Electrostatic Effect on Synergism of Wormlike Micelles and Hydrophobically Modified Polyacrylic Acid

The electrostatic effects on the synergism between wormlike micelles and hydrophobically modified polyacrylic acid (HMPA) have been investigated by rheological measurements and dissipative particle dynamics molecular simulation (DPD). Both cationic surfactants, cetyltrimethylammonium bromide (CTAB), and anionic surfactant, sodium oleate (NaOA), were employed to construct wormlike micelles, and the influences of both simple salts, NaBr or NaAc, and hydrophobic salts, sodium benzoate (NaBen) and benzyltrimethyl ammonium bromide (BTAB), were discussed. The synergistic effects vary with the headgroup charge and the counterions property of surfactants. For the NaOA system, the obvious viscosity maximum was observed only at low NaAc content, while a monotonous viscosity increase appeared at a high content of BTAB. However, the optimal synergism can be only observed in the presence of concentrated NaBen in CTAB system. DPD molecular simulation provides a support and favorable illustration for the synergism mechanism. It suggests that not only the hydrophobic interaction but also the electrostatic interaction has an important impact on the synergism between ionic wormlike micelles and HMPA.