Division of Molecular and Materials Simulation, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China.
Langmuir. 2012 May 22;28(20):7730-6. doi: 10.1021/la300647s. Epub 2012 May 11.
Using molecular dynamics simulations on the microsecond time scale, we investigate the nucleation and growth mechanisms of CO(2) hydrates in a water/CO(2)/silica three-phase system. Our simulation results indicate that the CO(2) 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 CO(2) hydrate. After nucleation, the nucleus grows along the three-phase contact line and prefers to develop toward the CO(2) phase as a result of the hydrophilic nature of the modified solid surface and the easy availability of CO(2) 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 CO(2) molecules.
我们使用微秒时间尺度上的分子动力学模拟，研究了 CO2 水合物在水/CO2/二氧化硅三相体系中的成核和生长机制。我们的模拟结果表明，CO2 水合物在三相接触线附近成核，而不是在两相界面处，然后沿着接触线生长形成非晶态晶体。在成核阶段，羟基化的二氧化硅表面可以被理解为一种稳定剂，通过氢键延长与二氧化硅表面相互作用的吸附水合物笼的寿命，并且吸附笼作为形成非晶态 CO2 水合物的成核位点。成核后，核沿着三相接触线生长，并由于改性固体表面的亲水性和 CO2 分子的易获得性，优先向 CO2 相发展。在生长过程中，形成的非晶态晶体中 sI 笼的种群增加速度明显快于 sII 笼，这与自然界中只有 sI 水合物才能形成 CO2 分子的事实一致。
