Diffusiophoresis in narrow channel flows

Flows containing suspended colloidal particles and dissolved solutes are found in a multitude of natural and man-made systems including hydraulic fractures, water filtration systems and microfluidic devices, e.g. those designed for biological or medical applications. In these types of systems, unexpected particle dynamics such as rapid particle transport and focusing has been observed in the presence of local solute gradients due to the cooperating or competing effects of fluid advection and particle diffusiophoresis, the latter driven by local chemical gradients. We develop analytical expressions for the fluid, solute and particle dynamics in long, narrow channels due to the combined influence of pressure-driven channel flow with diffusiophoretic and diffusioosmotic effects. The results confirm a rapid particle focusing effect that can be controlled by manipulating the particle, solute and flow properties, as well as the channel's geometry and surface chemistry. Thus, we propose a new approach for performing microfluidic zeta potentiometry, as well as techniques for sorting, concentrating and/or capturing particles based on their sizes or zeta potentials. Finally, we demonstrate that diffusioosmotic effects can be used to pump fluid against a pressure gradient.