Design and development of a PZT based active microfluidic droplet generator for lab on a chip devices

Abstract

Microfluidic droplet generation is a critical technique in Lab on a Chip (LoC) system, where precise size control and stability are important than throughput. This thesis presents the design, modelling, fabrication, and experimental validation of an active microfluidic droplet generator. The multilayer device design integrates two piezoelectrically actuated valveless micropumps to a Polymethyl Methacrylate (PMMA) based droplet generation geometry layers. The methodology combined numerical simulation and experimental evaluation of the active microfluidic droplet generator. In this study, water and coconut oil were used as the dispersed phase and the continuous phase, respectively. Initially, the effect of the flow-rate ratio between the dispersed phase and the continuous phase on the droplet diameter was numerically simulated. In the experiments, the dispersed phase fluid flow was pulsed, hence generating an intermittent flow in the droplet generator. The ON-time of the piezoelectric micropump, which drives the dispersed phase, affects the droplet diameter. Therefore, the ON-time injection dose of the micropump was evaluated. Numerical simulations employed the Volume-of-Fluid (VOF) method as the baseline steady-flow behaviour, while the level-set method was used for intermittent actuation due to its superior interface tracking. In the experiments, repeatable droplet formation was observed, with average diameters of 1.98 ± 0.03 mm and 3.96 ± 0.14 mm under different flow rate and ON-time conditions for the dispersed phase, while the continuous phase conditions were unchanged. Furthermore, increasing the dispersed phase voltage increased the flow rate of the dispersed phase. This produced larger droplets at higher dispersed phase voltages for a fixed actuation cycle time (ON/OFF), showing tuneable droplet generation. In addition, the droplet generation frequency was between 5.4 and 14.8 droplets/min for different flow/actuation conditions. Therefore, this work demonstrates that intermittent piezoelectric actuation enables repeatable, tuneable, and low-throughput droplet generation.