The first sample were pure PPY particles, 100 nm in diameter with density of 1500 kg m"3. They were charged successfully and the resulting mass:velocity distribution is shown in Fig. la. The cluster of data at mass 1.1 x 10"18 kg represents the individual particles. Higher mass data occurs when individual particles clump together. The data for the individual particles covers the velocity range 26 - 37 km s"1. This is significantly higher than previously [10] reported for these low density particles.

The second type of particle used was a PPY coated bromostyrene latex of diameter 590 nm. In the latex synthesis a chemical substitution had been made, such that bromine accounted for 40% of the mass of the particle. This changed the mean density to 1603 kg rrf3, compared to the typical 1100 kg m"3 for the previous coated latex particles [10]. The particles charged well and the mass:velocity distribution measured in flight is shown in Fig. lb. The average particle mass was 1.9 x 10"16 kg. The velocity range covered was 4 to 10 km s"1. There were a few faster, smaller particles recorded. However, these are probably fragments of the PPY coating which have detached themselves during acceleration.

The final type of particle tested was a PPY-silica mixture. Here the small grains of PPY (10 nm or less) are mixed with 20 nm grains of silica. The resulting composite particles were nominally 270 nm in diameter, with density 1637 kg m~3. Given the bulk densities of PPY and the silica, this suggests the particles are typically 21% silica by mass. They charged well and

Figure 1. Mass velocity distributions for (a) pure PPY, (b) bromine doped latex, (c) PPY-silica mixed particles.

were accelerated, giving the mass:velocity distribution shown in Fig lc. The single particles have an average mass of 2.3 x 10"'7 kg and cover a velocity range 7 to 15 km s"1. Again, some larger mass clumps of particles were observed during the measurements.

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