Ionic-Electrostatic Model of the Wedge Pressure and Specific Area of Colloidal Systems

Abstract

A physically substantiated ionic-electrostatic model of the wedge pressure by Deryagin, modified for definition of the water retentivity of natural and artificial colloidal dispersions with a variable moisture content (soils, grounds, clay minerals, wood, caustobioliths, synthetic polymeric hydrogels), is considered. In this model, the relation between the moisture content and dispersivity (effective specific area) of a colloidal system serves as a phase variable. For the first time, with the use of the sorption-equilibrium, moisture-thermodesorption, and equilibrium-centrifugation methods, wedge-pressure isotherms, representing the dependence of the thermodynamic moisture potential (specific Gibbs energy) of a material on the mass fraction of moisture in it, were obtained for materials different in genesis and dispersivity, whose thermodynamic moisture potential varies in absolute value within the wide range 0.1–260 kJ/kg, and the wedge pressure of colloid-bonded disperse systems was quantitatively estimated with regard for the variable factors (temperature, composition, liquid-phase concentration) of the aggregative stability of their colloidal complex determining the phenomenon of dynamics of the dispersivity and water retentivity of such systems. A methodology of calculating the effective specific area of a material by the slope of its wedge-pressure isotherms, constructed at the logarithmic scale, is proposed as an alternative to the standard Brunauer–Emmett–Teller method. The new method is close to the traditional one in the specific area of a material obtained with them, but the method proposed differs favorably from the standard method by the temperature invariance and the possibility of calculating the energy of interphase interactions in the material with the use of the generalized Hamaker constant.