Cloud Point Phenomenon in Anionic Surfactant + Quaternary Bromide Systems and Its Variation with Additives

Abstract

Clouding phenomena generally occur with nonionic surfactants when the temperature of the system is raised to a certain value. This critical temperature is termed the cloud point (CP). Here we report the CP phenomenon with anionic surfactant sodium dodecyl sulfate in combination with a few symmetrical quaternary bromides (tetra-n-butylammonium/phosphonium and tetra-n-amylammonium bromides). The CP has been found to depend upon the nature and concentration of the salt and the surfactant concentration. The CP appearance in these systems is discussed in terms of increased hydrophobic interactions due to the alkyl chains of the quaternary bromides. Measurements show that the viscosity either increases or decreases as the system approaches the CP. Most of the organic additives (aliphatic alcohols (C6−C8), amines (C6−C8), and hydrocarbons (n-hexane and n-heptane)) generally decrease the CP, while nonelectrolytes increase or decrease the CP depending upon their effect on water structure or interaction with the anionic micelle.