Swelling of composite microgels with soft cores and thermo-responsive shells

This study deals with constitutive modeling and numerical simulation of equilibrium swelling of composite microgels with soft temperature-insensitive cores and thermo-responsive (TR) shells. Our analysis takes into account a pronounced increase in the elastic moduli of TR gels of the LCST (lower critical solution temperature) type driven by aggregation of hydrophobic segments into clusters above the volume phase transition temperature. Material parameters are found by fitting observations on poly(acrylamide) and poly(N-isopropylacrylamide) gels with various concentrations of cross-linkers. Good agreement is demonstrated between the experimental data and results of numerical analysis. The effects of mechanical properties of the core and the shell and geometry of composite microgels on distribution of water molecules are studied numerically. Several unexpected phenomena are discovered in simulation.