Time-varying solute strategies to maximize diffusiophoretic extraction from confined geometries

Diffusiophoresis has emerged as an excellent candidate for driving the targeted motion of colloidal particles in confined systems. For example, recent research on diffusiophoresis in dead-end pores has shown that exposing a pore to a nearly-discontinuous solute concentration can generate a powerful diffusiophoretic transport of suspended particles that can greatly enhance their motion by orders-of-magnitude beyond simple Brownian motion, which has applications for problems such as particle injection and withdrawal. Here, we consider the efficiency of such a process, both for the case of injection and withdrawal. For example, in the case of withdrawal, a certain fraction of the particles initially occupying the pore can be predicted to be extracted throughout this diffusiophoretic cycle. This efficiency will be a function of the diffusiophoretic mobility, solute diffusivity, length of the pore, and the solute contrast ratio that drives the dynamics. Finally, we show how a modified, time-varying diffusiophoresis strategy can be used to increase the efficiency of these injection and withdrawal processes. This work has applications from targeted drug delivery to enhanced oil recovery.