Exploration for Micelles Driving Force from Determination of Critical Micelle Concentration of Ionic Surfactants in Presence of Hydrocortisone Acetate

Abstract

It is well known that the hydrophobic group of surfactants is the main driving force for forming micelles. Chemists some times suspect by this phenomenon and, therefore, it requires further confirmations. The hydrophobic characteristics of hydrocortisone acetate (HA) may aid for understanding the latter phenomenon when use it as an additive in determinations of critical micelle concentrations (CMC) of surfactants. The effect of HA as an additive on the CMCs of anionic (sodium dodecyl sulfate, SDS, and cationic cetyltrimethylammonium bromide, CTAB) surfactants at different pH and temperatures using electrical conductivity has been investigated. It was found that the CMCs of anionic and cationic surfactants increased with increasing HA concentration at their natural media. This phenomenon is opposite to that found in the recent investigations using polar amino substituents as additives. Interestingly, it has been found that the presence of HA changes the negative sign of standard enthalpy of micellization (ΔH ^o ) of anionic SDS to positive. It has been concluded that the addition of HA causes unfavorable factor for micellar formation and the hydrophobic interactions should not be considered as the main driving force for micellization process.

Keywords:

• Critical micelle concentration
• hydrocortisone acetate
• micellization driving force
• thermodynamic functions of micellization