Mixed monolayers of simple saturated and unsaturated fatty acids

Abstract

The conventional surface pressure-area per molecule isotherms of single and binary films in the acid series, (Z)-octadec-9-enoic (?oleic?), its (E) isomer (?elaidic?), octadecanoic (?stearic?) and eicosanoic (?arachidic?), have been obtained up to and including collapse. While the films formed from binary mixtures of saturated fatty acids were ideal at all mole fractions, the binary films formed with a saturated acid and the (E) isomer of octadec-9-enoic acid produced negative deviations from ideality; films of a saturated acid and the (Z) isomer produced positive deviations from ideality. Mixed films of the two unsaturated acids showed negative deviations at low mole fraction of (Z) isomer and positive deviations at low mole fraction of the (E) isomer. The role of chain stereochemistry and the effect of (Z) and (E) double bonds on hydrophobic interactions in mixed monolayers is considered.