The Effect\nof Wettability on Confinement-Induced Phase\nBehavior and Storage of Alkane in Nanoporous Media

The impact of wettability on the confined phase behavior\nof fluids\nis paramount for various applications, such as gas storage, carbon\ndioxide sequestration, and water purification. However, the understanding\nof the fluid–solid intermolecular interactions in confined\nsystems is still limited and requires further investigation. This\nwork investigates the effect of hydrophilic and hydrophobic nanoporous\nmaterials on the adsorption and desorption isotherms of <i>n</i>-butane. The hydrophilic samples in this research are MCM-41 silica\npowder with two different pore sizes (80 and 100 Å). MCM-41 samples\nwere successfully treated with hexamethyldisilazane (HMDS) to create\nhydrophobic adsorbents. Isotherms of <i>n</i>-butane in\nmaterials with different wetting states were generated at various\ntemperatures using an upgraded gravimetric apparatus. The results\ndemonstrated that <i>n</i>-butane was adsorbed more onto\nthe hydrophilic MCM-41 materials during the initial adsorption process.\nThe lower affinity between <i>n</i>-butane and the modified\nMCM-41 samples slightly increased the capillary condensation and evaporation\npressures in these materials compared to those in the original ones.\nHowever, it is noted that wettability’s influence on the confined\nphase transitions of <i>n</i>-butane was not significant\nin this study. Interestingly, the hysteresis behavior of the vapor–liquid\nand liquid–vapor phase transitions due to confinement was independent\nof the surface’s wetting properties. Kelvin’s equation\nfor a hemispherical meniscus was adopted to evaluate the capillary\nevaporation pressures of <i>n</i>-butane in nanopores. The\ncalculated pressures showed agreement with experimental data when\nappropriate pore size and surface tension values were applied. These\nfindings provide valuable insights into the impacts of surface chemistry\nand wettability on the phase behavior of hydrocarbon gas in nanoporous\nmedia. Furthermore, this study enriches the experimental database\non confined fluids, which is essential for developing accurate theoretical\nand modeling tools for numerous industrial and scientific applications.