Systematic investigation of a two-fluid model describing ion-induced volume phase transition in polyelectrolyte gels

An important feature of many charged polymers in solution is that they undergo a large and often discontinuous volume change in response to various environmental parameters, including pH, temperature, and ionic composition. This reversible transition plays an important role in various biological processes (e.g., swelling of secretory products, formation of membraneless organelles, and changing the hydraulic resistance of Xylem in plants) as well as in soft and “smart” materials (e.g., ion-exchange resins and controlled release). Here we report a systematic investigation of a two-fluid model describing the dynamic response of the coupled components (polymer network, solvent, and charged ions). The effects of crosslink density, concentration of ionized groups on the network chains, composition of the equilibrium salt solution containing both mono- and divalent cations, and the drag coefficient between polymer and solvent on the swelling degree of these gels, ion partitioning, and electric potential field are systematically investigated and compared to experimental results in sodium polyacrylate gels.