Adsorption of surface active agents in a non-aqueous solvent

Abstract

Measurements have been made of the surface tension of solutions of sodium dodecyl sulphate, dodecyltrimethylammonium bromide, decanol, and of n-dodecyl and n-tetradecyl hexaoxyethylene monoethers in pure formamide and in salt solutions. Adsorbed films of the ionic surfactants exert low surface pressures (about 15 mN m^–1 near the solubility limit) and exhibit no discontinuity characteristic of micellar aggregation. The monoethers exert surface pressures up to 25 mN m^–1 and show a critical micelle concentration of 0.039 mol dm^–3(C₁₂E₆) and 0.013 mol dm^–3(C₁₄E₆) with aggregation numbers of about 40 and 64 respectively at 25°C. The lower surface activity and higher solubility of the surfactants in formamide compared with water indicate the lower stability of adsorbed and micellar states in the former solvent. Similarly the aggregation numbers of the micelles of monoethers in formamide are much lower than those in water.