The Behavior of Methyl Esters Sulphonate at the Water–Oil Interface: Straight-Chained Methyl Ester from Lauryl to Stearyl as an Oil Phase

Abstract

The interfacial behavior of four sodium salt of alpha-sulphonated methyl ester derived from palm oil (C12MES, methyl laurate sulphonate; C14MES, methyl myristate sulphonate; C16MES, methyl palmitate sulphonate; and C16/18MES, mixtures of palmitate and methyl stearate sulphonate) was determined at the water–oil interface. Five linear hydrocarbon chained methyl esters from methyl laurate (C12ME) to methyl stearate (C16ME) were used as an oil phase. From the interfacial tension measurements the following values were calculated: critical micelle concentration (CMC), the interfacial tension at the CMC (γ CMC), surface pressure at the CMC (πCMC), area per molecule at the CMC (A CMC), standard free energy of micellization , and standard free energy of adsorption . The C12MES had the highest CMC values and C16/18MES had the largest molecular area than the other MES surfactants. With the same oil phase, the γ CMC was slightly lowered as the hydrophobicity of the methyl ester sulfonate was increased. was less negative for C12MES and the value was slightly more negative for C16/18MES. The effect of the oil phase was obvious, where by increasing the hydrocarbon chain length of the oil phase increases both the γCMC and cmc values while A CMC was decreased. However the difference between πCMC values of the four MES was small. As the length of the hydrocarbon chain of the oil phase was increased, and became less negative.