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Steady and dynamic oscillatory shear rheological behaviors of two aqueous mixed cationic/anionic surfactant systems: the sodium dodecanoate (SL)/hexadecyltrimethylammonium bromide (CTAB)/H2O system and the sodium dodecylsulfonate (AS)/CTAB/H2O system with excess CTAB, were investigated and compared. The role of matching water affinities between oppositely charged headgroups has been explored. Both the headgroups of AS and CTAB are soft, they are matched in water affinities, while the headgroups of SL and CTAB are mismatched in water affinities due to the hard headgroup of SL. At lower temperature, the degree of matching in water affinities between oppositely charged headgroups is a crucial factor influencing the synergism, self-assembly of wormlike micelles and their rheological behaviors: in comparison with the SL/CTAB/H2O system, the AS/CTAB/H2O system shows much stronger synergism in zero-shear viscosity η0, stronger ability of wormlike micelles formation and elongation, much higher scission energy, much longer relaxation time and lower plateau modulus. While the role of matching water affinities is less important at higher temperature. |
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