Using Microfluidics to Probe Mass Transport and Aggregation in Nanoparticle Suspensions
S. Ozturk, Y.A. Hassan, V.M. Ugaz
Texas A&M University, US
Keywords: nanoparticles, nanofluids, aggregation, diffusion
Abstract:Recent experimental and theoretical studies have demonstrated that extremely low volume-fraction colloidal suspensions of solid nanoparticles (i.e. nanofluids) exhibit remarkably enhanced heat transfer properties. There have also been reports of corresponding enhancements in diffusive mass transfer, but the available data are inconsistent and make it difficult to draw definitive conclusions about the origin and magnitude of these effects. Here we address this issue by investigating the mass transport properties of these next generation fluids using a microfluidic approach that allows us to directly observe diffusive mass transport of tracer dyes between nanoparticle-laden fluid streams as they flow through a microchannel network. We observe only a minimal change in diffusion of Rhodamine 6G and Rose Bengal dyes with addition of alumina nanoparticles to the aqueous system. But we also find a strong dependence of these effects on flow conditions and the composition of the suspensions that can trigger localized aggregation, disrupting the flow in a way that could be erroneously interpreted as enhanced mass transport by diffusion. We also explore a new adaptation of our microfluidic approach that harnesses the ability to establish steep chemical gradients to provide a simple quantitative probe of interparticle interactions in non-idealized multi-component suspensions.