Intermolecular Interaction in the Egg Lecithin Monolayers spread on Aqueous Alcohol Solutions

Abstract

The egg lecithin (PC) monolayer was spread on an aqueous butanol or hexanol solution, and the surface pressure-molecular area curves were obtained. From the increase of surface pressure by penetration of alcohol molecules into lecithin monolayer, the amount, penetrated or adsorbed amount, was calculated from the following equation [numerical formula] and the adsorption isotherms of Langmuir type were obtained. The amount of saturated adsorption of alcohol and k, the parameter which represents the affinity of adsorption, were calculated from the linear relation between C/T and C (alcohol concentration). The saturated amount of alcohol decreased with increase in surface concentration of lecithin, but k became minimum. This was explained by the cavity model. The lecithin monolayer penetrated by alcohol molecules forms a mixed monolayer of lecithin and alcohol. The mean area of mixed monolayer was larger than the area calculated by assuming additivity of the area of each component. It was concluded that alcohol molecules penetrating into the lecithin monolayer decrease the cohesive force between lecithin molecules.