Accurate Measurement of the Isothermal Heat of Capillary Condensation in Nanopores Using Differential Scanning Calorimetry and Adsorption/Desorption Experiments

An accurate measurement of the isothermal heat of capillary condensation in nanopores by the tandem use of differential scanning calorimetry (DSC) and adsorption/desorption experiments, for the first time, has been developed. To demonstrate the method, propane confined in SBA-15 mesoporous silica is used as the system. This is also the first time that the conditions of capillary condensation measured by those two different experimental methods using identical mesoporous adsorbent-adsorbate systems are compared and found to agree with each other, the fact of which allows us to accurately determine the isothermal heat of capillary condensation. The isothermal heat of capillary condensation of this system is found to be lower than the heat of bulk condensation and to decrease with temperature following the trend of that of bulk, just the opposite behavior of the isosteric enthalpy of capillary condensation, the magnitude of which is constant and higher than the heat of bulk condensation.