Dielectric Relaxation Spectroscopic Measurements on a Novel Electroactive Polyimide
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properties. These developments, along with theoretical advances have led to increasing knowledge of structure-property relations. Development of polymers based on aromatic structure, led high performance polymers with high thermal and electrical stability. An intensive research work was performed on this class of polymers in order to relate the structure to physical and mechanical properties. The development of polymers as structural materials focused attention on the consideration of change of polymer physical properties with temperature and frequency. A new class of highly stable aromatic polyimide with electro-optic and photo-refractive properties has been reported. An intensivework has been published concerning the synthesis' and properties' of these materials. The interest behind this is the potential applications of these materials in threedimensional holography, light processing, phase conjugation and the handling of large quantities of information in real time 3.. Other dielectric relaxation spectroscopic measurements were performed on reactive polymerss and to investigate the changes in molecular dynamics during bulk polymerization of an epoxide -amine system6 . In addition dielectric relaxation was also used to study relaxation in nonlinear optical materials" 9 . In this paper, the ac electrical behavior of a novel electro-optic polyimide will be reported as a function of frequency and temperature,
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Mat. Res. Soc. Symp. Proc. Vol. 600 @ 2000 Materials Research Society
EXPERIMENTAL The polymer used inthis study was prepared according to a procedure similar to that described by Yu et.al ". The structure is shown below
0
0
N
N0 N N
NO 2
The polymer film was cast onto an ITO glass with thickness of 6.16 gt. The number
average molecular weight (Mn) = 27,000 and the weight average molecular weight (Mw) -- 42,000. The ac impedance measurements were carried out in the temperature range 253000 C, and covering a frequency range 1Hz to 106 Hz, using a Solarton - 1260 Impedance/Gain Phase Analyzer (Shlumberger Instrument). The instrument is co~ntrolled by Z-60 and Z-View package, which maximizes the performance and data handling of the system. An aluminum electrode was evaporated on the surface of the film. The sample
setup was then kept ina shielded cavity to improve low frequency measurements. Best signal generator amplitude and dc bias, were selected after performing a series of
amplitude and dc bias sweeping tests. Then for the measurements 0.5 V for amplitude and zero dc bias were chosen. Using this setup, ac complex impedance Z* and the phase angle
o were measured.
From the measurements of Z* and 0, the real and imaginary
components of ac-impedance (Z*), permittivity(s*) and electric modulus (M*) were determinied as function of frequency at different temperatures. RESULTS AND DISCUSSION In alternating field, different regions in a sample will oscillate with different relaxation times. These regions may be characterized by resistance and capacitor in parallel, and each will have an associated f
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