The rheological behavior of chemically crosslinked hydrogels based on poly(acrylamide)

The effects of different ratios of monomer/crosslinking agent and initiator/activator (potassium peroxydisulfate/ascorbic acid) concentrations on the polymerization of acrylamide (AAm) crosslinked with N,N-methylene-bis-acrylamide (Bis) were studied by dynamic oscilatory testing and gel point (GP) quantitative determination. In the studied conditions, rheological response of PAAm gelation - elastic and viscous moduli, loss tangent and complex dynamic viscosity - indicates these properties could transit between elasticity and viscoelasticity dependently on the reaction time and reactants' ratios. After a certain induction period during which the elastic modulus is close to zero, it increases monotonically until equilibrium is reached.