Generation of Geometrically Confined Droplets Using Microchannel Arrays: Effects of Channel and Step Structure

Abstract

The aim of this study was to investigate the generation characteristics of geometrically confined droplets using microchannel (MC) arrays made of single crystal silicon. Twelve MC array devices, each consisting of four MC arrays, were used in this study. Each MC array consists of rectangular MCs (5 μm in height) with or without a step. This study focused on the effects of the MC width and step height. Refined soybean oil was used as a dispersed phase, and a Milli-Q water solution containing 1.0 wt % sucrose monolaurate was used as a continuous phase. When rectangular MCs with a step height of 4.8 ,um were used, geometrically confined droplets with a height of 9.8 μm were obtained, and their diameter and volume gradually increased with increasing MC width. In particular, highly uniform discoid droplets with coefficients of variation below 4% were obtained using the rectangular MCs with an appropriate width range. In contrast, droplets could not be generated from rectangular MCs without a step. When rectangular MCs with a width of 27.6 μm were used, the step height affected the resultant droplet shape. Highly uniform discoid droplets were generated via rectangular MCs with step heights below a critical value of ∼13 μm. Further increase in the step height resulted in the generation of highly uniform spherical droplets. The volume of the discoid droplets was somewhat larger than that of the spherical droplets.