Phase Transition of a Polymer Gel in Pure and Mixed Solvent Media

A volume phase transition of poly-N-isopropylacrylamide (NIPA) gel immersed in some pure and mixed solvents has been investigated experimentally. A slightly discontinuous transition of NIPA get in water changed to a more distinctly first-order transition on adding a small amount (<20%) of alcohols to water. As the concentration of alcohols in the mixed solvent increased further, the volume transition blurred and eventually disappeared. Analyzing the experimental results on the basis of the mean field theory of polymer solution, it has been shown that the polymer-solvent interaction parameter χ exhibits a drastic change at the volume transitions. This indicates that the enthalpy and entropy of solution depend strongly on polymer concentration.