RHEOLOGICAL PROPERTIES OF SEMIDILUTE AND CONCENTRATED AQUEOUS-SOLUTIONS OF CETYLTRIMETHYLAMMONIUM CHLORIDE IN THE PRESENCE OF SODIUM-SALICYLATE AND SODIUM-CHLORIDE

The rheological behavior of the elongated flexible micelles present in aqueous solutions of cetyltrimethylammonium chloride (CTAC) in the presence of sodium salicylate (NaSal), at a more ratio [NaSal]/[CTAC] = 0.6, has been investigated as a function of the surfactant concentration C, temperature T, and NaCl content. The results show that the stress relaxation function characterizing the systems tends toward a single exponential as C increases and/or T decreases. These results are in agreement with the prediction of the theory of the rheological behavior of semidilute solutions of "living" polymer chains (polymer chains whose length varies on a time scale comparable to the reptation time). However, the quantitative analysis of the results (changes of terminal viscoelastic relaxation time T(R), zero shear viscosity eta, and time for reversible micelle breaking, with T) on the basis of this theory reveals some inconsistencies. Also, the exponents of the power laws describing the changes of T(R) and eta with C differ from those predicted by the model at high NaCl content and/or C. It is likely that these departures from the theoretical predictions arise from the nonuniform distribution of the bound chloride and salicylate counterions in the hemispherical endcaps and cylindrical body of the elongated micelles present in the system.