BINARY MIXTURE OF MONOSTEARIN-DISTEARIN MONOLAYERS AT THE AIR-WATER-INTERFACE

The study of mixed films has become of consider able interest both fro m theoretical and practical points of view. The pi-A isotherms of mono stearin-distearin (about 50% 1,3- and 50% 1,2-isomers) mixed films spr ead on water as a function of emulsifier ratio and temperature were st udied in an automated Langmuir-type film balance. When molecules of bo th emulsifiers are spread on the air-water interface they are packed m ore closely together than when either emulsifier is present alone, and they enter into some form of association This association can be demo nstrated by surface pressure-area isotherms and by thermodynamic studi es. The characteristics of the mixed films, their elasticity and misci bility, which are of interest in emulsion ol foam stability are discus sed. A molecular model established can explain the interactions betwee n film and subphase molecules and their relationships with variables o f the process (pressure and temperature). This model fits the calculat ed thermodynamic parameters.