A stabilized vapor liquid interface in deuterated cyclohexane–methanol mixtures

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Abstract
The ellipticity of the vapor–liquid interface above mixtures of methanol (CH3OH) and deuterated cyclohexane (C6D12) has been measured in the vicinity of the consolute point. The data above and below Tc are consistent with models for the structure of the interface adapted from the theory of Widom and Ramos-Gomez and Widom. As three-phase coexistence is approached, the quantity of methanol adsorbed at the interface increases whether ordinary or deuterated cyclohexane is used in the mixture. If ordinary cyclohexane were used for studies within the three-phase region below Tc, thick, unstable, lenticular films of the methanol-rich liquid phase would form at the interface and lead to nonreproducible data. In the present measurements lenticular films do not form when deuterated cyclohexane is used in the mixture. (The entire methanol-rich phase then forms on top.) The gravitationally stable interface above the deuterated mixture can be studied reliably in the three-phase region below Tc even though the liquid phases are nearly density matched.