Alkyl-thiol Langmuir Films on the Surface of Liquid Mercury

• Published in: Langmuir Vol. 23; no. 14; pp. 7571 - 7582
• Main Authors: Kraack, H, Tamam, L, Sloutskin, E, Deutsch, M, Ocko, B. M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 03.07.2007
• Subjects: CHEMISORPTION; Chemistry; Colloidal state and disperse state; COMPARATIVE EVALUATIONS; Exact sciences and technology; General and physical chemistry; GOLD; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; LAYERS; MERCURY; MORPHOLOGY; national synchrotron light source; PHASE STUDIES; SUBSTRATES; Surface physical chemistry; THIOLS; Monolayer; Gold; Thiol; Film; Chain length; Surface layer; Crystals; Transition metal; Molecular chain; Liquid; Alkyl; X ray scattering; Sulfur; Structure; Mercury; Long range order
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la0701430

The coverage dependent phase behavior of monolayers of alkyl thiols (CH3(CH2) n - 1SH, denoted as CnSH) on mercury was studied for chain lengths 9 ≤ n ≤ 22, using surface tensiometry and surface-specific X-ray scattering methods. At low coverage, a disordered single layer of surface-parallel molecules is found for all n. At high coverage, a monolayer of standing-up molecules is formed, exhibiting well-ordered phases, the structure of which is n- and coverage-dependent. The molecular chains pack in a centered rectangular unit cell, with an ∼27° tilt from the surface normal toward nearest neighbors. The strong sulfur−mercury bond induces a noncentered unit cell for the headgroups, incorporating one mercury atom per two thiol molecules. The small but significant differences in structure of these films on gold and on mercury are discussed and assigned to the different structure of the subphase:  long-range-ordered crystal for gold and short-range-ordered liquid for mercury.