Neutron transmission and quasielastic neutron scattering in polymer hydrogels

Investigations of hydrogels with a high water content have recently acquired special significance. A hydrogel is a cross-linked three-dimensional network of water-soluble macromolecules saturated by water or water solutions of different substances. The interest in an examination of the fundamental physical properties of such systems is closely related to their numerous applications. Using neutron transmission and quasielastic neutron scattering (QENS), the mass transfer and self-diffusion processes of water in gelatin and poly(acrylamide) hydrogels were studied. QENS data were interpreted using an approach which accounts for the hierarchy of time scales of molecular motions: slow collective motions of liquid molecules in the content of Lagrange's clusters and rapid single-particle motions. It was shown that the macroscopic liquid flow through a network of quasi-porous polymer gels at a relatively low pressure gradient, as well as the self-diffusion of water in the above systems, are adequately described by the effective medium approach.