Equilibrium Swelling Study of Cationic Acrylamide-Based Hydrogels: Effect of Synthesis Parameters, and Phase Transition in Polyelectrolyte Solutions

Cationic copolymer gels of acrylamide and [(methacrylamido) Propyl] trimethyl ammonium chloride (MAPTAC) were synthesized by free radical aqueous solution polymerization. The Taguchi method, a robust experimental design, was employed for the optimization of the synthesis based on the equilibrium swelling capacity of the hydrogels. Based on Taguchi method a standard L16 orthogonal array with five factors at four levels was designed and experiments were done in accordance with it. The effects of network composition such as cross-linker density, ionizable monomer and total monomer concentration together with the initiator concentration on the equilibrium swelling capacity of hydrogels in distilled water were studied. From the analysis of variance (ANOVA) of the test results, the most effective factor controlling equilibrium swelling capacity was obtained and maximum water absorbency of the optimized hydrogel was found to be 3570 g/g. The presence of counterions in the external solution suppressed swelling of optimized hydrogel and this effect was pronounced with bivalent counterions. By using the thermodynamic model, the experimental data were analyzed and the cross-linking efficiency for the polymerization reaction was calculated to be about 40%.