Three Regimes of Charge Transport in Aged Polytetrafluoroethylene*

Dielectric materials are important in myriad applications from high voltage DC power transmission to spacecraft charging. Charge transport within these dielectric materials can be the difference between a successful space mission and catastrophic failure of a satellite. It is important to understand the evolution of the charge transport properties as a function of aging as well, as radiation can significantly alter these properties due to the harsh space environment. A common material, polytetrafluoroethylene, was aged at three different total ionizing doses with three different dosing sources. The aged materials were subjected to an 80 keV monoenergetic electron beam to deposit charge deep within the bulk of the sample. The resulting embedded charge distribution was measured via the pulsed electroacoustic (PEA) method which allows for non-destructive measurements of internal charge distributions within dielectric materials. The materials were measured grounded, with a small DC bias applied, and then grounded again. It was observed that there were three distinct charge transport regimes as a function of aging. The first regime was observed to have a typical single peaked, negative charge distribution that was immobile upon application of an electric field. The second regime was identified by the appearance of multiple negative peaks that were again immobile with application of an electric field. The final regime, due to the highest degree of aging, was characterized by mobile charge within the sample.

Approved for public release; distribution is unlimited. Public Affairs release approval # AFRL-2024-4857