THE PHASE-TRANSITION AND SHEAR MODULUS OF IONIC N-ISOPROPYLACRYLAMIDEGELS IN CONCENTRATED SALT-SOLUTIONS

The swelling and mechanical properties of thermally sensitive N-isopro pylacrylamide (NIPA) hydrogels containing 0-35 mM sodium acrylate como nomer have been investigated at room temperature. The swelling medium is an aqueous solution with an NaCl concentration varying from 0 to 3. 0 M. As the NaCl concentration increases, the ionic NIPA gels shrink. In a dilute sodium chloride solution with NaCl less than 0.1M, the con formational change of the gels is a simple process of osmotic deswelli ng. As the sodium chloride concentration increases above 0.8M, the gel s 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. (C) 1997 John Wiley & Sons, I nc.