Volume Phase Transition in Polymer Gels Induced by Uniaxial Stress

We have measured the changes in diameter and length of cylindrical N-isopropylacrylamide gels of sub-millimeter diameter under uniaxial stress along the axis The measurements have been carried out on two types of gels with low and high den sity of cross-linking. As a result, the transition temperature and discontinuity were increased with increasing stress, which indi cates the possibility of the uniaxial stress-induced phase transition of gels The swelling curves obtained under the small stress region were quite successfully described by the phenomenological model on the basis of the extended Flory-type free energy. With increas ing stress, mechanical work at the transition point increased, and thereafter decreased under the larger stress. The peak of mechan ical work depends strongly on the degree of cross-linking