Characterization of network structure of poly(N-vinyl 2-pyrrolidone/acrylic acid) polyelectrolyte hydrogels by swelling measurements

Poly(N-vinyl 2-pyrrolidone/acrylic acid) IP(VP/AA)I polyelectrolyte network s were prepared from the ternary mixtures N-vinyl 2-pyrrolidone/acrylic aci d/water by using gamma rays at ambient temperature. Equilibrium swelling be havior of these hydrogels was studied using an equation, based on the James -Guth phantom network theory and the approaches of Peppas et al., which was modified by the authors for determination of the (M) over bar (c) and chi parameters. The (M) over bar (c) and chi parameters were related to the equ ilibrium swelling behavior of the charged copolymeric network, pH, temperat ure, and ionic strength of the surrounding medium. The degree of swelling o f these hydrogels was decreased with these variables, as expected. Oscillat ory swelling behavior was also observed and investigated in response to cha nges in pH of the solution. (C) 2000 John Wiley & Sons, Inc.