Numerical analysis of air bubble formation in PDMS micro-channels in negative pressure-driven flow

Unexpected air bubbles during microfluidic device operation always are problematic, while the underlying mechanism of the bubble formation is not well understood systematically. Here we elucidate the mechanism of air bubble nucleation in PDMS microfluidic channel during negative pressure-driven flow by theoretical analysis and numerical calculations. In negative pressure-driven flow, the unwanted air bubbles mostly originate from trapped air cavities, which are mainly due to the hydrophobicity of PDMS channel surface. Specific channel geometries and surface conditions, such as small channel corners and surface impurities, also catalyze the air bubble formation. The mechanism is developed in theoretical analysis to explain the air bubble formation process and numerical calculation is further developed based on two-phase flow to compare the influence of different parameters. Experimental observation validates the developed theory and the simulation. We believe that this study could help understand the problem more methodically and systemically in physics level, and benefit the gas bubbles prevention and removal strategy development.