Kinetic effect on the thermal behavior in the volume phase transiton of poly (N-isopropylacrylamide) gels

摘要

It is well known that poly(N-isopropylacrylamide)(NIPA)gels in water exhibit a discontinuous volume change between a swollen state and a collapsed state (i.e., volume phase transition of gels) at about 34 deg C. Thermal analyses by a differential scanning calorimetry (DSC) on the transition of NIPA gel shows a single endothermic peak at the transition when increasing temperature. The endothermic heat has been suggested to originate from the dehydration of NIPA chains at the transition. Time required to reach the equilibrium volume of gels has been known to be proportional to the square of a characteristic length of the typical size of gels due to the collective diffusive process of gel-network. These kinetic factors on the volume shrinking may affect the thermal behavior of NIPA gel. In this study, the kinetic effect of the volume shrinkage on the thermal behavior of NIPA gel were investigated by DSC and the volume measurement at the same heating rate as the DSC.