Physicochemical controls on absorbed water film thickness in unsaturated geological media

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Adsorbed water films commonly coat mineral surfaces in unsaturated soils and rocks, reducing flow and transport rates. Therefore, it is important to understand how adsorbed film thickness depends on matric potential, surface chemistry, and solution chemistry. Here, the problem of adsorbed water film thickness is examined through combining capillary scaling with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Novel aspects of this analysis include determining capillary influences on film thicknesses, and incorporating solution chemistry-dependent electrostatic potential at air-water interfaces. Capillary analysis of monodisperse packings of spherical grains provided estimated ranges of matric potentials where adsorbed films are stable, and showed that pendular rings ... continued below

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Tokunaga, T. June 14, 2011.

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Adsorbed water films commonly coat mineral surfaces in unsaturated soils and rocks, reducing flow and transport rates. Therefore, it is important to understand how adsorbed film thickness depends on matric potential, surface chemistry, and solution chemistry. Here, the problem of adsorbed water film thickness is examined through combining capillary scaling with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Novel aspects of this analysis include determining capillary influences on film thicknesses, and incorporating solution chemistry-dependent electrostatic potential at air-water interfaces. Capillary analysis of monodisperse packings of spherical grains provided estimated ranges of matric potentials where adsorbed films are stable, and showed that pendular rings within drained porous media retain most of the 'residual' water except under very low matric potentials. Within drained pores, capillary contributions to thinning of adsorbed films on spherical grains are shown to be small, such that DLVO calculations for flat surfaces are suitable approximations. Hamaker constants of common soil minerals were obtained to determine ranges of the dispersion component to matric potential-dependent film thickness. The pressure component associated with electrical double layer forces was estimated using the compression and linear superposition approximations. The pH-dependent electrical double layer pressure component is the dominant contribution to film thicknesses at intermediate values of matric potential, especially in lower ionic strength solutions (< 10 mol m{sup -3}) on surfaces with higher magnitude electrostatic potentials (more negative than - 50 mV). Adsorbed water films are predicted to usually range in thickness from 1 to 20 nm in drained pores and fractures of unsaturated environments.

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  • Journal Name: Water Resources Research; Journal Volume: 47; Journal Issue: 8; Related Information: Journal Publication Date: 2011

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  • Report No.: LBNL-4943E
  • Grant Number: DE-AC02-05CH11231
  • DOI: 10.1029/2011WR010676 | External Link
  • Office of Scientific & Technical Information Report Number: 1048287
  • Archival Resource Key: ark:/67531/metadc844219

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Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • June 14, 2011

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  • May 19, 2016, 9:45 a.m.

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  • Sept. 29, 2017, 5:24 p.m.

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Tokunaga, T. Physicochemical controls on absorbed water film thickness in unsaturated geological media, article, June 14, 2011; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc844219/: accessed June 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.