A model describing the internal structure of core/shell hydrogels

Abstract

We apply a theory to the constrained swelling of gel particles, explicitly accounting for the propagation of elastic forces through the particle. This approach, together with conventional thermodynamics of gel swelling, allows modelling of the equilibrium state of gels with properties that are spatially inhomogeneous. In our case we consider both a discrete inhomogeneity in the form of assigning different water solubilities to the core and shell domains of the particle, and a continuous inhomogeneity in allowing the density of chemical cross-links to vary gradually through the network. The model is used to understand the behaviour of temperature-sensitive poly(N-isopropyl acrylamide) core/poly(N-isopropyl methacrylamide) shell microgels investigated in an earlier experimental study. How the swelling of the core and shell is affected by the presence of each other at different temperatures is investigated and explained from a mechanical and thermodynamic perspective.