Swelling equilibria for positively ionized polyacrylamide hydrogels

Authors: Herbert H. Hooper, John P. Baker, Harvey W. Blanch, John M. Prausnitz - Macromolecules 1990 cited by 237

Swelling equilibria are reported for polyacrylamide gels in water and for copolymer gels containing acrylamide and methacrylamidopropyltrimethylammonium chloride (MAP-TAC) in aqueous NaCl solutions.Gel swelling was investi~ated as a function of gel structure (crosslink density and monomer concentration), degree of gel ionization (relative amount of charged comonomer) and solution ionic strength.A gel-swelling model is presented which describes polymer/solvent mixing effects using a recently proposed lattice model developed for aqueous/polymer systems; this model accounts for hydrogen-bonding in aqueous solutions by distinguishing between different types of contact sites on a solvent molecule or polymer segment.The elastic contribution to swelling is represented using a network theory which accounts for nonaffine displacement of network junctions under strain; polyelectrolyte effects on swelling are described using ideal Donnan theory.Swelling equilbria for uncharged polyacrylamide networks in water are correlated using the gelswelling model.The model describes reasonably well the effect of crosslink density on swelling, but fails to reproduce accurately the dependence of swelling on monomer concentration at preparation.Exchange-energy parameters obtained from polyacrylamide-gel swelling measurements are used to predict swelling in salt solutions for acrylamide/MAPTAC copolymer gels.The model predicts well the effect of gel charge density and solution ionic strength on swelling; however, the effect of monomer concentration is not accurately predicted.Further work is needed to quantify the effect of monomer concentration on the swelling and elastic properties of acrylamide hydrogels.