Surfactant solubility and micellization in ternary eutectic melt (acetamide + urea + ammonium nitrate)

Cationic surfactants such as dodecyltrimethylammonium bromide (DTAB), tetradecyltrimehtylammonium bromide (TTAB) and hexadecyltrimethylammonium bromide (HTAB); and anionic surfactants such as sodium decyl sulphate (SDeS), sodium dodecyl sulphate (SDS) and sodium tetradecyl sulphate (STDS) have been used to determine their solubility and micellization in ternary eutectic melt (acetamide + urea + ammonium nitrate) at 50 °C. We employed the electrical conductivity and the surface tension measurement techniques to determine the critical micelle concentration (CMC). The deviation in the slope of the specific conductance/surface tension against surfactant concentration plots indicated the aggregations of surfactants and hence, their CMC. CMC decreases with increase of alkyl chain length due to the increased van der Waals forces. The calculated increment in Gibb's energy per methylene group for cationic and anionic surfactants is about −6 kJ mol−1 and −4 kJ mol−1 respectively. It is found that, the CMCs of the surfactants in the ternary melt are higher than the CMCs of same surfactants in water (∼25 °C).

Plot shows the deviation in the slope of specific conductance (○) and surface tension (□) against surfactant sodium tetradecyl sulphate. The deviation point is known as the critical micelle concentration.Figure optionsDownload as PowerPoint slideHighlights
► Ternary eutectic melt of acetamide, urea and ammonium nitrate was prepared.
► Surfactant solubility and its micellization in ternary eutectic melt were studied.
► The break point in the slope of specific conductivity/surface tension give the CMC.
► Gibbs free energy decreases with increase of alkyl chain length.