Dispersion of Metal Oxide Nanoparticles in Conjugated Polymers: Investigation of the Tio 2 /PPV Nanocomposite
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*LMCTS, Faculty of Sciences, 123 Av. A. Thomas, F-87060 Limoges (France), [email protected] **CEKAMEC R&D, 64 avenue de la Liberation, F-87000, Limoges, (France) + Polymer Program at the Institute of Materials Science & IDepartment of Chemistry, University of Connecticut, Storrs, CT 06269
ABSTRACT It is well established that the dispersion of nanosized metal particles in a polymer matrix can induce non linear optical properties, yet very little is known about the effect of semiconducting transition metal oxide nanoparticles on both electrical and luminescence properties of conjugated polymers. In this paper, we report the synthesis of a nanostructured TiO 2/poly(pphenylenevinylene) system and show by diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) that a stable conjugated nanocomposite is obtained. Investigation of the photoluminescence (PL) properties reveals both a broadening and a blue shift of the emission spectra. Adsorption of oxygen is found to be stronger on the nanocomposite than on PPV and to reversibly quench the PL emission, thus suggesting enhanced gas sensing properties. A tentative mechanism explaining the role of n-TiO 2 is briefly discussed. INTRODUCTION Among the nt-conjugated polymers which are the most suitable for industrial applications [1], poly(p-phenylenevinylene) (PPV) has proved its usefulness in the fabrication of bright light emitting diodes (LED) [2] leading now to marketable information displays. Nevertheless, current
issues such as long-term photostability, nature of photoexcitation, effect of molecular oxygen in conjugated polymers and increase of the quantum efficiency for luminescence remain key research activities. Recently, both the anomalous current-voltage characteristics and the light emission variations of PPV-LEDs, when subjected to different gases, have been reported [3]. This suggests that gas sensing properties are worth a more detailed investigation. The standard approach to PPV-LED optimization is the systematic modification of the side groups of the PPV units through complex synthesis methods involving various precursors. In this paper, we propose an alternative approach based on the synthesis of a nanocomposite through the dispersion of a nanosized transition metal oxide in the PPV precursor. Nanosized particles exhibit a very high surface to bulk ratio making them extremely reactive and show unusual optical, electronic, magnetic, catalytic and mechanical properties compared to their micron size counterpart [4]. The fact that titania is one of the most studied transition metal oxides for various applications ranging from catalysis to gas sensing [5], motivated its choice as a constituent of the nanocomposite. Moreover, compared to its coarse grain counterpart, n-TiO 2 (anatase phase) shows quite a different photoluminescence spectrum at room temperature with a strong band at 3.1 eV [6]. This may be taken advantage of in the TiO 2/PPV nanocomposite. For the first time to our knowledge, we report preliminary results on the TiO 2IPPV nanocomposite
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