Phase and rheological behavior of the hexadecyl(trimethyl)azanium; 2-hydroxybenzoate/water system

The temperature-composition phase diagram in the diluted region of the cationic surfactant cetyldimethylbenzylammonium salicylate/water system was studied with a battery of techniques. The Krafft temperature (Tk = 33 1 °C) was measured by differential scanning calorimetry, polarizing microscopy, conductimetry, viscosimetry, and rheometry. The critical vesicle concentration (cvc, ? 0.002 wt%) and a vesicle-micellar transition (cvm, ? 0.005 wt%) was detected at a temperature of 35 °C. Below T k and concentrations ? 2 wt%, a transparent solution is formed (I). Above 2-8.5 wt%, a lamellar (L1) phase forms. At higher concentrations and up to 12 wt%, a second lamellar phase (L2) is detected. From 12.4 to 15.5 wt%, an emulsion phase (E) is formed. Rheological dynamic measurements for the I phase indicate that the system exhibits a predominantly viscous behavior (G? < G?) for concentrations lower than the overlap or entanglement concentration (Ce, ? 0.75 wt%). At higher concentrations, wormlike micelles form and the elastic behavior predominates (G? > G?). The elastic (G?) modulus collapses in a concentration-time master curve in the whole reduced frequencies range ??c examined, whereas the viscous modulus (G?) collapses only at reduced frequencies lower than 0.1. Reduced stress plotted as a function of the reduced shear rate yields a good superposition of the curves at the different concentrations up to the onset of the non-linear behavior. " AOCS 2010.",,,,,,"10.1007/s11743-010-1223-6",,,"http://hdl.handle.net/20.500.12104/43557","http://www.scopus.com/inward/record.url?eid=2-s2.0-79958812450&partnerID=40&md5=8cc199675c5cf67cae6623a8c9cf782e",,,,,,"2",,"Journal of Surfactants and Detergents",,"26