Wetting transition and pretransitional thin films in binary liquids: alcohol/perfluoromethylcyclohexane mixtures studied by x-ray reflectivity
| Autor: | J. Peisl, Anton Plech, Uwe Klemradt |
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| Rok vydání: | 2001 |
| Předmět: | |
| Zdroj: | Journal of Physics: Condensed Matter. 13:5563-5576 |
| ISSN: | 1361-648X 0953-8984 |
| DOI: | 10.1088/0953-8984/13/24/302 |
| Popis: | In this study the wetting transition at the liquid-vapour interface of binary organic liquid mixtures has been investigated by x-ray reflectivity. Mixtures of various isomeric alcohols with perfluoromethylcyclohexane (PFMC) served as model systems, with alcohol carbon numbers ranging from 1 to 4. Remarkably different pretransitional behaviour of the thin films below the wetting temperature was observed, which could be classified according to the carbon number. At two-phase coexistence, no pretransitional thin films could be detected for methanol and ethanol, whereas thin-to-thick-film transitions were found for propanol and butanol and their isomers. For 1-propanol and 2-propanol, the surface of the upper, alcohol-rich phase of the gravity-separated mixture displays a wetting transition at Tw = 31.5??C and 38.3??C, respectively, where the thickness of a PFMC-rich film jumps from less than 25?? to values exceeding the experimental resolution of about 1200??. For 1-butanol, 2-butanol and i-butanol, we found pretransitional film thicknesses increasing up to 100??, with wetting transitions at Tw = 45.0??C, 34.2??C and 40.1??C, respectively. In the single-phase region, the study of adsorption isotherms above Tw revealed novel behaviour of the adsorbed PFMC-rich film. We observed both a growing film thickness and a significantly changing composition as the coexistence line was approached. Nevertheless, the variation of the excess adsorption with distance from coexistence could still be described by a power law. |
| Databáze: | OpenAIRE |
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