SHEAR THICKENING AND TIME-DEPENDENT PHENOMENA - THE CASE OF POLYACRYLAMIDE SOLUTIONS

In this paper, the theological properties of solutions of high molecul ar weight partially hydrolysed polyacrylamide in mixtures of glycerol and water are presented. The influence of the amount of glycerol and o f salt on the conformation of the macromolecules is studied through th e measurement of the reduced viscosity. When shear stress or shear rat e is applied to the sample, the viscosity depends on time and displays a transient regime with strong instabilities followed by a steady sta te. Then, the non-Newtonian viscosity appears as a superposition of tw o effects: a sharp increase of the viscosity, which is an effect of ti me, and a slight shear thickening. All these phenomena depend on tempe rature and on polymer and salt concentrations. They can be interpreted as a consequence of the formation and destruction of aggregates, depe nding on the balance between intra- and inter-molecular interactions.