Publications Details

Optimization of piezo-electric PVDF polymers for adaptive optics in space environments

Clough, Roger L.; Celina, Mathias C.; Dargaville, Tim R.; Martin, Jeffrey W.

Piezoelectric polymers based on PVDF are of interest for use in large aperture space-based telescopes similar to the James Web Space Telescope. Dimensional adjustments of polymer films depend on their piezoelectric properties with wireless (electron beam) shape control methods having been successfully demonstrated in the past. Such electron beam controls require a detailed understanding of the piezoelectric material responses. Similarly, space applications demand consistent, predictable, and reliable performance. While PVDF as a generic polymer type is a suitable piezoelectric material, it is also well known that fluorinated polymers are highly radiation-sensitive. Mechanical and other physical properties will suffer under various types of radiation (strong vacuum UV, {gamma}-, X-ray, e-beam, ion-beam) and atomic oxygen exposure. Likewise, extreme temperature fluctuations in space environments will result in annealing effects and cyclic stresses. While the radiative degradation chemistry of polymers is an established field there is little information available on the performance of piezoelectric features in PVDF with respect to their expected changes in these environments. Therefore, understanding such fundamental issues becomes mandatory for the design and deployment of satellite systems utilizing these materials/technology. We have investigated the degradation of PVDF and copolymers under a range of stress environments, and have studied the implications with regard to piezoelectrical properties necessary for reliable operation of thin films in space environments. Initial aging studies using {gamma}- and e-beam irradiation to explore material sensitivities for comparison with expected UV doses have shown complex material changes with lowered Curie temperatures, crystallinity, melting points and significant crosslinking, but little affect on piezoelectric d{sub 33} constants. Similar complexities of the aging processes have been observed in accelerated temperature environments. Overall, the results suggest that poling and polymer orientation are negatively affected by radiation effects and temperature. We have established fundamental correlations between chemical (structural) and physical (morphology) features of various PVDF copolymers and their piezoelectric properties. A frame work for material qualification issues and overall system survivability predictions in low earth orbit conditions has been developed. It will allow for improved material selection, feedback for manufacturing and processing technologies, avenues for material optimization/stabilization strategies and provide the necessary guidance on any alternative materials.