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Surface pressure—area (π-A) isotherms for the non-ionic surfactant sorbitan sesquioleate (Arlacel 83) have been measured at both the water/air and water/oil interfaces. The effect of high concentrations of ammonium nitrate on the monolayer was assessed. Equations of state are applied Gaines' equation is found to be particularly useful. Mixed monolayers with a non-ionic A-B-A block copolymer, where A is poly(12-hydroxystearic) acid B is polyethylene oxide, have been examined. The two surfactants show efficient packing at both the water/air and water/oil interfaces. It is shown that there is no significant effect of the electrolyte on the surfactant close-packed molecular areas up to the maximum electrolyte concentration studied (8.75 mol dm −3 ). There is evidence to suggest that at the water/oil interface the block copolymer improves the stability of the sorbitan sesquioleate film by reducing its tendency for dissolution into the oil phase.

Pressure-area (π-A) isotherms of a nonionic polymeric surfactant have been obtained at the water/air and water/oil interfaces using a Langmuir trough. The surfactant is an ABA block copolymer, where A is poly (12-hydroxystearic) acid and B is poly (ethylene oxide). The effect of high concentrations of ammonium nitrate in the aqueous phase was investigated, using new ideas recently suggested for the interpretation of electrolyte effects on monolayers. Equations of state were applied to the π-A data for the water/air and water/oil systems. The Gaines equation was particularly successful and predicted chain segment desorption of the polymer on compression. The electrolyte had no significant effect on the close-packed molecular area at the water/air or water/oil interface up to an electrolyte concentration of 8.75 mol dm−3 (the maximum studied).

A light reflectance technique has been used to determine the thickness of water-in-oil films stabilised with three oil-soluble surfactants taken singly and as mixtures. These surfactants were a non-ionic ABA block copolymer [A is poly(12-hydroxystearic acid) and B is poly(ethylene oxide); B246], Arlacel 83 (sorbitan sesquioleate) and soya bean lecithin. The film thicknesses, calculated using an iterative procedure, were generally in-keeping with a sterically-stabilised film. The values for B246 and Arlacel 83 were in agreement with calculated figures based on molecular models and with other experimental data both from this work and the literature. However, the lecithin films were inexplicably considerably thicker than anticipated. For the mixed films, film stability generally decreased with increasing lecithin content and the film thickness was dominated by the polymer at relatively low mole fractions.