(160i) Controlled Liquid Entrapment through Photo-Patterned Obstacles and Patterned Surfaces

We present a novel method to trap liquid (either oil or water) in a microfluidic channel by sequentially injecting two immiscible liquids over photo-patterned obstacles or patterned surfaces. By using geometrical arguments, we develop an analytical solution for liquid-liquid interface evolution, and demonstrate that the wetting and shape of the patterned objects govern the trapping process. The solution is consistent with experiments for circular, square, half-moon and raindrop shaped obstacles, and allows us to understand the relative importance of shape and wetting. We also predict the condition for formation of a liquid bridge for two circular obstacles separated by a distance. Based on our understanding of trapping process over isolated obstacles, we trap liquid over sawtooth and sinusoidal patterned surfaces. By varying the amplitude and frequency of the patterned surface, we are able to control and predict the amount of liquid trapped. Our platform can have diverse applications in diagnostics, drug discovery, reaction engineering, material synthesis and printing processes.