Microfluidique à l'échelle micrometrique et sub-micrometrique : NanoPTV, formation des gouttes, et modèle sub-micrometrique
In this work, we have addressed three projects with the application of Microfluidics: With the technology of Total Internal Reflection Velocimetry, we realised the nano-PTV of fluid flow within 800 nm close to solid surface. We achieved unprecedented accuracy of measurement compared with the state of art, by determining precisely the wall position, and by Langevin simulation, which takes into account of the sources of biases, such as Brownian motion, shear stress, electrostatic repulsion between particles and the wall, effect of out of focus, etc. We achieved ±5 nm and ± 10 nm accuracy on the slip length determination for sucrose solution and for water. The no-slip condition on hydrophilic surface is confirmed, and a positive slip length on hydrophobic surface is clearly illustrated. This result demonstrated that the nano-PTV by TIRF is a quantitative methodology for the study of fluid flow near solid surface. We collaborated with A. Leshansky to study quantitatively the mechanism of step emulsification. The dispersed fluid and continuous fluid are co-flowing in a confined Hele-Shaw channel, before going into an unconfined pool. Drops are formed at the intersection between shallow channel and the pool. Two phases - step emulsification and large drops - are distinguished based on a well defined capillary number. We found good agreement between experiments and theory, on the step emulsification droplet size, dispersed fluid pinching dynamics, and on the shape of free interface between dispersed fluid and continuous fluid prior to pinching. We collaborated with a group of petroleum companies (AEC), to develop a technology which has potential application to the Enhanced Oil Recovery. Nano particles synthesized by the AEC is supposed to perform phase transition or deliver signals once in touch with oil. The principal idea consists in sending these nano particles into the porous media underground along with the injection fluids, and recollect them on the production well side. According to the information they deliver, the distribution of oil may be mapped. We constructed a micro model based on microfluidic technology, which mimics the complex structure of porous media of rocks. The AEC synthesized nano particles are injected into the micro model, their motion and retention can be observed in real time. This work provides important information on the particle motion in porous media, which cannot be realised in conventional core experiments.