Swelling equilibria for heterogeneous polyacrylamide gels

To correlate swelling equilibria for heterogeneous polyacrylamide gels in water to the monomer concentration at preparation, it is necessary to modify the classic Flory-Rehner theory. The necessary modification concerns the relation which links the number of segments between junction points to the monomer concentration at preparation; that relation is here adjusted empirically. Modified theory is compared to experimental swelling equilibria for polyacrylamide gels synthesized in water by free-radical copolymerization of acrylamide (AAm) and N,N′-methylenebis(acrylamide) (BIS) at various monomer concentrations. Synthesis conditions studied are (1) different AAm-to-BIS ratios with fixed total monomer concentrations, (2) different total monomer concentrations with fixed AAm-to-BIS ratios, and (3) different AAm-to-BIS ratios with a fixed number of BIS molecules. The modified theory and experiment show good agreement.