THE SCALING EXPONENTS OF POLYACRYLAMIDE AND ACRYLAMIDE-SODIUM ACRYLATE COPOLYMER GELS

The ratio of bulk modulus to shear modulus, K(e)/G(e), of polyacrylamide (PAAM) gels was studied. This ratio is directly related to a scaling exponent, delta, which is related to the concentration dependence of both bulk modulus and shear modulus. It was found that delta depends on the details of chemical ingredients and process. It increases as the crosslinker or monomer concentration increases. The behavior of acrylamide/sodium acrylate gel was found to be dramatically different from the nonionic gels. As sodium acrylate (SA) concentration increases from zero to 2 mol %, delta decreases from 2.09 to 1.08. Further increase of SA results in the formation of surface pattern and the value of delta increases slightly, eventually reaching a plateau around 1.25.