Preparation And Characterization Of Conductive Polymer Composites

Conductive polymers, also called as conductive macromolecules, are a type of materials possessing the properties both of macromolecules and conductors. Conductive polymers are lightweight, easy shaping, low cost, structure flexible, macromolecule designing and possess a wide range of controllable conductivities. Its special electrical, optical and magnetic properties give conductive polymers the wide applications in electrode materials, electromagnetic shielding materials, stealth materials, anti-corrosion materials, sensor materials, electrochromic materials and so on. In the family of conductive polymers, polyaniline(PANI) and polypyrrole(PPy) have attracted increasing attentions both in scientific researches and practical applications due to their good environmental stability, high doping conductivities, simple preparation and easy obtention of raw materials. The research of PANI and PPy has become as one of the hot spots in the research of materials. However, both of them possess rigid π-conjugated structures and therefore their solubility, fusibility, and processibility are bad. These defects seriously restrict the practical applications of PANI and PPy. To composite conductive polymers with other materials can not only significantly improves the solubility and processibility of conductive polymers, but also can endows conductive polymers with some special functions such as photocatalytic properties, wave absorbing properties and gas sensing properties. In this paper, to aim for the conductive polymer composites, we optimized the structure, recipes and experimental technology of conductive polymer composites and prepared polystyrene-poly(styrene-co-sodium4-styrenesulfonate)(PS-PSS)/PANI core-shell microparticles, SnO2/PANI nanocomposites, PPy/poly(methyl methacrylate)(PMMA) core-shell nanocomposites and SnO2/PPy nanocomposites. We analysed the influencing factors for the morphology, size, dispersity and conductivities of conductive polymer composites. The main contents could be summarized as follows:In the third chapter, nanostructured SnO2was prepared via a sol-gel process of SnCl4. SnO2/PANI nanocomposites were prepared by microemulsion polymerization in which aniline was polymerized on the surface of SnO2nanoparticles. In the reaction process, complex reaction was occurred between SnCl4and ethylene glycol. Sn atoms were linked with each other through the-OCH2CH2O-group after HCl and H2O was removed. The products were calcined and SnO2nanoparticles were obtained. In the microemulsion system, aniline salt was dissolved in micelles of SDS, and SnO2nanoparticles were enwrapped by SDS micelles. In the presence of oxidant APS, aniline monomer was polymerized on the surface of SnO2nanoparticles and SnO2/PANI nanocomposites were obtained. Comparing with the results prepared with different conditions, we found that the size of SnO2nanoparticles became big at high calcined temperature. However, when the calcined temperature was low, the SnO2nanoparticles showed a bad crystallinity. Similar results were found when we studied the influence of calcined time on the morphology and size of SnO2nanoparticles. Results showed that calcined at500℃for6h was the optimum condition to get the monodisperse nanoscale SnO2particles. The diameter of SnO2nanoparticles prepared on the above condition was around15nm. In the composites the SnO2nanoparticles with a diameter of ca.15nm were embedded well in the porous PANI. The SnO2particles and PANI were successfully composited with each other and there was an interaction between them. The crystal structure of SnO2was not modified by PANI. However, the crystallization of PANI was hampered by the SnO2nanoparticles. Conductivity analysis showed that the conductivity of SnO2/PANI nanocomposites was between the conductivity of PANI and SnO2particles. With the decrease of n (SnO2):n (aniline), the conductivity of the nanocomposites was increased. When the molar ratio of SnO2to aniline was kept at0.5:5, the conductivity of SnO2/PANI nanocomposites was1.75×10-1S/cm, which was very close to the conductivity of PANI.In the fourth chapter, the monodispersed PS microparticles were prepared by dispersion polymerization. Through the copolymerization of styrene and sodium4-styrenesulfonate (SSS) on the surface of PS, the PS particles was modified with negatively charged sulfonic groups(PSS). Then through the chemical oxidation method, aniline monomer was polymerized on the surface of PS-PSS particles and PS-PSS/PANI core-shell conductive composites with a diameter around0.9μm were obtained. Comparing with the results of composites prepared with different conditions, when SSS was5%of the amount of styrene, the PS-PSS particles were uniform and monodispersed. The growth process of PANI on the surface of PS-PSS particles was changing from protrusions, incomplete coating shell to complete coating shell. The shell of the composite particles was complete and continuous, when the ratio was [m(PS-PSS):m(aniline)=0.6:0.5]. The conductivity of the core-shell (PS-PSS)/PANI particles was2.11S/cm, which was very close to the conductivity value of pure PANI. The hollow PANI microspheres could be prepared by putting the composite particles into chloroform to extract the plastic core. When the ratio was [m(PS-PSS):m(aniline)=0.6:0.5], the hollow PANI microspheres possessed spherical shape with diameter around0.9μm and thickness around50nm. The conductivity of hollow PANI microspheres prepared in this paper was2.17S/cm.In the fifth chapter, PPy core particles with good dispersity were prepared in a four-component microemulsion system, which was formed with surfactant cetyltrimethyl ammonium bromide (CTAB), cosurfactant n-pentanol, water and pyrrole. On the basis of PPy nanoparticles, methyl methacrylate monomer (MMA) was dissolved in micelles and polymerized on the surface of PPy nanoparticles to form the PMMA shell. The PPy/PMMA nanocomposites showed obvious core-shell structure with good dispersity. Comparing with the results of composites prepared with different conditions, we found that the reaction conditions such as the concentration of surfactant, the droping rate of oxidant, and the reaction temperature can influence the dispersity and size of the composites. It was found that when the using amount of CTAB was1.7g and n-pentanol1.0g with low oxidant dropping rate at low reaction temperature, the size of PPy nanoparticles was around50nm. The thickness of PMMA shell could be controlled by changing the using amount of MMA monomer. As the thickness of the PMMA shell increased, the conductivity of the composite particles decreased. Iodine could greatly improve the conductivity of PPy nanoparticles, when it was used as a dopping agent in the polymerization of PPy. The conductivity of doping PPy nanoparticles could reach to10.425S/cm. The PPy/PMMA nanocomposites, which were composed of a doping PPy core and a thin PMMA shell, could gain a conductivity of7.856×10-1S/cm.In the sixth chapter, we combined the merits of reverse microemulsion and hydrothermal method and successfully synthesized SnO2nanoparticles. The typical quaternary microemulsion was formed with surfactant CTAB, cosurfactant n-pentanol, n-hexane, and water. SnCl4and urea was used as the starting material to synthesize SnO2nanoparticles. Then pyrrole monomer was polymerized in the microemulsion system to form SnO2/PPy nanocomposites. In the nanocomposites, SnO2nanoparticles were embedded well in the porous PPy. Results showed that the crystal structure of SnO2is not modified by PPy. However, the crystallization of PPy was hampered by the SnO2nanoparticles. The particle size of SnO2and SnO2/PPy was calculated by XRD as3.9and3.6nm, respectively. FT-IR and UV-vis spectra proved that SnO2was successfully enwrapped by PPy with an interaction between them.