Acrylamide gels were prepared from acrylamide (AAm) with various N,N'-methylenebis(acrylamide) (Bis) contents by free-radical crosslinking copolymerization (FCC) in water and dried before used for swelling experiments. Photon transmission measurements were performed using a UV-visible (UVV) spectrometer during the swelling of polyacrylamide gels. Transmitted light intensity I-tr increased linearly at very early times when acrylamide gels were immersed in water, then decreased continuously as swelling time increased. The behavior of I-tr was modeled assuming two-stage swelling mechanisms for the swelling acrylamide gels. The increase in I-tr at early times was quantified using a linear diffusion model and a linear relaxation constant ko was measured. The decrease in I-tr was modeled using the Li-Tanaka equation, from which time constants tau (1) and cooperative diffusion coefficients D-0 were determined for acrylamide gels with varying Bis content. (C) 2001 John Wiley & Sons, Inc.