Critical Surface Tension and Specific Surface Free Energy of Clathrate Hydrate

The specific surface free energy (γsv) of a solid is the work required to create a unit area of a solid in a vacuum. γsv is a fundamental physical quantity that plays a central role in cohesion, adhesion, and premelting of a solid and other phenomena like the nucleation work of a solid phase. However, due to experimental difficulties, no specific surface free energy values have been reported for clathrate hydrates. Here we applied the "Zisman plot" to the determination of the critical surface tension, γc, of ice and tetrahydrofuran (THF) hydrate. The γc value of ice was found to be very similar to the value reported by Adamson et al. (J. Colloid Interface Sci. 1970, 34, 461–468) for the same homologous series. Then we used the measured γc value of THF hydrate and the γsv values of ice reported in the literature to deduce the γsv value of THF hydrate. The deduced γsv value of THF hydrate was somewhat lower than that of ice and in the range from 60.4 to 124.2 mJ/m2, with an average of 92.3 mJ/m2.