Brotherton Emma E, Chan Derek H H, Armes Steven P, Janani Ronak, Sammon Chris, Wills Jessica L, Tandy Jon D, Burchell Mark J, Wozniakiewicz Penelope J, Alesbrook Luke S, Tabata Makoto
Dainton Building, Department of Chemistry, University of Sheffield, Brook Hill, Sheffield, South Yorkshire S3 7HF, U.K.
Materials and Engineering Research Institute, Sheffield Hallam University, Sheffield, South Yorkshire S1 1WB, U.K.
J Am Chem Soc. 2024 Jul 31;146(30):20802-20813. doi: 10.1021/jacs.4c04330. Epub 2024 Jul 15.
Polycyclic aromatic hydrocarbons (PAHs) are found throughout the interstellar medium and are important markers for the evolution of galaxies and both star and planet formation. They are also widely regarded as a major source of carbon, which has implications in the search for extraterrestrial life. Herein we construct a melting point phase diagram for a series of phenanthrene/pyrene binary mixtures to identify the eutectic composition (75 mol % phenanthrene) and its melting point (83 °C). The molten oil obtained on heating this eutectic composition to 90 °C in aqueous solution is homogenized in the presence of a water-soluble polymeric emulsifier. On cooling to 20 °C, polydisperse spherical phenanthrene/pyrene hybrid microparticles are obtained. Varying the stirring rate and emulsifier type enables the mean microparticle diameter to be adjusted from 11 to 279 μm. Importantly, the phenanthrene content of individual microparticles remains constant during processing, as expected for the eutectic composition. These new hybrid microparticles form impact craters and undergo partial fragmentation when fired into a metal target at 1 km s using a light gas gun. When fired into an aerogel target at the same speed, microparticles are located at the ends of characteristic "carrot tracks". Autofluorescence is observed in both types of experiments, which at first sight suggests minimal degradation. However, Raman microscopy analysis of the aerogel-captured microparticles indicates prominent pyrene signals but no trace of the more volatile phenanthrene component. Such differential ablation during aerogel capture is expected to inform the analysis of PAH-rich cosmic dust in future space missions.
多环芳烃（PAHs）存在于整个星际介质中，是星系演化以及恒星和行星形成的重要标志。它们也被广泛认为是碳的主要来源，这对寻找外星生命具有重要意义。在此，我们构建了一系列菲/芘二元混合物的熔点相图，以确定共晶组成（75摩尔%菲）及其熔点（83°C）。将该共晶组成在水溶液中加热至90°C得到的熔油，在水溶性聚合物乳化剂存在下进行均质化处理。冷却至20°C时，可得到多分散的球形菲/芘混合微粒。改变搅拌速率和乳化剂类型可使微粒的平均直径从11μm调整到279μm。重要的是，单个微粒中的菲含量在加工过程中保持恒定，这与共晶组成的预期情况一致。这些新型混合微粒在使用轻气枪以1千米/秒的速度射向金属靶时会形成撞击坑并发生部分破碎。当以相同速度射向气凝胶靶时，微粒位于特征性“胡萝卜轨迹”的末端。在这两种类型的实验中均观察到自发荧光，乍一看表明降解程度最小。然而，对气凝胶捕获的微粒进行拉曼显微镜分析表明芘信号显著，但没有更易挥发的菲成分的痕迹。气凝胶捕获过程中的这种差异烧蚀预计将为未来太空任务中富含PAH的宇宙尘埃分析提供信息。
