Jong Hun Han

Transparent organic p-dopant in carbon nanotubes: bis(trifluoromethanesulfonyl)imide.

We propose bis(trifluoromethanesulfonyl)imide [(CF(3)SO(2))(2)N](-) (TFSI) as a transparent strong electron-withdrawing p-type dopant in carbon nanotubes (CNTs). The conventional p-dopant, AuCl(3), has several drawbacks, such as hygroscopic effect, formation of Au clusters, decrease in transmittance, and high cost in spite of the significant increase in conductivity. TFSI is converted from bis(trifluoromethanesulfonyl)amine (TFSA) by accepting electrons from CNTs, subsequently losing a proton as a characteristic of a Brønsted acid, and has an inductive effect from atoms with high electronegativity, such as halogen, oxygen, and nitrogen. TFSI produced a similar improvement in conductivity to AuCl(3), while maintaining high thermal stability, and no appreciable change in transmittance with no cluster formation. The effectiveness of TFSI was compared with that of other derivatives.

PURITY MEASUREMENT OF SINGLE-WALLED CARBON NANOTUBES BY UV-VIS-NIR ABSORPTION SPECTROSCOPY AND THERMOGRAVIMETRIC ANALYSIS

We measured the content of single-walled carbon nanotubes (SWCNTs) in SWCNT soot within 3.7% error using UV-VIS-NIR absorption spectroscopy. We also propose a better overall evaluation method by combining thermogravimetic analysis with UV-VIS-NIR absorption spectroscopy to analyze the purity of SWCNT providing the accurate assessment of the amounts of noncarbonaceous impurity, carbonaceous impurity, and SWCNT each with respect to a highly purified reference.

Enhanced Thermal Conductivity of Epoxy/Three-Dimensional Carbon Hybrid Filler Composites for Effective Heat Dissipation

Graphitic carbon nanomaterials (CNMs) are recognized as next-generation heat dissipating materials (HDMs) for efficient thermal conduction within a polymer composite. Commercially used carbon-based HDMs, including carbon blacks, carbon nanotubes (CNTs), and graphites, are limited by low thermal conductivity under 50% filler content. Two-dimensional graphenes show high thermal conductivity in their major (xy) planes; however, they still exhibit low thermal conductivity in the z direction, i.e., perpendicular to the major plane, because of the difficulty in obtaining a proper vertical alignment. Here, we introduce a straightforward strategy to improve the thermal conductivity of graphene-based HDMs in both the xy- and z-directions and report the results of our investigation of the thermal conductivity behavior of the epoxy composites. Our newly designed graphene-based HDMs were observed to adopt directly anchored and ohmic-contact morphologies between graphene nanoplatelets (GNP) and CNTs via bimetallic nanoparticle decoration on the GNP surface and subsequent carbon vapor deposition (CVD), and their epoxy composites showed an approximately two-fold enhancement of both in- and through-plane thermal conductivities compared to those of bare GNPs.

Liquid-phase exfoliation of expanded graphites into graphene nanoplatelets using amphiphilic organic molecules

Graphenes with a two-dimensional lattice of carbons have been widely employed in diverse applications owing to their excellent electrical, thermal, mechanical, and gas-barrier properties. However, the frequently-used reduced graphene oxide (rGO), which is synthesized from natural graphites by strong oxidation and subsequent reduction via highly toxic components, exhibits imperfect characteristics because of remaining defect sites on its basal planes. Therefore, in this work, we present a convenient way to prepare graphene nanoplatelets (GNPs) with minimized defect sites on their basal planes employing liquid-phase exfoliation of edge-functionalized expanded graphites (EGs) with amphiphilic organic molecules. Exfoliated GNPs revealed approximately sub-7-nm-thickness and showed stable dispersibility in an organic media during 9 months. Furthermore, spray-coated GNP films presented homogeneously stacked morphologies without noticeable agglomerations.

Patterned transparent electrode with a continuous distribution of silver nanowires produced by an etching-free patterning method

The outstanding electrical, optical, and mechanical properties of silver nanowire transparent electrodes are attractive for use in many optoelectronic devices, and the recent developments related to these electrodes have led to their commercialization. To more fully utilize the advantages of this technology, developing new process technologies in addition to performance improvements is important. In this report, we propose a novel ultra-simple patterning technology to generate a silver nanowire transparent layer and a unique patterned structure with continuously distributed silver nanowires without any etched areas. The patterning is conducted by exposure to ultraviolet light and rinsing. The exposed and unexposed regions of the resulting layer have dramatically different electrical conductivities, which produces an electrical pathway without using any etching or lift-off processes. The unique patterned structure produced by this etching-free method creates hardly any optical difference between the two regions and results in excellent visibility of the patterned transparent electrode layer.

Fabrication of durable and flexible single-walled carbon nanotube transparent conductive films

In the present work, flexible, durable, transparent, conductive films (TCFs) were fabricated with the use of aqueous dispersed single-walled carbon nanotubes (SWCNTs). A small amount of the synthesized sulfonated poly(ether sulfone) (SPES) was used to effectively disperse SWCNTs with high aspect ratios. The lengths and heights of the dispersed SWCNTs were 2.5 ± 1.0 μm and 2 ± 1 nm, as determined by TEM and AFM, respectively. TCFs were fabricated using spray coating on a PET substrate; the best performance among the TCFs was achieved with a sheet resistance (Rs) of 125 Ω sq−1 and optical transmittance of 87.1%. Moreover, no appreciable change in the Rs was observed after repeated bending cycles and adhesive peel-off tests, which indicate that SPES acts as a good dispersant and effective binder for the improvement in durability and adhesion behavior of the resulting TCFs in the absence of additional binders. Therefore, this material holds great potential for scalable and facile production of flexible SWCNT-TCFs for various electronic applications.

Mechanical interfacial adhesion of carbon fibers-reinforced polarized-polypropylene matrix composites: effects of silane coupling agents

Thermoplastic composites are used in a variety of applications such as mass transit, auto-motive parts, and military structures [1-6]. Their appeal compared to conventional materials such as aluminum, steel, and thermoset composites for these applications lies in their high specific strength, corrosion resistance, superior impact resistance, high toughness, and ease of recycling [1-7].In recent years, carbon fibers (CF) have been widely used as reinforcing materials in high performance composites. CF present several advantages, including high modulus and strength, good stiffness, and creep resistance [8-10]. Despite these advantages, the CF/ther-moplastic composites have unsatisfactory mechanical properties because CF have poor in-terfacial adhesion with most thermoplastic polymers due to their non-polar surface.The interfacial adhesion between reinforcing fibers and polymer matrices in composites is the controlling factor in obtaining optimum mechanical properties of composites [11-13]. To achieve good interfacial adhesion between CF and thermoplastic matrices, it is necessary to increase the surface polarity. In this light, increasing the surface polarity for van der Waals forces and hydrogen bonding can improve the interfacial adhesion. In efforts to increase the surface polarity of CF, various surface treatment techniques have been applied, including plasma treatment, anodic oxidation, metal plating, and cou-pling treatment [14,15]. Among the various treatments, coupling treatment is known to be a very effective method for improving the interfacial adhesion between the fibers and the thermoplastic matrices [16].The role of coupling agents in improving the interfacial adhesion between polymers and inorganic surfaces has been widely documented [17,18]. However, the effects of different coupling agents on interfacial adhesion between CF and polar-modified thermoplastic matri-ces have yet to be explicitly identified. Therefore, the first objective of this study is to evaluate the influence of sizing treatments by silane-based coupling agents on the interfacial adhesion properties between the fibers and the thermoplastic matrix. Another objective is to investigate the effects of the presence of surface functional groups containing silane-oxygen groups on the mechanical properties of carbon fiber-reinforced maleic anhydride-grafted polypropylene.The CF used in this work were polyacrylonitrile based high strength fibers, T-700SC-13000 (12K unidirectional fabric; Toray, Tokyo, Japan). The average diameter of these CF was around 7 μm. A highly polarized polypropylene sheet prepared by maleic anhydride grafting (Homan Petrochemical Co, Seoul, Korea) was used as a matrix. The reagents used for the coupling treatments were vinyltriethoxy silane (VTES), 3-ami-no propyl triethoxy silane (APS), and 3-methacryloxy propyl trimethoxy silane (MPTS; Aldrich, St. Louis, MO, USA), denoted as VTES, APS, and MPTS, respectively. The acid and silane treatments of the CF were carried out by the following procedure. For the acid

Facile tuning of a polymeric dispersant for single-walled carbon nanotube dispersion

We designed and synthesized a polymeric dispersant for use with single-walled carbon nanotubes (SWCNTs). Poly((furfuryl methacrylate)-co-(2-(dimethylamino)ethyl methacrylate)) (p(FMA-co-DMAEMA)) was synthesized, and its solubility was tuned by the quaternization of a tertiary amine. Quaternized p(FMA-co-DMAEMA) (p(FMA-co-QDMAEMA)) changed the dispersibility of SWCNTs in various polar solvents, such as ethylene glycol (EG), methanol (MeOH), water and dimethylformamide (DMF). The chemical structures of the synthesized and modified polymeric dispersants were confirmed using 1H NMR. The dispersion quality of SWCNTs by p(FMA-co-QDMAEMA) was estimated using a particle stability analyzer, zeta-potential, UV-vis-NIR spectroscopy, transmission electron microscopy, and atomic force microscopy. The diameters and degree of defects of the dispersed SWCNTs were estimated using Raman spectroscopy. The dispersed SWCNTs in EG and MeOH display heights between 1.45 and 1.78 nm and a diameter of 1.17 nm, which corresponds to 1 or 2 bundled SWCNTs.

Increased environmental stability of a tungsten bronze NIR-absorbing window

We developed a facile method for increasing the environmental stability of a tungsten bronze near-infrared (NIR)-absorbing window using tetraethyl orthosilicate (TEOS) and 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (FDS). The environmental stability of the tungsten bronze NIR-absorbing window could be enhanced by applying a variety of protective layers (i.e., TEOS, fluoropolymer (CYTOP), FDS). The protective characteristics of each layer type are discussed. The protection of tungsten bronze surfaces by TEOS and FDS layers enormously enhanced the environmental stability of the NIR absorbing window, whereas an untreated tungsten bronze film rapidly lost its NIR absorption properties. The protection efficiency followed the order: TEOS/FDS>FDS>TEOS>CYTOP. The improved environmental stability arose from the closely packed structure of FDS, which can self-assemble on an oxide surface, such as the tungsten oxide or silicon oxide surfaces. The method developed here provides a simple, robust, and versatile way to improve the environmental stability of a NIR-absorbing window.

Quantitative Evaluation of Non-Carbon Content in the Single Wall Carbon Nanotube Soot using Thermogravimetric Analysis

We measured the non-carbon content of single-walled carbon nanotubes (SWCNTs) in SWCNT soot using thermogravimetric analysis. The weight increased percentage by the oxidation of metal in the raw soot is well obtained by TGA graph which was confirmed with ICP-AES, XRD, and XPS. This work will be very useful for the purity precise evaluation of SWCNT with UN-vis-NIR spectroscopy. Keywords : Single wall carbon nanotubes, Non-carbon contents, TGA