Anomalous diffusion of water in a hydrogel of sucrose and diepoxide monomers

Abstract

This article is concerned with the study of the diffusion of water molecules in a hydrogel, obtained by controlled hydration of a cross-linked polymer of sucrose and diepoxide monomers. The diffusion measurements were performed by means of H1(NMR) nuclear magnetic resonance techniques in the fringe field of a superconductor magnet with a field gradient G≃36.3 T m−1. This large field gradient and the stimulated echo pulse sequence allows to obtain time-dependent diffusion coefficients and to observe a non-Debye feature of the relaxation attenuation function. The behavior of the diffusion follows a stretched exponential function plus a Debye term, allowing the determination of different water domains. In the long time limit the diffusion follows a long tail Lévy function, whose asymptotic limit is related to the fractal dimension of the underlying polymer structure.