Interface conditions for a polyelectrolyte gel in a viscous salt solution in the thin-EDL limit

Polyelectrolyte gels are electro-active soft materials that are often surrounded by a viscous salt solution. The formation of an electrical double layer (EDL) at the interface between the gel and the solution can give rise to fluid-structure interactions driven by Coulomb forces. However, resolving the EDL is computationally difficult because the EDL thickness is often orders of magnitude smaller than the typical gel size. In this talk, we show how matched asymptotic expansions can be used to derive interface conditions that capture the impact of a thin EDL on the gel and surrounding fluid. A key result is the derivation of a Helmholtz--Smoluchowski slip condition that describes how shear stresses in the EDL lead to a bulk flow in the surrounding salt solution. The talk will conclude with some model predictions of how the EDL can impact the gel behaviour in surprising ways.