I currently investigate fundamental and applied problems related to soft materials, more specifically, colloids, polymers, and emulsions. The research work, which is mainly experimental, can be broadly divided into two main projects (i) Designer emulsions using droplet-based microfluidics and their applications, and (ii) Intermolecular and interparticular interactions of crude oil asphaltenes. This poster will describe the first project on emulsions using microfluidics.

An emulsion is a mixture of two immiscible liquids, where one liquid is dispersed in the form of small drops in another liquid. Most conventional methods for making emulsions involve drop breakup using shear stresses. However, such stresses are not uniform across the system, nor are they finely controlled; emulsions formed in these ways thus consist of drops that are highly polydisperse in size. Microfluidic devices offer an alternate and versatile route to produce emulsions. In contrast to bulk emulsification methods, an emulsion in a microfluidic device is made by precisely fabricating one drop at a time: this process results in a highly monodisperse emulsion. One of the most attractive features of microfluidic techniques is that they enable the fabrication of double, triple, and even higher order emulsions, where the size and number of the encapsulated droplets can be manipulated with unprecedented accuracy. [1-2]

Such monodisperse emulsions can serve as templates for the fabrication of monodisperse particles, vesicles, and “supraparticles”. We demonstrate the fabrication of particles with different internal structures [3-4], and second order particles (supraparticles) by guided self assembly of sub-micron size colloidal polymeric solids in droplets [5-6]. The diameters of these particles can be precisely controlled over a range of 10-1000 microns by controlling the droplet size which is a function of the fluid flow rates and device geometry. Such designer particles can be used in numerous applications as rheological probes, particle surfactants, micro-valves, and bio-vehicles for encapsulating and delivering macromolecules in pharmaceutical and cosmetics formulations.

Relevant Publications

1. Shah R.K., Shum H.C., Rowat A., Lee D., Agresti J.J., Utada A.S., Chu L.Y., Kim J.W., Fernandez-Nieves A., Martinez C.J., and Weitz D.A. Designer emulsions using microfluidics; MATERIALS TODAY 2008; 11(4): 18-27.

2. Chu L.Y., Utada A.S., Shah R.K., Kim J.W., and Weitz D.A. Controllable monodisperse multiple emulsions; ANGEWANDTE CHEMIE INT. ED. 2007; 46(47): 8970-8974.

3. Shah R.K., Kim J.W., Agresti J.J., Weitz D.A., and Chu L.Y. Fabrication of monodisperse microgels and gel microcapsules in microfluidic devices; SOFT MATTER 2008; submitted.

4. Chu L.Y., Kim J.W., Shah R.K., and Weitz D.A. Monodisperse thermo-responsive microgels with tunable volume-phase transition kinetics; ADVANCED FUNCTIONAL MATERIALS 2007; 17(17): 3499-3504.

5. Shah R.K., Kim J.W., and Weitz D.A. Fabrication of monodisperse biphasic Janus supraparticles using microfluidics – in preparation;

6. Shah R.K., Lee D., Kim J.W., and Weitz D.A. Monodisperse thermo-responsive microgel vesicles by self assembly of microgels in droplets – in preparation;