Preparation, Characterization and Studies of Conducting Polymer Composites and Blends

Abstract

This work mainly concerns with the preparation, characterization and studies of some nanostructured composites and blends of Intrinsic Conducting Polymers (ICPs) with special reference to their charge transport mechanisms and device applications. These nanostructured composites consisted of two phases; a conducting phase and an insulating phase. Different series of nanocomposites with ICPs; Polypyrrole (PPy), Polyaniline (PANI) and Poly (p-phenylene vinylene) (PPV) as conducting phase and MMT clays and other lamellar structured materials such as CdPS 3 as an insulating phase were prepared and studied. A series of Polyaniline / Montmorillonite clay (PANI.MMT) composites was synthesized by in situ polymerization of aniline in the presence of varying amount of MMT clays in acidic medium. DC electrical conductivity was studied as a function of MMT loading and temperature to understand the charge transport mechanism in these composites. The conductivity followed quite well the temperature-dependence relationship σ(T) = σ 0. exp[-T o /T) 1/2 ], characteristic of one-dimensional variable-range hopping (1-D VRH). Frequency dependant AC conductivity followed the universal power law; this work is described in chapter 3. Another series of nanocomposites; PPy intercalated in the interlamellar region of Aluminum Pillared Montmorillonite (Al PMMT) clay with varying amounts of Al PMMT were prepared and studied. The Pyrrole was polymerized into the layers of Al PMMT replacing the Aluminum pillars and forming regular aligned chains of PPy, which not only enhanced AC and DC conductivities, but also affected the mechanism of conduction to switched from 3-D VRH in case of pristine PPy to 1-D VRH in all PPy Al PMMT nanocomposites. Maxwell Wagner effect was observed in dielectric spectroscopy. TGA curves of both the series of clay based ICP nonocomposites showed that the thermal stability is enhanced by insertion of ICPs in MMT clays. Blends of Polypyrrole and Polyaniline with poly (methyl methacrylate) (PMMA) in the presence of Hydroquinone were also prepared and studied. The percolation threshold in PANI.DBSA PMMA with 1% hydroquinone blends was observed as low as 3% which is very low as compared to that of theoretical value of 16%. iiThe percolation threshold in PPy.DBSA PMMA was recorded as 7% which shows that PPy.DBSA has less interaction with PMMA as compared to that of PANI.DBSA. These results were further confirmed by FT-IR, Raman spectroscopy and dielectric spectroscopy. Single crystal Cadmium hexathiohypodiphosphates Cd(PS 3 ) 2 generally written as CdPS 3 and Poly (p-phenylene vinylene) (PPV) were successfully synthesized. PPV was synthesized by chemical polymerization method. Intercalation of K + , Eu + and then PPV into the layers of CdPS 3 was confirmed by XRD. PPV intercalated in layers of CdPS 3 and heated at 120°C (CPPV120) show enhanced conductivity and luminescence properties. Electrical Properties of polypyrrole (PPy) doped with dodecylbenzene sulfonic acid (DBSA) were studied with and without a plasticizing agent hydroquinone. Hydroquinone was used as a compatibilizer to maximize solubility of PPy.DBSA in organic solvents which facilitated easy processing of flexible and mechanically strong PPy films for device applications. In order to assess the effect of hydroquinone on the electrical properties of PPy.DBSA /Aluminum (Al) Schottky junction, capacitance- voltage (C-V) and current density-voltage (J-V) characteristics were measured in Indium Tin Oxide (ITO)/PPy.DBSA /Al and ITO/PPy.DBSA .hydroquinone/Al structures. The observed J-V and C-V characteristics can be satisfactorily fitted to the modified Schottky equations. The junction parameters were found to be strongly influenced by hydroquinone. From C-V characteristics, the built-in voltage and charge concentration were also found to be influenced by the presence of hydroquinone. These results indicate that addition of hydroquinone to PPy.DBSA imparts better diode quality to the doped polymer/metal Schottky junction.