Investigation of hydrophilic modification for bubble-free operation in microfluidic systems and micropump applications

N B Le and Y C Hsu

Abstract

This study developed a bubble-free method for microfluidic devices and micropump applications by modifying the wetting characteristic of their chamber surfaces. Two methods of hydrophilic film formation were investigated, that is, microwave plasma surface modification and TiO₂ thin film deposition. The evaluation results indicated that TiO₂ thin film deposition showed better stability and it was therefore selected to improve the surface wettability and unify the spreading behavior. Different hydrophilic strip shape and strip numbers were investigated and the results indicated that the vertical design with trisection strip gives the best result and effectively discharges the bubbles of microfluidic devices. The results were then applied to a peristaltic micropump and very good results were obtained. That is, the micropump stability and robustness are enhanced significantly. Furthermore, in the pump operation frequency range (i.e. 75 ±10 Hz), bubbles are discharged effectively. The results show that when the micropump operated at frequencies lower than 100 Hz, air bubbles became insignificant; therefore, operation frequencies lower than 100 Hz are considered to be the micropump's stable performance range. From the results it was concluded that bubble formation is also responsible for the flow rate downhill effect.