SURFACE PRESSURE AREA ISOTHERMS FOR A BLOCK COPOLYMER SURFACTANT AT THE WATER AIR AND WATER OIL INTERFACES

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). © 1990.