Shear thickening in colloidal dispersion gel of partially hydrolyzed polyacrylamide/aluminum citrate

Shear thickening implies that the viscosity of a fluid increases with incre asing rates of shear, In the past work reported, all shear thickening pheno mena were observed in concentrated solid/liquid colloidal suspension, In th is paper, the shear thickening was observed in colloidal dispersion gel, wi th very lower volume fraction, of partially hydrolyzed polyacrylamide (PHPA )/aluminum citrate. Colloidal dispersion gels are made of low concentration s of polymer and crosslinker. Polymer mass fractions normally range from 0. 01% to 0.12%, In this concentration regime, there is not enough polymer to form a continuous network, so a conventional bulk type gel cannot form. Ins tead of a solution of separate gel bundles forms, and it is a mixture of pr edominantly intramolecular and minimal intermolecular crosslinks, In the wo rk reported here, the colloidal dispersion gels are made of PHPA of 0.03%, KCl of 0.5%, thiourea of 0.1% and Al3+ with a mass fractions range of 0-0.0 03%, the Al3+ : PHPA mass ratio changes from 0 to 0.1, The critical shear r ates(CSR) for the onset of shear thickening are about 200 s(-1) for all CDC systems studied, i. e., the Al3+ : PHPA mass ratio don't affect the CSR, I n the lower shear regime than CSR shear thinning was observed and in the hi gher shear regime than CSR the shear thickening was observed. The shear thi ckening may be explained with cluster-formation mechanism.