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

Permanent hysteresis, meaning the hysteresis,which is stable with rega rd to the change in the process rate, is known to occur in capillary c ondensation/evaporation of wetting fluid and intrusion/extrusion of no nwetting liquid in porous solids. No satisfactory thermodynamic descri ption of the permanent hysteresis in these processes exists at present , despite their use in thermodynamic interface characterization of dis persed systems. Also, in the case of lyophobic systems, no direct dete rmination of total energetic exchange of the system exhibiting hystere sis has been reported. Considering quasi-isothermal irreversible proce sses in capillary lyophobic systems, we obtained expressions of energy and entropy balances which relate equilibrium physical characteristic s of the system, energetic exchange, and internal entropy production. This provides a strict base for a modelless thermodynamic method of ev aluation of the cumulative interface areas and entropy of the change o f interface areas and then the pore volume distribution and surface fr actal dimension of porous solid. For the first time, along with p-V me asurements, 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 app roach.