Threshold-type shear-thickening in polymeric solutions

Threshold-type shear-thickening has been reported in the literature for relatively complex mixtures and one of the most famous is a solution of poly(vinylalcohol) in water in which a substantial amount of sodium borate is added. As far as we know, relatively few polymer solutions have been shown to be shear-thickening, even less of the threshold type. Two cases of threshold-type shear-thickening are examined. One of them is reversible [HPAM Pusher 700 or partially hydrolyzed poly(acrylamide) aqueous solution], the other one (in vitro-synthesized native dextran aqueous solution) leads to the formation of an irreversible structure provided sufficient strain is applied. In both cases, the occurrence of shear-thickening above a critical value of shear rate is related with a change in macromolecular conformation. This conformational change (reversible) can be followed by the formation of intermolecular bonds (irreversible).Presented at the 57^th Annual Meeting of the Society of Rheology, Ann Arbor, Michigan, Oct. 1985