Scaling arguments for tipstreaming of submicron droplets

Friday, December 11, 2009 - 9:00am - 9:40am
EE/CS 3-180
Shelley Anna (Carnegie-Mellon University)
Microfluidic devices are convenient for producing highly uniform droplets for precise emulsions and lab-on-a-chip devices. However, the minimum droplet size in a microfluidic process is determined by the smallest geometric feature size, typically on the order of tens of microns. Introducing additional physico-chemical effects can help overcome this fundamental limitation. For example, when dissolved surfactants are present in one of the liquid phases, a tipstreaming-like phenomenon occurs, leading to the formation of submicron droplets. We have characterized this phenomenon in detail as a function of fluid properties and flow kinematics. However, we still have only a phenomenological understanding of the role of surfactant in the tipstreaming process. Experiments and recent literature suggest that the adsorption and desorption of surfactants at the interface plays an important role. In this talk, we demonstrate the feasibility of this hypothesis via scaling arguments for the diffusion, adsorption, and desorption of soluble surfactants in micron-scale geometries.
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