الفهرس 
An Introduction to PolymersOnly 14 pages are availabe for public view
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Abstract
The aim of the present work is to study dielectric properties of pure poly (vinyl alcohol) PVA films and doped films of PVA with carbon black, in the frequency range 45Hz to 5MHz at various temperatures in the range 295 to 403 K. The crystalline nature of the films was verified by x-ray diffraction measurements. Al/PVA/Al, Au/PVA/Au and Al/PVA/Au structures were investigated. The electrodes were deposited by vacuum evaporation method. Equivalent circuits for the structures were proposed and the ac electrical characteristics derived. The dielectric constant (′), loss tangent (tan) and relaxation time () were found to be significantly influenced by the temperature and frequency. from the dielectric studies it is concluded that the dependence of dielectric properties on the degree of crystallinity is observed at temperatures above the glass transition temperature.
The effect of temperature and frequency on the dielectric modulus (M*) and impedance (Z*) of these PVA films are investigated and the results were discussed. The frequency dependence of the complex impedance (Z*) in the complex plane could be fitted by semicircles. The study of imaginary part of both the dielectric modulus (M″) and the impedance (Z″) as a function of frequency at constant temperature, for the investigated samples show clearly relaxation peaks but their structure features, peak positions and peak intensities depend on carbon concentration, temperature and frequency.
The ac conductivity of the samples has been studied as function of temperature, frequency and dopant concentration. The frequency dependence of conductivity satisfies the power law where s<1. The variation of s with temperature reveal that the a.c. conduction mechanism is due to the correlated barrier hopping (C.B.H.) .The dc conductivity of the structures were studied as a function of temperature and dopant concentration. The current- voltage characteristics for the Au/PVA/Au and Al/PVA/Au structures could be interpreted in terms of both Schottky and Poole Frenkel effects. The width of Schottky barrier is shown to increase with voltage, and decreases with increasing temperature. The temperature dependence of the dc conductivity of the samples has been described by Greaves variable rang hopping (VRH) model.