Radiotracer studies on soap films

Abstract

The areas per surfactant ion at the liquid-air interfaces of first and second black soap films formed from solutions of n-cetyltrimethylammonium bromide (CTAB) and sodium n-dodecylsulphate (SDS) containing added salts have been measured using radioactive surfactants. For CTAB the area is 44±2 × 10^–20 m² ion^–1 and is independent of sodium bromide concentration over the range 0.15–0.5 M. For SDS films areas between 36 and 42 × 10^–20 m² ion^–1 have been found depending on the ionic composition of the solutions. No significant change in the areas per ion on traversing the first black-second black film transition have been observed.