Abstract
Polyaromatic hydrocarbons (PAHs) are found throughout the universe. The ubiquity of these organic molecules means that they are of considerable interest in the context of cosmic dust, which typically travels at hypervelocities (>1 km s–1) within our solar system. However, studying such fast-moving micrometer-sized particles in laboratory-based experiments requires suitable synthetic mimics. Herein, we use ball-milling to produce microparticles of anthracene, which is the simplest member of the PAH family. Size control can be achieved by varying the milling time in the presence of a suitable anionic commercial polymeric dispersant (Morwet D-425). These anthracene microparticles are then coated with a thin overlayer of polypyrrole (PPy), which is an air-stable organic conducting polymer. The uncoated and PPy-coated anthracene microparticles are characterized in terms of their particle size, surface morphology, and chemical structure using optical microscopy, scanning electron microscopy, laser diffraction, aqueous electrophoresis, FT-IR spectroscopy, Raman microscopy, and X-ray photoelectron spectroscopy (XPS). Moreover, such microparticles can be accelerated up to hypervelocities using a light gas gun. Finally, studies of impact craters indicate carbon debris, so they are expected to serve as the first synthetic mimic for PAH-based cosmic dust.
Highlights
Polyaromatic hydrocarbons (PAHs) such as anthracene, phenanthrene, perylene, and pyrene are naturally occurring molecules found in coal and petroleum deposits, oil shale, hydrothermal vents, and volcanic ash.[1]
It is this chemical stability that has attracted growing interest from the space science community, not least because infrared emission spectroscopy studies have confirmed the ubiquitous presence of PAHs throughout the universe.[2−5] Greenberg et al have postulated that photoprocessing of organic dust mantles within the interstellar medium during solar irradiation may be a possible mechanism for generating PAHs.[6]
A substantial reduction in the mean size of the anthracene microparticles was achieved in both cases
Summary
Polyaromatic hydrocarbons (PAHs) such as anthracene, phenanthrene, perylene, and pyrene are naturally occurring molecules found in coal and petroleum deposits, oil shale, hydrothermal vents, and volcanic ash.[1]. We report the convenient preparation of micrometer-sized anthracene particles via ballmilling in the presence of a commercial dispersant (Morwet D425) and demonstrate that the controlled deposition of PPy from aqueous solution can be used to coat such microparticles with good precision These new microparticles are expected to become useful synthetic PAH mimics for laboratory-based hypervelocity experiments using either a light gas gun[27,33,34] or a van de Graaff accelerator.[17,35] www.acsami.org. The purified aqueous dispersions were either freeze-dried to recover anthracene microparticles in the form of a fine white powder or coated with an ultrathin overlayer of PPy prior to further characterization studies. The aluminum foil target was examined using a Hitachi S4700-N FEG-SEM instrument equipped with a Bruker Xflash EDX detector to identify impact craters caused by the impinging microparticles
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