Effect of Wettability on Nucleation Thermodynamics of Natural Gas Hydrate in Nanopores

Natural gas hydrate is taken as a promising future energy source that primarily forms and occurs in the pores of natural sediments. In this study, the effects of thermodynamics and surface wettability of mineral substrates on gas hydrate nucleation are investigated with a modified classical nucleation theory framework, revealing that the hydrophobic concave of a surface will lead to a lower energy barrier (ΔG*) and smaller equivalent critical radii (rec) for hydrate formation, and surface wettability exerts a greater influence in hydrate nucleation than pore curvature. As to the contact angles on minerals, layered silicates such as kaolinite (17.5 ± 2.5°) and montmorillonite (21.5 ± 6.5°) have strong hydrophilicity versus pronounced hydrophobicity as compared with nonpolar materials such as graphene (127 ± 4°) and graphite (98 ± 5°), while sulfide minerals are recognized with intermediate wettability due to their metal–sulfur bond polarity. The polarity based on the dielectric constant predicts that the contact angle of hydrate is greater than that of water on the hydrophilic surface while lower on hydrophobic substrates, and such a phenomenon can be demonstrated with the brass surface. Through a thermodynamic evaluation, this work elucidates the influence of curvature and wettability on hydrate nucleation and identifies a qualitative polarity-contact angle correlation, thereby contributing to the foundational knowledge of nucleation media.