The phase transition and shear modulus of ionicN-isopropylacrylamide gels in concentrated salt solutions

Abstract

The swelling and mechanical properties of thermally sensitive N-isopropylacrylamide (NIPA) hydrogels containing 0–35 mM sodium acrylate comonomer have been investigated at room temperature. The swelling medium is an aqueous solution with an NaCl concentration varying from 0 to 3.0M. As the NaCl concentration increases, the ionic NIPA gels shrink. In a dilute sodium chloride solution with NaCl less than 0.1M, the conformational change of the gels is a simple process of osmotic deswelling. As the sodium chloride concentration increases above 0.8M, the gels undergo a shrinkage phase transition. Corresponding to the shrinking of the gels, the shear modulus of the gels gradually increases at the transition point. It is found that the phase transition significantly affects the turbidity of the NIPA gels. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1851–1856, 1997