Nucleation of the CO2 Hydrate from Three-Phase Contact Lines
DS Bai and GJ Chen and XR Zhang and WC Wang, LANGMUIR, 28, 7730-7736 (2012).
Using molecular dynamics simulations on the microsecond time scale, we investigate the nucleation and growth mechanisms of CO2 hydrates in a water/CO2/silica three-phase system. Our simulation results indicate that the CO2 hydrate nucleates near the three-phase contact line rather than at the two-phase interfaces and then grows along the contact line to form an amorphous crystal. In the nucleation stage, the hydroxylated silica surface can be understand as a stabilizer to prolong the lifetime of adsorbed hydrate cages that interact with the silica surface by hydrogen bonding, and the adsorbed cages behave as the nucleation sites for the formation of an amorphous CO2 hydrate. After nucleation, the nucleus grows along the three-phase contact line and prefers to develop toward the CO2 phase as a result of the hydrophilic. nature of the modified solid surface and the easy availability of CO2 molecules. During the growth process, the population of sI cages in the formed amorphous crystal is found to increase much faster than that of sII cages, being in agreement with the fact that only the sI hydrate can be formed in nature for CO2 molecules.
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