Thermal detection of second critical micelle concentration in SDS and CTAB aqueous solutions using a modified Lewis-Nielsen effective thermal model

Abstract

When surfactant molecules are in solution, they self-assemble into various configurations, with the structural conformation changing upon concentration, temperature, and pH. The thermal transport of aqueous solutions containing anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant hexadecyltrimethylammonium bromide (CTAB) was investigated using the thermal wave resonant cavity (TWRC) technique. We use the Lewis-Nielsen effective thermal conductivity model to explain the observed behavior in a new way. We consider that the form factor of the Lewis-Nielsen model relies entirely on surfactant concentration rather than being a constant, as initially was proposed by Lewis and Nielsen. Our findings indicate that the proposed method can detect the transition between spherical and rod-like surfactant micelles. Additionally, this technique could be used to calculate the thermal conductivity of surfactant molecules in water.