Eutectic Mixtures of Polycyclic Aromatic Hydrocarbons and Nitrogen-Based Polycyclic Aromatic Hydrocarbons Enable the Rational Design of New Synthetic Mimics for Cosmic Dust Particles

Herein we report the preparation of new synthetic mimics for cosmic dust particles based on eutectic mixtures of polycyclic aromatic hydrocarbons (PAHs) and nitrogen-based polycyclic aromatic hydrocarbons (PANHs). Melting point phase diagrams were constructed for three binary mixtures comprising phenanthrene and N-ethylcarbazole, phenanthrene and N-phenylcarbazole, and pyrene and N-propylcarbazole. Each PAH/PANH eutectic composition was processed by hot emulsification above its eutectic temperature in the presence of a suitable water-soluble polymeric emulsifier. High-shear homogenization produced molten oil droplets, with the mean droplet diameter being adjusted from 13 to 177 μm by varying the stirring rate. The influence of the polymeric emulsifier type and molecular weight on the droplet diameter was also systematically investigated. Subsequently, these relatively coarse emulsions were subjected to high-pressure microfluidization to produce much finer droplets of 0.92 to 1.2 μm diameter. On cooling to 20 °C, the resulting hybrid PAH/PANH microparticles were coated with an ultrathin electrically conductive overlayer of polypyrrole (PPy) using a well-known aqueous deposition protocol. These PPy-coated hybrid microparticles were characterized by optical microscopy, laser diffraction, scanning electron microscopy, and FT-IR spectroscopy. Such well-defined hybrid microparticles are expected to be useful synthetic mimics for impact mass ionization mass spectrometry experiments conducted using dust accelerators, which should enable the robust calibration of cosmic dust detectors for both current and future space missions.