Rheology of dispersions of swollen gel particles

Abstract

AbstractA centrifugal technique was used to determine the swelling, Q (g swollen gel/g dry polymer), of crosslinked polyacrylate gel particles in water. Both centrifugal force and time of centrifugation affected the magnitude of Q but under constant centrifuge conditions it was found that Q−1 was proportional to μ1/2, μ being the ionic strength. The viscoelastic properties of water dispersions of these gel particles were measured as functions of concentration and ionic strength. Viscosity data were reducible to a normalized master curve by plotting (ηsp/cr) versus cr, where cr is a reduced concentration defined as cQ. Values of shear modulus, G, computed from the first normal stress difference measured at various concentrations and ionic strengths also fell on a single curve when plotted against the reduced concentration, cQ. Comparison of these results with those obtained earlier on a similar polyacrylate dispersion, but one in which as much as 20% of the polyacrylate is in a soluble, uncrosslinked form, shows that the soluble fraction has little effect on the magnitude of the viscosity and, moreover, that the presence or absence of the soluble fraction does not affect the transient stress overshoot phenomenon. As in the earlier work, high absolute values of viscosity occur when cQ ≧ 1, that is when the dispersion consists of close‐packed deformable gel particles in intimate contact with little or no interstitial solvent present.