Abstract

We generated silicone oil micro-droplet in deionized water with a microfluidic T-junction devices made on silicon-glass with different cross-sections (depth and width) of the continuous phase and the dispersed phase micro-channels. We experimentally show that the size of the droplet decreases when the width or the velocity of the dispersed phase micro-channel decreases but is almost insensitive to the channel depth. For describing the observed behaviour, we proposed a modified mechanism of droplet formation consisting of three stages, each with start and end precisely identified. Based on this mechanism, we developed an analytical model for obtaining the droplet diameter in dripping regime when there is partial wetting at the channel boundary. This model is in better agreement with the experiments than other analytical models from the literature, suggesting the effect of channel wetting is significant. We also discuss the use of the capillary number in models, and suggests that the velocity would be a better metrics for comparing different T-junction geometry. In the experiment, the generated droplet diameter is varied between 28 μm and 196 μm.

Keywords: Analytical model, capillary number, dripping regime, droplet generation, microfluidics, oil-in-water, T-Junction.