Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4.
J Phys Chem B. 2013 Feb 7;117(5):1403-10. doi: 10.1021/jp308395x. Epub 2013 Jan 29.
The early stage of formation of gas hydrates has recently attracted attention as amorphous intermediate gas hydrate structures have been observed, apparently contrary to a classical model of nucleation and some experimental observations. To date, essentially all reported molecular simulations of the nucleation of gas hydrates have been under constant temperature conditions, which does not consider the possible impacts of heat transfer on the nucleation processes. Here we show, using constant energy molecular simulations, that the nuclei at an early stage of the hydrate formation have relatively more crystalline order in comparison with those observed in previous isothermal (NPT or NVT) work. The current work suggests a more transient role for intermediate amorphous structures during hydrate nucleation, thereby providing a stronger link between molecular simulation and experimental observations. Our NVE results nevertheless support the two-step nucleation mechanism proposed in previous simulation studies under constant temperature conditions which features the initial formation of amorphous hydrate-like structures.
气体水合物形成的早期阶段最近引起了人们的关注，因为已经观察到无定形中间气体水合物结构，这显然与经典成核模型和一些实验观察结果相矛盾。迄今为止，基本上所有报道的气体水合物成核的分子模拟都是在恒温条件下进行的，这并没有考虑到可能的传热对成核过程的影响。在这里，我们使用恒能分子模拟表明，与以前的等温（NPT 或 NVT）工作相比，水合物形成早期的核具有相对更多的结晶有序性。目前的工作表明，在水合物成核过程中，中间无定形结构的作用更具瞬时性，从而在分子模拟和实验观察之间建立了更强的联系。然而，我们的 NVE 结果支持了以前在恒温条件下进行的模拟研究中提出的两步成核机制，该机制的特征是最初形成无定形水合物样结构。
