Please use this identifier to cite or link to this item: http://prr.hec.gov.pk/jspui/handle/123456789/11743
Title: Synthesis and Characterization of High Dielectric Constant Polymer Composites
Authors: Ahmed, Khalil
Keywords: Chemistry
Issue Date: 2012
Publisher: University of the Punjab , Lahore
Abstract: A number of series of two phase and three phase composites were synthesized and characterized, in order to induce high dielectric constant with low dielectric loss, using TiO2 and BaTiO3 as ceramic fillers and PVA as organic filler in low content (1 ̵ 5%) to avoid brittleness and film formation. The strategy of synthesis involved two steps, firstly the formation of suspensions of the fillers where TiO2 and BaTiO3 were prepared in acidic and aqueous medium at room temperature stirring magnetically overnight and PVA suspension was prepared at 60-70oC in water. Secondly in situ polymerization of pyrrole into polypyrrole in the suspension of filler through chemical oxidation method using FeCl3.6H2O as oxidant. Characterization techniques employed were FT-IR (in 400-4000 cm-1 range) and XRD (2θ= 5 to 85o) for structural analysis, TGA (25-600oC) for thermal stability behavior. The structural morphology was interpreted from the results of SEM images at different resolutions. Dielectric parameters were obtained using impedance analyzer which includes dielectric constant (ε՛), dissipation factor (tan δ), dielectric losses (εʺ) and the real and imaginary parts of the dielectric modulus (M՛ and Mʺ) The FTIR data confirmed the in situ formation of polypyrrole with all the characteristic peaks of the components of the formulations. XRD results revealed that both amorphous regions and crystallites of nano sized particles are present which enhanced the interfacial polarization being the major reason of high dielectric constant. TGA results confirmed the increase in thermal stability first due to introduction of TiO2 then PVA. The stability was greatly enhanced with the doping of BaTiO3 which was more than 2 times to that of caused by TiO2 and similarly another small increase due to PVA. The composite with 5% BaTiO3+ 5%PVA in polypyrrole was found the most thermally stable blend. The SEM results broadly classified the composites into two ii categories, the one containing TiO2 were found heterogeneous and the other containing BaTiO3 were visualized as much homogeneous. The data obtained from dielectric measurements and calculations revealed that the dielectric constant (ε՛) decreases exponentially with increase in frequency of the applied electric field but increases with increase in the filler content for all the composites and at 1 MHz (where the value of ε՛ is usually reported in the literature) its value was 284 with dissipation factor of 0.084 with PPy/ 5% TiO2 composition. The introduction of third phase also causes a further increase in the dielectric constant and the value reached 354 with (tanδ) at 0.0576. By changing the ceramic filler from TiO2 to BaTiO3 an increase in dielectric constant of about 2 times was observed and at 5% BaTiO3 in Ppy the ε՛ value was found 522 with little increase in dissipation factor to (tanδ) 1.01. The involvement of PVA affected both the parameters effectively and it increased the dielectric constant and decreased the (tanδ) to 595 and 0.21 respectively. Hence the desired dielectric parameters were achieved in the formulation with composition of 5% BaTiO3/ 5% PVA in PPy matrix. Finally the dielectric modulus data confirmed the low conductivity in almost all the composites with negligible exceptions. The trend in all these properties concerned to the results of dielectric behavior of the composites could be explained in terms of Maxwell-Wagnar and Sillars theory and the presence of unique interfaces developed.
Gov't Doc #: 19077
URI: http://prr.hec.gov.pk/jspui/handle/123456789/11743
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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