Rheological properties of semidilute hydrophobically modified alkali-soluble emulsion polymers in sodium dodecyl sulfate and salt solutions

The rheological properties of semidilute hydrophobically modified alkali-soluble emulsion polymers in the presence of 0.4 M NaCl and various concentrations of anionic surfactant were investigated. The viscosity profile consists of a zero-shear Newtonian region at low stresses and a shear-thickening region at intermediate stresses, followed by a catastrophic decrease in the viscosity at moderate to high stresses. The viscosity and the dynamic modulus peaked at c/cmc of similar to 11, in contrast to 1 in the absence of NaCl. The activation energies determined at the zero-shear and the shear-thickening regime (denoted by E-a0 and E-a,E-max respectively) increase to a maximum and subsequently decrease as a function of surfactant concentration. Two critical SDS concentrations defined by the crossover of the E-a curves (at similar to 0.001 and 0.009 M SDS) are related to the balance in the inter- and intramolecular association.