On the Spontaneous Formation of Clathrate Hydrates at Water-Guest Interfaces

The formation of hydrates, cage-like water-gas structures, is of tremendous importance both in industries and research. Although of major significance, the formation process is not completely understood so far. We present a comprehensive study of hydrate formation at liquid-liquid interfaces between water and isobutane, propane, carbon dioxide, and at the liquid-gas interface between water and xenon. We investigated the structure of these interfaces under quiescent conditions in situ by means of X-ray reflectivity measurements both inside and outside the zone of hydrate stability. At the interfaces between water and liquid alkanes, no evidence for a structural change was found. In contrast, the accumulation of guest molecules inside nanothick interfacial layers was observed at the water-xenon and liquid-liquid water-CO2 interfaces. We show that only those systems initially exhibiting such guest-enriched interfacial layers developed into macroscopic gas hydrates within our observation times (similar to 12h). Therefore, these layers act as triggers for the spontaneous formation of macroscopic hydrates.