Polycyclic aromatic hydrocarbons (PAHs) can be found throughout the universe, e.g., as part of cosmic dust in the interstellar space. They are associated with star and planet formation, as well as galaxy evolution. The detection of PAHs can provide useful insights in astrochemistry.

Since cosmic dust generally travels very fast, it can undergo impact ionization when it hits a suitable metal target. This can be used to investigate the chemical composition of cosmic dust in space missions using time-of-flight mass spectrometry. To calibrate the spectrometers in the laboratory, microparticles that mimic cosmic dust can be used. They are coated with a layer that holds a surface charge and accelerated to high speeds towards the target. However, there had been a lack of suitable synthetic mimics for PAH-rich cosmic dust until recently.

Steven P. Armes, University of Sheffield, UK, and colleagues have developed a hybrid phenanthrene/pyrene-based mimic for PAH-based cosmic dust. The team used molten phenanthrene as a solvent for pyrene. The resulting mixtures show eutectic behavior, i.e., the mixtures melt at temperatures that are lower than the melting points of the separate constituents. The researchers found the eutectic composition contains 75 mol% phenanthrene and melts at 83 °C. This mixture was then used to obtain microparticles with a fixed composition.

The team heated a phenanthrene/pyrene mixture and homogenized the resulting molten liquid in an aqueous solution containing a polymer-based emulsifier to obtain microparticles. The size of the particles can be tuned by changing the stirring rate during the homogenization and the type of emulsifier. According to the researchers, the developed PAH-based hybrid microparticles could be useful for the calibration of next-generation cosmic dust detectors.

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• Synthesis of Phenanthrene/Pyrene Hybrid Microparticles: Useful Synthetic Mimics for Polycyclic Aromatic Hydrocarbon-Based Cosmic Dust,
  Emma E. Brotherton, Derek H. H. Chan, Steven P. Armes, Ronak Janani, Chris Sammon, Jessica L. Wills, Jon D. Tandy, Mark J. Burchell, Penelope J. Wozniakiewicz, Luke S. Alesbrook, Makoto Tabata,
  J. Am. Chem. Soc. 2024.
  https://doi.org/10.1021/jacs.4c04330

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