Study of an Alcohol’s Influence on the CMC and Thermodynamic Functions of Anionic Surfactants in DMA/Long-chain Alcohol Solutions Using a Microcalorimetric Method

Abstract

The power-time curves for the micelle formation process were determined for two anionic surfactants, sodium laurate (SLA) and sodium dodecyl sulfate (SDS), in mixed alcohol + N,N-dimethylacetamide (DMA) solvent using titration microcalorimetry. From the data of the lowest point and the area of the power-time curves, their critical micelle concentration (CMC) and ΔH m o were obtained. The other thermodynamic functions of the micellization process (ΔG m o and ΔS m o ) were also calculated with thermodynamic equations. For both surfactants, the effects of the carbon number (chain length) of the alcohol, the concentration of alcohol, and the temperature on the CMC and thermodynamic functions are discussed. For systems containing identical concentrations of a different alcohol, values of the CMC, ΔH m o and ΔS m o increased whereas ΔG m o decreased with increasing temperature. For systems containing an identical alcohol concentration at the same temperature, values of the CMC, ΔH m o ,ΔG m o and ΔS m o decrease with increasing carbon number of alcohol. For systems containing the same alcohol at the same temperature, the CMC and ΔG m o values increase whereas ΔH m o and ΔS m o decrease with increasing alcohol concentration.