GELATION OF SEMIDILUTE POLYMER-SOLUTIONS BY ION COMPLEXATION - CRITICAL-BEHAVIOR OF THE RHEOLOGICAL PROPERTIES VERSUS CROSS-LINK CONCENTRATION

The gelation of hydrolyzed polyacrylamide solutions by addition of chromium(III) has been investigated by using physicochemical and rheological approaches. First, we have studied the formation of cross-links by complexation using UV-visible spectroscopy and dialysis. Comparison with a low molecular weight model of the polymer has allowed us to understand the influence of specific polymer effects and to delimit the range of HP AM and Cr(III) concentrations within which the link concentration can be determined. Second, we have investigated the steady-state viscosity and the steady-state elastic modulus of samples of constant polymer concentration and various Cr(III) concentrations. In the vicinity of the gelation threshold, the variations of the rheological quantities versus the cross-link concentration have been interpreted in terms of critical behavior. The exponents have been found in good agreement with the scalar percolation predictions; the prefactors and the width of the critical region have been described in terms of the gelation of semidilute polymer solutions. © 1990, American Chemical Society. All rights reserved.