Equilibrium swelling of thermo-responsive core-shell microgels

Design of new routes for preparation of hydrogels with fast response and enhanced mechanical and physical properties requires adequate modeling of their swelling. A model is developed for the equilibrium swelling of thermo-responsive gels. A characteristic feature of the model is that it accounts for a strong increase in the elastic moduli above the volume phase transition temperature T_c driven by aggregation of hydrophobic segments into clusters that serve as extra physical bonds between chains. The model is applied to the analysis of swelling diagrams on poly(N-isopropylacrylamide) macroscopic gels, microgel latices, and core-shell microgels with rigid cores. Good agreement is shown between the experimental data and results of simulation. It is demonstrated that the elastic moduli of microgels are higher, while their degrees of swelling in the stress-free state are lower compared with those of macroscopic gels.