On the microscopic origin of the hysteresis loop in closed end pores - adsorbate restructuring

Phadungbut, Poomiwat, Do, D. D. and Nicholson, D. (2016) On the microscopic origin of the hysteresis loop in closed end pores - adsorbate restructuring. Chemical Engineering Journal, 285 428-438. doi:10.1016/j.cej.2015.10.008

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Author Phadungbut, Poomiwat
Do, D. D.
Nicholson, D.
Title On the microscopic origin of the hysteresis loop in closed end pores - adsorbate restructuring
Formatted title
On the microscopic origin of the hysteresis loop in closed end pores - adsorbate restructuring
Journal name Chemical Engineering Journal   Check publisher's open access policy
ISSN 1385-8947
Publication date 2016-02-01
Year available 2015
Sub-type Article (original research)
DOI 10.1016/j.cej.2015.10.008
Open Access Status File (Author Post-print)
Volume 285
Start page 428
End page 438
Total pages 11
Place of publication Amsterdam, Netherlands
Publisher Elsevier
Language eng
Subject 1600 Chemistry
2304 Environmental Chemistry
1500 Chemical Engineering
2209 Industrial and Manufacturing Engineering
Abstract We present here compelling evidence for adsorbate restructuring as the microscopic origin of hysteresis in closed end pores. Our argument is based on molecular simulations in the grand canonical (GCE) and meso-canonical (MCE) ensembles, for argon adsorbed at 87 K in slit mesopores of different topologies (open end, closed end and closed pores). The MCE isotherms have sigmoidal van der Waals type loops, while the GCE isotherms exhibit hysteresis loops, which are confined between the gas-like and liquid-like spinodal points. One interesting feature, not previously recognized, is that the condensation in the MCE isotherms for pores of different topologies is identical, and it occurs at the same chemical potential, which is the coexistence chemical potential of two phases in equilibrium: the liquid-like condensate and the gas-like phase. At the onset of the condensation, the liquid-like condensate is a thin liquid bridge formed by taking molecules from the metastable adsorbed film, resulting in a thinner and stable adsorbed film. As more molecules are added into the pore, the liquid bridge thickens along the axial direction and both menisci advance toward the pore mouth. As the menisci approach the pore mouth, the liquid condensate is progressively restructured to become more cohesive. When the pressure is reduced in the grand canonical ensemble (open system), a lower pressure is required to disrupt this cohesive structure, resulting in hysteresis in the closed end pores. The classical theories, which conclude that isotherms for closed end pores must be reversible, are in error because they assume that the interfacial energy parameter (the product of the surface tension and the liquid molar volume) has the same value as in a bulk liquid.
Keyword Adsorption
Adsorbate restructuring
Closed end pore
Monte Carlo simulation
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemical Engineering Publications
Official 2016 Collection
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Citation counts: TR Web of Science Citation Count  Cited 3 times in Thomson Reuters Web of Science Article | Citations
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