Exploration of Low-Dimensional Gas Clathrate Hydrates

水分子由两个氢原子和一个中心氧原子组成，形成回旋镖形状。当许多水分子凝结成液态水或固态冰时，原子的这种简单放置导致了独特的分子水平结构和复杂的性质，这些性质仅取决于水分子中原子的排列，而不是其放置的容器。 至少对于大型集装箱来说是如此。随着容器的尺寸减小到纳米（比一张纸薄约10万倍），液体的结构也受到单个分子与容器侧面相互作用的影响。 纳米尺度的限制可以导致结构和性质，显着不同于散装水。本研究由化学系化学结构动力学与机理（CSDM-A）项目资助。内布拉斯加大学林肯分校（UNL）的弗朗西斯科、曾晓成、张钦立和白洁正在使用计算机模拟与实验室实验相结合的方法，探索水和水/甲烷混合物（称为笼形水合物）在被限制在纳米狭缝和孤立的碳纳米管中时的物理性质。从这项工作中获得的基本见解有助于我们理解广泛的社会问题，包括土壤中的冻胀（在冻结条件下土壤向上膨胀）和从页岩中提取天然气。此外，该项目还在计算机辅助化学研究和设计先进实验装置方面培训学生和博士后助理。 测量是在能源部国家实验室进行的。该项目的重点是对高度封闭的水和冰的物理性质和相变的分子见解，低维多晶型和多晶型转变，以及低维冰和笼形水合物的新相的预测。更具体地说，UNL团队正在追求三个目标：在宽度为8 - 12埃的纳米狭缝中寻找水和气体水合物的新的多晶和多晶相（或双层到三层形式的冰）;研究低维二氧化碳（CO2）和一氧化碳（CO）水合物形成的机制;以储氢为重点，研究了纳米尺度下分子氢水合物的形成机理。使用分子动力学（MD）模拟，包括用于计算受限流体的自由能表面的最先进的复制交换MD模拟。

Water molecules consist of two hydrogen atoms bound to a central oxygen in a boomerang shape. When many water molecules condense into liquid water, or solid ice, this simple placement of atoms results in a unique molecular-level structure and complex properties that depend only on the arrangement of atoms in the water molecule, and not the container in which its placed. At least this is true for large containers. As the size of the container is reduced to nanometers (about 100,000 times thinner than sheet of paper), the structure of the liquid is also affected by the interaction of the individual molecules with the sides of the container. Nanoscale confinement can result in structures and properties that differ dramatically from bulk water. In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) Program of the Chemistry Division, Professors Joseph S. Francisco, Xiao Cheng Zeng, Chin Li Cheung, and Jaeil Bai of the University of Nebraska-Lincoln (UNL) are using computer simulations combined with laboratory experiments to explore the physical properties of water and water/methane mixtures (known as clathrate hydrates) when they are confined to nano-slits and isolated carbon nanotubes. The fundamental insights gained from this work contribute to our understanding of a broad range of societal problems, including frost heaving in soil (an upwards swelling of soil during freezing conditions) and the extraction of natural gas from shale rock. In addition, the project is training students and postdoctoral associates in computer-aided chemical research and in the design of advanced experimental devices. Measurements are carried out in a Department of Energy National Laboratory. The project focuses on molecular insights into physical properties and phase transitions of highly confined water and ice, low-dimensional polymorphous and polyamorphous transitions, as well as the prediction of new phases of low-dimensional ice and clathrate hydrates. More specifically, the UNL team is pursuing three objectives: seek new polymorphous and polyamorphous phases of water and gas hydrate in nano-slits with widths of 8 - 12 Angstroms (or the bilayer to trilayer forms of ice); investigate the mechanism of low-dimensional carbon dioxide (CO2) and carbon monoxide (CO) hydrate formation; study the molecular hydrogen hydrate formation mechanism in nanoscale confinement focusing on hydrogen storage. Molecular dynamics (MD) simulations, including the state-of-the-art, replica-exchange MD simulations for computing the free-energy surface of confined fluids, is used.