Chaotic Mixing of Microdroplets Using Surface Acoustic Waves Device

Abstract

Small-scale mixing or actively known as micromixing had an utmost importance in the biological and chemical applications using micro total analysis systems (TAS) or lab-on?chips. Micromixing is achieved by stirring or agitating liquid or particles. However, in microfluidic technology, it is very difficult to do mixing for a very small amount of liquid including microliter volume. Chemical reactions are often involved in most microfluidic applications, hence making the fluid diffusivity to become very low. Thus, chaotic advection was introduced in this study to shorten the reaction time. Conveniently, a new method was proposed to actively mix micro volume liquid. In this study, we developed focused-surface acoustic wave (F-SAW) fabricated on a piezoelectric substrate to manipulate or mix two different color dyes with low concentration. Operation frequency of 50 MHz was used to generate acoustic waves along the substrate surface and we varied the droplet volume and input power on the F-SAW mixing. Method comparison between passive and active mixing was done by studying the time taken for diffusion mixing. Designing, fabrication and test on Y-junction channel micromixers were done to compare and examine the mixing performance and time. Experimental results showed that mixing by F-SAW device has achieved high efficiency of 91 – 84% in droplet volume of 1 – 5 µL. Therefore, F-SAW mixing has been proven more efficient and fast response compared to diffusion mixing.