Calculation of temperature effects on wetting coefficients of porous solids and their capillary pressure functions

We explored the notion that changes in wetting coefficients of porous solids contributed to the temperature sensitivities of capillary pressure functions (CPFs). A chemical-thermodynamic explanation for these contributions was developed. If the temperature sensitivities of CPFs were due to capillarity (i.e., due to temperature-induced changes in liquid-gas interfacial tensions or wetting coefficients), then for a given degree of saturation the ratios of capillary pressures to their temperature derivatives should have been linear functions of thermodynamic temperature with slopes equal to 1. This indeed was the case for samples of both synthetic and natural porous media. Further, the estimated intercepts of these linear functions indicated that changes with temperature of these porous materials' wetting coefficients had pronounced effects on temperature sensitivities of their CPFs. A simple model for temperature effects on CPFs, which was derived from the linear relationship between temperature and the ratio of capillary pressure to its temperature derivative, could be fitted precisely by nonlinear regression to CPFs of two soils determined at four temperatures.