Equilibrium Swelling of Thermo-Responsive Gels in Mixtures of Solvents

Thermo-responsive (TR) gels of the LCST (lower critical solution temperature) type swell in water at temperatures below their volume phase transition temperature Tc and collapse above temperature. When is partially replaced with an organic liquid, these materials demonstrate three different types equilibrium solvent uptake diagrams below, above, close vicinity Tc. A model developed for swelling TR binary mixtures solvents. It takes into account transitions driven by (i) aggregation hydrophobic side groups clusters from which molecules are expelled, (ii) replacement cosolvent cage-like structures surrounding groups, (iii) as main element hydration shells around backbone chains. The involves a relatively small number material constants that found matching observations on covalently cross-linked poly(N-isopropylacrylamide) macroscopic microgels. Good agreement demonstrated between experimental data results numerical analysis. Classification provided points diagrams.