Orthophosphoric acid doped polyaniline carbon nanotube composites for anode layers of polymer LEDs

Abstract

Among the conducting polymers, polyaniline (PANI) gains prime importance due to its relatively easy and cheap synthesis route, high yield of polymerization and tunable electrical and optical properties. By making composites with other suitable materials, the DC electrical conductivity of polyaniline can be improved. Multiwalled Carbon Nano Tube (MWNT) is one such material used for making composites of PANI to enhance the conductivity. Mechanical strength and thermal stability of the samples are also enhanced by making PANI-MWNT composites. Polyaniline-Multiwalled Carbon Nano Tube composites have been widely pursued in recent times owing to their enhanced electrical and thermal properties. In the present work, we have carried out systematic investigations on the temperature variation of DC electrical conductivity in orthophosphoric acid (H3PO4) doped PANI and H3PO4 doped PANI-MWNT composite samples in the form of pressed pellets. PANI-MWNT composites with various feed ratios have been synthesized by chemical oxidative polymerization technique using orthophosphoric acid as dopant. We have attempted a comparative study of the DC electrical conductivities of H3PO4 doped PANI and H3PO4 doped PANI-MWNT composites in bulk forms. The conductivity of these composites increases with increase in MWNT feed ratio and saturates at higher feed ratios. The highlight of the present investigations is the observation of high DC electrical conductivity in these samples, which stays almost constant from room temperature to 373K. The conductivity of the composites drops marginally with temperature, only above 373K. The conductivity in the 3-dimensional PANI-MWNT networks have been enhanced as compared to pure PANI sample. The observed enhancement in the DC conductivity can be explained in terms of the ‘bridging effect’ and ‘barrier resistance’. X-Ray Diffraction (XRD) and Fourier Transform Infra-Red (FTIR) Spectroscopic techniques were used to study the morphology of the samples.