Author Description

The current limited understanding of phase behavior of fluids confined in nanopores restricts the applications of nanoporous media ranging from energy and environment to biology and medicine, such as recovery of hydrocarbons from shale resources, drug delivery, catalysis, gas storage, and separation. Although capillary condensation/evaporation and pore critical point (PCP) of fluids have been extensively studied using various experimental methods, certain features of phase behavior of fluids confined in nanopores have hardly or never been experimentally studied due to either detection limit of experimental system or inapplicability of current experimental methods, such as the phase behavior of nanoconfined methane, gradual phase transition, fluid-solid phase transitions, pore triple point, and heat of capillary condensation. Furthermore, experimental results measured from different methods can barely be comparable due to different adsorbent-adsorbate systems. he challenges mentioned above have been successfully addressed by two established experimental systems and a newly developed experimental method, i.e., BT 2.15 differential scanning calorimetry (DSC) system, IGA-001 gravimetric sorption analyzer system, and isothermal DSC measurement. Specifically, the phase transition and criticality of methane in nanopores have been measured using the BT 2.15 DSC system, which can operate at very low temperature and high pressure. The validity is confirmed by the fact that the measured bulk condensation of methane is in excellent agreement with the literature data. The gradual phase transition of ethane confined in MCM-41 is then demonstrated through a multistep process with paths proceeding around PCP without crossing the capillary-condensation curve. The occurrence of gradual phase transition in nanopores, thus the confined supercriticality, for the first time, has been confirmed. Furthermore, capillary phase transitions (evaporation, melting, and sublimation) and the pore