[Show abstract][Hide abstract] ABSTRACT: We have experimentally and theoretically clarified the effect of oxygen functional groups on capacitive performance of the photochemically treated activated carbon electrode. A high density of C=O group at the mouth of the micropores, where the chemically active edge sites are predominantly available, increase the energy barrier for ions to enter the pores, thereby resulting in a large decrease in the specific capacitance.
[Show abstract][Hide abstract] ABSTRACT: The industrial scale application of graphene and other functional materials in the field of electronics has been limited by inherent defects, and the lack of simple deposition methods. A simple spray deposition method is developed that uses a supersonic air jet for a commercially available reduced graphene oxide (r-GO) suspension. The r-GO flakes are used as received, which are pre-annealed and pre-hydrazine-treated, and do not undergo any post-treatment. A part of the considerable kinetic energy of the r-GO flakes entrained by the supersonic jet is used in stretching the flakes upon impact with the substrate. The resulting “frozen elastic strains” heal the defects (topological defects, namely Stone-Wales defect and C2 vacancies) in the r-GO flakes, which is reflected in the reduced ratio of the intensities of the D and G bands in the deposited film. The defects can also be regenerated by annealing.
[Show abstract][Hide abstract] ABSTRACT: Nanoscale defects in the outer tube to preserve the electrical and optical features of the inner tube can be engineered to exploit the intrinsic properties of double walled carbon nanotubes (DWCNTs) for various promising applications. We demonstrated a selective way to make defects in the outer tube by the fluorination of DWCNTs followed by the thermal detachment of the F atoms at 1000 degrees C in argon. Fluorinated DWCNTs with different amounts of F atoms were prepared by reacting with fluorine gas at 25, 200, and 400 degrees C that gave the stoichiometry of CF0.20. CF0.30, and CF0 43, respectively. At the three different temperatures used, we observed preservation of the coaxial morphology in the fluorinated DWCNTs. For the DWCNTs fluorinated at 25 and 200 degrees C, the strong radial breathing modes (ABMs) of the inner tube and weakened RBMs of the outer tube indicated selective fluorine attachment onto the outer tube. However, the disappearance of the RBMs in the Raman spectrum of the DWCNTs fluorinated at 400 C showed the introduction of F atoms onto both inner and outer tubes. There was no significant change in the morphology and optical properties when the DWCNTs fluorinated at 25 and 200 degrees C were thermally treated at 1000 degrees C in argon. However, in the case of the DWCNTs fluorinated at 400 degrees C, the recovery of strong RBMs from the inner tube and weakened RBMs from the outer tube indicated the selective introduction of substantial defects on the outer tube while preserving the original tubular shape. The thermal detachment of F atoms from fluorinated DWCNTs is an efficient way to make highly defective outer tubes for preserving the electrical conduction and optical activity of the inner tubes.
Chinese Journal of Catalysis 06/2014; 35(6):864–868. DOI:10.1016/S1872-2067(14)60107-8 · 1.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Carbon nanotubes have shown great potential as conductive fillers in various composites, macro-assembled fibers, and transparent conductive films due to their superior electrical conductivity. Here, we present an effective defect engineering strategy for improving the intrinsic electrical conductivity of nanotube assemblies by thermally incorporating a large number of boron atoms into substitutional positions within the hexagonal framework of the tubes. It was confirmed that the defects introduced after vacuum ultraviolet and nitrogen plasma treatments facilitate the incorporation of a large number of boron atoms (ca. 0.496 atomic %) occupying the trigonal sites on the tube sidewalls during the boron doping process, thus eventually increasing the electrical conductivity of the carbon nanotube film. Our approach provides a potential solution for the industrial use of macro-structured nanotube assemblies, where properties, such as high electrical conductance, high transparency, and lightweight, are extremely important.
The Journal of Physical Chemistry C 02/2014; 118(8):4454–4459. DOI:10.1021/jp410732r · 4.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Water-soluble, highly functionalized multiwalled carbon nanotubes (MWNTs) were prepared via a facile, environmentally benign method. The effectiveness of the highly functionalized MWNTs as a reinforcing filler in a water-soluble mechanically weak chitosan biopolymer was evaluated. We observed a substantial improvement in the mechanical properties of the film; the stretchability of the film was maintained when 5 wt% MWNTs was added. In addition, the biocomposite film exhibited long-term antibacterial activity. The reinforcing effect can be explained by the homogeneous dispersion of the nanotubes in the polymer matrix through the strong hydrogen bonding between the sulfonic acid groups (-SO3H) on the sidewalls of the MWNTs and the amine (-NH2) and hydroxyl (-OH) groups on the chitosan backbone. The improvement in the mechanical properties of the MWNT-chitosan biocomposite may make it suitable for many environmental and clinical applications.
[Show abstract][Hide abstract] ABSTRACT: Functionally graded materials graded continuously and discretely, and are modeled using modified Mori- Tanaka and self-consistent methods. The proposed micromechanics model accounts for multi-phase heterogeneity and arbitrary number of layers. The influence of geometries and distinct elastic material properties of each constituent and voids on the effective elastic properties of FGM is investigated. Numerical examples of different functionally graded materials are presented. The predicted elastic properties obtained from the current model agree well with experimental results from the literature.
[Show abstract][Hide abstract] ABSTRACT: We have demonstrated an effective way of covalently functionalizing graphene with a chitosan polymer via nitrene chemistry. The biofunctionalized graphene was prepared by the chemical reduction of graphene oxide using a nitrene chemistry, and then covalently grafting chitosan to the graphene surface. The effectiveness of the biofunctionalized graphene as a reinforcing filler (4 wt %) in a chitosan polymer matrix was verified by the dramatic enhancement of the mechanical properties (breaking stress = 330%, Young’s modulus = 243%) and the electrical conductivity (0.3 S/m) without much loss in the elongation-at-break. The reinforcing effect can be explained by both the homogeneous dispersion of graphene within the matrix and the strong bond arising from the intrinsically intimate contact between the graphene and the matrix. The high antimicrobial activity of the biofunctionalized graphene compared with graphene oxide and chemically reduced graphene may be because of the presence of chitosan polymer on the edges of the graphene. Our strong, antimicrobial graphene-filled composite film can be used for food packaging and for coating various biomedical devices, where bacterial surface colonization is undesirable.
Particle and Particle Systems Characterization 08/2013; 30(8). DOI:10.1002/ppsc.201300044 · 3.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Electrospun biopolymer-derived nanofiber webs are promising scaffolds for growing tissue and cells. However, the webs are mechanically weak and electrically insulating. We have synthesized a polyethylene oxide (PEO) nanofiber web that is pliable, tough and electrically conductive, by incorporating optically active, DNA-wrapped, double-walled carbon nanotubes. The nanotubes were individually trapped along the length of the PEO nanofiber and acted as mechanically reinforcing filler and an electrical conductor.
[Show abstract][Hide abstract] ABSTRACT: We report a mechanically strong, electrically and thermally conductive, and optically transparent shape-memory polyurethane composite which was fabricated by introducing a small amount (0.1 wt%) of high-quality graphene as a filler. Geometrically large (≈4.6 μm(2)), but highly crystallized few-layer graphenes, verified by Raman spectroscopy and transmission electron microscopy, were prepared by the sonication of expandable graphite in an organic solvent. Oxygen- containing functional groups at the edge plane of graphene were crucial for an effective stress transfer from the graphene to polyurethane. Homogeneously dispersed few-layered graphene enabled polyurethane to have a high shape recovery force of 1.8 MPa cm(-3). Graphene, which is intrinsically stretchable up to 10%, will enable high-performance composites to be fabricated at relatively low cost and we thus envisage that such composites may replace carbon nanotubes for various applications in the near future.
[Show abstract][Hide abstract] ABSTRACT: A method of dispersing strongly bundled double-walled carbon nanotubes (DWNTs) via a homogeneous coating of mussel protein in an aqueous solution is presented. Optical activity, mechanical strength, as well as electrical conductivity coming from the nanotubes and the versatile biological activity from the mussel protein make mussel-coated DWNTs promising as a multifunctional scaffold and for anti-fouling materials.
Small 12/2011; 7(23):3292-7. DOI:10.1002/smll.201100668 · 8.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Superhydrophobic surfaces have considerable technological potential for various applications due to their extreme water-repellent properties. When two hydrophilic bodies are brought in contact, any liquid present at the interface forms menisci, which increases adhesion/friction and the magnitude is dependent upon the contact angle. The superhydrophobic surfaces may be generated by the use of hydrophobic coating, roughness and air pockets between solid and liquid. The geometric effects and dynamic effects, such as surface waves, can destroy the composite solid-air-liquid interface. Studies on silicon surfaces patterned with pillars of varying diameter, height and pitch values and deposited with a hydrophobic coating were performed to demonstrate how the contact angles vary with the pitch. A criterion was developed to predict the transition from Cassie and Baxter regime to Wenzel regime, considering water droplet size as a parameter on the patterned surfaces with various distributions of geometrical parameters. The trends are explained based on the experimental data and the proposed transition criterion.
[Show abstract][Hide abstract] ABSTRACT: Nature has developed materials, objects, and processes that function from the macroscale to the nanoscale. The emerging field of biomimetics allows one to mimic biology or nature to develop nanomaterials, nanodevices, and processes which provide desirable properties. Hierarchical structures with dimensions of features ranging from the macroscale to the nanoscale are extremely common in nature to provide properties of interest. There are a large number of objects including bacteria, plants, land and aquatic animals, and seashells with properties of commercial interest. Certain plant leaves, such as Lotus leaves, are known to be superhydrophobic and self-cleaning due to the hierarchical roughness of their leaf surfaces. The self-cleaning phenomenon is widely known as the “Lotus effect.” These surfaces with high contact angle and low contact angle hysteresis with a self-cleaning effect also exhibit low adhesion and drag reduction for fluid flow. In this article, the theoretical mechanisms of the wetting of rough surfaces are presented followed by the characterization of natural leaf surfaces. The next logical step is to realize superhydrophobic surfaces based on understanding of the leaves. Next, a comprehensive review is presented on artificial superhydrophobic surfaces fabricated using various fabrication techniques and the influence of micro-, nano- and hierarchical structures on superhydrophobicity, self-cleaning, low adhesion, and drag reduction.
[Show abstract][Hide abstract] ABSTRACT: Nature has developed materials, objects, and processes that function from the macroscale to the nanoscale. The emerging field
of biomimetics allows one to mimic biology or nature to develop nanomaterials, nanodevices, and processes which provide desirable
properties. Hierarchical structures with dimensions of features ranging from the macroscale to the nanoscale are extremely
common in nature to provide properties of interest. There are a large number of objects including bacteria, plants, land and
aquatic animals, and seashells with properties of commercial interest. Certain plant leaves, such as Lotus leaves, are known
to be superhydrophobic and self-cleaning due to the hierarchical roughness of their leaf surfaces. The self-cleaning phenomenon
is widely known as the “Lotus effect”. These surfaces with high contact angle and low contact angle hysteresis with a self-cleaning
effect also exhibit low adhesion and drag reduction for fluid flow. In this article, the theoretical mechanisms of the wetting
of rough surfaces are presented followed by the characterization of natural leaf surfaces. The next logical step is to realize
superhydrophobic surfaces based on understanding of the leaves. Next, a comprehensive review is presented on artificial superhydrophobic
surfaces fabricated using various fabrication techniques and the influence of micro-, nano- and hierarchical structures on
superhydrophobicity, self-cleaning, low adhesion, and drag reduction. An aquatic animal, such as a shark, is another model
from nature for the reduction of drag in fluid flow. The artificial surfaces from the shark skin have been created, and the
influence of structure on drag reduction efficiency is discussed. Furthermore, oleophobic surfaces can be used as a biomimetic
coating that prevents contamination of the underwater parts of ships by biological and organic contaminants, including oil.
The article discusses the wetting behavior of oil droplets on various superoleophobic surfaces.
[Show abstract][Hide abstract] ABSTRACT: Commercially mass-produced multi-walled carbon nanotubes, i.e., VGNF (Showa Denko Co.), were applied to support materials for platinum-ruthenium (PtRu) nanoparticles as anode catalysts for direct methanol fuel cells. The original VGNFs are composed of high-crystalline graphitic shells, which hinder the favorable surface deposition of the PtRu nanoparticles that are formed via borohydride reduction. The chemical treatment of VGNFs with potassium hydroxide (KOH), however, enables highly dispersed and dense deposition of PtRu nanoparticles on the VGNF surface. This capability becomes more remarkable depending on the KOH amount. The electrochemical evaluation of the PtRu-deposited VGNF catalysts showed enhanced active surface areas and methanol oxidation, due to the high dispersion and dense deposition of the PtRu nanoparticles. The improvement of the surface deposition states of the PtRu nanoparticles was significantly due to the high surface area and mesorporous surface structure of the KOH-activated VGNFs.
Journal of Nanoscience and Nanotechnology 01/2011; 11(1):675-80. DOI:10.1166/jnn.2011.3229 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A shape memory polymer wire for orthodontic application was prepared by melt-spinning of polyurethane block copolymer (PU) which was synthesized in a two-step process from a reaction of 4,4'-methylene bis(phenylisocyanate), poly(ε-caprolactone)diol (PCL), and 1,4-butanediol. An orthodontic test using the PU wire was carried out in an orthodontic model with a metal bracket. High shape recovery force of 70 gf for PU wire at 40 wt% hard segment content could be preserved for even 1 month after a shape recovery force test at a constant temperature of 50°C. The shape recovery force decreased exponentially during the initial 2 h, but reached an equilibrium shape recovery force of 50 gf after about 20 days. It was found that this shape recovery force was sufficient to correct misaligned teeth in the orthodontic test. The shape memory PU wire possesses strong potential as a novel orthodontic appliance with esthetically appealing appearance.
Journal of Materials Science Materials in Medicine 10/2010; 21(10):2881-6. DOI:10.1007/s10856-008-3538-7 · 2.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We carried out covalent functionalization of single- and double-walled carbon nanotubes (SWNTs and DWNTs) comparatively by using isocyanate chemistry. The introduction of aromatic diisocyanate on the sidewalls of the tubes was verified by the strong IR peak around 2272 cm–1 arising from the NCO asymmetric stretching mode, by the intensified sp3 peak at 285.2 eV in the C1s photoemission spectra, and by a typical TEM image of the amorphous-like coating. The suppression of the optical properties in a covalently isocyanate-functionalized SWNT is due to a breakdown of the van Hove singularities, whereas the strong optical activity in a covalently isocyanate-functionalized DWNT originates from the geometrically shielded inner tubes. The chemically active isocyanate groups at the end of the phenyl diisocyanate that are covalently attached to the sidewalls of the DWNTs will allow us to utilize isocyanate chemistry in synthesizing functional organic–inorganic hybrid materials as well as high-performance polymer composites.
Berichte der deutschen chemischen Gesellschaft 09/2010; 2010(27):4305 - 4308. DOI:10.1002/ejic.201000507 · 2.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We fabricated nitrogen-decorated porous carbon exhibiting high capacitance per unit volume and unit weight via chemical activation of novolac resin containing peptide linkage. The porosity and the amount of nitrogen atoms were controlled by changing the molecular weight of novolac resin, the added amount of potassium hydroxide, or both. After chemical activation, positively charged nitrogen atoms (i.e., pyridine/pyrrole) at 400.3eV in photoemission spectra contributed to both a shift in the point of zero charge toward negative potential and the generation of pseudocapacitance. Suitably developed pores and the positively charged nitrogen atoms make nitrogen-decorated novolac resin-derived porous carbon a promising material for electrodes in high-performance supercapacitors.
[Show abstract][Hide abstract] ABSTRACT: We have fabricated electrically conductive, optically transparent, and mechanically strong shape-memory polyurethane film by incorporating photochemically surface-modified multiwalled carbon nanotubes (MWNTs). The oxygen functional groups on the sidewall of the MWNTs, created by vacuum ultraviolet light, provide reactive sites to bind strongly with polyurethane. The homogeneous dispersion of MWNTs is confirmed by the optical signals coming from the innermost tube (ca. 0.9 nm) of the MWNTs, not from isolated single walled carbon nanotubes. The optimally introduced functional groups as well as the judicious selection of organic solvent, both for dispersing MWNTs homogeneously and dissolving the polymer completely, are critical to fabricate high functional polyurethane film.