Volume
11, Issue 2, 2002
Dielectric
studies of phase morphology and molecular mobility in novel nanocomposites
based on polyimide
P.
Pissis1, A. Kanapitsas1, G. Georgoussis1, V.A. Bershtein2 and P. Sysel3
1
National Technical University of Athens, Physics Department, Zografou
Campus, 15780 Athens, Greece
2 Ioffe Physico-Technical
Institute, Russian Academy of Sciences, 194021 St.Petersburg, Russia
3 Institute of Chemical Technology, Technica 5, 16628 Prague, Czech
Republic
(Received 9/01;
accepted 5/02)
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.
|
