Thermodynamic studies on thin liquid films IV. Foam film stabilized by sodium dodecyl sulfate

Thermodynamic treatment of thin liquid films in Part III of this series was applied to foam films stabilized by sodium dodecyl sulfate. Miscibility of sodium chloride and sodium dodecyl sulfate in the adsorbed films at the film surfaces and transition between the black films were studied by measuring film thickness and contact angle. A discontinuous change in the thickness and a break on the contact angle vs. concentration curve appeared at the transition. Judging from the phase diagram of adsorption, sodium chloride and sodium dodecyl sulfate are a little miscible in the adsorbed films. The miscibility was ascribed to specific interaction between sodium ion and dodecyl sulfate ion in the adsorbed films. The miscibility in an adsorbed film was compared between the film surface and meniscus and between the common black and Newton black films.

Phase transition between the black films is accompanied by the discontinuous changes in the core-thickness and in the surface densities of NaCl and SDS at the film surfaces.Figure optionsDownload high-quality image (44 K)Download as PowerPoint slideHighlights
► Film thickness and surface densities change discontinuously at the transition between black films.
► The transition occurs only above 0.193 mol kg−1 NaCl.
► Miscibility of NaCl and SDS increases in the order, water/air interface < common black film < Newton black film.