Rheological studies of the gelation kinetics of Cr+3-polyacrylamide solutions

A new rheological approach for the study of the gelation kinetics of aqueous Cr+3 polyacrylamide solutions has been investigated which relies on the assumption that at the gel point, GP, a constant amount of Cr+3 will have reacted, independent of the initial Cr+3 concentration. From this, a kinetic expression relating GP to the initial concentrations of Cr+3 and reactive groups on the polymer has been derived for the case of a crosslinking reaction first order in Cr+3 and polymer. Experimental evidence that the amount of Cr+3 reacted at the GP is constant for a given polymer and solution pH has been obtained. The good fit of the kinetic expression to the rheological data provides new evidence that the gelation reaction is first order in Cr+3 rather than second order as claimed previously.