Bubble generation and acoustic cavitation for microfluidic mixing of highly viscous liquids

Abstract

In microfluidics, it is well-known that if the Reynolds number is much smaller than unity, it is difficult to mix rapidly and homogenously two adjacent fluids. In this regard, acoustofluidics is a promising technique to help overcome this issue. In this Thesis, we report a bubble-induced acoustic method to enhance mixing efficiency for fast and homogenized mixing of highly viscous liquid. This device generates the random size of air bubbles in the microchannel. A piezoelectric transducer was used to activate bubbles in their resonant frequencies. When acoustically driven by a function generator and stereo-amplifier, the bubbles implode and fragment into smaller bubbles. Due to ultrasonic velocity which is different in bubble and liquid, the interface (membranes of bubbles) of these two different media which is a critical area, started to oscillate. The bubble oscillation resulted in a microstreaming phenomenon creating strong pressure divergence in the bulk liquid, thus giving rise to fast and homogenized mixing of two side-by-side flowing fluids. The performance of the mixer was characterized by mixing various high viscosity PDMS-toluene solutions at different flow rates.