Premium
The configuration of water on rough natural surfaces: Implications for understanding air‐water interfacial area, film thickness, and imaging resolution
Author(s) -
Kibbey Tohren C. G.
Publication year - 2013
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1002/wrcr.20383
Subject(s) - capillary action , materials science , surface roughness , surface finish , porosity , capillary pressure , porous medium , surface water , composite material , mechanics , optics , environmental science , physics , environmental engineering
Previous studies of air‐water interfacial areas in unsaturated porous media have often distinguished between interfacial area corresponding to water held by capillary forces between grains and area corresponding to water associated with solid surfaces. The focus of this work was on developing a better understanding of the nature of interfacial area associated with solid surfaces following drainage of porous media. Stereoscopic scanning electron microscopy was used to determine surface elevation maps for eight different surfaces of varying roughness. An algorithm was developed to calculate the true configuration of an air‐water interface in contact with the solid surface as a function of capillary pressure. The algorithm was used to calculate surface‐associated water configurations for capillary pressures ranging from 10 to 100 cm water. The results of the work show that, following drainage, the configuration of surface‐associated water is dominated by bridging of macroscopic surface roughness features over the range of capillary pressures studied, and nearly all of the surface‐associated water is capillary held. As such, the thicknesses of surface‐associated water were found to be orders‐of‐magnitude greater than might be expected at the same capillary pressures based on calculations of adsorbed film thickness. The fact that capillary forces in air‐water interfaces dominate surface‐associated water configuration means that interface shapes are largely unaffected by microscopic surface roughness, and interfaces are considerably smoother than the underlying solid. As such, calculations suggest that microscopic surface roughness likely has minimal impact on the accuracy of surface‐associated air‐water interfacial areas determined by limited‐resolution imaging methods such as computed microtomography.