Enhanced luminescence observed in polyaniline–polymethylmethacrylate composites

Polyaniline (PANI) is one of the highly pursued conducting polymers owing to its high electrical conductivity, interesting optical properties and excellent environmental stability. Recently, it is also being used extensively as hole-injecting electrodes in polymer LEDs. Inspite of its excellent electrical properties, the mechanical strength and processibility are not very attractive. It is reported that making composites of PANI with conventional polymers such as polymethylmethacrylate (PMMA), significantly improves the mechanical strength and processibility. Recently, we have observed that the DC electrical conductivity of HCl doped PANI can be further enhanced by making composites with PMMA. PMMA has been reported to have excellent optical properties such as very good transparency in the visible region and fairly good photoluminescence emission. This prompted us to carry out investigations on the optical properties of this composite, especially the photoluminescence characteristics. In the present work, we have synthesized PANI–PMMA composites using bulk polymerized PMMA. The FTIR spectrum reveals that PANI has been dispersed as an interpenetrating network in the PMMA matrix. The change in the photoluminescence (PL) behaviour of PANI–PMMA composites with different aniline to PMMA feed ratios has been investigated. It is observed that the photoluminescence intensity increases with increase in the PMMA content in the composite, possibly due to greater chances of exciton formation and subsequent radiative decay to the ground state. The PL spectrum of PMMA is also taken for comparison. The enhancement in the PL intensity of the composites with increase in the aniline to PMMA feed ratio is quite comparable with the enhancement in the DC electrical conductivity of these composites.