The Influence of Side-Chain Modification on Shear Thickening in Solutions of Some High Molecular Weight Copolymers

Abstract

An investigation has been carried out on the influence of chemical structure on the rheological properties of polymer solutions over a range of shear rates. Previous research has shown that the size of droplets produced when a fluid is dispersed in air is related not only to the structure and concentration of any dissolved polymers, but also depends upon the extensional strain rates imposed during the break-up process. Under both strong shear and elongational flows, complexation of the polymer molecules can be induced, leading, with the correct solvent, to a change of phase. The polymer molecules separate into a gelled or crystalline region surrounded by a solvent rich layer. These two phases have different break-up characteristics, thereby indicating the importance of the type of polymer, and its interactions, in controlling drop size. At high rates of shear, such polymers would be expected to show shear thickening, which can be attributed to the transition from intra- to stronger intermolecular associations made possible by elongation under shear flow. The viscosity of such a solution will initially decrease with shear rate, then at intermediate values of shear rate will start to increase with shear rate, as the number of interchain junctions is increased. Ultimately, at very high shear rates, the inter-chain junctions are broken more rapidly than they can reform, and shear thinning occurs once again.KeywordsShear RateHigh Shear RateNormal Stress DifferenceDeborah NumberZero Shear ViscosityThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.