Transport properties of polyaniline-cellulose-acetate blends

Transport properties of polyaniline (PANI)–cellulose acetate (CA) conducting blends have been investigated at various length scales and temperatures. We report on the results of dc and ac conductivity measurements, magnetoresistance and electron-spin resonance (ESR) performed on composite films with PANI weight fraction $p$ ranging from the percolation threshold—$p_c\simeq 0.1\%$—to a few percent. Three different PANI doping agents have been tested, namely, camphor sulfonic acid (CSA), di$(i$-octyl phosphate) (DiOP) and phenyl phosphonic acid (PPA). The percolative behavior of ${\sigma }_{\mathrm{dc}}$ resembles that of published results on PANI/PMMA blends. The onset frequency ${\omega }_{\xi }$ of the dispersion in ${\sigma }_{\mathrm{ac}}$ appears to follow the scaling law: ${\omega }_{\xi }\propto {\sigma }_{\mathrm{dc}}^z$ with $z\simeq 1.$ The temperature dependence is of the form of $\ln \sigma \mathrm{}\left(T\right)\mathrm{}\propto -{(T}_0{/T)}^{\gamma }$ the exponent decreasing from 0.75 to 0.5 with increasing $p.\mathrm{}$ The microscopic metallic character of transport is found in ESR and microwave measurements. Spin-dependent conductivity is inferred from the ${\mathrm{}(B/T)\mathrm{}}^2$ universal behavior of magnetoresistance. Those results are discussed in conjunction with the ongoing debate on the nature of disorder in conducting polymers—homogeneous versus heterogeneous.