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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. [ABSTRACT FROM AUTHOR]

Numerous light emitting polymers and copolymers with excellent luminescence characteristics and thermal stability are being synthesized and extensively investigated for applications as emissive layers in polymer light emitting diodes. In the present study, three novel, thermally stable, segmented block copolymers (SBC) and two hybrid polymers with excellent photoluminescence (PL) and electroluminescence emission (EL) characteristics were subjected to spectroscopic investigations to explore the effect of various aromatic and non-aromatic solvents on the photoluminescence emission characteristics. Dilute solutions of the SBCs and the hybrid polymers were made from various solvents like dichloromethane, chlorobenzene, tetrahydrofuran, xylene, chloroform, etc. UV-Vis absorption and PL emission spectra of these polymer solutions were recorded simultaneously. No significant changes in the PL emission peaks were observed, depending on the nature of solvents. The effect of solvents in terms of aggregation effects in these polymers was studied. The low aggregation effects and solvent independent nature of the polymers offer very high prospects in various optoelectronic device applications. The present study can be of great use in designing efficient polymer LEDs based on these SBCs and hybrid polymers as emissive layers. The efficiency and stability of the polymer LEDs can be considerably improved by suitably choosing the solvent for the emissive polymers. [ABSTRACT FROM AUTHOR]

From its very inception and development, degradation of Organic Light Emitting Diodes has been a problem before researchers. How the degradation affects the output current in small molecule based Organic Light Emitting Diodes and Polymer light Emitting Diodes is discussed. Non emissive dark spot leads to degradation was the initial understanding with respect to this phenomenon and later perimeter leakage current also assumed to contribute to this. Here the observations in the variations in leakage current and bulk resistance against operational hours are presented. [ABSTRACT FROM AUTHOR]