(256b) Efficiency of Colloid Separation through Diffusiophoresis

The phenomenon of diffusiophoresis —the migration of solid particles in a fluid induced by a chemical gradient— has attracted increasing attention in recent years, with studies showing its relevance in processes ranging from fabric cleaning to particle delivery in porous materials. One of its particularly promising applications is water remediation, recently demonstrated using a CO2 gradient perpendicular to a flow of water contaminated with solid micro-beads. The resulting phoretic motion concentrates the solids on the channel sides and, after the particle-rich stream is diverted, results in membraneless water cleaning. Such an approach is particularly appealing to address the remediation of microplastics under roughly ten microns in size, due to the elevated costs inherent to micro- and ultra-filtration. Quantifying this filtration process driven by diffusiophoresis is therefore key to inform the development of scalable new approaches to microplastic removal. Here, we present a model for the species and particle concentrations in a fully-developed channel flow under a chemical cross-gradient, producing quantitative predictions for the maximum separation efficiency produced by diffusiophoresis. Three key dimensionless parameters are identified, and the separation efficiency is shown to be critically mediated by chemical boundary layers near the channel walls. Experiments using model colloids in microfluidics channels are compared to the model predictions, yielding good agreement.