through), high-resolution image characteristics are interpretable directly in terms of projections of individual atomic positions. As the wavelength of electrons is much smaller than that of light, the optimal resolution of transmission electron microscope images is many orders of magnitude better than that of a light microscope. Imaging with the HRTEM enables individual atomic columns to be resolved in most inorganic materials, making it possible to determine the atomic-scale microstructure of lattice defects and other inhomogeneities. Structural features of interest include planar faults such as grain boundaries, interfaces and crystallographic shear planes, linear faults such as dislocations and nanowires, as well as point defects, nanosized particles and local surface morphology. Additional information can be obtained from high-resolution studies, including unique insights into the controlling inuence of structural discontinuities on a range of physical and chemical processes such as phase transformations, oxidation reactions, epitaxial growth and

Scanning electron microscopy is a very useful technique in the characterization of thin films and undoubtedly the most widely used of all electron beam instruments. SEM is a method for high-resolution imaging of surfaces. Scanning electron microscopy provides magnified images by using electrons instead of light waves (in case of conventional light microscopes). The advantages of SEM over light microscopy include much higher magnification (> 1,000,000×) and greater depth of field up to 100 times. The resolution of modern scanning electron microscopes is typically <10 nm (image resolution of about 0.5 nm can be now achieved in the most recent generation field-emission-gun SEM), so in principle SEM could be used to measure nanocrystalline grain size. The problem is obtaining the appropriate surface contrast for grain sizes in the nanoscale regime. To create the SEM image, the incident electron beam is scanned in a raster pattern across the sample's surface. When an electron beam interacts with a bulk specimen, a variety of signals can be generated. Figure 7 shows the various types of electrons and electromagnetic radiation produced when a high

The popularity of the SEM can be attributed to many factors: the versatility of its various modes of imaging, the excellent spatial resolution, the very modest regarding sample preparation, the relatively straightforward interpretation of the acquired images, the accessibility of associated spectroscopy and diffraction techniques. Most electron microscopes have extra attachments to allow them to generate and analyse X-rays or generate and analyse the energy spectra of the secondary emission electrons. These

**3. Characterization of nanocomposite films**

**3.1 High resolution transmission electron microscope (HRTEM)**

catalysis (Materials Evaluation and Engineering, Inc., 2010; Smith, 2005).

energy electron beam interacts with a bulk specimen (Liu, 2005).

**3.2 Scanning electron microscope (SEM)**

nanocomposite coatings.

X-ray photoelectron spectroscopy is the most useful analysis technique used to obtain chemical information about different elements at sample surfaces. In XPS the sample is placed in a high vacuum environment and the beam of low-energy X-rays (or electron) irradiates the sample and produce photo-ionisation. The energy of the ejected photoelectrons is a function of its binding energy (which is the energy required to remove the electron from its atom) and is characteristic of the element from which it was emitted. The equation which describes the energy of the photo-ionisation process is:

$$E\_B = \text{hnp- Ex-W} \tag{2}$$

where EB is binding energy of the electron from a particular energy level, hυ is the incident X-ray photon (or electron) energy, EK is the kinetic energy of the ejected photoelectron, W is the spectrometer work function (Clarke & Eberhardt, 2002).

From the binding energy we can obtain some important information about the samples (Fig. 8) under investigation: the relative quantity of each element, the elements from which it is made, the chemical state of the elements present, depth distribution (Zhang, 2007).

Fig. 8. Typical XPS core-level spectra of (a) Si 2p and (b) N 1s from several Ti–Si–N lms (Jiang et al., 2004).

Review of Nanocomposite Thin Films and Coatings Deposited by PVD and CVD Technology 155

In most studies of the grain size of nanocrystalline materials X-ray line-broadening analysis or direct measurements by transmission electron microscopy are performed. To estimate the grain size, the well-known Scherrer formula is used by measuring the full width at half

> cos

where d is crystallite size, K is the shape factor, is the wavelength of the X-rays , is the full width at half-maximum XRD peak in radians, and is the position of the peak

The Scherrer equation is limited to nano-scale particles. It is not applicable to grains larger than about 100 nm. Otherwise, other methods, in particular transmission electron

Atomic force microscopy has become a powerful tool to detect structural changes at the nanoscale and the importance of AFM, as characterization technique, is further increasing with recent developments in nanoscience and nanotechnology. The scope of AFM applications includes high-resolution examination of surface topography (Fig. 10), compositional mapping of heterogeneous samples and studies of local mechanical, electric, magnetic and thermal properties. These measurements can be performed on scales from hundreds of microns down to nanometers. Areas as large as about 100 µm square to less

In conjunction with the atomic force microscopy nanoindenting is performed. Nanoindenting is a new method to characterize material mechanical properties on a very small scale. Features less than 100 nm across, as well as thin films less than 5 nm thick, can

than 100 nm square can be imaged (Magonov & Yerina, 2005; Roa et al., 2011).

K d (3)

**3.6 Grain size**

maximum.

maximum (FWHM) of the XRD diffraction peak:

microscopy, must be used (Koch et al., 2007).

Fig. 10. AFM topography of the CrN/DLC coating.

**3.7 Atomic force microscopy (AFM)**

#### **3.4 Auger electron spectroscopy (AES)**

Auger electron spectroscopy provides information about the chemical composition of the outermost material comprising a solid surface or interface. The principal advantages of AES over other surface analysis methods are excellent spatial resolution, surface sensitivity (~20 Ǻ), and detection of light elements (Materials Evaluation and Engineering, Inc., 2010). Different penetrations and accuracies of selected compositions analysis method presents Table 2.

Table 2. Composition analysis methods (Zhang, 2007).

#### **3.5 Raman spectroscopy**

Raman spectroscopy is a method of chemical analysis, based on inelastic scattering of monochromatic light, usually from a laser source. Photons of the laser light are absorbed by the sample and then reemitted. Frequency of the reemitted photons is shifted up or down in comparison with original monochromatic frequency, which is called the Raman effect. This shift provides information about vibrational, rotational and other low frequency transitions in molecules. The sample is illuminated with a laser and scattered light is collected. The wavelengths and intensities of the scattered light can be used to identify functional groups in a molecule (Fig. 9) (Xu & Kumar, 2007).

Fig. 9. Raman spectra of the AlCrSiN/DLC coating.

#### **3.6 Grain size**

154 Nanomaterials

Auger electron spectroscopy provides information about the chemical composition of the outermost material comprising a solid surface or interface. The principal advantages of AES over other surface analysis methods are excellent spatial resolution, surface sensitivity (~20 Ǻ), and detection of light elements (Materials Evaluation and Engineering, Inc., 2010). Different penetrations and accuracies of selected compositions analysis method presents

> Detection limits (at. %)

XPS Li-U 0.1÷1 100 µm 1.5 nm AES Li-U 0.5 10 nm 0.5÷7.5 nm RBS Li-U 1.0 1÷4 mm 2÷30 nm EDX Be-U 0.1 0.5÷2.0 µm 1÷3 µm

Raman spectroscopy is a method of chemical analysis, based on inelastic scattering of monochromatic light, usually from a laser source. Photons of the laser light are absorbed by the sample and then reemitted. Frequency of the reemitted photons is shifted up or down in comparison with original monochromatic frequency, which is called the Raman effect. This shift provides information about vibrational, rotational and other low frequency transitions in molecules. The sample is illuminated with a laser and scattered light is collected. The wavelengths and intensities of the scattered light can be used to identify functional groups

200 400<PHONE_NUMBER> 1400 1600 1800 2000

]

Raman Shift [cm-1

Spatial

resolution Penetration

**3.4 Auger electron spectroscopy (AES)**

Elemental range

Table 2. Composition analysis methods (Zhang, 2007).

in a molecule (Fig. 9) (Xu & Kumar, 2007).

1000

Fig. 9. Raman spectra of the AlCrSiN/DLC coating.

1100

1200

1300

1400

Intensity

1500

1600

1700

1800

Table 2.

Analysis method

**3.5 Raman spectroscopy**

In most studies of the grain size of nanocrystalline materials X-ray line-broadening analysis or direct measurements by transmission electron microscopy are performed. To estimate the grain size, the well-known Scherrer formula is used by measuring the full width at half maximum (FWHM) of the XRD diffraction peak:

$$\mathbf{d} = \frac{\mathbf{K}\lambda}{\beta \cos \theta} \tag{3}$$

where d is crystallite size, K is the shape factor, is the wavelength of the X-rays , is the full width at half-maximum XRD peak in radians, and is the position of the peak maximum.

The Scherrer equation is limited to nano-scale particles. It is not applicable to grains larger than about 100 nm. Otherwise, other methods, in particular transmission electron microscopy, must be used (Koch et al., 2007).

#### **3.7 Atomic force microscopy (AFM)**

Atomic force microscopy has become a powerful tool to detect structural changes at the nanoscale and the importance of AFM, as characterization technique, is further increasing with recent developments in nanoscience and nanotechnology. The scope of AFM applications includes high-resolution examination of surface topography (Fig. 10), compositional mapping of heterogeneous samples and studies of local mechanical, electric, magnetic and thermal properties. These measurements can be performed on scales from hundreds of microns down to nanometers. Areas as large as about 100 µm square to less than 100 nm square can be imaged (Magonov & Yerina, 2005; Roa et al., 2011).

Fig. 10. AFM topography of the CrN/DLC coating.

In conjunction with the atomic force microscopy nanoindenting is performed. Nanoindenting is a new method to characterize material mechanical properties on a very small scale. Features less than 100 nm across, as well as thin films less than 5 nm thick, can

Review of Nanocomposite Thin Films and Coatings Deposited by PVD and CVD Technology 157

Nanocomposite coatings can be used for biomedical applications. Implant biomaterials interact with the body through their surface. Consequently, the properties of the material surfaces are critically important in determining biocompatibility, biological responses and bone-implants interface reaction. Surface coatings like traditional amorphous diamond-like carbon modified by doping with silicon and chromium biocompatible coatings are one of the ways of improving both the mechanical, physical and chemical properties of implants in direct contact with the blood (Okpalugo et al., 2007). In orthopaedic and dental implant application, surface coatings have been used to impart bioactivity to the metal substrates to

Nanocomposite coatings are widely used in solar energy conversion and optoelectronic applications. Nanocomposite thin films or coatings for solar energy conversion should have a high absorption of solar radiation and low thermal emission at their operating temperatures. There are many different thin films solar cells system, such as: a-Si:H/a-SiGe:H/nc-Si:H, a-Si:H/nc-Si:H/nc-Si:H, a-Si:H/nc-Si:H. Other promising thin films solar cells may include CuInS2, CuInGaSe, CdTe, TiO2, CdS (Yin, 2007). Hydrogenated amorphous silicon (a-Si:H) or nanocrystalline silicon (nc-Si) is currently used in thin film

The nanocomposite coatings are still at the beginning of their development. Further research activity in the field of nanocomposite films and coatings should be concentrated on the

development of new technology system for production of nanocomposite coatings in

increased utilization of coatings in many types of applications including those in the

development of hybrid coatings with nanophase biomaterials for biomedical

development of new advanced coatings with unique physical and functional properties.

The interest, caused by Feynman in the sixties of the last century, in processes occurring in nanometric scale has resulted in a very dynamical development of investigation projects in nanotechnology, nanomechanics and nanomaterials. Nanocomposite thin films and coatings

Nanocomposite thin films and coatings, that characterised with nanocrystalline grains of transition-metal nitride or carbide embedded in an amorphous phase, are a promising instrument for improving the characteristics of various functional surfaces and are rapidly trend of surface engineering. To date, several hard coatings based on nanocomposites

development of protective coatings with oxidation resistance exceeding 2000ºC,

enhance and accelerate skeletal fixation.

transistor liquid displays (TFT-LCDs).

following problems (Musil, 2007; Voevodin et al., 2005): development of films with controlled grains size,

new physical and/or chemical conditions,

aerospace and automotive industries,

 nanocrystallisation of amorphous materials, development and scale-up of deposition processes, development of high fracture toughness coatings,

**5. Future trends**

applications,

**6. Summary**

are also the part of these activities.

be evaluated. Test methods include indentation for comparative and quantitative hardness determination and scratching for evaluation of wear resistance and thin film adhesion. Indentation forces ranging from 1 µN to 100 mN can be made to measure material hardness (Materials Evaluation and Engineering, Inc., 2010).

#### **4. Applications of nanocomposite films**

Since the introduction in 1993 of nc-Ti1-xAlxN/a-Si3N4 nanocomposite coatings for machining applications, such as steel turning, drilling and milling (Holubar et al., 2000), many new nanocomposite coatings have been developed in order to increase the machining speed, the lifetime of the coated tools and improve the quality of the machined surface.

Due to high hardness and wear resistance nanocomposite coatings show excellent results even at normal cutting conditions. The high hardness of the nanocomposite coatings can be maintained at high temperatures. The enormous hardness will be extremely important for dry cutting and for machining with minimum quantity lubrication.

Modern nanostructured coatings for structural and functional applications, are used mainly for wear protection of machining tools and for the reduction of friction in sliding parts. The nanocomposite coatings find increasing number of applications also on tools for forming, e.g. extrusion, stamping, etc. The demands on the tool material of an extrusion die are high hardness, creep resistance, yield strength, toughness at elevated temperatures, wear and corrosion resistance. It should be suitable for surface coatings. Hard coating, such as nc-AlCrN/a-Si3N4, nc-AlTiN/a-Si3N4 deposited by physical vapour deposition on extrusion dies have been used in order to increase their life time and properties (Fig. 11) (Faga et al., 2007; Veprek & Veprek-Heijman, 2008).

Fig. 11. The performance of uncoated and coated tool for folding boxes for cigarettes (Veprek & Veprek-Heijman, 2008).

An important advantage of the nc-TiN/a-Si3N4, nc-AlTiN/ a-Si3N4, and nc-AlCrN/ a-Si3N4 nanocomposites coatings is their high thermal stability and high oxidation resistance up to temperatures of more than 800ºC (Veprek & Veprek-Heijman, 2008).

Nanocomposite coatings can be used for biomedical applications. Implant biomaterials interact with the body through their surface. Consequently, the properties of the material surfaces are critically important in determining biocompatibility, biological responses and bone-implants interface reaction. Surface coatings like traditional amorphous diamond-like carbon modified by doping with silicon and chromium biocompatible coatings are one of the ways of improving both the mechanical, physical and chemical properties of implants in direct contact with the blood (Okpalugo et al., 2007). In orthopaedic and dental implant application, surface coatings have been used to impart bioactivity to the metal substrates to enhance and accelerate skeletal fixation.

Nanocomposite coatings are widely used in solar energy conversion and optoelectronic applications. Nanocomposite thin films or coatings for solar energy conversion should have a high absorption of solar radiation and low thermal emission at their operating temperatures. There are many different thin films solar cells system, such as: a-Si:H/a-SiGe:H/nc-Si:H, a-Si:H/nc-Si:H/nc-Si:H, a-Si:H/nc-Si:H. Other promising thin films solar cells may include CuInS2, CuInGaSe, CdTe, TiO2, CdS (Yin, 2007). Hydrogenated amorphous silicon (a-Si:H) or nanocrystalline silicon (nc-Si) is currently used in thin film transistor liquid displays (TFT-LCDs).

### **5. Future trends**

156 Nanomaterials

be evaluated. Test methods include indentation for comparative and quantitative hardness determination and scratching for evaluation of wear resistance and thin film adhesion. Indentation forces ranging from 1 µN to 100 mN can be made to measure material hardness

Since the introduction in 1993 of nc-Ti1-xAlxN/a-Si3N4 nanocomposite coatings for machining applications, such as steel turning, drilling and milling (Holubar et al., 2000), many new nanocomposite coatings have been developed in order to increase the machining speed, the lifetime of the coated tools and improve the quality of the machined surface. Due to high hardness and wear resistance nanocomposite coatings show excellent results even at normal cutting conditions. The high hardness of the nanocomposite coatings can be maintained at high temperatures. The enormous hardness will be extremely important for

Modern nanostructured coatings for structural and functional applications, are used mainly for wear protection of machining tools and for the reduction of friction in sliding parts. The nanocomposite coatings find increasing number of applications also on tools for forming, e.g. extrusion, stamping, etc. The demands on the tool material of an extrusion die are high hardness, creep resistance, yield strength, toughness at elevated temperatures, wear and corrosion resistance. It should be suitable for surface coatings. Hard coating, such as nc-AlCrN/a-Si3N4, nc-AlTiN/a-Si3N4 deposited by physical vapour deposition on extrusion dies have been used in order to increase their life time and properties (Fig. 11) (Faga et al.,

Fig. 11. The performance of uncoated and coated tool for folding boxes for cigarettes

temperatures of more than 800ºC (Veprek & Veprek-Heijman, 2008).

An important advantage of the nc-TiN/a-Si3N4, nc-AlTiN/ a-Si3N4, and nc-AlCrN/ a-Si3N4 nanocomposites coatings is their high thermal stability and high oxidation resistance up to

(Materials Evaluation and Engineering, Inc., 2010).

dry cutting and for machining with minimum quantity lubrication.

**4. Applications of nanocomposite films**

2007; Veprek & Veprek-Heijman, 2008).

(Veprek & Veprek-Heijman, 2008).

The nanocomposite coatings are still at the beginning of their development. Further research activity in the field of nanocomposite films and coatings should be concentrated on the following problems (Musil, 2007; Voevodin et al., 2005):

#### **6. Summary**

The interest, caused by Feynman in the sixties of the last century, in processes occurring in nanometric scale has resulted in a very dynamical development of investigation projects in nanotechnology, nanomechanics and nanomaterials. Nanocomposite thin films and coatings are also the part of these activities.

Nanocomposite thin films and coatings, that characterised with nanocrystalline grains of transition-metal nitride or carbide embedded in an amorphous phase, are a promising instrument for improving the characteristics of various functional surfaces and are rapidly trend of surface engineering. To date, several hard coatings based on nanocomposites

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Park, I.W.; Choi, S.R.; Lee, M.H. & Kim, K.H. (2003). Effects of Si addition on the

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have been successfully developed and commercialized for engineering applications. There are many possible future applications of nanocomposite thin films and coatings. Further improvement of the presently available and newly developed nanocomposite coatings will push the technology towards new horizons. Several techniques, in particular PVD and CVD are now available for the deposition of nanocomposite films on various kinds of substrates.

Despite the big number of scientific investigations in the field of nanocomposite thin films and coatings, with results published in professional and competent literature, still some lack and deficiency of verified material knowledge occurs.

#### **7. Acknowledgment**

The research was partially financed within the framework of the Polish State Committee for Scientific Research Project No N N507 550738 headed by Dr Krzysztof Lukaszkowicz.

#### **8. References**

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Despite the big number of scientific investigations in the field of nanocomposite thin films and coatings, with results published in professional and competent literature, still some lack

The research was partially financed within the framework of the Polish State Committee for Scientific Research Project No N N507 550738 headed by Dr Krzysztof Lukaszkowicz.

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**Part 3**

**State-of-the-Art Polymers**

Zou, C.W.; Wang, H.J.; Li, M.; Yu, J.F.; Liu, C.S.; Guo, L.P. & Fu, D.J. (2010). Characterization and properties of TiN-containing amorphous Ti-Si-N nanocomposite coatings prepared by arc assisted middle frequency magnetron sputtering. *Vacuum*, vol. 84, (February 2010), pp. 817-822, ISSN 0042-207X.

## **Part 3**

**State-of-the-Art Polymers**

162 Nanomaterials

Zou, C.W.; Wang, H.J.; Li, M.; Yu, J.F.; Liu, C.S.; Guo, L.P. & Fu, D.J. (2010). Characterization

(February 2010), pp. 817-822, ISSN 0042-207X.

and properties of TiN-containing amorphous Ti-Si-N nanocomposite coatings prepared by arc assisted middle frequency magnetron sputtering. *Vacuum*, vol. 84,

**8**

*Korea*

**Polymer/Montmorillonite/Silver**

**Electrospraying Technique**

 *Kyungpook National University, Daegu,*

*3R&D Division, Taihan Textile Co. Ltd., Daegu,*

**Nanocomposite Micro- and Nanoparticles**

*4Department of Materials and Components Engineering, Dong-eui University, Busan,*

Polymer nanocomposite materials have the capacity for producing a synergetic association with surpassing merit properties which cannot be obtained from the individual components. Such materials can be obtained by simply mixing required organic and inorganic components. The introduction of inorganic material into the polymer matrix has proved to be an effective and low-cost method to improve the performance of the existing polymer materials (Okamoto et al., 2000; Ramos et al., 2000; Wu et al., 2006; Zhu et al., 2000). It has various applications, such as new biological materials (biosensors and biochips), biocompatible thin coatings for medical applications, biodegradable scaffolds, drug delivery system and filter systems (Matsumoto et al., 2005; Okuda et al., 1996; Salata et al., 1997;

The synthesis of polymer nanocomposites can be carried out by many different methods. For example, in-situ polymerization of monomers inside the galleries of the inorganic host has been one of the common methods for preparation of nanocomposites. Another common methods are based on melt intercalation, solventless melt intercalation, using microwaves, latex-colloid interaction, solvent evaporation, spray drying, shirasu porous glass membrane emulsification technique and electrospraying, etc. (Berkland et al., 2001; Ma et al., 1999; Messersmith et al., 1993; Mu et al., 2001; Oriakhi et al., 1995; Rosca et. al.,2004; Usuki et al., 1993). This article is concerned with fabrication of polymer nanocomposite particles by *in-situ* suspension polymerization and electrospraying which are represented as a traditional and current general method for synthesis of nanocomposite. The effectiveness of these nanocomposite particles are demonstrated with a field emission-type scanning electron microscope (FE-SEM), a transmission electron microscopy (TEM), an optical microscope, a reflection type X-ray diffraction (XRD), a

**1. Introduction**

Sinha et al., 2004).

**Prepared by** *In-Situ* **Polymerization and**

Jeong Hyun Yeum1, Jae Hyeung Park1, Jae Young Choi1 Jong Won Kim2, Sung Kyou Han3 and Weontae Oh4 *1Department of Advanced Organic Materials Science & Engineering,*

*2R&D Division, Korea Dyeing Technology Center, Daegu,*

### **Polymer/Montmorillonite/Silver Nanocomposite Micro- and Nanoparticles Prepared by** *In-Situ* **Polymerization and Electrospraying Technique**

Jeong Hyun Yeum1, Jae Hyeung Park1, Jae Young Choi1 Jong Won Kim2, Sung Kyou Han3 and Weontae Oh4 *1Department of Advanced Organic Materials Science & Engineering, Kyungpook National University, Daegu, 2R&D Division, Korea Dyeing Technology Center, Daegu, 3R&D Division, Taihan Textile Co. Ltd., Daegu, 4Department of Materials and Components Engineering, Dong-eui University, Busan, Korea*

#### **1. Introduction**

Polymer nanocomposite materials have the capacity for producing a synergetic association with surpassing merit properties which cannot be obtained from the individual components. Such materials can be obtained by simply mixing required organic and inorganic components. The introduction of inorganic material into the polymer matrix has proved to be an effective and low-cost method to improve the performance of the existing polymer materials (Okamoto et al., 2000; Ramos et al., 2000; Wu et al., 2006; Zhu et al., 2000). It has various applications, such as new biological materials (biosensors and biochips), biocompatible thin coatings for medical applications, biodegradable scaffolds, drug delivery system and filter systems (Matsumoto et al., 2005; Okuda et al., 1996; Salata et al., 1997; Sinha et al., 2004).

The synthesis of polymer nanocomposites can be carried out by many different methods. For example, in-situ polymerization of monomers inside the galleries of the inorganic host has been one of the common methods for preparation of nanocomposites. Another common methods are based on melt intercalation, solventless melt intercalation, using microwaves, latex-colloid interaction, solvent evaporation, spray drying, shirasu porous glass membrane emulsification technique and electrospraying, etc. (Berkland et al., 2001; Ma et al., 1999; Messersmith et al., 1993; Mu et al., 2001; Oriakhi et al., 1995; Rosca et. al.,2004; Usuki et al., 1993). This article is concerned with fabrication of polymer nanocomposite particles by *in-situ* suspension polymerization and electrospraying which are represented as a traditional and current general method for synthesis of nanocomposite. The effectiveness of these nanocomposite particles are demonstrated with a field emission-type scanning electron microscope (FE-SEM), a transmission electron microscopy (TEM), an optical microscope, a reflection type X-ray diffraction (XRD), a

Polymer/Montmorillonite/Silver Nanocomposite

polymerization conditions are listed in Table 1.

are listed in Table 1.

Initiator concentration

**microparticles**

Micro- and Nanoparticles Prepared by *In-Situ* Polymerization and Electrospraying Technique 167

suspending agent was first dissolved in water under nitrogen atmosphere with constant stirring. Surfactant was dissolved in VAc monomer. After the surfactant was dissolved, Ag nanoparticle in water suspension and desired initiator was mixed with VAc monomer under ultrasonification for 5 min using Bandelin UW 3,100 equipment. The above mixture was poured into a flask and charged at once at a fixed polymerization temperature. After prefixed reaction time, the reaction liquor was cooled and kept for more than 24 h to allow complete sedimentation of PVAc/Ag nanocomposite microparticles. The PVAc/Ag nanocomposite microparticles were then filtered and washed with warm water to eliminate residual VAc and suspending agent, and dried under vacuum. Conversion was calculated by gravimetric method. In the case of calculating of conversion, weight of Ag was ignored because the total weight of used Ag nanoparticles is less than 0.5% of polymer weight. Conversions were averages of three measurements. The detailed polymerization conditions

Suspending agent was dissolved in water under a nitrogen atmosphere with constant stirring in a 250 ml reactor fitted with a condenser. CTAB was mixed with the MMT in the monomer phase prior to suspension polymerization. The ADMVN was added at a fixed polymerization temperature. After predetermined times, the reaction mixture was cooled and kept for 24 h to allow the precipitation and separation of the PVAc/MMT nanocomposite microparticles. The collected PVAc/MMT nanocomposite microparticles were further washed with warm water. Conversion was calculated by measuring the weight of the PVAc/MMT using the average value from three determinations. The detailed

Condition PVAc/Ag PVA/PVAc/MMT

10-4, 5×10-4, 10-3 mol/mol of VAc

10-4, 5×10-4, 10-3 mol/mol of VAc

**2.1.3 Preparation of PVA/PVAc/MMT nanocomposite microparticles**

Type of initiator ADMVN ADMVN Type of suspending agent PVA PVA

VAc/water 0.5 l/l 0.5 l/l Rpm 500 500

Table 1. Reaction conditions for the suspension polymerization

Temperature 30, 40, 50 oC 30, 40, 50 oC Inorganic material concentration 3 wt.% of VAc 1 wt.% of VAc Surfactant concentration 0, 0.06 wt.% of VAc 0.5 wt.% of VAc

**2.1.4 Heterogeneous saponification of PVA/PVAc/MMT nanocomposite**

To prepare PVA/PVAc/MMT nanocomposite microparticles, heterogeneous saponification of PVAc/MMT nanocomposite microparticles was conducted in a flask equipped with a reflux condenser, a thermocouple, a dropping funnel, and a stirring device. The alkali solution used

Suspending agent concentration 1.5, 5, 9 g/dl of water 1.5 g/dl of water

Fourier transform spectroscopy (FT-IR), a thermogravimetric analysis (TGA), a nuclear magnetic resonance Spectrometer (1H-NMR), and the anti-bacterial performance was also discussed.

#### **2.** *In-Situ* **suspension polymerization for polymer/silver and polymer/montmorillonite nanocomposite microparticles**

For a long time, quite a range of polymer/inorganic nanocomposites have been investigated via *in-situ* suspension polymerization. Using suspension polymerization to prepare polymer/inorganic nanocomposite particle is interesting in terms of an easy manipulation, low cost, and controllable particle size. It is well known that a range of variables, such as the type and amount of initiator and suspending agent, the polymerization temperature, the monomer to water ratio, and the agitation speed, affect the molecular weight of the polymer synthesized (Gotoh et al., 2000; Giannetti et al.,1986; Hatchett et al., 1999; Huang et al., 1991; Lee et al., 2004).

In this section, we are reporting the *in-situ* synthesis of poly(vinyl acetate) (PVAc)/silver (Ag) and poly(vinyl alcohol) (PVA)/PVAc/montmorillonite (MMT) nanocomposite particles using a suspension polymerization technique (Jung et al., 2006; Jung et al., 2007; Yeum et al., 2005). The effects of MMT and Ag on the morphology, size, conversion rate, and polymerization time of nanocomposite particles were examined. According to the inorganic materials and polymerization process, diffrent type of particles such as spherical, rugged surface and golf ball shape microparticles are successfully prepared. The X-ray diffraction analysis illustrated that the clay silicate layer are intercalated in the polymer matrix.

### **2.1 Experimental**

#### **2.1.1 Materials**

Vinyl acetate (VAc) purchased from Sigma-Aldrich was washed with an aqueous solution of NaHSO3 and water, and then dried with anhydrous CaCl2 followed by distillation under nitrogen atmosphere at a reduced pressure. The initiator, 2,2'-azobis (2,4-dimethylvaleronitrile) (ADMVN) (Wako Co.) was recrystallized twice in methanol before use. PVA with number average molecular weight of 127,000 and degree of saponification of 88% (Aldrich Co.) was used as a suspending agent. Aqueous Ag nanoparticles dispersion (AGS-WP001,10 000 ppm) with diameters ca. 15–30 nm were purchased from Miji Tech. Co., Ltd., Korean. Pristine Na-MMT, Kunipia-F from Kunimine, Japan, was used as received. It consists of exchangeable sodium ions with cationic exchange capacity of ca. 119 meq/100 g. The average particle size and surface area of Na-MMT were 100–1,000 nm and 750 m2/g, respectively. Polyethylene glycol dipolyhydroxystearate (Arlacel P135), purchased from Uniquema, and cationic surfactant, such as cetyltrimethylammonium bromide (CTAB), obtained from Aldrich, are used as surfactants in order to disperse the Ag and MMT in polymer matrix, respectively. Deionized water was used for all of the experiments.

#### **2.1.2 Preparation of PVAc/Ag nanocomposite microparticles**

To prepare PVAc/Ag nanocomposite microparticles, a suspension polymerization approach in the presence of aqueous Ag nanoparticle was used. The polymerization was conducted in a 250 ml three-neck round bottom flask fitted with a condenser. In a typical run, the

Fourier transform spectroscopy (FT-IR), a thermogravimetric analysis (TGA), a nuclear magnetic resonance Spectrometer (1H-NMR), and the anti-bacterial performance was also

For a long time, quite a range of polymer/inorganic nanocomposites have been investigated via *in-situ* suspension polymerization. Using suspension polymerization to prepare polymer/inorganic nanocomposite particle is interesting in terms of an easy manipulation, low cost, and controllable particle size. It is well known that a range of variables, such as the type and amount of initiator and suspending agent, the polymerization temperature, the monomer to water ratio, and the agitation speed, affect the molecular weight of the polymer synthesized (Gotoh et al., 2000; Giannetti et al.,1986; Hatchett et al., 1999; Huang et al., 1991;

In this section, we are reporting the *in-situ* synthesis of poly(vinyl acetate) (PVAc)/silver (Ag) and poly(vinyl alcohol) (PVA)/PVAc/montmorillonite (MMT) nanocomposite particles using a suspension polymerization technique (Jung et al., 2006; Jung et al., 2007; Yeum et al., 2005). The effects of MMT and Ag on the morphology, size, conversion rate, and polymerization time of nanocomposite particles were examined. According to the inorganic materials and polymerization process, diffrent type of particles such as spherical, rugged surface and golf ball shape microparticles are successfully prepared. The X-ray diffraction analysis illustrated that the clay silicate layer are intercalated in the

Vinyl acetate (VAc) purchased from Sigma-Aldrich was washed with an aqueous solution of NaHSO3 and water, and then dried with anhydrous CaCl2 followed by distillation under nitrogen atmosphere at a reduced pressure. The initiator, 2,2'-azobis (2,4-dimethylvaleronitrile) (ADMVN) (Wako Co.) was recrystallized twice in methanol before use. PVA with number average molecular weight of 127,000 and degree of saponification of 88% (Aldrich Co.) was used as a suspending agent. Aqueous Ag nanoparticles dispersion (AGS-WP001,10 000 ppm) with diameters ca. 15–30 nm were purchased from Miji Tech. Co., Ltd., Korean. Pristine Na-MMT, Kunipia-F from Kunimine, Japan, was used as received. It consists of exchangeable sodium ions with cationic exchange capacity of ca. 119 meq/100 g. The average particle size and surface area of Na-MMT were 100–1,000 nm and 750 m2/g, respectively. Polyethylene glycol dipolyhydroxystearate (Arlacel P135), purchased from Uniquema, and cationic surfactant, such as cetyltrimethylammonium bromide (CTAB), obtained from Aldrich, are used as surfactants in order to disperse the Ag and MMT in polymer matrix, respectively.

To prepare PVAc/Ag nanocomposite microparticles, a suspension polymerization approach in the presence of aqueous Ag nanoparticle was used. The polymerization was conducted in a 250 ml three-neck round bottom flask fitted with a condenser. In a typical run, the

**2.** *In-Situ* **suspension polymerization for polymer/silver and polymer/montmorillonite nanocomposite microparticles**

discussed.

Lee et al., 2004).

polymer matrix.

**2.1 Experimental 2.1.1 Materials**

Deionized water was used for all of the experiments.

**2.1.2 Preparation of PVAc/Ag nanocomposite microparticles**

suspending agent was first dissolved in water under nitrogen atmosphere with constant stirring. Surfactant was dissolved in VAc monomer. After the surfactant was dissolved, Ag nanoparticle in water suspension and desired initiator was mixed with VAc monomer under ultrasonification for 5 min using Bandelin UW 3,100 equipment. The above mixture was poured into a flask and charged at once at a fixed polymerization temperature. After prefixed reaction time, the reaction liquor was cooled and kept for more than 24 h to allow complete sedimentation of PVAc/Ag nanocomposite microparticles. The PVAc/Ag nanocomposite microparticles were then filtered and washed with warm water to eliminate residual VAc and suspending agent, and dried under vacuum. Conversion was calculated by gravimetric method. In the case of calculating of conversion, weight of Ag was ignored because the total weight of used Ag nanoparticles is less than 0.5% of polymer weight. Conversions were averages of three measurements. The detailed polymerization conditions are listed in Table 1.

#### **2.1.3 Preparation of PVA/PVAc/MMT nanocomposite microparticles**

Suspending agent was dissolved in water under a nitrogen atmosphere with constant stirring in a 250 ml reactor fitted with a condenser. CTAB was mixed with the MMT in the monomer phase prior to suspension polymerization. The ADMVN was added at a fixed polymerization temperature. After predetermined times, the reaction mixture was cooled and kept for 24 h to allow the precipitation and separation of the PVAc/MMT nanocomposite microparticles. The collected PVAc/MMT nanocomposite microparticles were further washed with warm water. Conversion was calculated by measuring the weight of the PVAc/MMT using the average value from three determinations. The detailed polymerization conditions are listed in Table 1.

Table 1. Reaction conditions for the suspension polymerization

#### **2.1.4 Heterogeneous saponification of PVA/PVAc/MMT nanocomposite microparticles**

To prepare PVA/PVAc/MMT nanocomposite microparticles, heterogeneous saponification of PVAc/MMT nanocomposite microparticles was conducted in a flask equipped with a reflux condenser, a thermocouple, a dropping funnel, and a stirring device. The alkali solution used

Polymer/Montmorillonite/Silver Nanocomposite

Micro- and Nanoparticles Prepared by *In-Situ* Polymerization and Electrospraying Technique 169

Fig. 1. Conversion vs. polymerization time (a,b,c) at different polymerization temperatures with [ADMVN]=10-4 mol/mol of VAc and (d,e,f) at different [ADMVN] with reaction

SEM photographs of (a) pure PVAc microparticles, (b) PVAc/Ag nanocomposite microparticles without surfactant and (c) PVAc/Ag nanocomposite microparticles with surfactant suspension-polymerized with a suspending agent concentration of 5.0 g/dl of water are presented in Figure 2, respectively. It is surprising that three different appearances of microparticles, one with smooth surface, and another with rugged surface and the other with golf ball shape were observed. From the SEM observation, it is estimated that ca. 10– 20% of particles when polymerized without surfactant are rugged surface. We believe this phenomenon must be related to the aggregation of Ag nanoparticles during the polymerization. It should be noted that the Ag nanoparticles used in this study are in an aqueous suspension form, so the Ag nanoparticles are relatively hydrophilic. For this reason, the Ag particles aggregate to small clusters when they are encapsulated in polymer phase. If these aggregated silver particles stay on the surface of the polymer microparticles, rugged microparticles may be obtained. On the other hand, PVAc/Ag nanocomposite microparticles which were polymerized with modified Ag nanoparticles have golf ball shape. Because of the low hydrophile–lyophile balance number of Arlacel P135, the surface of the Ag nanoparticles was converted from hydrophilic to hydrophobic by the adsorption of Arlacel P135, which resulted in a good dispersion of the Ag nanoparticles in monomerdroplets and polymer matrix. The detailed mechanism, such as why PVAc/Ag nanocomposite microparticles have different appearances according to surfactant, is shown in Figure 3. But the reason why only about 10–20% of the microspheres are in rugged

temperature at 30 oC. (suspending agent concentration: 1.5 g/dl of water)

surface, is not clear. Further work in this area definitely is needed.

**<IP_ADDRESS> Morphology and structure property**

for saponification contains 10 g of sodium hydroxide, 10 g of sodium sulfate, 10 g of methanol and 100 g of water. The prepared PVAc/MMT nanocomposite microparticles were slowly added into the alkali solution at 50 °C with gentle stirring. The saponification was stopped at the required time and a PVA shell was formed on the surface of the PVAc/MMT microparticles. After the required reaction time, the mixture was poured into cold water and kept for 1 day to allow the precipitation of spherical core/shell PVA/PVAc/MMT nanocomposite microparticles. Finally, the solid saponification product was filtered and washed several times with water and dried in a vacuum at 40 oC for 1 day.

#### **2.1.5 Characterizations**

The morphology of nanocomposite microparticles were examined using a SEM(Hitachi S-570). To obtain the average size and size distribution, five SEM photographs and more than 200 particles were collected by computer, which linked with the SEM, followed by statistical analysis of data by computer. FT-IR spectrum of the sample was obtained using a Perkin-Elmer 1650 that cast on potassium bromide. XRD measurements were performed at room temperature on a Rigaku (D/Max IIIB) X-ray diffractometer using Ni-filtered CuKα (λ=1.54 Å) radiation. The core/shell structure of PVA/PVAc/MMT nanocomposite microparticles was examined using an optical microscope (Leica DC 100). The degree of saponification (DS) of PVA/PVAc/MMT nanocomposite microparticles was determined by the ratio of methyl and methylene proton peaks in the 1H-NMR spectrometer (Varian, Sun Unity 300).

#### **2.2 Results and discussion**

#### **2.2.1 PVAc/Ag nanocomposite microparticles**

#### **<IP_ADDRESS> Suspension polymerization behaviour**

Figure 1(a,b,c) presents the conversion-time relationship at different polymerization temperatures with initiator concentration at 10-4 mol/mol of VAc. Generally speaking, the reaction conversion increased with increasing polymerization temperature, regardless of the presence of Ag nanoparticles. Although a low initiator concentration (10-4 mol/mol of VAc)was used, the conversion increased steadily with the reaction time at a reaction temperature of 30 oC until ca. 95% of conversion was arrived. In contrary, such a high conversion is impossible in the bulk polymerization of PVAc. The high molecular weight and high conversion obtained suggest that the chain transfer and termination reactions were not significant at the conditions used in this study. As the slope of the curve on the conversion-time plot represents the polymerization rate, the bigger the slope (steeper), the higher the polymerization rate. As can be seen from Figure 1, the introduction of unmodified silver nanoparticles into the system slightly decreased the polymerization rate, in comparison with the absence of them. Otherwise, the rates of polymerization with modified silver nanoparticles are slightly higher than these without silver nanoparticles. The actual reason for the increase in the polymerization rate when the silver nanoparticles were dispersed in the water phase, but the decrease in the polymerization rate when the silver nanoparticles were dispersed in monomer phase is not clear and more work is needed(Lee et al., 2008; Yeum et al., 2005; Yeum et al., 2005). As shown in Figure 1(d.e.f), the polymerization rate, at a reaction temperature of 30 oC, increased with increasing initiator concentration, in accordance with theoretical prediction (Odian, 1981).

Fig. 1. Conversion vs. polymerization time (a,b,c) at different polymerization temperatures with [ADMVN]=10-4 mol/mol of VAc and (d,e,f) at different [ADMVN] with reaction temperature at 30 oC. (suspending agent concentration: 1.5 g/dl of water)

#### **<IP_ADDRESS> Morphology and structure property**

168 Nanomaterials

for saponification contains 10 g of sodium hydroxide, 10 g of sodium sulfate, 10 g of methanol and 100 g of water. The prepared PVAc/MMT nanocomposite microparticles were slowly added into the alkali solution at 50 °C with gentle stirring. The saponification was stopped at the required time and a PVA shell was formed on the surface of the PVAc/MMT microparticles. After the required reaction time, the mixture was poured into cold water and kept for 1 day to allow the precipitation of spherical core/shell PVA/PVAc/MMT nanocomposite microparticles. Finally, the solid saponification product was filtered and

The morphology of nanocomposite microparticles were examined using a SEM(Hitachi S-570). To obtain the average size and size distribution, five SEM photographs and more than 200 particles were collected by computer, which linked with the SEM, followed by statistical analysis of data by computer. FT-IR spectrum of the sample was obtained using a Perkin-Elmer 1650 that cast on potassium bromide. XRD measurements were performed at room temperature on a Rigaku (D/Max IIIB) X-ray diffractometer using Ni-filtered CuKα (λ=1.54 Å) radiation. The core/shell structure of PVA/PVAc/MMT nanocomposite microparticles was examined using an optical microscope (Leica DC 100). The degree of saponification (DS) of PVA/PVAc/MMT nanocomposite microparticles was determined by the ratio of methyl and methylene proton peaks in the 1H-NMR spectrometer (Varian,

Figure 1(a,b,c) presents the conversion-time relationship at different polymerization temperatures with initiator concentration at 10-4 mol/mol of VAc. Generally speaking, the reaction conversion increased with increasing polymerization temperature, regardless of the presence of Ag nanoparticles. Although a low initiator concentration (10-4 mol/mol of VAc)was used, the conversion increased steadily with the reaction time at a reaction temperature of 30 oC until ca. 95% of conversion was arrived. In contrary, such a high conversion is impossible in the bulk polymerization of PVAc. The high molecular weight and high conversion obtained suggest that the chain transfer and termination reactions were not significant at the conditions used in this study. As the slope of the curve on the conversion-time plot represents the polymerization rate, the bigger the slope (steeper), the higher the polymerization rate. As can be seen from Figure 1, the introduction of unmodified silver nanoparticles into the system slightly decreased the polymerization rate, in comparison with the absence of them. Otherwise, the rates of polymerization with modified silver nanoparticles are slightly higher than these without silver nanoparticles. The actual reason for the increase in the polymerization rate when the silver nanoparticles were dispersed in the water phase, but the decrease in the polymerization rate when the silver nanoparticles were dispersed in monomer phase is not clear and more work is needed(Lee et al., 2008; Yeum et al., 2005; Yeum et al., 2005). As shown in Figure 1(d.e.f), the polymerization rate, at a reaction temperature of 30 oC, increased with increasing initiator

concentration, in accordance with theoretical prediction (Odian, 1981).

washed several times with water and dried in a vacuum at 40 oC for 1 day.

**2.1.5 Characterizations**

Sun Unity 300).

**2.2 Results and discussion**

**2.2.1 PVAc/Ag nanocomposite microparticles <IP_ADDRESS> Suspension polymerization behaviour**

SEM photographs of (a) pure PVAc microparticles, (b) PVAc/Ag nanocomposite microparticles without surfactant and (c) PVAc/Ag nanocomposite microparticles with surfactant suspension-polymerized with a suspending agent concentration of 5.0 g/dl of water are presented in Figure 2, respectively. It is surprising that three different appearances of microparticles, one with smooth surface, and another with rugged surface and the other with golf ball shape were observed. From the SEM observation, it is estimated that ca. 10– 20% of particles when polymerized without surfactant are rugged surface. We believe this phenomenon must be related to the aggregation of Ag nanoparticles during the polymerization. It should be noted that the Ag nanoparticles used in this study are in an aqueous suspension form, so the Ag nanoparticles are relatively hydrophilic. For this reason, the Ag particles aggregate to small clusters when they are encapsulated in polymer phase. If these aggregated silver particles stay on the surface of the polymer microparticles, rugged microparticles may be obtained. On the other hand, PVAc/Ag nanocomposite microparticles which were polymerized with modified Ag nanoparticles have golf ball shape. Because of the low hydrophile–lyophile balance number of Arlacel P135, the surface of the Ag nanoparticles was converted from hydrophilic to hydrophobic by the adsorption of Arlacel P135, which resulted in a good dispersion of the Ag nanoparticles in monomerdroplets and polymer matrix. The detailed mechanism, such as why PVAc/Ag nanocomposite microparticles have different appearances according to surfactant, is shown in Figure 3. But the reason why only about 10–20% of the microspheres are in rugged surface, is not clear. Further work in this area definitely is needed.

Polymer/Montmorillonite/Silver Nanocomposite

surfactant

Micro- and Nanoparticles Prepared by *In-Situ* Polymerization and Electrospraying Technique 171

Fig. 4. XRD patterns of (a) pure PVAc and (b) PVAc/Ag nanocomposite microparticles with

Figure 5(a) presents the conversion of the polymerization as a function of reaction time in the presence of MMT. The initiator concentration used in these reactions is 10-4 mol/mol of VAc. The results indicate that the rate of the polymerization decreased with increasing MMT addition. The reduction in the polymerization rate is probably due to the reduction of the diffusion rate of both monomer molecules and polymer chains in the intergalleries of nanoclay particles. For the polymerization without MMT, Figure 5(a) indicates that the conversion of the polymerization continually increased up to ~40 h, and reached a conversion of ~90% in spite of the low polymerization temperature (30 oC), which suggests

that ADMVN is an effective initiator for low-temperature polymerization.

Fig. 5. Conversions of VAc into PVAc/MMT suspension polymerized using ADMVN concentration of 0.0001 mol/mol of VAc (a) with different MMT contents, (b) with different polymerization temperatures, and (c) suspension polymerized using 30 oC with different

initiator concentrations with polymerization time, respectively

**2.2.2 PVA/PVAc/MMT nanocomposite microparticles**

**<IP_ADDRESS> Suspension polymerization behavior**

Fig. 2. SEM images of (a) pure PVAc microparticles, (b) PVAc/Ag nanocomposite microparticles without surfactant and (c) PVAc/Ag nanocomposite micropartices with surfactant (ADMVN concentration of 10-4 mol/mol of VAc, suspending agent concentration of 5.0 g/dl of water)

Fig. 3. Schematics of suspension polymerization of PVAc/Ag nanocomposite microparticles (a) without surfactant and (b) with surfactant

The PVAc microparticles and PVAc/Ag nanocomposite microparticles with modified silver nanoparticle contents of 3 wt% were characterized by XRD, and the results are shown in Figure 4. The XRD pattern of PVAc/Ag nanocomposite microparticles shows diffraction peaks at 2θ of ca. 15°, 22.7°, 38.2°, 44.6°, and 52°, respectively. Except the diffraction peaks of PVAc(15°, 22.7°), all the other peaks are corresponding to the silver phase. The XRD pattern clearly indicates that PVAc/Ag nanocomposite microparticles were successfully prepared with modified silver nanoparticles. These peaks are corresponding to the (111) and (200) planes of the silver nanocrystals with cubic symmetry (Dong et al., 2002). XRD results indicate that modified Ag nanoparticles are well dispersed in the PVAc matrix.

Fig. 4. XRD patterns of (a) pure PVAc and (b) PVAc/Ag nanocomposite microparticles with surfactant

#### **2.2.2 PVA/PVAc/MMT nanocomposite microparticles**

#### **<IP_ADDRESS> Suspension polymerization behavior**

170 Nanomaterials

Fig. 2. SEM images of (a) pure PVAc microparticles, (b) PVAc/Ag nanocomposite microparticles without surfactant and (c) PVAc/Ag nanocomposite micropartices with surfactant (ADMVN concentration of 10-4 mol/mol of VAc, suspending agent concentration

Fig. 3. Schematics of suspension polymerization of PVAc/Ag nanocomposite microparticles

The PVAc microparticles and PVAc/Ag nanocomposite microparticles with modified silver nanoparticle contents of 3 wt% were characterized by XRD, and the results are shown in Figure 4. The XRD pattern of PVAc/Ag nanocomposite microparticles shows diffraction peaks at 2θ of ca. 15°, 22.7°, 38.2°, 44.6°, and 52°, respectively. Except the diffraction peaks of PVAc(15°, 22.7°), all the other peaks are corresponding to the silver phase. The XRD pattern clearly indicates that PVAc/Ag nanocomposite microparticles were successfully prepared with modified silver nanoparticles. These peaks are corresponding to the (111) and (200) planes of the silver nanocrystals with cubic symmetry (Dong et al., 2002). XRD results

indicate that modified Ag nanoparticles are well dispersed in the PVAc matrix.

(a) without surfactant and (b) with surfactant

of 5.0 g/dl of water)

Figure 5(a) presents the conversion of the polymerization as a function of reaction time in the presence of MMT. The initiator concentration used in these reactions is 10-4 mol/mol of VAc. The results indicate that the rate of the polymerization decreased with increasing MMT addition. The reduction in the polymerization rate is probably due to the reduction of the diffusion rate of both monomer molecules and polymer chains in the intergalleries of nanoclay particles. For the polymerization without MMT, Figure 5(a) indicates that the conversion of the polymerization continually increased up to ~40 h, and reached a conversion of ~90% in spite of the low polymerization temperature (30 oC), which suggests that ADMVN is an effective initiator for low-temperature polymerization.

Fig. 5. Conversions of VAc into PVAc/MMT suspension polymerized using ADMVN concentration of 0.0001 mol/mol of VAc (a) with different MMT contents, (b) with different polymerization temperatures, and (c) suspension polymerized using 30 oC with different initiator concentrations with polymerization time, respectively

Polymer/Montmorillonite/Silver Nanocomposite

effect improved the dispersion of silicates in the polymer matrix.

nanocomposite microparticles with MMT concentration of 1 wt.% **<IP_ADDRESS> Heterogeneous saponification of PVAc/MMT microparticles**

saponification (DS) is defined by the volume ratio of PVAc/PVA.

Micro- and Nanoparticles Prepared by *In-Situ* Polymerization and Electrospraying Technique 173

The detail structure of the clay nanocomposites has been established using XRD analysis. Figure 7 shows the XRD patterns of the PVAc, MMT, and PVAc/MMT with MMT content of 1 wt.%. The MMT shows a diffraction pattern peak at 2θ =7.2o, which corresponds to the average basal spacing (d-spacing) of 12.3 Å. In the PVAc/MMT nanocomposite microparticles, the peak moved to a lower angle, i.e., 2θ =2.7o. The basal spacing increased from 12.3 to 32.6 Å. This spacing indicates that long alkyl (cetyltrimethyl) ammonium ions were inserted into the gallery of MMT; as a result, an intercalated structure formed. The inserted long alkyl chains caused the hydrophilic nature of the clay to decrease, and this

Fig. 7. XRD patterns of (a) pure PVAc microparticles, (b) pure MMT, and (c) PVAc/MMT

The PVA obtained by the saponification of poly(vinyl ester) is a linear semicrystalline polymer and has been widely used as fibers for textile industries, films, membranes, and drug delivery systems. In this study, the PVA/MMT nanocomposite microspheres were prepared by a simple heterogeneous saponification method. To preserve the spherical shapes of PVAc/MMT nanocomposite particles, the saponificaion was carried out by disperse PVAc/MMT nanocomposite particles in alkali aqueous solution with very gentle agitation. The effect of MMT on the PVAc saponification rate was recorded by optical microscope observation. In this study, the heterogeneous saponifications of pure PVAc and PVAc/MMT microspheres were conducted under the same conditions. Degree of

Figure 8 shows the optical micrographs of PVAc/PVA (Figure 8a,b) and PVA/PVAc/MMT (Fig. 8. c,d) nanocomposite microspheres prepared by heterogeneous saponification at different reaction times. As shown in Figure 8c,d, partially saponified nanocomposite microparticles (MMT content of 1 wt.%, degrees of saponification are 18.2 and 51.3%, respectively) with a PVAc core and PVA shell structure could be obtained by controlling the saponification degrees. It can be seen that the MMT presented in the PVAc microparticles

In a free radical polymerization, the rate of polymerization(Rp) could be expressed by Eq. (1)

$$R\_p = K\_p \{M\} \{I\}^{0.5} (\not\mathbb{k}\not\!\!\!\!k\not\!\/)^{0.5} \tag{1}$$

where *f* is the initiator efficiency; [*M*] and [*I*] are the concentrations of monomer and initiator; and *kd*, *kp*, and *kt* are the rate constants of initiator decomposition, polymer propagation, and termination, respectively (Odian, 1981). This expression predicts that the rate of polymerization increases as the efficiency and concentration of the initiator are increased. The reduction in the polymerization rate in the presence of MMT suggests that either the efficiency of the initiator, *f*, or the propagation rate constant, *kp*, were decreased when MMT was added into the suspension polymerization system. We believe the reduction of the diffusion rate in the nanoclay intergallerries may reduce both *f* and *kp* in Eq. 1. It has been known that ADMVN is an effective low temperature initiator (the 10h half-life decomposition temperature of ADMVN is 51 oC) for preparing highmolecular-weight polymer with high yield. In this study, ADMVN was used for preparing PVAc/MMT nanocomposite microspheres at room temperature. Figure 5(b) presents the conversion-time relationship for the reactions carried at different temperatures with a constant initiator concentration. Although a low initiator concentration (10-4 mol/mol of VAc) and low reaction temperatures were employed, the conversion increased steadily up to 85-95%, depending on the MMT content in the system. The effect of initiator concentration on the polymerization rate is shown in Figure 5(c). It can be seen that the polymerization rate, at a reaction temperature of 30 oC, increased with the increasing initiator concentrations, in accordance with theoretical prediction (Odian, 1981).

#### **<IP_ADDRESS> Morphology and structure property**

SEM photographs of pure PVAc and PVAc/MMT nanocomposite microspheres with 1 wt.% MMT contents are presented in Figure 6. As expected, the surface of pure PVAc microparticles shown in Figure 6(a) is smooth. Figure 6(b) shows that the roughness of the microsphere surface is increased by adding the MMT. To further study the distribution of MMT particles in the PVAc microspheres, the fracture surfaces of the PVAc/MMT nanocomposite microparticles were investigated. Although it is not shown here, MMT particles were embedded inside the composite microspheres, which indicate that PVAc/MMT microspheres could be prepared by *in-situ* suspension polymerization.

Fig. 6. SEM images of (a) pure PVAc microparticles and (b) PVAc/MMT nanocomposite microparticles with MMT concentration of 1 wt.%

In a free radical polymerization, the rate of polymerization(Rp) could be expressed by Eq. (1)