Phase Separation for Langmuir Monolayer in Binary System Based on a π-A Isotherm Measurement

The mixing behavior of binary monolayer of fatty acid was investigated on the basis of p-A isotherm measurements. The (palmitic acid(C(16))/arachidic acid(C(20))) and (C(20)/lignoceric acid(C(24))) mixed monolayers were in a miscible state, whereas the (C(16)/C(24)) mixed monolayer was an immiscible state. The (C(16)/behenic acid(C(22))) and (stearic acid(C(18))/C(24)) mixed monolayers were in an incomplete miscible state. The dependence of mixing behavior on the difference in the number of methylene group between components in monolayer is probably due to an enthalpic contribution based on the difference in cohesive energy between the monolayer components.