Fatty acid langmuir films on liquid mercury: X-ray and surface tension studies

H. Kraack, B. M. Ocko, P. S. Pershan, E. Sloutskin, L. Tamam, M. Deutsch

Research output: Contribution to journalArticlepeer-review

29 Scopus citations

Abstract

The structure and phase behavior of liquid-mercury-supported molecular films of fatty acids (CH3(CH2)n-2COOH, denoted CnOOH) were studied for molecular lengths 7 ≤ n ≤ 24, by surface tensiometry and X-ray methods. Two qualitatively different film structures were found, depending on coverage. For high coverage, the film consists of a monolayer of roughly surface-normal molecules, showing a pressure-dependent sequence of structures similar, though not identical, to that of the corresponding water-supported Langmuir films. At low coverage, phases consisting of surface-parallel molecules are found, not observed on the aqueous subphases employed to date. In this range, a two-dimensional (2D) gas followed by a single and, for 14 ≤ n ≤ 24, also by a double layer of surface-parallel molecules is found as coverage is increased. Depending on chain length, the flat-lying phases have a crystalline 2D- ordered, a smectic-like 1D-ordered, or a disordered in-plane structure consisting of molecular dimers. The structure and thermodynamics of the films are discussed.

Original languageEnglish
Pages (from-to)5375-5385
Number of pages11
JournalLangmuir
Volume20
Issue number13
DOIs
StatePublished - 22 Jun 2004

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