Simulation of soft smart hydrogels responsive to pH stimulus: Ionic strength effect and case studies

In this paper, the influence of the ionic strength of surrounding bath solution is presented and discussed on the responsive performance of soft pH-sensitive hydrogels to environmental change in solution pH. The numerical simulations are based on a chemo-electro-mechanical formulation previously termed the multi-effect-coupling pH-stimulus (MECpH) model. It is improved further in this paper via incorporation of the finite deformation theory into the mechanical equilibrium governing equation. The MECpH model is composed of coupled nonlinear partial differential equations and solved by a meshless numerical approach called the Hermite-cloud method with the modified Newton iteration technique. After examination of the improved MECpH model by comparing the simulation results with experiments available in literature, several case studies are carried out to discuss the effects of the ionic strength of surrounding solution on the distributive variations of the diffusive ion concentrations and electric potential as well as the deformation of the pH-stimulus-responsive hydrogels, when the hydrogels are immersed in buffered bath solutions.