RHEOLOGY OF CETYLTRIMETHYLAMMONIUM TOSILATE-WATER SYSTEM .1. RELATIONTO PHASE-BEHAVIOR

The partial phase behavior of CTAT/water is investigated here as a fun ction of temperature by WAXS, DSC, polarizing microscopy, conductometr y, H-1-NMR, and FTIR spectroscopy. Oscillatory strain and temperature sweeps are also reported. The Krafft temperature (T-K) Of CTAT/water i s 23 degrees C. Below this value, triclinic crystals of CTAT coexist w ith an isotropic solution. Above T-K and at low concentrations, spheri cal micellar solutions are Newtonian and exhibit low viscosities. At h igher concentrations (c(t)), cylindrical micelles form and viscosity i ncreases dramatically with CTAT concentration, but no elastic effects are noticed. When micelles are long enough to entangle (0.9-27 wt % at 25 degrees C), clear viscoelastic solutions form. At higher concentra tions and up to 47 wt %, an hexagonal phase appears. This phase exhibi ts yield stress and viscoelasticity. At higher concentrations, a nonel astic, viscous solid paste forms. Micellar solutions and hexagonal pha se depicts three regimes of viscoelasticity with temperature. These re gimes are bounded by T-K and by the temperature (T-tau) at which the s ystem exhibits its main relaxation time. T-tau moves to lower temperat ures as CTAT concentration increases indicating that the main relaxati on time decreases upon increasing concentration.