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Mirko Bacani - University of Zagreb, Croatia

Electromagnetic properties of DBSA-doped polyaniline: from fundamentals towards application

We have carried out a comparative experimental study of the dc electrical conductivity - and
magnetic susceptibility - of own-made polyaniline (PANI) pellets doped with dodecybenzenesulfonic
acid (DBSA), a long molecule with surfactant properties. For all the samples, we find [1] that - at low
temperatures (T) is governed by the variable-range hopping (VRH) in a homogeneously disordered
three-dimensional (3D) system of coupled 1D chains. Depending on the doping and the corresponding
disorder level, the VRH exponents are either 1/2, 2/5 or 1/4. At higher T, in all the samples we find the
exponent 1 that signifies nearest-neighbour hopping. All these exponents are predicted in a model by
Fogler, Teber and Shklovskii [2] for the charge transport in quasi-1D Mott-Anderson insulators, and
conditions for their appearance depend on disorder and T. We identified the presence of a soft
Coulomb gap in our samples, which signifies a long-range Coulomb interaction.


Changes from one exponent into another in -(T) appear at crossover temperatures T*, where
there are also noticeable features in -(T). This coupling of charge and spin is discussed in the spirit of
kBT* being the thermal energy which causes an enhancement of the density of delocalised (Pauli)
spins at the expense of localised (Curie) spins as T rises above T*.


Utilising a property that both PANI-DBSA and multi-wall carbon nanotubes (CNT) are
soluble in chloroform, we have produced bulk blends of these two materials, the achieved mass
fraction of CNT being up to 40%. This is as remarkable as the accompanying effective loss of the
temperature dependence of -: it decreases by only 3 times from room temperature to 10 K, whereas
this decrease for pure PANI-DBSA is by a factor of 106. Thus, our blends simultaneously solve the
problem of application of CNT in bulk form, as well as that of poor conductivity of PANI-DBSA at
low T. It is also possible to make thin films of the blends on a commercial plastic substrate.


[1] M. Bacani, M. Novak, I. Kokanovic, D. Babic, Synth. Met. 172, 28 (2013)

[2] M. M. Fogler, S. Teber, B. I. Shklovskii, Phys. Rev. B 69, 035413 (2004)