Swelling Behavior and Determination of Diffusion Characteristics of Acrylamide-Acrylic Acid Hydrogels

In this study, a random copolymer of acylamide and acrylic acid [poly(AAm-co-AA)] was prepared by a redox copolymerization method of their aqueous solutions. The effects of initial AAm/AA mole ratio, PEG 4000 content, and N,N′-methylenebisacrylamide concentration on swelling behavior were investigated in water. Average molecular weights between crosslinks, percentage swelling, swelling equilibrium values, and diffusion/swelling characteristics (i.e., the structure of network constant, the type of diffusion, the initial swelling rate, swelling rate constant) were evaluated for every hydrogel systems. The hydrogels showed mass swelling capabilities in the range 789-1040% (for AAm/AA hydrogels), 769-930% (for AAm/AA hydrogels in the presence of PEG 4000), and 716-1040% (for AAm/AA hydrogels containing different concentrations of the crosslinker). The swelling capabilities of the hydrogels decreased with the increasing AA, PEG 4000, and crosslinker concentrations. The diffusion of water into AAm/AA hydrogels was found to be a non-Fickian type.