Ethanol Vapor Modulates Hydrate Shell Growth and Persistence on Ice

Abstract Hydrate formation on ice is an interfacial crystallization process governed by thermodynamic driving force and the evolving state of the ice surface and hydrate shell. Here, in situ micro-X-ray computed tomography was used to visualize xenon hydrate formation on single ice particles after ethanol-vapor exposure from −50 to −5 °C under different operational ethanol addition levels. These levels were defined by injection duration and do not represent measured interfacial ethanol doses. Without ethanol, hydrate formation proceeded slowly through surface-layer growth; at −50 °C, only a very thin local hydrate layer was observed after 77.8 h. Under high operational ethanol addition at −10 °C, the ice surface evolved before xenon charging, followed by loose flocculent hydrate formation, shell growth around a shrinking ice core, and late-stage hydrate dissociation. At −20 °C, increasing operational ethanol addition was associated with an ordered progression toward greater shell roughness and spatial heterogeneity. At −50 °C, a clear shell was visible by 620 min after xenon charging without XCT-resolved pre-charging surface deformation. Thus, the XCT observations establish distinct, condition-dependent pathways of hydrate-shell development and persistence following ethanol-vapor conditioning, while their molecular origins require further compositional and spectroscopic verification.