The factor governing the stability of micelles and hence controlling the rheological behavior of aqueous solutions of cetyltrimethylammonium bromide (CTAB) containing sodium salicylate (NaSal) was investigated.The solutions containing fully entangling threadlike micelles of CTAB-NaSal complexes may be modeled by a Maxwell model with a single relaxation time. Concentrations Cs* of free salicylate ions in the systems were estimated by carrying out XH NMR measurement on deuterium oxide solutions with varying CTAB (CD) and NaSal (Cs) concentrations. The results of NMR measurement suggested that the threadlike micelles existed in the form of a 1:1 complex between CTAB and NaSal. Thus, the relation Cs* = Cs -CD was obtained in the range Ds > CD. On the other hand, we confirmed that the relaxation time rm is influenced only by Cs* independently of Cd, and thus the factor controlling rm is Cg*. Furthermore, consideration on the basis of a quasi-network model led to an idea that the free salicylate ions are behaving as a catalyst for a disentangling reaction.
Viscoelastic properties of aqueous solutions of cetyltrimethylammonium bromide (CTAB) containing sodium salicylate (Nasal) were examined by varying the CTAB, CD, and Nasal, CS, concentrations. The results were compared with those of flexible-chain polymer solutions. With increasing salt-to-detergent ratio, C&D-l, up to a certain critical value close to 1 for the solutions of a given CD, the rheological behavior changed from that of low molecular weight polymer solutions in which the polymer chains are not entangling to behavior similar to that of high molecular weight polymer solutions in which polymer chains are fully entangling. These results suggest that threadlike micelles composed of CTAB/NaSal complexes began to form as C8Cp-l increased, resulting in an entanglement network exhibiting pronounced viscoelasticity. However, at high CSCD-~ above the critical value, their behavior can be represented by a Maxwell model with a constant plateau compliance JNO and a single relaxation time 7,. Interestingly, JNo waa proportional to CD-2.2 but independent of CSCD-', but the relaxation time 7 , decreased with increasing CSCD-l. The complex dependence of 7 , of all the solutions at high CSCD-~ may be reduced to a single composite function of CSC~-'/~. These results suggest that relaxation of the entanglement network took place by chemical processes involving actual breakdown and re-formation of the threadlike micelles.
Viscoelastic properties were examined in aqueous solutions of cetyltrimethylammonium bromide (CTAB) complexed salicylic acid (HSal), coded as CTAB:HSal/W (W represents water), as a function of the detergent, CD, and acid, CA, concentrations. Effects of adding NaBr were also examined. The results were compared with those of CTAB:NaSal/W containing sodium salicylate (NaSal) instead of HSal. In the solutions of CD > 1.0 X 10~2 mol Lr1 and CACD-1 > 0.5, the CTAhHSal complex formed fully entangling threadlike micelles. NMR spectroscopy conducted on the D20 solutions with a similar range of CD and CA suggested that besides free HSal of concentration CA* existing in the aqueous medium, HSal molecules immobilized in the micelles appear to exist in at least two different states through complexation with CTA+. One is the state equivalent to that occupied by Sal" in CTAB:NaSal micelles, and the other is a more nonpolar environment.
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