Molecular dynamics study on the nucleation of methane + tetrahydrofuran mixed guest hydrate

Abstract

The nucleation of methane (CH₄), tetrahydrofuran (THF), and CH₄ + THF hydrates are investigated by microsecond MD simulations. These three systems exhibit distinct structural developments in the aqueous phase quantified by the formation of cage structures of hydrogen bonded water molecules. The development of a cluster of cages in the CH₄ system is limited by the scarce CH₄ molecules in the solution, while in the THF system it is limited by the short lifetime of cages. In the CH₄ + THF mixed guest system, a small cluster of caged CH₄ molecules can be rapidly stabilized by abundant neighboring cages of THF molecules. Therefore, the induction time of the CH₄ + THF mixed guest system is found to be significantly shorter than that of the pure CH₄ and pure THF systems. Furthermore, the structure of cages found in the initially formed cage clusters are often different from the typical 5¹²6ⁿ (n = 0, 2, 3, 4) cages observed in clathrate hydrate systems. The cluster of cages may grow or transform into structure I or II clathrate hydrate in the later stages.