Rheological properties of multisticker associative polyelectrolytes in semidilute aqueous solutions

Multisticker associative polyelectrolytes of acrylamide (approximate to86 mol %) and sodium 2-acrylamido-2-methylpropanesulfonate (approximate to12 mol %), hydrophobically modified with NN-dihexylacrylamide groups (approximate to2 mol %), were prepared with a micellar radical polymerization technique. This process led to multiblock polymers in which the length of the hydrophobic blocks could be controlled through variations in the surfactant-to-hydrophobe molar ratio, that is, the number of hydrophobes per micelle (N-H). The rheological behavior of aqueous solutions of polymers with the same molecular weight and the same composition but with two different hydrophobic block lengths (N-H = 7 or 3 monomer units per block) was investigated as a function of the polymer concentration with steady-flow, creep, and oscillatory experiments. The critical concentration at the onset of the viscosity enhancement decreased as the length of the hydrophobic segments in the polymers increased. Also, an increase in the No value significantly enhanced the thickening ability of the polymers and affected the structure of the transient network. In the semidilute unentangled regime, the behavior of the polymer with long hydrophobic segments (N-H = 7) was studied in detail. The results were well explained by the sticky Rouse theory of associative polymer dynamics. Finally, the viscosity decreased with an increase in the temperature, mainly because of a lowering of the sample relaxation time. (C) 2004 Wiley Periodicals, Inc.