Byung Cheol Sin

Synthesis of electrically conductive and superparamagnetic monodispersed iron oxide-conjugated polymer composite nanoparticles by in situ chemical oxidative polymerization

Core-shell nanocomposites composed of iron oxide (Fe3O4) nanoparticles and conjugated polymer, poly(3, 4-ethylenedioxythiophene) (PEDOT), were successfully synthesized from a simple and inexpensive in situ chemical oxidative polymerization of EDOT with Fe3O4 nanoparticles in the micellar solution of lignosulfonic acid (LSA) which serves as both a surfactant and a dopant. These nanocomposites (Fe3O4-PEDOT) were subsequently characterized for morphological, crystalline, structural, electrical and magnetic properties by high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), four-probe meter and superconductor quantum interference device (SQUID), respectively. Results show that the nanocomposites have a spherical core-shell shape, are approximately 10 nm in size and are superparamagnetic with good magnetic saturation and good electrical conductivities. Existence of Fe3O4 in the nanocomposites was confirmed by using Energy dispersive X-ray photoelectron spectroscopy (EDAX) and X-ray photoelectron microscopy (XPS). We also investigated a possible formation mechanism of the core-shell nanocomposites, and the effect of Fe3O4 nanoparticles on the electro-magnetic properties of the nanocomposites. Such novel conducting and superparamagnetic composite nanomaterials can be applied to sensors, magnetic data storage, electro-magnetic resonance wave absorption, etc.

Coating of multiwalled carbon nanotubes with polymer nanospheres through microemulsion polymerization

We report a simple and noncovalent method for coating multiwalled carbon nanotubes (MWCNTs) with polyaniline (PANI) nanospheres using a microemulsion polymerization method. In this method, aniline polymerization is performed with MWCNTs in the presence of sodium dodecyl sulfate (SDS), which serves as both a surfactant and a dopant. Morphological, structural, thermal, and electrical properties of MWCNT-PANI nanocomposites were analyzed. The TEM results of the nanocomposites prepared with surfactant reveal that 30-50-nm-diameter PANI nanospheres were coated on the surface of the MWCNTs. Composites prepared without surfactant were found to be in core-sheath-type cable structures. The conductivities of the nanocomposites synthesized through microemulsion polymerization were found to be one order of magnitude higher than both the conductivities of pure PANI and the composites prepared via in situ chemical polymerization without an assisting SDS surfactant. The mechanism for the formation of nanostructured composites is presented.

Dielectric studies of a nano-crystalline CaCu2.90Zn0.10Ti4O12 electro-ceramic by one pot glycine assisted synthesis from inexpensive TiO2 for energy storage capacitors

A facile way for the synthesis of nano-crystalline CaCu2.90Zn0.10Ti4O12 (CCZTO) using a solution combustion technique based on the glycine–nitrate process with inexpensive solid TiO2 powder as the raw material is introduced in this manuscript, for the first time. The precursor powder was calcined between 200 °C and 850 °C for 3 h in air. Phase formation, crystalline nature, morphology and chemical purity of the fabricated CCZTO were investigated with TG/DTA, FT-IR, FT-Raman, XRD, SAED patterns, SEM, TEM, EDX and XPS analyses, respectively. The XRD results indicated that all sintered samples had a major CaCu3Ti4O12 structure with some amount of CaTiO3 and CuO. The bright-field TEM micrographs revealed that the particle size was in the range of 15–50 nm, which was in good agreement with the average crystallite size obtained from XRD. SEM micrographs of the sintered CCZTO ceramics showed the average grain sizes were in the range of 800 nm–7 μm. EDX and XPS studies confirmed the stoichiometry and purity of the ceramics. The nature of the relaxation behavior of the ceramics was rationalized using impedance and modulus spectroscopy. The activation energies calculated from the grain-boundary relaxation time constant were found to be in the range of 0.79–0.52 eV, which confirmed the Maxwell–Wagner type of relaxation present in the ceramic. Our inexpensive novel solution chemistry based method for CCZTO_16h gives a high dielectric constant (799) and low dielectric loss (0.091) at 100 Hz at room temperature, which has potential significance for cost-effective technological applications in microelectronic devices.

Structural, impedance, and modulus spectroscopic studies on Y2/3Cu3Ti3.95In0.05O12 polycrystalline material prepared by flame synthesis method

ABSTRACT The polycrystalline material Y2/3Cu3Ti3.95In0.05O12 (YCTInO) having giant dielectric constant was prepared by the flame synthesis method using metal nitrate and solid TiO2 in ethylene glycol mono-methyl ether. X-ray powder diffraction (XRD) study on the material sintered at 1,050°C for 15 h reveals the single phase cubic perovskite structure. In Fourier transform infrared (FT-IR) spectroscopy, absorption bands were observed at 583 and 521 cm−1 corresponding to vibrations of Cu–O and 441 cm−1 of Ti–O–Ti, which are confirmed the single phase formation. X-ray photoelectron spectroscopy (XPS) data of YCTInO reveal the presence of Y 3d, Cu 2p, Ti 2p, In 3d, and O1s peaks of the elements, which justify the energy dispersive X-ray spectroscopy (EDX) results and compositional purity of the materials synthesized by the flame synthesis. The dielectric property of this material was studied in the frequency range of 0.01–100 kHz and the temperature range from 298 to 440 K. The electrical behavior of the ceramic studied by impedance and modulus spectroscopy reveal that the dielectric permittivity (ϵr) values of the YCTInO were dominantly affected by the electrical properties of grain-boundary.

Fabrication of composites of conjugated polymers with magnetic nanoparticles

Conjugated polymers such as polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT) were coated on Fe₃O₄ magnetic nanoparticles via two different methods. Core-shell Fe₃O₄-PANI nanocomposite was synthesized through graft polymerization, whereas Fe₃O₄-PEDOT nanocomposites were synthesized by <i>in</i> <i>situ</i> chemical oxidative polymerization. Resulted nanocomposites were characterized for structural, morphological, electrical and magnetic properties by TEM, XRD, FT-K four-probe and SQUID, respectively. Both composites showed high electrical conductivity and magnetic saturation than that of the pure polymers.