Rheology of diluted and semi-diluted partially hydrolyzed polyacrylamide solutions under shear: Experimental studies

Rheological properties of hydrolyzed polyacrylamide (HPAM) solutions were measured in oscillatory and flow shear. In oscillatory shear the storage and loss moduli increased as the concentrations of the solutions increased, but they decreased as salinity increased. The relaxation spectra were plotted using the Kontogiorgos method. As shown in the relaxation spectra, the number of density of segmental units increased at first and then the peaks shifted and split into several as the concentration increased. With salinity increasing, the number of motion units increase and the peaks of segmental units became broader. In flow shear tests, the curves of viscosity versus shear rate were fitted by a power law equation. The result showed that the flow behavior index decreased with increasing concentration, while it generally increased with increasing of salinity. Furthermore, the first normal stress difference increased as the concentration was increased, while it decreased as the salinity was increased. The first normal stress differences measured by the rheometer were compared with the first normal stress differences calculated by the Laun equation and the results showed that Laun equation deviates the experimental results.