SELF-DIFFUSION OF WATER IN THERMOREVERSIBLE GELS NEAR VOLUME TRANSITION - MODEL DEVELOPMENT AND PFG NMR INVESTIGATION

Pulsed field gradient spin echo (PFG-SE) NMR technique has been used t o measure the self-diffusion coefficient (D-self) of water in a thermo reversible hydrogel, Poly(N-isopropylacrylamide). D-self, was measured as a function of temperature (-5-50 degrees 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 full y swollen gel did not show any discontinuous change in D-self with tem perature, Whereas, a partially swollen gel, showing the existence of t wo kinds of water having diffusivities differing by order of magnitude , exhibits a discontinuous change in D-self. These results were explai ned within the theoretical framework developed by us. The present work thus enables an elucidation of diffusion phenomenon at the volume tra nsition point for the first time. (C) 1998 Elsevier Science Ltd. All r ights reserved.