Diffusiophoresis-driven exclusion zone formation near an ion-exchange interface and onset of hydrodynamic instability: experiments and simulations

Symmetry breaking at fluid–solid interfaces drives particle repulsion in aqueous suspensions, giving rise to a particle-free region known as the exclusion zone (EZ), which can extend hundreds of micrometers. Despite its broad implications across biology and materials science and its potential to inspire novel applications, the full physical picture underlying this phenomenon remains elusive. Recent studies have identified diffusiophoresis, driven by interfacially induced multi-ionic concentration gradients, as the primary mechanism behind EZ formation. However, this process is also accompanied by notable particle focusing and longer-range effects that extend well beyond the EZ, including the emergence of complex flow patterns and hydrodynamic instabilities. In this work, we combine experiments with high-fidelity multiphysics simulations to investigate EZ formation next to ion-exchange membranes and the resulting flow instabilities. Our numerical model quantitatively reproduces key experimental observations and enables systematic exploration of how physical and chemical properties of the suspension influence these phenomena. In particular, we examine the roles of solute composition, colloidal concentration, and system geometry in modulating EZ growth and the instabilities.