On-demand double emulsification utilizing pneumatically actuated multilayer PDMS microstructures

We have successfully demonstrated an active, 2-step emulsification scheme that is capable of producing double emulsions with desired geometries and compositions on demand. PDMS micro-structures with pneumatically actuated membrane-valves constructed on top of specially designed fluidic-channels are utilized to meter and shape immiscible fluids into double emulsions. By varying the timings of membrane actuation, the structures of resulting double-emulsions can be adjusted in a real-time manner. In the prototype demonstration, a three-layer PDMS molding and irreversible bonding process is employed to fabricate the proposed microfluidic devices. It has been demonstrated that (1) the inner and outer diameters can be controlled independently, (2) volume ratios (droplet to drop) ranging from 0.01 to 0.4 can be readily achieved, and (3) adjacent drops with varying sizes, droplet diameters, and numbers of droplets inside can be produced on demand. As such, the demonstrated emulsification scheme could potentially realize the real-time controllability on emulsion geometries and compositions, which is desired for a variety of applications.