Open AccessCapillary stress in microporous thin films
Author(s) -
J Samuel,
A J Hurd,
L Frink,
Frank van Swol,
C Brinker,
N.K. Raman
Publication year - 1996
Language(s) - English
Resource type - Reports
DOI - 10.2172/244630
Subject(s) - microporous material , materials science , thin film , capillary action , composite material , mesoporous material , deflection (physics) , porosity , stress (linguistics) , capillary pressure , porous medium , optics , nanotechnology , chemistry , organic chemistry , linguistics , philosophy , physics , catalysis
Development of capillary stress in porous xerogels, although ubiquitous, has not been systematically studied. The authors have used the beam bending technique to measure stress isotherms of microporous thin films prepared by a sol-gel route. The thin films were prepared on deformable silicon substrates which were then placed in a vacuum system. The automated measurement was carried out by monitoring the deflection of a laser reflected off the substrate while changing the overlying relative pressure of various solvents. The magnitude of the macroscopic bending stress was found to reach a value of 180 MPa at a relative pressure of methanol, P/Po = 0.001. The observed stress is determined by the pore size distribution and is an order of magnitude smaller in mesoporous thin films. Density Functional Theory (DFT) indicates that for the microporous materials, the stress at saturation is compressive and drops as the relative pressure is reduced