Competitive surface enrichment of alcohols in ternary water–alcohol mixtures

Molecular beams generated from the vapors above the surfaces of ternary mixtures, water–methanol–ethanol, water–ethanol–1-propanol and water–methanol–1-propanol have been examined by mass spectrometry. The propensity for surface enrichment of the alcohols is obtained in terms of the vapor mole fractions of the alcohols, which in turn were estimated from the cluster populations in the molecular beam. The enriching propensities in the ternary mixtures are compared with those in the binary mixtures. The net surface enrichment in ternary mixtures is generally lowered in comparison to that in the binary mixtures, except in the case of water–methanol–ethanol, where it is similar. While the surface enriching ability of methanol is nearly unaffected, that of ethanol is enhanced. The enriching ability of the longer chain propanol, however decreases significantly.