THE INFLUENCE OF SALT CONCENTRATION ON NEGATIVE THIXOTROPY IN SOLUTIONS OF PARTIALLY HYDROLYZED POLYACRYLAMIDE

The influence of NaCl concentration on negative thixotropy in aqueous glycerol solutions of partially hydrolyzed polyacrylamide have been in vestigated. It was found that negative thixotropy type I (a slow incre ase in viscosity with time of shearing) sets in at higher critical she ar rates when the salt is present. On the other hand, critical shear r ates for negative thixotropy type II (a rapid increase in viscosity fo llowed by viscosity oscillation) did not depend on the salt addition. Using the critical shear stress as a hydrodynamic criterion for the oc currence of negative thixotropy, a possible explanation of the behavio r is proposed.