RUBBER ELASTICITY OF POLYACRYLAMIDE GELS IN HIGH NETWORK CONCENTRATION

Shear modulus of polyacrylamide (PAAM) gels has been measured with the network concentration ranging from 0.02 to 1.0 g/cm(3). In the low co ncentration region, the shear modulus is a scaling function of network concentration with the exponent equal to 1/3, which is expected by cl assical rubber elasticity theory. As the concentration increases, the behaviour of shear modulus deviates the scaling law significantly. Thi s deviation has been observed from all six series of gels with cross-l inking concentrations varying from 0.61 to 4.91 mol%. The modified Moo ney theory which incorporated a second higher order term is used to ex plain the results. This second term is believed to be a result of gel inhomogeneity. The measured shear modulus data can be fitted well with the new theory, with two exponents equal to 0.33 and around 2.0-2.5, respectively. The crossover concentration from the classical behaviour to the non-classical behaviour was found to be cross-linking concentr ation dependent. (C) 1998 Elsevier Science Ltd. All rights reserved.