Origin of interfacial nanoscopic gaseous domains and formation of dense gas layer at hydrophobic solid-water interface

Peng, Hong, Birkett, Greg R. and Nguyen, Anh V. (2013) Origin of interfacial nanoscopic gaseous domains and formation of dense gas layer at hydrophobic solid-water interface. Langmuir, 29 49: 15266-15274. doi:10.1021/la403187p

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Author Peng, Hong
Birkett, Greg R.
Nguyen, Anh V.
Title Origin of interfacial nanoscopic gaseous domains and formation of dense gas layer at hydrophobic solid-water interface
Journal name Langmuir   Check publisher's open access policy
ISSN 0743-7463
1520-5827
Publication date 2013-12-10
Year available 2013
Sub-type Article (original research)
DOI 10.1021/la403187p
Open Access Status File (Author Post-print)
Volume 29
Issue 49
Start page 15266
End page 15274
Total pages 9
Place of publication Washington, United States
Publisher American Chemical Society
Language eng
Abstract Interfacial gas enrichment (IGE) covering the entire area of hydrophobic solid-water interface has recently been detected by atomic force microscopy (AFM) and hypothesized to be responsible for the unexpected stability and anomalous contact angle of gaseous nanobubbles and the significant change from DLVO to non-DLVO forces. In this paper, we provide further proof of the existence of IGE in the form of a dense gas layer (DGL) by molecular dynamic simulation. Nitrogen gas adsorption at the water-graphite interface is investigated using molecular dynamic simulation at 300 K and 1 atm normal pressure. The results show that a DGL with a density equivalent to a gas at pressure of 500 atm is formed and equilibrated with a normal pressure of 1 atm. By varying the number of gas molecules in the system, we observe several types of dense gas domains: aggregates, cylindrical caps, and DGLs. Spherical cap gas domains form during the simulation but are unstable and always revert to another type of gas domain. Furthermore, the calculated surface potential of the DGL-water interface, -17.5 mV, is significantly closer to 0 than the surface potential, -65 mV, of normal gas bubble-water interface. This result supports our previously stated hypothesis that the change in surface potential causes the switch from repulsion to attraction for an AFM tip when the graphite surface is covered by an IGE layer. The change in surface potential comes from the structure change of water molecules at the DGL-water interface as compared with the normal gas-water interface. In addition, the contact angle of the cylindrical cap high density nitrogen gas domains is 141. This contact angle is far greater than 85 observed for water on graphite at ambient conditions and much closer to the 150 contact angle observed for nanobubbles in experiments.
Keyword Chemistry, Multidisciplinary
Chemistry, Physical
Materials Science, Multidisciplinary
Chemistry
Materials Science
CHEMISTRY, MULTIDISCIPLINARY
CHEMISTRY, PHYSICAL
MATERIALS SCIENCE, MULTIDISCIPLINARY
Q-Index Code C1
Q-Index Status Confirmed Code
Grant ID DP0985079
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemical Engineering Publications
Official 2014 Collection
 
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Created: Tue, 31 Dec 2013, 10:40:51 EST by System User on behalf of School of Chemical Engineering