Alternating current ͑ac͒ and direct current ͑dc͒ conductivities have been measured in polymer-nanotube composite thin films. This was carried out for a range of concentrations of multiwall nanotubes in two polymer hosts, poly͑m-phenylenevinylene-co-2,5-dioctyloxyp-phenylenevinylene͒ ͑PmPV͒ and polyvinylalcohol ͑PVA͒. In all cases the dc conductivity DC was ohmic in the voltage range studied. In general the ac conductivity displayed two distinct regions, a frequency independent region of magnitude 0 at low frequency and a frequency dependent region at higher frequency. Both DC and 0 followed a percolation scaling law of the form ϰ(pϪp c ) t with p c ϭ0.055% by mass and tϭ1.36. This extrapolates to a conductivity of 1ϫ10 Ϫ3 S/m for 100% nanotube content. Such a low value reflects the presence of a thick polymer coating, resulting in poor electrical connection between tubes. This leads to the suggestion that charge transport is controlled by fluctuation induced tunneling. In the high frequency regime the conductivity increases with frequency according to an approximate power law with exponent sϷ0.92, indicative of hopping transport. The onset of this frequency independent conductivity scales with mass fraction for the PmPV composite due to the variation of correlation length with nanotube content. This behavior is discussed in terms of a biased random walk in three dimensions. In addition ac universality is demonstrated by the construction of a mastercurve.

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Production of stable polymer-nanotube composites depends on good wetting interaction between polymer and nanotube, which is polymer specific, and depends in particular on chain conformation. In this paper, we examine this interaction for a conjugated, semiconducting polymer by a range of microscopic and spectroscopic techniques, to gain a greater understanding of the binding. Several interesting effects are observed, including an order to the interaction between the polymer and nanotube, the tendency of defects in the nanotube structure to nucleate crystal growth, and substantial changes in the spectroscopic behavior of the polymer due to the effect of the nanotubes on polymer conformation. This is substantiated by computational modeling, which demonstrates that these conformational modifications are due to the interaction with the nanotubes.