Temperature variation in liquid infiltration and defiltration in a MCM41

In a calometric measurement of infiltration and defiltration of pressurized liquid in a hydrophobic MCM41, it is observed that in nanopores the energy change between solid and liquid phases is dependent on the direction of liquid motion: liquid infiltration is exothermic and liquid defiltration is endothermic. The sorption curves and the temperature variation are insensitive to the loading rate. The magnitude of temperature decrease in defiltration is smaller than the temperature increase in infiltration, fitting well with the hysteresis of the sorption curve. These phenomena can be attributed to the confinement effect of nanopore walls and the thermally/mechanically aided surface diffusion of liquid molecules.