Low frequency a.c. conductivity of fresh and thermally aged polypyrrole–polyaniline conductive blends

doi:10.1016/j.synthmet.2003.07.013

Synthetic Metals

Volume 142, Issues 1–3, 13 April 2004, Pages 81-84

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Abstract

The low frequency (10⁻² to 10⁶ Hz) a.c. conductivity of fresh and thermally aged polypyrrole–polyaniline blends of various compositions was studied at room temperature. The cross-over frequency that separates the d.c. regime from the dispersive region is a function of the composition and is influenced by the thermal aging for the polyaniline-rich blends. The frequency-dispersive conductivity is determined by a sublinear law. The fractional exponent is close to unity for the fresh samples. The thermal aging results in values of the fractional exponent, which depend on the composition. This picture reflects what has been observed previously in d.c. vs. temperature studies: thermal aging reduces the size of conducting grains in polyaniline, while in polypyrrole, results in a modification of the backbone matrix. It seems that a.c. measurements at room temperature may well serve as a parallel way to the time consuming d.c. conductivity vs. temperature technique, to detect thermal degradation of the transport properties in conducting polymers.

Introduction

A serious problem in using conducting polymers in technological applications is the thermal degradation of their electrical conductivity. Polyaniline and polypyrrole are exceptionally stable under environmental conditions. The mechanisms of thermal degradation of the electrical conductivity have been studied experimentally recently and the results were viewed in terms of different models [1], [2]. Additionally, thermally stimulated currents [3], [4] and high-pressure experiments [5] in fresh and aged polypyrrole–polyaniline blends were published recently. The mechanisms of degradation in polyaniline is different from that of polypyrrole. Both polymers have an inhomogeneous structure of the granular metal type and the thermal degradation of the conductivity is attributed to the reduction of size of the conducting islands [1], [2]. On the other hand, what distinguishes the two conductive polymers, is that different laws govern the change of their conductivity vs. temperature, suggesting that the distance between conductive grains in polypyrrole is less than in polyaniline. In the present work, we intent to investigate these different modes in non-aged (fresh) and thermally aged polypyrrole–polyaniline blends by measuring the a.c. conductivity at room temperature in the frequency range from 10⁻² to 10⁶ Hz.

Section snippets

Results and discussion

The d.c. and a.c. transport are both due to the same mechanism. A proper understanding of the a.c. conductivity is significant to have a complete picture of the d.c. transport [6]. The low frequency a.c. conductivity of conducting polymers consists of a frequency-independent behavior in the limit of low frequencies and a sublinear response at higher frequencies. The real part of the electrical conductivity σ′(ω) can be expressed as: $σ′(ω)=σ_{0} +Aω^{n}$ where σ₀ denotes the d.c. conductivity, A the

Conclusion

The room temperature a.c. conductivity of fresh and thermally aged polypyrrole–polyaniline blends of various compositions is determined by a d.c. plateau followed by a fractional dispersive region on increasing working frequency. The cross-over frequency of the aforementioned frequency regions is a function of the composition and is reduced by the thermal aging in polyaniline-rich blends. The reduction of the size of the conductive grains seems to interrelated with the reduction of the size of

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Low frequency a.c. conductivity of fresh and thermally aged polypyrrole–polyaniline conductive blends

Abstract

Introduction

Section snippets

Results and discussion

Conclusion

Synth. Met.

Synth. Met.

J. Phys. Chem. Solids

Synth. Met.

J. Mater. Sci.

J. Phys. D

J. Appl. Phys.