Polypyrrole/silicon carbide nanocomposites with tunable electrical conductivity

Conductive polypyrrole/SiC nanocomposites are fabricated via a facile oxidative polymerization approach using p-toluene sulfonic acid as a dopant and ammonium persulfate as an oxidant. The effects of the nanoparticle loading, ratio of oxidant to monomers, and nanoparticle morphology (spheres and rods) on the hysicochemical properties are investigated. Various characterization methods are carried out to determine the material properties. Thermal gravimetric analysis demonstrates an improved thermal stability of polypyrrole in the polymer nanocomposites (PNCs) with a higher decomposition temperature. The glass-transition temperature and melting temperature of the polymer and its nanocomposites are determined by differential scanning calorimetry with a decreased melting temperature of polypyrrole in the PNCs. The microstructures of pure polypyrrole and PNCs are observed by scanning electron microscopy. Powder X-ray diffraction analysis demonstrates the crytallinity of polypyrrole, and poor crystallinity is observed for the PNCs with higher nanoparticle loading. Fourier transform infrared spectrometry analysis shows a strong interaction between the SiC nanoparticles and the polypyrrole matrix with a shift of C=C stretching vibration of PPy to a lower band. The electron transport in PNCs follows a quasi 3-d variable range hopping conduction mechanism as evidenced by the temperature-dependent conductivity function. Experimental results demonstrate that PPy/SiC PNCs have higher conductivity than that of the pure PPy. The nanorods are also introduced into the polypyrrole matrix. Their effects on the physicochemical properties are investigated and compared. © 2010 American Chemical Society

Polypyrrole-titania nanocomposites derived from different oxidants

Polypyrrole(PPy)titania(TiO2) nanocomposites were prepared by an in situ oxidative polymerization method with two different oxidants, namely ammonium persulfate (APS) and ferric chloride. The effects of oxidant type and TiO2 particle loading level on the physiochemical properties of the PPyTiO2 nanocomposites were investigated in details. The intermolecular interactions within the polymer nanocomposites were explored by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). While scanning electron microscopy (SEM) was used to characterize surface morphology, transmission electron microscopy (TEM) revealed the well-dispersed TiO2 nanoparticles in the PPy matrix. The thermogravimetric analysis (TGA) revealed improved thermal stability of PPy with addition of the nanofillers. The nanocomposites prepared by APS oxidation exhibited lower electrical conductivity at room temperature than that of the PPy nanocomposites from FeCl3 oxidation polymerization. Both nanocomposites and pure PPy follow the three-dimensional variable range hopping (VRH) electron conduction mechanism. The frequency dependent dielectric constants of PPyTiO2 nanocomposites were measured in the range of 20 Hz-2 MHz. © 2011 The Electrochemical Society

Conductive Polypyrrole/Tungsten Oxide Metacomposites with Negative Permittivity

Polypyrrole (PPy) nanocomposites reinforced with tungsten oxide (WO 3) nanoparticles (NPs) and nanorods (NRs) are fabricated by a surface-initiated polymerization method. The electrical conductivity is observed to depend strongly on the particle loadings, molar ratio of oxidant to pyrrole monomer, and the filler morphology. The electron transportation in the nanocomposites follows a quasi-three-dimensional variable range hopping (VRH) conduction mechanism as evidenced by the temperature-dependent conductivity function. Unique negative permittivity is observed in both pure PPy and its nanocomposites, and the switching frequency (frequency where the real permittivity switches from negative to positive) can be tuned by changing the particle loading, ratio of oxidant to pyrrole monomer, and the filler morphology. The extent of charge carrier localization calculated from the VRH mechanism is well-correlated to the dielectric properties of the nanocomposites. WO3 NRs are observed to be more efficient in improving the electrical conductivity, dielectric permittivity, and thermal stability of the resulting nanocomposites as compared to those with WO3 NPs. The microstructures of pure PPy and its nanocomposites are observed by scanning electron microscopy and transmission electron microscopy. Powder X-ray diffraction analysis demonstrates the crystalline structure of WO3 nanostructures, as well as their corresponding nanocomposites. Thermogravimetric analysis reveals a significantly enhanced thermal stability with the addition of nanofillers. © 2010 American Chemical Society

Giant Magnetoresistive Phosphoric Acid Doped Polyaniline–Silica Nanocomposites

The phosphoric acid doped conductive polyaniline (PANI) polymer nanocomposites (PNCs) filled with silica nanoparticles (NPs) have been successfully synthesized using a facile surface initiated polymerization method. The chemical structures of the nanocomposites are characterized by Fourier transform infrared (FT-IR) spectroscopy. The enhanced thermal stability of the PNCs compared with that of pure PANI is observed by thermogravimetric analysis (TGA). The dielectric properties of these nanocomposites are strongly related to the silica nanoparticle loading levels. Temperature dependent resistivity analysis reveals a quasi 3-dimensional variable range hopping (VRH) electrical conduction mechanism for the synthesized nanocomposite samples. A positive giant magnetoresistance (GMR) is observed with a maximum value of 95.5% in the PNCs with a silica loading of 20.0 wt % and 65.6% for the pure PANI doped with phosphoric acid. The observed MR is well explained by wave function shrinkage model by calculating the changed localization length (ξ), density of states at the Fermi level (N(EF)), and reduced average hopping length (Rhop). The effects of particle size on the properties including thermal stability, dielectric properties, temperature dependent resistivity, electrical conduction mechanism, and GMR of the nanocomposites are also studied. © 2013 American Chemical Society