BEHAVIOR OF ALKYL ARYL SULFONATE IN HEPTANE

The interfacial tension, surface tension, intrinsic viscosity and solubilization of a series of Hexadecyl long chain, alkyl cycloalkyl and alkyl aryl sulfonates have been studied in Heptane as the hydrocarbon medium. It was observed from a distinct and significant change in the properties of sulfonate in Heptane media, within a narrow range of concentration, upon micellization (1,2). A decrease in magnitude of hydrocarbon/water interfacial tension continues even after micellization, indicating that surfactant continues to contribute to surface concentration at hydrocarbon/air & hydrocarbon/water interface even beyond cmc. The surface tension starts increasing after certain concentration beyond cmc, which indicates that number of surfactant molecules at air/hydrocarbon interface, decrease and instead, contribute to micellization. The axial ratio and micellar weights show that medium size micelles of un-spherical shape and narrow size distribution are formed in hydrocarbon medium (3,4). The solubilization of alkanes in aqueous sulfonates does not depend upon the hydrocarbon/ water interfacial tension but is directly related to the structure of the hydrocarbon portion of the sulfonate. While saturates hardly increases the solubilization (5.6). The mono and di- rings aromatic derivatives, Hexadecyl Naphthalene sulfonate in particular, greatly enhances the solubilization. The structure of hydrocarbon solubilized as well as that of sulfonate influences the amount of solubilization. The studies are important from the point of view of application of sulfonates as surfactants and additives. KEYWORDS : Sulfonates, Heptane, Interfacial Tension, Surface Tension, Intrinsic viscosity, Micelle, Solubilization, Thermodynamic, Shape & Size