(98bf) A Fluid-Structure Interaction Study of Surface Acoustic Wave Interaction With a Sub-Micron Sized Droplet

Liquid droplet based microfluidic systems find extensive applicability in biological applications, such as carriers to target drug delivery to the intended diseased tissue, encapsulation agents for various biological entities, micro-reactors for rapid mixing and reaction of reagents, liquid reaction vessels for protein crystallization, biosensing, DNA analysis, sampling glucose concentrations in bodily fluids, to name a few. In droplet-based microfluidics, discrete droplets are created via the use of two immiscible phases in micro-channels. All applications require a great control on droplet size, shape, and distribution; mono-dispersed droplets are typically required which can be used as micro-reactors and for achieving hands-free contact of reagents in biological applications such as in Lab-On-a-Chip systems. Recent studies suggest that surface acoustic wave (SAW) devices, with hydro-phobically modified surfaces, can be used for efficient microfluidic control and generation as well as actuation of droplets. In this work, we investigate using 2-D and 3-D Fluid-Structure Interaction Model, the phenomenon of droplet actuation in SAW devices as well as the acoustic streaming velocity fields generated in micro-liter size droplets as a result of interaction with SAW devices. Simulations indicate that the Rayleigh wave generated in the SAW device impinges on the fluid medium and imparts momentum generating fluid motion known as acoustic streaming. The simulated fluid velocity profiles inside the droplet exhibit recirculation, thereby indicating an enhancement in mixing and agitation in droplets. The influence of various parameters, namely fluid viscosity, applied voltage, and droplet size on the droplet actuation and acoustic streaming is studied using the developed fluid-structure finite element model.