Anomalies in the Kinetics of Swelling of the Cyclochain Copolymer of Dimethyldiallylammonium Chloride and Acrylamide in Water

Swelling of the cyclochain copolymer of N,N-dimethyl-N,N-diallylammonium chloride with acrylamide in water was studied. Examination of the kinetics of this process revealed an abnormal, two-stage sorption process. The degree of swelling was found to be dependent on the copolymer composition, as well as on the hydration numbers of the polar groups of the polymer, the volume of water taken as a swelling medium, the surface area of the samples, and the structural changes in them due to uptake of large amounts of water. An increase in the maximum possible moisture capacity of the copolymer of dimethyldiallylammonium chloride and acrylamide with increases in the relative volume of water and in the specific surface area of the hydrogel was revealed. This unusual feature was interpreted on the basis of a two-stage water absorption scheme including the equilibrium stages of hydration of the water-soluble macromolecules of the copolymer and of the subsequent absorption of a part of the hydrated water by the insoluble fraction of the hydrogel. The water absorption features were considered in relation to physical parameters: the divergence of the Cauchy stress tensor at the water-hydrogel interface and the divergence of the fields of the vectors of movement of water deep into the polymer matrix and of the vectors of change in the volume of the copolymer, the diffusive flux density of water, the hydrogel permeability, and the mechanical equilibrium conditions.