Microfluidic device incorporating closed loop feedback control for uniform and tunable production of micro-droplets.

Both micro- and nanofluidics are finding increasing use in the growing toolbox of nanotechnology; for the production of nanoparticles, and as micro-reactors for carefully controlled chemical reactions. These laboratories-on-a-chip hold vast potential for industrial application, however, only the most simple are truly starting to emerge as commercially viable, particularly in the area of droplet formation and emulsion creation. In order to automate droplet production with a desired size and dispersity, we have designed a microfluidic-based technology utilizing elementary microchannel geometries in combination with a closed loop feedback system to control the continuous- and dispersed-phase flow rates. Both the device geometry and control system have been optimized to allow for the production of a tunable emulsion. By utilizing discrete linear control theory, the device is able to produce the desired results with little to no prior knowledge of the fluid material properties to be used in either phase. We present our results from initial development using flow-focusing microfluidic geometry for droplet formation, computer-tethered syringe pumps to individually control the continuous and dispersed phase flow rates, a high-speed camera, and a controller and driver system for the optical measurements and pumps, respectively. We will show the efficacy of this technique for Newtonian and viscoelastic liquids, with and without the presence of surfactants. It can be envisioned that through careful control optimization, such a system can be developed to a point that will allow the production of "designer" emulsions with droplets eventually reaching the nanoscale.