Colloid dynamics near phase transition: A model for the relaxation of concentrated layers

The dynamics of concentrated colloidal dispersion close to a phase transition are challenging to predict. The presence of attractive interactions leads to hindered motions through the change in transport properties such as collective diffusion. We propose a continuum mechanical model to describe the dynamics of the relaxation of concentrated colloids near a phase transition. The model relies on a specific description of the equation of state of colloids, the osmotic pressure deriving from a free energy double-well function, that induces a decrease in collective diffusion close to the phase transition. The implementation of such transport properties in Computational Fluid Dynamics (CFD) codes enabled the description of a fast expansion of accumulated gels near an interface (induced for instance by evaporation or filtration processes) followed by a relaxation stage, where particles are progressively released from the layer toward the dilute bulk region. The model proposed in this work captures the increase of the relaxation time when approaching the transition, a feature of interest for engineering colloidal mixtures with concentration gradients.