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Surface Premelting and Interfacial Interactions of Semi-Clathrate Hydrate

Clathrate hydrates are a demanding field of research because of their fundamental impact on human life and the environment. Interfacial forces involving hydrates are vital factors in numerous natural and industrial processes, but the topic has been relatively neglected in the scientific literature. By using atomic force microscopy, we are now able to measure for the first time the forces between a semi-clathrate hydrate formed by tetrabutyl ammonium bromide and a silica microsphere in air and in undecane. Significantly, the analyses of jump-in (attractive) and pull-off (adhesive) forces in force–distance curves indicate the presence of a quasi-liquid layer (QLL) on the hydrate surface resulting from interfacial premelting. We have shown that interfacial forces between the sphere and the hydrate surface are dominated by the capillary formation between the QLL and the sphere. van der Waals forces are still active in the region several nm above the QLL, prior to the sphere touching the QLL. Our study introduces a new quantitative parameter to the hydrate literature, that is, the thickness of the QLL on the hydrate surface. This parameter, being around 11 nm at −4 °C, is crucial to the modeling of hydrate interactions and agglomerations.