Investigation of the polyvinyl fluoride degradation mechanism under atomic oxygen exposure

• Elucidation of the long-term degradation mechanism of polyvinyl fluoride • Multi-method approach to elucidate the degradation process • Multivariate statistical analysis helps to unravel the degradation process • Quasi-equilibrium at the sample surface after exposure of 0.22 mmol AO/cm 2 • Degradation occurs preferentially at the non-fluorinated carbon atoms Materials degradation in the Low-Earth-Orbit (LEO) can be attributed to a combination of environmental factors, one of the most impactful of which is atomic oxygen (AO). Simulation of these conditions often employs ground-based facilities, such as low-temperature oxygen plasmas that contain AO. Here we focus on the degradation of polyvinyl fluoride (PVF), a material of interest in space applications. The degradation mechanism of PVF under AO is not completely understood, knowledge of which is essential for developing better materials for use in the LEO. A self-constructed capacitively driven 13.56 MHz RF low temperature reactor flooded witch oxygen was used as the source of AO in this study. The chemical changes in the surface of PVF samples during the exposure to the oxygen plasma were investigated using surface sensitive techniques, such as scanning electron microscopy (SEM), X-ray photoelectron microscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The composition inside the reactor was monitored using operando quadrupole mass spectrometry (QMS). Multivariate statistical methods were applied to the data to improve the analysis. The degradation occurs steadily, as evidenced by mass loss measurements, up to a point of a quasi-equilibrium after an exposure to 1.30∙10 20 AO/cm 2 . Water content in the sample and reactor increased during the exposure, as well as the presence of fragments indicating the chemical insertion of oxygen into the polymer. Fragments, such as CO 2 + , F + and H 2 O + in the plasma atmosphere hint towards a near total oxidation of fragments that desorb form the PVF surface. SEM micrographs revealed changes in the morphology of the sample surface during the degradation process.