Preparation Of Inorganic Nanoparticle-Polyimide Film And Study Of Relaxation Properties On PI/Nano-SiO₂ Composites Under The High Pressures

Nano-compositive material is a new material. Especially, Scientist paid close attention to organic and inorganic nano-compotitive material and had done many researches on them. PI is a kind of macromolecule film material. Its intensity and transparency are excellent. Its heat-resistance degree is highest of all many polymer materials in industrial apply up to now. PI has very good machine, chemistry, radiation-resistant and electric properties in very broad temperature range, so it has been extensive applied to electric insulation, aviation, space flight and microelectronic industry fields and so on. PI can compound with many materials to manufacture compound film. So it is necessary to study PI film. In this paper, the materials used are PI /nano-SiO₂composites and PI films.Thermally stimulated current (TSC), as a tool to study structures of trap, charge storing and transport controlled by the trap and molecule motions of polymer, has been applied extensively. But in the previous TSC experiments heating rate and some poling parameters are often changed such as polarization temperature, time and field intensity. The new parameter used in measurement of TSC will lead us to obtain more information and enlarge its efficient. For example, the measurement of thermally stimulated current under high pressure can differentiate electron or ion trap, calculate activation volume, obtain dependence of relaxation parameters on pressure and so on. In the paper, we have built up an experiment set-up for TSC measurement under high-pressure and measured of TSC curves under different pressures successfully. The results of TSC curves of polyimide film and PI /nano-SiO₂composite undervarious pressures showed that with the increasing pressure, the peaks of TSC curves shifted to higher temperatures and the activation enthalpy increased. By an analysis of TSC curves measured at glassy state, we found that activation enthalpy of polyimide film increased 0.02eV while the pressure changed from 70MPa to 140MPa. Activation volume of polyimide film and PI /nano-SiO₂composite film at the same state were 10×10-6m3mol-1 and 15×10-6m3mol-1 respectively, the former was in a good agreement with the references. We found the peak temperature in TSC curves of PI /nano-SiO₂composite film is lower than that of polyimide film. Our initial conclusion considers that size effect affects the properties of PI /nano-SiO₂ composite film.