Abstract
The accurate measurements on density of the binary mixtures of cetyltrimethylammonium bromide and sodium dodecyl sulphate in pure water and in methanol(1) + water (2) mixed solvent media containing (0.10, 0.20, and 0.30) volume fractions of methanol at 308.15, 318.15, and 323.15 K are reported. The concentrations are varied from (0.03 to 0.12) mol.l-1 of sodium dodecyl sulphate in presence of ~ 5.0×10-4 mol.l-1 cetyltrimethylammonium bromide. The results showed almost increase in the densities with increasing surfactant mixture concentration, also the densities are found to decrease with increasing temperature over the entire concentration range, investigated in a given mixed solvent medium and these values are found to decrease with increasing methanol content in the solvent composition. The concentration dependence of the apparent molar volumes appear to be negligible over the entire concentration range, investigated in a given mixed solvent medium and the apparent molar volumes increase with increasing temperature and are found to decrease with increasing methanol content in the solvent composition.
Highlights
The surfactants used in a multitude of industrial products, processes, and other practical applications almost always consist of a mixture of surfactants
The mixture was thoroughly shaken, and kept 24 hours for the released air bubbles to escape before attempting to make the solution of cetyltrimethylammonium bromide which was used to make the final solution of sodium dodecyl sulphate
The densities for the sodium dodecyl sulphate in presence of cetyltrimethylammonium bromide in pure water and in three different methanol–water mixtures at 308.15, 318.15, and 323.15 K are depicted in (Figures 1, 2 and 3)
Summary
The surfactants used in a multitude of industrial products, processes, and other practical applications almost always consist of a mixture of surfactants. Mixed surfactant systems are encountered in most practical and industrial applications of surfactants. This is due to the natural poly-dispersity of commercial surfactants, which results from impurities in starting materials and variability in reaction products during their manufacture (Mata et al 2004). Mixed surfactant systems are much favored from the view-point of economy and performance. They are less expensive than isomerically pure surfactants and they often provide better performance. In mixed micellar systems of ionic, nonionic and zwitterionic surfactants, three types of interactions may operate, viz., favorable (ionic-nonionic, ionic-zwitterionic and cationic-anionic), unfavorable and ideal mixing (nonionic mixtures)
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