SWELLING AND ELASTIC PROPERTIES OF POLYELECTROLYTE GELS

Ionized poly(acrylic acid) gels were studied both at concentrations cl ose to the concentration of preparation and at swelling equilibrium. I n the first experimental condition, the introduction of electrostatic interactions decreases the shear modulus. The addition of salt screens these interactions and allows one to recover the shear modulus of unn eutralized gels. The correlation of these effects with light scatterin g results suggests that they are related to a change of the gel micros tructure with electrostatic interactions. The swelling equilibrium of these gels if found to scale like the ratio of the ionization degree t o the Debye-Huckel screening parameter with an exponent 6/5. The shear modulus at swelling equilibrium is given by the simple affine deforma tion law for not too high smelling degrees (<200). For larger swelling ratios, the shear modulus increases with swelling ratio due to deviat ions from Gaussian elasticity. These results can be partly explained b y a recently proposed model. Finally, the cooperative diffusion coeffi cient can be measured by kinetics of swelling experiments and its beha vior does not follow the predictions of the same model, possibly due t o the coupling of cooperative diffusion with the establishment of a Do nnan equilibrium.