Carbon nanoparticles as absorbers in PVC for laser ablation propulsion: size effects

During laser ablation a mechanical impulse is generated on the target material. This allows to generate thrust on far objects, becoming an attractive space propulsion technique for space debris removal and nanosatellite propulsion. Polymers showed promising results as fuel materials for laser ablation propulsion (LAP) for nanosatellites, and among the commercial ones poly(vinyl chloride) (PVC) gave the best performances. This polymer, however, is transparent for wavelengths>200nm, so that strategies have been tried to increase its absorption and enable laser ablation, among which the loading of carbon nanoparticles (CNPs) as absorbers. Despite the growing number of reports, the role of CNPs size and concentration is still not clear. In this work, different sizes and number density of CNPs are employed as absorbers in order to investigate their role in the impulse generation process. Samples are characterized from the structural, optical and thermodynamical point of view, and laser generated impulse is measured for fluences <7J/cm2 by using a specifically designed ballistic pendulum. Our results show that the main parameter is CNPs number density. For a fixed total mass concentration, a reduced CNP size increases optical absorption and lowers the fluence threshold of impulse generation (Fth) because of a better heat distribution in the sample. A lower limit was also found for Fth at high absorption. Additionally, a considerable enhancement in impulse generation was observed by confining laser ablation with a transparent PVC layer.