EFFECT OF SURFACTANT AND TEMPERATURE ON THE RHEOLOGICAL PROPERTIES OFAQUEOUS-SOLUTIONS OF UNMODIFIED AND HYDROPHOBICALLY-MODIFIED POLYACRYLAMIDE

Linear and nonlinear viscoelasticity of semidilute aqueous solutions o f an unmodified reference polyacrylamide (PAM) and of a hydrophobicall y modified polyacrylamide (HM-PAM) in the presence of various amounts of sodium dodecyl sulfate (SDS) and at different temperatures have bee n examined. Oscillatory shear experiments in the linear viscoelastic d omain revealed significant polymer-surfactant interaction for the HM-P AM-SDS system at a surfactant concentration of ca. 8 mmol/kg, whereas practically no surfactant effect is observed for the PAM-SDS system. T he rheological features for the HM-PAM-SDS system are found to be stro ngly dependent upon the level of surfactant addition, with first an in crease and then a decrease in the values of parameters such as the dyn amic viscosity. While the position of the maximum of the viscosity cur ve, with regard to the surfactant concentration, is independent of pol ymer concentration and temperature, the strength of the network is pro moted by increasing polymer content and decreasing temperature. At hig her surfactant concentrations, a breakdown of chain associations occur red. A non-Newtonian shear thinning behavior, as well as a thixotropy, is detected for HM-PAM solutions in the presence of surfactant. These effects are most pronounced at ca. 8 mmol/kg SDS at the lowest temper ature. The rheological features reveal that the hydrophobic associatio ns, induced by HM-PAM-SDS interactions, play an important role for the viscoelastic properties of the system.