Hysteresis Loop and Scanning Curves for Argon Adsorbed in Mesopore Arrays Composed of Two Cavities and Three Necks

Abstract

Hysteresis loops and scanning curves for argon adsorbed in sequential mesopore arrays consisting of two cavities and three necks have been studied using Grand Canonical Monte Carlo simulation. We examined four different pore configurations and find that there are two patterns for scanning: (i) Type S1, the scanning curve crosses the hysteresis loop from one boundary to the opposite boundary with the possibility that condensation/evaporation occurs within the hysteresis loop; and (ii) Type S2, the scanning curve leaves one boundary and then returns to the same boundary. The first array has three necks with sizes that are smaller than the critical width (which demarcates cavitation from pore blocking as the mechanism for evaporation from a cavity). The second, third, and fourth arrays are the same as the first with the exception that one neck is larger than the critical width. This large neck connects the large cavity to the gas surroundings in array 2, connects the two cavities in array 3, and connects the small cavity to the gas surroundings in array 4. The mechanism of evaporation from the arrays 1 and 3 is found to be cavitation, they have the same type of hysteresis loop (H2a), but their descending scanning curves (DSC) are different. The DSC of array1 scans across the hysteresis loop (Type S1), while that of array 3 is of Type S2. In arrays 2 and 4, the evaporation follows a sequence of pore blocking and cavitation from the two cavities; a double loop of Type H2a. Although these two arrays have the same type of hysteresis loop, their scanning curves are different. Array 2 has Type S1 scanning with a subloop within the primary hysteresis loop, while array 4 has Type S2 scanning curve with a subloop.