Phase transition in swollen gels

Summary

The swelling and mechanical behaviour of networks of copolymers of acrylamide, methylenebisacrylamide and sodium 2-(2-carboxybenzoyloxy)ethylmethacrylate (mole fraction of salt x _s =0–0.2) in water-acetone mixtures was investigated. In the range x _s ≥0.01 phase transition (collapse) was observed, with both the extent of the collapse and the critical acetone concentration in the mixture at collapse, a _c , increasing with increasing concentration of the salt. A comparison between these results and those obtained for networks with a quaternary ammonium salt led to a conclusion that an exchange of the positive charge of the ammonium salt (N^⊕Cl^⊖) for the negative charge of the sodium salt (COO^⊖Na^⊕) in the side chain decreases the critical content of salt necessary for the collapse, X ^c _s , from 0.03 to 0.01, and the collapse takes place at lower concentrations of acetone. The collapse may also take place in a mixed solvent waterethanol; the dependence of network swelling on the concentration of ethanol is roughly the same as that on the concentration of acetone.