Surface freezing in chain molecules. II. Neat and hydrated alcohols
| Autor: | Benjamin M. Ocko, E. B. Sirota, Oleg Gang, Moshe Deutsch, X. Z. Wu |
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| Rok vydání: | 1998 |
| Předmět: | |
| Zdroj: | Physical Review E. 58:6086-6100 |
| ISSN: | 1095-3787 1063-651X |
| Popis: | Surface freezing is studied in dry and hydrated normal-alcohol melts by x-ray scattering and surface tensiometry. A single crystalline bilayer forms at the surface, for even carbon numbers only, at temperatures up to 1{degree}C (dry) or 2{degree}C (wet) above the bulk freezing, and persists without change down to bulk freezing. The packing is hexagonal, with untilted molecules for short chains and tilted molecules for long chains. The lattices of the upper and lower monolayers are shifted along the next-nearest-neighbor direction. Hydration is found to swell the bilayer by {approximately}2.5 {Angstrom} due to water intercalation into the bilayer, at a molecular water:alcohol ratio of {approximately}1:2. It also increases the transition temperatures, and the temperature and chain-length ranges for which surface crystallization is observed. These effects are accounted for quantitatively by considering the surprising {ital increase} in hydration upon freezing, and taking into account the Gibbs-rule-predicted water depletion at the surface in the liquid surface phase. {copyright} {ital 1998} {ital The American Physical Society} |
| Databáze: | OpenAIRE |
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