Thermodynamic characteristics of the water weakly bound with the surface of layer silicates

The isochoric-isothermal potential ΔF of the interaction of weakly (osmotically) bound water with the kaolinite surface has been determined. In terms of magnitude this potential does not exceed 1.5% of free surface energy of kaolinite. The heat released during the interaction of boundary layers of water with kaolinite is evaluated. This heat is positive (enthalpy −ΔH = Q is negative) and does not exceed 1% of total integral heat of wetting. Entropy ΔS of weakly bound water is determined from the values of ΔF and ΔH.The entropy is compared with the excess entropy of surface layers of liquid water. The positive sign of the entropy indicates a larger disorder of the structure of boundary layers as compared with the bulk phase. Judging from the relationship between ΔH and TΔS the osmotic swelling of clays is determined just by the entropy component of the isochoric-isothermal potential.