Byungwoo Kim

Characteristics and field emission of conducting poly (3,4-ethylenedioxythiophene) nanowires

Conducting poly (3,4-ethylenedioxythiophene) nanowires were synthesized by using an electrochemical polymerization method with a nanoporous template. Scanning and transmission electron microscopy confirmed the formation of conducting polymer nanowires (CPNWs) with an open end. The formation and the electrical properties of the CPNWs formed were dependent on synthetic conditions, such as the doping level, the polymerization time, and the applied current. The measured electrical conductivity of a single strand of CPNW was ∼3.4×10−3 S/cm at room temperature. From the ultraviolet and visible absorbance spectra, we observed a π–π* transition at ∼2.1 eV for the de-doped systems. A field emission cell of CPNW nanotips was fabricated. The turn-on field of the CPNWs was 3.5∼4 V/μm at 10 μA/cm2, and the current density increased up to 100 μA/cm2 at ∼4.5 V/μm. The field enhancement factor of CPNW nanotips was ∼1200, which is comparable to those of carbon nanotubes.

High-performance supercapacitors based on vertically aligned carbon nanotubes and nonaqueous electrolytes

We demonstrate the high performance of supercapacitors fabricated with vertically aligned carbon nanotubes and nonaqueous electrolytes such as ionic liquids and conventional organic electrolytes. Specific capacitance, maximum power and energy density of the supercapacitor measured in ionic liquid were ~75 F g(-1), ~987 kW kg(-1) and ~27 W h kg(-1), respectively. The high power performance was consistently indicated by a fast relaxation time constant of 0.2 s. In addition, electrochemical oxidation of the carbon nanotubes improved the specific capacitance (~158 F g(-1)) and energy density (~53 W h kg(-1)). Both high power and energy density could be attributed to the fast ion transport realized by the alignment of carbon nanotubes and the wide operational voltage defined by the ionic liquid. The demonstrated carbon-nanotube- and nonaqueous-electrolyte-based supercapacitors show great potential for the development of high-performance energy storage devices.

Physical characterization of emulsion intercalated polyaniline-clay nanocomposite

Using emulsion polymerization method, polyaniline (PAN)‐Na a ‐montmorillonite (MMT) clay nanocomposites were synthesized. Dodecylbenzenesulfonic acid (DBSA) was used as an emulsifier and dopant during emulsion polymerization. The X-ray diAraction patterns showed that PAN‐DBSA was intercalated between clay layers in the order of nanoscale. The room temperature (RT) dc conductivities of nanocomposites were 1‐10 ˇ3 S=cm depending on the molar ratio of dopants used. Temperature dependence of dc conductivity for the nanocomposites followed a quasi-one-dimensional (1D) variable range hopping (VRH) model. From temperature dependence of electron paramagnetic resonance experiments, magnetic properties and the density of states of the systems were obtained. The doping level of the nanocomposites was deduced from the results of X-ray photoelectron spectroscopy experiments. From the comparison of physical properties between PAN with clay and PAN without clay, the eAects of dopant and the layer of clay on charge transport and structure are discussed. ” 2001 Elsevier Science B.V. All rights reserved.

Conducting Polymer Nanotube and Nanowire Synthesized by Using Nanoporous Template: Synthesis, Characteristics, and Applications

We synthesized nanotubes and nanowires of conducting polypyrrole, poly(3,4-ethylenedioxythiophene), and polyaniline by using nanoporous template through electrochemical polymerization method. The DBSA, CSA, TBAPF 6 , or HClO 4 was used for dopant, and distilled water, acetonotrile, or NMP was used for solvent. From the SEM and TEM pictures, the formation of conducting polymer nanotube (CPNT) and nanowire (CPNW) was confirmed. The diameter and length of CPNT and CPNW were 200 nm and 10 40 μm. The length, nanotube, nanowire, and thickness of wall were determined from synthetic conditions such as polymerization time, current, and dopant. For structure, we investigated UV/Vis absorbance spectra and X-ray diffraction patterns. DC conductivity and I-V characteristic curve were measured for the systems prepared with various conditions of synthesis. For applications for CPNT and CPNW, we measured field emission characteristic curve for FED and capacitance.

Effect of dopant and clay on nanocomposites of polyaniline (PAN) intercalated into Na+-montmorillonite (Na+-MMT)

The nanocomposites of polyaniline (PAN) and Na + -montmorillonite (Na + - MMT) were synthesized by emulsion polymerization using dodecylbenzenesulfonic acid (DBSA) or camphorsulfonic acid (CSA) as dopant and emulsifier. In the X-ray diffraction patterns of the systems, we observed that the layer of conducting PAN-DBSA or PAN-CSA between the clay layers was in nanoscale layers (< 10 A). The temperature dependence of dc conductivity [σ dc (T)] for the nanocomposites followed a quasi-one dimensional (ID) variable range hopping (VRH) model. The σ dc (T) varied with the dopant used and the molar ratio. From temperature dependent EPR experiments, we obtained the magnetic susceptibility and the line width of the system. The Na + -MMT clay layer plays important role for interchain interaction of the system. The effects of dopant and the layer of Na + -MMT on charge transport and structure are discussed.

Polypyrrole-montmorillonite nanocomposites synthesized by emulsion polymerization

The structural, electrical, magnetic, and thermal properties were investigated for the nanocomposites of polypyrrole (PPy) and inorganic clay (Na+-montmorillonite) prepared by emulsion polymerization. Dodecylbenzenesulfonic acid (DBSA) was used as emulsifier (surfactant) and dopant. The X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images showed that the conducting PPy was intercalated into the clay layers in nanoscale (<10 A). The dc conductivity (σdc) of PPy–DBSA with clay was ∼6 S/cm, while that of PPy–DBSA without clay was ∼20 S/cm at room temperature (RT). Temperature dependence of σdc of both samples followed the three dimensional variable range hopping (VRH) model. From the g-value and the temperature dependence of EPR linewidth, paramagnetic signals were strongly affected by the partially negatively charged clay layers. The thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC) showed that the clay induced the thermal stability of the systems.

Characteristics and photoluminescence of nanotubes and nanowires of poly (3-methylthiophene)

We synthesized nanotubes and nanowires of π-conjugated poly (3-methylthiophene) (P3MT) by using nanoporous anodic aluminum oxide (Al2O3) template through electrochemical polymerization method. From scanning electron microscope and transmission electron microscope photographs, we observed the formation of nanotubes with diameters of 100–200 nm and wall thicknesses of 5–10 nm. Relatively long nanotubes and nanowires of P3MT (about 40μm in length) were obtained. To discern the structural and optical properties of the systems, we measured ultraviolet and visible absorbance and Fourier transform-infrared spectroscopy. We observed that the doping level, the π‐π* transition peak, and bipolaron peaks in P3MT nanotubes varied with synthetic temperature. The photoluminescence (PL) spectra of the P3MT nanotubes solution were observed at ∼490nm. For the P3MT nanotubes synthesized at lower temperatures, the PL peaks became sharper and the resistance decreased.

2.5 V compact supercapacitors based on ultrathin carbon nanotube films for AC line filtering

A high volumetric energy density, and hence compactness, is an essential property for the supercapacitors needed to replace the bulky aluminum electrolytic capacitors currently used for alternating current (AC) line filtering. In this paper, we demonstrate the fabrication of AC-line-filtering supercapacitors with unprecedentedly high volumetric energy densities (Evol ≈ 4.1 mW h cc−1 at 120 Hz). This high density is achieved by using ultrathin and dense carbon nanotube (CNT) films as electrodes (t ≈ 300 nm, d ≈ 1.1 g cc−1). Importantly, the mesopores and short pore length of the ultrathin films enable sufficiently fast electrolyte ion movement, even with organic electrolytes, for AC line filtering (impedance phase angle, ϕ ≈ −82.2° at 120 Hz). The use of organic electrolytes extends the operating voltage window (V = 2.5 V), and therefore significantly increases the energy density (Evol ∝ V2). Moreover, we show that a gold insertion layer provides the excellent interfacial qualities between the CNTs and aluminum current collector that are required for fast-response applications. Our findings may greatly advance supercapacitor research and technology for emerging high-frequency applications.

Fabrication and magnetic characteristics of hybrid double walled nanotube of ferromagnetic nickel encapsulated conducting polypyrrole

This letter is a report on hybrid double walled nanotubes (HDWNTs) of crystalline ferromagnetic nickel (Ni) nanotubes encapsulated conducting polypyrrole (PPy) nanotubes through a sequentially electrochemical synthetic method. Ferromagnetic Ni nanotubes were fabricated by an electrochemical deposition method outside the wall of the conducting PPy nanotubes. The formation and structure of HDWNTs of conducting PPy nanotubes and ferromagnetic Ni nanotubes were confirmed by transmission electron microscopy, high-resolution transmission electron microscopy, and elementary analysis. From the angular dependences of the magnetic hysteresis curves of the HDWNTs, the authors observed that the Ni nanotubes of the HDWNT systems had an anisotropic ferromagnetic nature with the maximum of coercivity and remanent-saturation magnetization when applying a magnetic field along the parallel direction of the tubes.

Electrical, magnetic, and structural properties of lithium salt doped polyaniline

Abstract We report the results of temperature dependence of dc conductivity σ dc ( T ), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) experiments for the polyaniline (PAN) doped with various lithium (Li) salts such as LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , and LiCF 3 SO 3 . A quasi one-dimensional (1D) variable range hopping (VRH) model provide the best fitting for σ dc ( T ) the Li salt doped PAN samples, which is similar to that of protonic acid (HCl) doped polyaniline samples. The σ dc and its temperature dependence vary with the kind of Li salts used. Temperature dependence of thermoelectric power of PAN doped with LiPF 6 shows the metallic behavior. From EPR experiments, we obtain that χ P depends on the kind of Li salts. The results of XPS experiments are discussed to account for the doping procedure with Li salts. Temperature dependence of EPR linewidths and X-ray diffraction patterns are compared for the various Li salt doped PAN samples. The insulator–metal transition of PAN-LiPF 6 samples is also discussed.