Effects of NaCl and temperature on rheological characteristics and structures of CTAB/NaSal wormlike micellar solutions

[Display omitted] Sodium chloride (NaCl) is the most abundant salt in seawater, which showed the strongest effect in lowering the viscosity of wormlike micellar solutions (WMS) compared to other investigated ionic compounds. In this study, we examined the effect of NaCl addition on the structure of wormlike micelles using the semi-quantitative rheo-structure relations provided by the reaction-reptation model. Prior to addition of NaCl, the structure of wormlike micelles ([CTAB]/[NaSal]=1 at [CTAB]=100mM) in the solution were investigated at different temperatures (25 ℃ ≤ T≤60℃). At higher temperatures, shorter relaxation times and lower ratio values for the local minimum of loss modulus Gmin'' over the plateau modulus (G0' ) were observed. Our results showed that while the zero-shear viscosity of WMS decreased by NaCl addition (S=[NaCl]/[CTAB] varied from 0 to 9), its first critical shear rate and shear stress plateau were observed at their higher values. In addition, while the relaxation time of WMS decreased by adding NaCl, values of Gmin''/G0' did not change accordingly. These results indicate that branch points were formed upon the addition of NaCl and led to the shorter relaxation time and lower zero-shear viscosity.