A kinetic model of a polyelectrolyte gel undergoing phase separation

Abstract

In this study we use non-equilibrium thermodynamics to systematically derive a phase-field model of a polyelectrolyte gel coupled to a hydrodynamic model for a salt solution surrounding the gel.The governing equations for the gel account for the free energy of the internal interfaces which form upon phase separation, the nonlinear elasticity of the polyelectrolyte network, and multicomponent diffusive transport following a Stefan-Maxwell approach. The time-dependent model describes the evolution of the gel across multiple time and spatial scales and so is able to capture the large-scale solvent flux and the emergence of long-time pattern formation in the system. We explore the model for the case of a constrained gel undergoing uni-axial deformations. Numerical simulations show that rapid changes in the gel volume occur once the volume phase transition sets in, as well as the triggering of spinodal decomposition that leads to strong inhomogeneities in the lateral stresses, potentially leading to experimentally visible patterns.

Fluid-fluid phase separation in a soft porous medium

“…Recently, the problem of liquid-liquid phase separation within an elastic network has attracted substantial attention from the perspective of droplet formation within living cells [15][16][17][18][19][20]. Elastically modulated phase separation has also been studied within the context of hydrogels [21][22][23][24]. It is now well understood that the presence of an elastic network fundamentally alters the phase-separation process by introducing an energetic cost to the rearrangements that are needed for phase separation to occur.…”