INTERFACIAL-TENSIONS FOR LECITHIN MICROEMULSIONS INCLUDING THE EFFECTOF SURFACTANT AND POLYMER ADDITION

Lecithin is lipophilic in a water-hydrocarbon system and tends to form aggregates which are curved toward water. By changing the polarity of the polar solvent by adding a short-chain alcohol to water, three-pha se systems of aqueous alcoholic solution, lecithin, and hexadecane wer e formed at a low lecithin concentration. A balanced lecithin film can stabilize (swell) large amounts of aqueous and hydrocarbon solutions. About 2.3 wt % lecithin/system is the minimum amount needed to form a single microemulsion phase, i.e., to swell 48.8 wt % aqueous and 48.8 wt % hexadecane phases. The interfacial tension between aqueous solut ion and hexadecane in the presence of lecithin at the optimum propanol concentration is 0.0003 mN/m, and the minimal interfacial tensions be tween aqueous and lecithin phases and hexadecane and lecithin phases w ere both approximately 0.0002 mN/m. These experimental observations sh ow that lecithin behaves as an idealized surfactant under suitable con ditions. In order to mimic the stability of the cell membrane, the eff ect of added hydrophilic polymer and amphiphile was studied. The inter facial tension between water and lecithin is depressed on adding a hyd rophilic polymer (dextrin). The effect of adding a hydrophilic nonioni c surfactant (dodecyl oligoglucoside) is to depress the concentration of alcohol needed to reach a balanced state of aggregated lecithin.