ON THERMODYNAMICS OF PERMANENT HYSTERESIS IN CAPILLARY LYOPHOBIC SYSTEMS AND INTERFACE CHARACTERIZATION

Permanent hysteresis, meaning the hysteresis,which is stable with regard to the change in the process rate, is known to occur in capillary condensation/evaporation of wetting fluid and intrusion/extrusion of nonwetting liquid in porous solids. No satisfactory thermodynamic description of the permanent hysteresis in these processes exists at present, despite their use in thermodynamic interface characterization of dispersed systems. Also, in the case of lyophobic systems, no direct determination of total energetic exchange of the system exhibiting hysteresis has been reported. Considering quasi-isothermal irreversible processes in capillary lyophobic systems, we obtained expressions of energy and entropy balances which relate equilibrium physical characteristics of the system, energetic exchange, and internal entropy production. This provides a strict base for a modelless thermodynamic method of evaluation of the cumulative interface areas and entropy of the change of interface areas and then the pore volume distribution and surface fractal dimension of porous solid. For the first time, along with p-V measurements, direct determinations of heats of high-pressure intrusion and extrusion of water in pores of hydrophobized silica gel have been undertaken. Analysis of these data shows validity of the developed approach.