Impact ionization experiments with low density conducting polymer-based micro-projectiles as analogues of solar system dusts

Results for electrostatic acceleration of organic, silica- and metal-based micro-projectiles (<1 mu m diameter) are presented. These micro-projectiles, which are mimics for cosmic dust, are accelerated by using a conducting polymer (polypyrrole or polyaniline) to provide a thin electrically conductive overlayer on core particles (polystyrene latex or poly(4-bromostyrene) latex), or by the in situ polymerization of pyrrole in the presence of an ultrafine silica sol (or tin(IV) oxide) to produce polypyrrole-silica (or polypyrrole-tin(IV) oxide) nanocomposite particles. In addition. sterically stabilized polypyrrole particles were also examined. The particles can be charged and electrostatically accelerated to hypervelocities (up to 38 km s(-1)) using a Van de Graaf accelerator. The ionization resulting from their impacts on metal targets (copper, rhodium or gold) was measured. It was found that, for impacts on a given target, the various organic-based and organic-inorganic hybrid dusts had similar ionization yields when normalized to particle mass. However, it was only at high impact speeds (greater than 10 km s(-1)) that this yield was similar to that from impacts of iron particles. At lower speeds the organic-based and organic-inorganic hybrid particles have ionization yields for impacts on copper that exceeded that of iron by a factor of three at 5 km s(-1) and by a factor of ten at 1 km s(-1). This behaviour was dependent on the nature of the metal target (with a smaller difference for impacts on gold and rhodium). Furthermore, it was found that for some metal targets (gold and rhodium) there was little difference in ionization yield between the targets. The relatively easy synthesis of this wide range of conducting polymer-based micro-particles strongly indicates their suitability as mimics of solar system dusts for the calibration of impact ionization detectors for spacecraft. (C) 2002 Elsevier Science Ltd. All rights reserved.