Abstract
Broadband dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarisation currents (TSDC) techniques were employed to investigate molecular mobility in relation to phase morphology in novel nanocomposites based on polyimide (PI). In addition to dielectric techniques, differential scanning calorimetry (DSC) and creep rate spectroscopy (CRS) provided information on phase transitions and relaxation behaviour of the composites. The systems investigated include nanophase-separated polyimide-silica (PI-SiO2) hybrid materials with covalent bonds between the components and rod-like polyimide (PIR) / flexible chain polyimide (PIF) molecular composites. The combination of several complementary techniques allowed to investigate the dynamic behaviour of PI in these systems in wide ranges of frequency and temperature. All the experiments indicated pronounced deviations from additivity in the dynamics of the composites. The results are discussed in terms of enhancement of small-scale motion due to loosened molecular packing of PI chains confined in nanovolumes and of reduction of large-scale chain mobility due to constraining effects and due to chemical bonds between the components.
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