The glass-liquid transition of water on hydrophobic surfaces

Interactions of thin water films with surfaces of graphite and vitrified room-temperature ionic liquid [1-butyl-3-methylimidazolium hexafluorophosphate ( [ bmim ] [ P F 6 ] ) ] were investigated using time-of-flight secondary ion mass spectrometry as a function of temperature and annealing time to e...

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Bibliographic Details
Published in:The Journal of chemical physics 2008-09, Vol.129 (12), p.124707-124707-8
Main Author: Souda, Ryutaro
Format: Article
Language:English
Subjects:
Diffusion
Glass - chemistry
Graphite - chemistry
Hydrophobic and Hydrophilic Interactions
Imidazoles - chemistry
Phase Transition
Surface Properties
Temperature
Water - chemistry
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Summary:Interactions of thin water films with surfaces of graphite and vitrified room-temperature ionic liquid [1-butyl-3-methylimidazolium hexafluorophosphate ( [ bmim ] [ P F 6 ] ) ] were investigated using time-of-flight secondary ion mass spectrometry as a function of temperature and annealing time to elucidate the glass-liquid transition of water at the molecular level. Surface diffusion of water occurs at temperatures higher than 120 K , thereby forming three-dimensional clusters (a two-dimensional layer) on the [ bmim ] [ P F 6 ] (graphite) surface. The hydrophobic effect of the surface decreases with increasing coverage of water; the bulklike properties evolve up to 40 ML, as evidenced by the occurrence of film dewetting at around the conventional glass transition temperature ( 140 K ) . Results also showed that aging is necessary for the water monolayer (a 40 ML water film) to dewet the graphite ( [ bmim ] [ P F 6 ] ) surface. The occurrence of aging is explainable by the successive evolution of two distinct liquids during the glass-liquid transition: low density liquid is followed by supercooled liquid water. The water monolayer on graphite is characterized by the preferred orientation of unpaired OH groups toward the surface; this structure is arrested during the aging time despite the occurrence of surface diffusion. However, the water monolayer formed on the [ bmim ] [ P F 6 ] surface agglomerates immediately after the commencement of surface diffusion. The structure of low density liquid tends to be arrested by the attractive interaction with the neighbors.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.2980041