Effect of additives on the clouding behavior of sodium dodecyl sulfate + tetra-<Emphasis Type="Italic">n</Emphasis>-butylammonium bromide system

The effect of additives on the cloud point (CP) of nonionic surfactants has been studied for more than six decades. Ionic surfactants, however, generally do not show clouding. Recently, CP in ionic surfactant solutions have been reported in the presence of a few quaternary bromides. In this study, we report the effect of various additives (e.g., ureas, sugars, salts, organic solvents, acids) on the CP of sodium dodecyl sulfate (SDS) + tetra-n-butylammonium bromide (Bu₄NBr) systems. An increase in CP of the system with urea concentration is explained by its water structure-breaking ability. An opposite effect of thiourea may be due to the direct interaction of the compound with the SDS-Bu₄NBr mixed micelle. The CP-decreasing effect of sugars is due to their water structure-making ability. All the salts decrease the CP, owing to increased counterion binding. The organic solvents used here raise the CP, whereas the other organic additives decrease the CP. The overall criteria of CP variation seemingly depend upon the solubilities of the additive in the micellar interfacial region and the background solvent.