Articles written in Bulletin of Materials Science
Volume 25 Issue 7 December 2002 pp 613-618 Polymers
Doped polyaniline materials with metal oxalate complexes of Cr, Fe, Mn, Co and Al were synthesized by in situ chemical oxidative polymerization of aniline using potassium perdisulphate as oxidant in aqueous sulphuric acid medium. These polymer materials were characterized by chemical analyses, spectral studies (UV-visible and IR), X-ray diffraction and thermal techniques and also by conductivity measurements by four-probe technique. The presence of complex anion in polyaniline material was confirmed by chemical and spectral analyses. The yield and conductivity of metal oxalate doped polyanilines were found to be high when compared to the simple sulphate ion doped polyaniline prepared under similar condition. UV-visible and IR spectral features not only confirmed the polyaniline doping by complex anions but also substantiated their facilitating effect on conductivity. The X-ray diffraction patterns indicated some crystalline nature in metal oxalate doped polyaniline and amorphous in polyaniline sulphate salt. The conductivity of the polymer samples strongly depended on the degree of crystallinity induced by complex counter anions as dopant. All the polymer materials, as evident from TGA curves, were observed to undergo three-step degradation of water loss, de-doping and decomposition of polymer. Further, the thermal stability of polyaniline was found to improve on doping with metal oxalate complex.
Volume 26 Issue 5 August 2003 pp 529-535 Polymers
Polyaniline (Pani) and its metal oxalate composites (∼ 10 wt.%) of trivalent metal ions of Cr, Fe, Mn, Co and Al were synthesized by chemical oxidative polymerization technique with potassium perdisulphate oxidant in aqueous sulphuric acid medium. These materials were characterized by UV–VIS and EPR spectral techniques. Their d.c. electrical conductivities at room temperature and also as a function of temperature (307–453 K) were measured by four-probe technique. Presence of radical cation/polaron transition was indicated by UV–VIS absorption peak and EPR signals. Further, a close correlation existed between the conductivities and EPR parameters such as line width and peak ratio, which demonstrated that both mobile and fixed spins are involved in these composites. The dependence of conductivity on temperature, when analysed graphically by VRH, GB and TC mechanisms, pointed out that VRH is the predominant charge transport mechanism in these materials.
Volume 28 Issue 1 February 2005 pp 55-61 Conducting Polymers
An investigation on the effect of 𝛽-cyclodextrin (CD) in both free and inclusion-complexed forms with a guest anionic metal complex, dioxalatodiaquochromate(III) (DDC), on the characteristics of conducting 2–polyaniline (PANI) is carried out. Four materials, PANI (i.e. PANI–SO4), PANI–DDC, PANI–CD and PANI–CD + DDC were prepared by in situ chemical oxidative polymerization in aqueous H2SO4 at pH 1 and subjected to electrical conductivity and spectral (IR and UV-vis) measurements. DDC and CD when separately incorporated, reduce the conductivity of PANI by about half whilst their inclusion complex CD + DDC enhances it. Spectral characterization reveals that DDC as a dopant and CD as an encapsule exhibit their effects through adverse interaction with imine–amine N centres and benzenoid moiety of PANI. The inclusion complex CD + DDC, on the contrary, functions as a dopant by lying in between the chains and seems to promote the extended conformation of PANI chain and hence the 𝜋-electron delocalization. Exposure of the material to methanol vapour causes a decrease in conductivity in PANI and PANI–CD while an increase in PANI–CD + DDC. This study makes explicit the distinct role of CD as an encapsule and CD + DDC inclusion complex as a dopant in altering the electrical property of PANI.
Volume 42 | Issue 1