High-pressure spectroscopic, structural and mechanochemical studies of molecular materials

使用金刚石砧室（DAC）对固体施加高的外部压力可以导致材料中的显著结构变化，例如，相变和原子间距离（键角和键长）的变化、构象、分子轨道中的电子分布、氢键相互作用和分子轨道的相对能量。这种结构变化通常会导致压色性，即，压力引起的颜色变化。通过使用可商购获得的DAC，高达10 GPa（~ 100，000 atm，即，接近地质领域）可以在实验室中容易地实现，因为材料在两个小的宝石级金刚石（底托，~ 0.6mm）的平行面之间被机械挤压。金刚石对大多数种类的电磁辐射是透明的，并且随着压力增加而发生的任何结构变化可以通过显微光谱技术（例如红外、拉曼、紫外-可见和发光光谱）以及通过粉末X射线衍射和差示扫描量热法通过金刚石在真实的时间内监测。我们的长期实验计划是使用传统和水热（温度控制）HDAC来促进高压下的固态化学反应，以努力合成以前未知的材料和相，包括纳米材料，并扩展我们在超临界水条件下（221 bar，374 °C）的生物质转化工作，以产生氢气作为替代燃料来源。此外，由于在球磨机米尔斯中研磨固体（机械化学）涉及适度的机械压力（~500 MPa）以及由于摩擦引起的一些局部加热（有时可能实际熔化），因此该方法与熔融相中的化学密切相关。因此，在短期内，我们将使用特殊的热台在高达~600 °C的温度下检查材料的红外和拉曼光谱以及固态反应。在未来5年内，将在DAC和HDAC中以及在机械化学和变温条件下进行检查的材料示例包括粘土矿物，药物多晶型物，地质矿物，艺术家颜料，有机金属和聚合物材料。

The application of high external pressures on solids using diamond-anvil cells (DACs) can lead to dramatic structural changes in materials, e.g., phase transitions and changes in interatomic distances (bond angles and bond lengths), conformations, electronic distributions in molecular orbitals, hydrogen bonding interactions, and relative energies of molecular orbitals. Such structural changes can often lead to piezochromism, i.e., color changes induced by pressure. By using commercially available DACs, pressures of up to 10 GPa (~100,000 atm, i.e., approaching the geological realm) can readily be achieved in the laboratory as materials are squeezed mechanically between the parallel faces of two small gemstone quality diamonds (culets, ~0.6 mm). Diamonds are transparent to most kinds of electromagnetic radiation and any structural changes that occur with increasing pressure can be monitored in real time through the diamonds by microspectroscopic techniques, such as infrared, Raman, UV-visible and luminescence spectroscopy, as well as by powder X-ray diffraction and differential scanning calorimetry. Our long-range experimental plan is to employ conventional and hydrothermal (temperature controlled) HDACs to facilitate solid-state chemical reactions under high pressures in an effort to synthesize previously unknown materials and phases, including nanomaterials and to extend our work on biomass conversion under supercritical water conditions (221 bar, 374 °C) to produce hydrogen gas as an alternative fuel source. Moreover, since grinding solids in ball mills (mechanochemistry) involves moderate mechanical pressures (~500 MPa) and also some local heating (possibly sometimes actual melting) due to friction, this approach is closely related to chemistry in the melt phase. For this reason, in the short term we will examine the infrared and Raman spectra of materials and solid-state reactions at temperatures up to ~600 °C using a special thermal stage. Examples of the materials that will be examined in DACs and HDACs, and under mechanochemical and variable-temperature conditions over the next 5 years include clay minerals, drug polymorphs, geological minerals,artists' pigments, organometallics and polymeric materials.