Small-angle neutron-scattering and viscosity studies of CTAB/NaSal viscoelastic micellar solutions

Micellar solutions of cationic surfactant cetyltrimethylammonium bromide (CTAB) in the presence of sodium salicylate (NaSal) show a viscoelastic behavior. Small-angle neutron-scattering (SANS) and viscosity studies from CTAB/NaSal micellar solutions are reported. Zero-shear viscosity of these solutions as a function of Nasal concentration (C-s), at all the four measured surfactant concentrations (C-d) of 12.5. 25, 50 and 100 mM, show a double-peak behavior. The effect of C-s/C-d on two viscosity mar;ima and a minimum has been examined, and the scaling relations are obtained. SANS experiments have been carried out at different Nasal concentrations, beyond the first viscosity maximum for two surfactant concentrations of 25 and 100 mM. It is found that micelles are rigid rods and their exponential length distribution shows that they behave as living polymers beyond the first viscosity maximum. The micellar structure does not change in the living polymer regime, whereas viscosity varies with increase in Nasal concentration. The variation in viscosity seems to be connected with the change in the intermicelle interactions.