Abstract
Pulsed filed gradient spin echo (PFG-SE) NMR technique has been used to measure the self-diffusion coefficient ( D self) of water in a thermoreversible hydrogel, Poly(N-isopropylacrylamide). D self, was measured as a function of temperature (−5–50°C) and hydration level. A theoretical model to predict D self was built by using a combination of lattice fluid hydrogen bond theory and free volume theory. The fully swollen gel did not show any discontinuous change in D self with temperature, Whereas, a partially swollen gel, showing the existence of two kinds of water having diffusivities differing by order of magnitude, exhibits a discontinuous change in D self. These results were explained within the theoretical framework developed by us. The present work thus enables an elucidation of diffusion phenomenon at the volume transition point for the first time.
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