(641c) Chemical Potential Difference between the Large and Narrow Pore Forms of MIL-53 (Al)

Flexible adsorbents are interesting class of materials. Upon adsorption of guest molecules, some of these materials exhibit phase transition. The isotherms usually exhibit a step and phase transition occurs over a range of pressures. It is important to correctly quantify the chemical potential difference (Δμ_s) between the solid in the two phases to be able to predict and/or model binary gas adsorption (using IAST for example).

In this work we present a consistent method to quantify Δμ_s as a function of temperature. As an example, MIL-53 (Al) is chosen as a solid. It will be shown that Δμ_s is independent of the gas used in the measurement, as is to be expected.

Moreover, the adsorption grand potential in the transition region can not be obtained using the thermodynamic framework for rigid solids. Some insights into the hysteresis and width of the transition region will also be presented.