Effect of radiation on the molecular and contamination properties of silicone-based coatings

The exclusion of dust, contamination and ice from sensors and structural surfaces is of paramount importance to ensure the efficient operation of air and space systems as well as the health and safety of the crew operating these systems. For example, dust contamination gathers on photonic sensors inhibiting motion and data gathering. In addition, devices that require transparency to light for maximum efficiency, such as power systems, video cameras and optical or infrared detectors, also suffer from contamination accumulation. For space exploration missions, a radiation environment can occur due to continuous exposure from ionizing and displacement radiations found in a myriad of space radiation sources including the solar wind (SW), solar event particles (SEP), galactic cosmic rays from outside the solar system (GCR) and from secondary radiations arising from the interaction of these primary radiations with structural and photonic materials. For polymeric materials, not all properties are affected to the same degree by radiation because radiation-induced excitation is not coupled to the entire chemical system, but is often localized at a specific bond. At the macro-scale, contaminant adhesion due to van der Waals' forces is very small and can be easily perturbed by other external forces. However, at the nano-scale, van der Waals forces can be significant. In general, these intermolecular forces are not affected by ionizing radiation unless the surface molecular structure is changed since van der Waals interactions are always present between molecules and only dependent on the number of electrons in the molecule and the distance between molecules. Silicon-based polymers perform well for use in a range of space and low-earth-orbit (LEO) applications and their properties can be tailored to also be radiation resistant. This paper will address a study performed on the structural and contamination adhesion of series of silicone and fluoroelastomer-based coatings, before- - and after exposure to high levels of proton and gamma radiation.