On the feasibility of (F)LIMM measurements on thin polymer films submitted to an external thermal stress

Abstract

A new bench for the behavior assessment of polymeric thin films submitted to an external thermal stress was developed. Based on the thermal (F)LIMM technique dedicated to space charge and polarization profiles studies, this set-up was applied to the study of two types of thin insulations (PTFE and PVDF) conditioned to a constant external temperature from RT up to $145 ^{\circ}\mathrm {C}$. Concerning PVDF, between 30 et $80 ^{\circ}\mathrm {C}$, its pyroelectric coefficient does not vary significantly, but begins to diminish at $80 ^{\circ}\mathrm {C}$ and falls drastically at $145 ^{\circ}\mathrm {C}$, close to the Curie temperature (between 150 and $160 ^{\circ}\mathrm {C})$, showing a beginning of a shift from a ferroelectric organization to a para electric one. The PTFE sample was first irradiated by an e-beam for negative charge implantation, then placed in the set-up for thermal studies. The temperature was raised up to $130 ^{\circ}\mathrm {C}$. No variation was observed on space charge profiles up to $102 ^{\circ}\mathrm {C}$, temperature at which a brutal change appeared with a quasi-complete detrapping of charges in the sample. Through these two different cases of application, it was shown that it was possible to study the inner space charge and polarization profiles evolutions versus external environmental temperature.