Inhomogeneity of polyacrylamide gel structure from permeability and viscoelasticity

Crosslinked polyacrylamide gels formed by copolymerisation of acrylamide and N,N′-methylenebisacrylamide in aqueous solution have been characterised by viscoelastic measurements in the frequency range 0.05–150 Hz. These data are consistent with the model, derived from permeability data, of a non-draining central core surrounded by a rather dilute freely draining zone. Rotary diffusional relaxation of the non-draining cores is the major mechanism which contributes to relaxation at times below the experimental frequency scale. The results are in quantitative agreement with the data derived from the permeability studies. Though more than two-thirds of the gel substance is packed into non-draining zones, macromolecular probes of radii up to 4 nm find access to all the network strands, as determined by a new analysis of literature results.