Network structure of a model HASE polymer in semidilute salt solutions

The effects of salt and temperature on a model hydrophobically modified alkali-soluble emulsion (HASE) associative polymer were investigated. The shear viscosities and viscoelastic properties decrease continuously as the salt concentration is increased. The decrease is attributed to the shielding of charged polyelectrolyte backbones by excess cations, which causes the “stiff” polymer backbone to shrink, leading to the destruction of intermolecular junctions. Smaller individual polymer clusters with predominantly intramolecular associations are then formed. At moderate deformation rates, the solutions exhibit a shear-thickening behavior, which is attributed to the conversion of intramolecular to intermolecular junctions [Tam et al. Polymer 1999, 40, 6369]. The activation energy determined from the zero-shear viscosity decreases with the salt concentrations, while that obtained from the maximum viscosity increases until 0.6M NaCl, beyond which it decreases. This trend indicates that the strength of the network is greater in the shear-thickening region due to the larger proportion of intermolecular junctions.