INTERACTIONS OF A NONIONIC SURFACTANT WITH MIXED PHOSPHOLIPID OLEIC-ACID MONOLAYERS - SURFACE-POTENTIAL AND SURFACE PRESSURE STUDIES AT CONSTANT AREA

Surface pressure and surface potential isotherms of mixed phospholipid-oleic acid monolayers were shown to be substantially modified in the presence of poloxamer non-ionic surfactant in the aqueous phase. The results reveal the ability of poloxamer molecules to penetrate these monolayers even at high compressional states. On addition of oleic acid molecules to the phospholipid, the compressibilities of the monolayers increased, giving rise to the enhanced poloxamer penetration. Although at the precollapse state poloxamer molecules seem to be unable to penetrate into these monolayers, as indicated by the negative DELTA-PI-values, the surface potential data indicate that poloxamer adsorption takes place beneath these films. The effect of oleic acid in the monolayers upon the orientation of adsorbing poloxamer molecules and monolayer surface potential is discussed.