Edge Contact Angle and Modified Kelvin Equation for Condensation in Open Pores.

0482991 - ÚCHP 2018 RIV US eng J - Journal Article
Malijevský, Alexandr - Parry, A.O. - Pospíšil, M.
Edge Contact Angle and Modified Kelvin Equation for Condensation in Open Pores.
Physical Review E. Roč. 96, č. 2 (2017), č. článku 020801. ISSN 2470-0045. E-ISSN 2470-0053
R&D Projects: GA ČR(CZ) GA17-25100S
Grant - others:EPSRC(GB) EP/L020564/1
Institutional support: RVO:67985858
Keywords : capillary condensation * Kelvin equation * density functional theory
OECD category: Physical chemistry
Impact factor: 2.284, year: 2017

We consider capillary condensation transitions occurring in open slits of width L and finite height H immersed in a reservoir of vapor. In this case the pressure at which condensation occurs is closer to saturation compared to that occurring in an infinite slit (H = infinity) due to the presence of two menisci that are pinned near the open ends. Using macroscopic arguments, we derive a modified Kelvin equation for the pressure p(cc) (L, H) at which condensation occurs and show that the two menisci are characterized by an edge contact angle theta(e) that is always larger than the equilibrium contact angle theta, only equal to it in the limit of macroscopic H. For walls that are completely wet (theta = 0) the edge contact angle depends only on the aspect ratio of the capillary and is well described by theta e approximate to root pi L/2H for large H. Similar results apply for condensation in cylindrical pores of finite length. We test these predictions against numerical results obtained using a microscopic density-functional model where the presence of an edge contact angle characterizing the shape of the menisci is clearly visible from the density profiles. Below the wetting temperature T-w we find very good agreement for slit pores of widths of just a few tens of molecular diameters, while above T-w the modified Kelvin equation only becomes accurate for much larger systems.
Permanent Link: http://hdl.handle.net/11104/0278398