Carmo Lança
Assistant Professor / Researcher /-/ Materials Science Dept. /-/ Professora Auxiliar / Investigadora /-/ Dept Ciências Materiais /-/ I3N/Cenimat
The electrical methods used to study the molecular movements are based on the movement of the dipoles under DC or AC electric field. We have proposed recently a combined measuring protocol to analyze charge injection/extraction, transport, trapping and de-trapping in polar or non-polar dielectric materials. The method is used here to analyze the molecular movements in polyimide in the temperature range from 293 to 572 K. A strong relaxation was observed around 402 K and a very weak relaxation around 345 K. This is the beta relaxation which is quite complex. As concern the behavior at high temperatures, above the beta relaxation, a high peak was observed that shifts continuously to higher temperatures as the charging temperature and/or the charging field increase. The maximum current of the peak increases and the temperature corresponding to the maximum current increases as the charging temperature and/or the charging field increase, given a direct observation of the so called cross-over effect related to current decay for sample charged at high fields and/or high temperatures.
Neagu, E. R. Dias, C. J. Lanca, M. C. Igreja, R. Inacio, P. Marat-Mendes, J. N. ICSD 2010 International Conference on Solid Dielectrics ICSD JUL 04-09, 2010 Potsdam, GERMANY