Complex conductance, σ * (f ) = σ (f ) + iσ"(f ), measurements of polyaniline/carnauba wax composites were carried out at room temperature in samples containing different amounts of PAni. While σ"(f ) ever grows as a function of the frequency f, σ (f ) was observed to vary as f n (n ≈ 1) in the high frequency domain, and to be frequency-independent for lower frequencies. This is the quasi-universal behavior characteristic of conduction in a disordered medium. Superposed on this, another signal was observed to occur, and the whole impedance response was then analysed in an Argand Diagram, disclosing an electrode process in series with the bulk one. An equivalent conductance expression was used to explain such electrical behavior, in which the bulk properties of the composite were represented through the Random Free Energy Barrier model, while the composite-electrode interface by a simple parallel combination of a capacitor and a resistor. From the theoretical fittings it was concluded that the increase of PAni concentration acts in the sense of increasing not only the sample conductance, but also the bulk capacitance. The separation of the bulk and the interface contributions was then achieved.
I IntroductionIn recent years, many authors have pointed out the possibility of producing organic composites that associate the low cost and the mechanical properties of natural materials, as rubber or waxes, with the electronic properties of conducting polymers [1,2]. Among such materials, carnauba wax (cw) and polyaniline (PAni) appears as potential candidates to be used in this class of composites. While PAni presents high electric conductivity when doped by acid solutions [3,4], cw -a natural product of the carnauba palm (Copernicia cerifera) [5,6] -is a dielectric material produced in abundance in northeast of Brazil. In this context, the preparation of materials based on the mixture of PAni and cw appears as an alternative to obtain organic composites with high electrical conductance at low cost.In this work we carried out a study of the electrical conductance of cw/PAni composites, at room temperature, prepared with different weights of PAni. It was observed that even small amounts of PAni cause a significant increase of the dc conductance. The present study is mainly concerned with this 'percolation' regime. The results show typical features of conduction in a disordered medium [7], usually displayed in a log-log plot of the complex conductivity as function of the frequency: for the real component, a plateau followed by an almost linear rise, while the imaginary component steadily rises from the lowest frequency on. Superposed on this process, another one at lower frequencies was detected and disclosed in an Argand Impedance diagram, as a series process with the bulk one. It is attributed to the metal/composite interface. The results were analyzed by an equivalent conductance expression, which represents the bulk properties of the composite by the Random Free Energy Barrier model (RFEB model) [7][8][9][10], and the...