Effects of the Environment and Molecular Additives on the Micellization of Hexadecyltrimethylammonium Bromide

Abstract

In this study, the effects of three anionic azo dyes, ponceau 4R (PR), sunset yellow (SY) and titan yellow (TY), on the micellization of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) in aqueous solutions at different temperatures, K 298.15–328.15, were investigated. Electrical conductivity measurements have been used to determine critical micelle concentrations (CMCs) and hydrophobic and electrostatic interactions in aqueous media for every dye + CTAB solution. One critical micelle concentration (CMC) was found for pure CTAB and every Dye + CTAB system. In the presence of dyes, micelles are formed at lower concentrations. The change in the CMC behavior of CTAB in the presence of dyes indicates that there is a strong interaction between them. Thermodynamic parameters such as the standard enthalpy (\(\Delta H_{{\text{m}}}^{{\text{0}}}\)), standard entropy (\(\Delta S_{{\text{m}}}^{{\text{0}}}\)), and standard Gibbs free energy of micellization (\(\Delta G_{{\text{m}}}^{{\text{0}}}\)) have also been evaluated from the CMC. values of ΔG⁰ were negative, which illustrates a thermodynamically spontaneous micellization process. In addition, thermodynamic data show that, whether in the presence or absence of dyes, the value of ΔH⁰ is negative and the value of ΔS⁰ is positive. However, the values of TΔS⁰ are much higher than ΔH⁰ values, which indicates that the process is entropically driven even though enthalpic effects are favored at higher temperatures.