Transport properties of polyaniline-cellulose-acetate blends

Abstract

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---${p}_{c}\ensuremath{\simeq}0.1%$---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 ${\ensuremath{\sigma}}_{\mathrm{dc}}$ resembles that of published results on PANI/PMMA blends. The onset frequency ${\ensuremath{\omega}}_{\ensuremath{\xi}}$ of the dispersion in ${\ensuremath{\sigma}}_{\mathrm{ac}}$ appears to follow the scaling law: ${\ensuremath{\omega}}_{\ensuremath{\xi}}\ensuremath{\propto}{\ensuremath{\sigma}}_{\mathrm{dc}}^{z}$ with $z\ensuremath{\simeq}1.$ The temperature dependence is of the form of $\mathrm{ln}\ensuremath{\sigma}(T)\ensuremath{\propto}\ensuremath{-}{(T}_{0}{/T)}^{\ensuremath{\gamma}}$ the exponent decreasing from 0.75 to 0.5 with increasing $p.$ The microscopic metallic character of transport is found in ESR and microwave measurements. Spin-dependent conductivity is inferred from the ${(B/T)}^{2}$ 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.