Phase and Rheological Behavior of Cetyldimethylbenzylammonium Salicylate (CDBAS) and Water |
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Authors: | Francisco Carvajal-Ramos Alejandro González-Álvarez J. Roger Vega-Acosta Donato Valdez-Pérez Víctor Vladimir Amilcar Fernández Escamilla Emma Rebeca Macías Balleza J. Félix Armando Soltero Martínez |
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Affiliation: | 1.Departamento de Ingeniería Química,Universidad de Guadalajara,Guadalajara,México;2.Instituto de Física,Universidad Autónoma de San Luis Potosí,San Luis Potosí,México;3.Departamento de Ciencias Tecnológicas,Universidad de Guadalajara,Ocotlán,México |
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Abstract: | 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 (T k = 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 (C e, ~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 ωτ 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. |
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