Charge transport properties of fully-sulfonated polyaniline

We present a charge transport study of a newly prepared fully sulfonated polyaniline (N-SPAN) with the sulfur-to-nitrogen (S/N) ratio ~ 1.0. The temperature dependent dc conductivity is fit by the quasi-1D variable range hopping model: σdc(T)σ0 exp [-(T0/T)γ]=, where γ ~ 0.5 with σRT ~ 0.02 S/cm and T0 = 1.5 × 104K. Thermoelectric power measurement shows a weak temperature dependence, which also is consistent with the quasi-1D variable range hopping model. The microwave conductivity follows a typical temperature dependence for materials in which the hopping conduction mechanism is dominant. The density of states at the Fermi level N(εF) is calculated as ~ 0.27 states/eV-2 rings for each sign of spin based on EPR measurements. The density of Curie spin is 0.0033 spins/2- rings. The origin of the lower room temperature conductivity, smaller density of states and fewer Curie spin than those of two previously reported SPANs with S/N ratio ~ 0.5 and 0.75 is suggested to be the larger twist of the phenyl rings relative to one another and increased interchain separation both due to the introduction of methoxy side groups and the higher density of SO3− groups. This morphology favors bipolaron formation.