Neutron transmission and quasi-elastic neutron scattering in polymer hydrogels

Investigations of hydrogels with high water contents have recently acquired special significance. Hydrogels are crosslinked three-dimensional networks of water-soluble macromolecules saturated by water or water solutions of different substances. The interest in examination the fundamental physical properties for such systems is related to their numerous applications. Using neutron transmission and quasi-elastic neutron scattering (QENS), the mass transfer and self-diffusion processes of water and water solutions in gelatin and poly(acrylamide) hydrogels were studied. It was shown that the macroscopic liquid flow through network of quasi-porous polymer gels at relatively low pressure gradients as well as self-diffusion of water and water solutions in the above systems are adequately described by "effective medium" approach. QENS data were also interpreted using an approach that accounts for the hierarchy of time scales of molecular motions: slow collective motions of liquid molecules contained in Lagrange's clusters and rapid single-particle motions. The friction and self-diffusion coefficient data were used to estimate the effective pore sizes of gels at different polymer concentrations as well as the mean Lagrange's cluster sizes.