The Nonlinear Conductivity Experiment and Mechanism Analysis of Modified Polyimide (PI) Composite Materials With Inorganic Filler

Abstract

A spacecraft interacts with its space plasma environment. The high-energy electrons in space can cause natural spacecraft surface charging and deep dielectric charging. Both surface charging and deep dielectric charging may affect the instruments and normal operation of the spacecraft. In this paper, we report on the conductivity property of modified polyimide (PI) matrix resin. The modification was obtained by adding micron powder filler to the resin, resulting in a new type of modified polyimide (PI) composite material. We carried out a conductivity experiment for the modified PI composite materials. The results showed: 1) a nonlinear decrease in conductivity when the electric field (E) increased to about 1.93 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> V/m; 2) the conductivity of modified PI composite materials decreased to an order of magnitude of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> Ω · cm; and 3) the nonlinear threshold field intensity of modified PI composites decreased by 50% compared with that of pure PI. We also attempt to provide a physical interpretation to the nonlinear conductivity of the modified PI composite materials. The addition of the modifier components into the modified PI enhanced the carrier concentration of the material. The enhancement may cause a local microscopic tunneling effect, which may occur when the internal electric fields reach a critical value. These local and sporadic phenomena may add up and manifest as a macroscopic conductivity phenomenon. We suggest that the modified PI composite materials, with the nonlinear conductivity characteristics, are excellent candidates for effectively mitigating the accumulation of deep dielectric charging in space.