The variation of surface tension of solutions of sodium hexadecyl sulphate with time

Abstract

The rate of fall of surface tension at the surfaces of solutions of sodium hexadecyl sulphate is shown to be greatly influenced by traces of electrolyte present even in treble distilled water. The rate of fall could be shown to be governed by diffusion through a, convecting system, hexadecanol being used as a tracer. Solutions of Na⁺ (1 x 10^-3M), Ca⁺ (1 x 10^-6M), Mg⁺⁺ (1 x 10^-6), or Fe⁺⁺ (1.8 x 10^-7M) produced rapid changes in surface tension. In the presence of a large excess of NaCl the rate of fall of surface tension became independent of trace impurities (at least for periods up to 4 hr) and this rate was approximately governed by diffusion of hexadecyl sulphate ion to the surface. The experiments could not detect any electrical energy barrier to adsorption.