STRUCTURE AND PROPERTIES OF PARTIALLY NEUTRALIZED POLY(ACRYLIC ACID) GELS

The compressional osmotic and shear moduli, the static structure factor, and the cooperative diffusion constant of partially neutralized poly(acrylic acid) gels have been measured in the reaction bath as a function of polymer concentration, ionization degree, salt concentration, and cross-linking degree. The variations of the compressional modulus with these parameters are in good agreement with those predicted from simple theroetical arguments. The structure factor obtained from small-angle neutron scattering exhibits a peak, in a limited range of ionization degree and salt concentration. The variations of the amplitude and the position of the peak as a function of the ionization degree, for a given polymer concentration, are reasonably described by a recent theoretical model developed for a semidilute solution of weakly charged polymers in a poor solvent. From the measurements of the cooperative diffusion coefficient, it is inferred that the friction coefficient is an increasing function of the polymer concentration and ionization degree.