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 C_16/18MES, 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 (π_CMC), 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 C_16/18MES 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 C_16/18MES. The effect of the oil phase was obvious, where by increasing the hydrocarbon chain length of the oil phase increases both the γ_CMC and cmc values while A _CMC was decreased. However the difference between π_CMC values of the four MES was small. As the length of the hydrocarbon chain of the oil phase was increased, and became less negative.

Keywords:

• Alpha-sulphonated methyl ester
• CMC
• interfacial tension
• methyl esters
• palm oil
• water–oil interface

Acknowledgments

The authors extend their gratitude to the Director-General of Malaysian Palm Oil Board (MPOB) for support and permission to publish this article.

Notes

^a Compositions contain less than 1% FAC is not listed in the table.