Structure and Properties of Polyaniline Nanotubes

The magnetoresistance of single PANI-NT is found to be very small even at 2K (magnetoresistance 5% at lOT) compared with that of the pellets (40-100% at lOT), and no evident and stable negative magnetoresistance has been observed above 50 K, indicating that the magnetoresistance in bulk pellet samples made of PANI-NTs is dominated by a random network [440]. 

The susceptibility data cannot be simply described as Curie-like susceptibility at lower temperatures and temperature-independent Pauli-like susceptibility at higher temperatures [441]. Some unusual transitions were observed in the temperamre dependence of susceptibility, for example paramagnetic susceptibility decreased gradually with lowering temperature, which suggests the coexistence of polarons and spinless bipolarons and the possible formation of bipolarons with changing temperature or doping level. 

PANI-p-NSA nanotubes show unusually high crystallinity [93]. It has been revealed that PANI-NTs are composed of crystalline and amorphous regions [341]. The crystallinity fraction Dg obtained from the specific heat was about 15% for the measured PANI-NTs, which indicated that most of the PANI chains in the nanotubes were disordered. 

A comparison of PANI-NTs synthesized by electrochemical and chemical methods inside the nanopores of AAO membrane and PC track-etched membrane was made [48]. The morphologies of PANI-NTs synthesized electrochemically in AAO membrane were found to be better than those synthesized in PC track-etched membrane. EPR spectra revealed that the degree of delocalization of those nanotubes synthesized electrochemically in the AAO membranes was better. Nanotubes synthesized electrochemically inside the pores of AAO membranes showed an enhancement of the electronic conductivity compared to PANI bulk materials. PANI-NTs synthesized by an electrochemical method showed better properties (morphology, degree of delocalization and conductivity) than the tubes synthesized by a chemical method in the same templates. 

The thermal stability and structural variation of the PANI-NT films produced on Si windows during a treatment at 80 °C for three months were studied by FTIR and Raman spectroscopies [442]. The morphology of the films was preserved during the degradation, but the molecular structure had been changed. The results indicate that the spectral changes correspond to deprotonation, oxidation, and chemical cross-linking reactions. The films of 

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Polyaniline Nanostructures 63 2.3.2 Structure and Properties of Polyaniline Nanotubes... 

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