Submitted to: Encyclopedia of Water Science
Publication Type: Literature Review
Publication Acceptance Date: January 26, 2004
Publication Date: May 14, 2004
Citation: Logsdon, S.D. 2004. Bound water in soils. Encyclopedia of Water Science. 1-4. Available: http://www.dekker.com. Product DOI/101081EEWS120025826.
General reviews on bound water discuss the historical development, and show that water associated with hydrophobic surfaces is more rigid than water associated with hydrophilic surfaces. These reviews show that bound water has higher heat capacity, higher relative viscosity, reduced self-diffusion, reduced dielectric constant, and lower density than free water. The properties of bound water are determined only indirectly because bound water can only be measured as part of the system to which it is bound. Early work emphasized properties of water bound to the inorganic colloids in soils, i.e. clays. Later work on bound water developed because the bulk dielectric constant measured at high frequencies showed reduced dielectric constants for soils high in montmorillonite clays. The reduced dielectric constants for bound water occur because of the increased rigidity, which decreases the ability of the water molecules to oscillate in an alternating electrical field. Not only is water oscillating, but polarities develop in the bound water-colloid system. The dielectric properties of bound water are difficult to separate from the induced polarities of the bound water-colloid system. Careful experimental determination of dielectric spectra combined with model development will enable us to separate these components and utilize the dielectric spectra as a characterization tool for soil-water systems.