Seunghyun Baik

Highly conductive, printable and stretchable composite films of carbon nanotubes and silver

Conductive films that are both stretchable and flexible could have applications in electronic devices, sensors, actuators and speakers. A substantial amount of research has been carried out on conductive polymer composites, metal electrode-integrated rubber substrates and materials based on carbon nanotubes and graphene. Here we present highly conductive, printable and stretchable hybrid composites composed of micrometre-sized silver flakes and multiwalled carbon nanotubes decorated with self-assembled silver nanoparticles. The nanotubes were used as one-dimensional, flexible and conductive scaffolds to construct effective electrical networks among the silver flakes. The nanocomposites, which included polyvinylidenefluoride copolymer, were created with a hot-rolling technique, and the maximum conductivities of the hybrid silver-nanotube composites were 5,710 S cm⁻¹ at 0% strain and 20 S cm⁻¹ at 140% strain, at which point the film ruptured. Three-dimensional percolation theory reveals that Poissons ratio for the composite is a key parameter in determining how the conductivity changes upon stretching.

Chemically driven carbon-nanotube-guided thermopower waves

Theoretical calculations predict that by coupling an exothermic chemical reaction with a nanotube or nanowire possessing a high axial thermal conductivity, a self-propagating reactive wave can be driven along its length. Herein, such waves are realized using a 7-nm cyclotrimethylene trinitramine annular shell around a multiwalled carbon nanotube and are amplified by more than 10(4) times the bulk value, propagating faster than 2 m s(-1), with an effective thermal conductivity of 1.28+/-0.2 kW m(-1) K(-1) at 2,860 K. This wave produces a concomitant electrical pulse of disproportionately high specific power, as large as 7 kW kg(-1), which we identify as a thermopower wave. Thermally excited carriers flow in the direction of the propagating reaction with a specific power that scales inversely with system size. The reaction also evolves an anisotropic pressure wave of high total impulse per mass (300 N s kg(-1)). Such waves of high power density may find uses as unique energy sources.

Hierarchical construction of self-standing anodized titania nanotube arrays and nanoparticles for efficient and cost-effective front-illuminated dye-sensitized solar cells.

We report on the influence of hierarchical structures, constructed via layer-by-layer assembly of self-standing titania nanotube arrays and nanoparticles, upon charge recombination and photoelectric performance of front-illuminated dye-sensitized solar cells. Both nanotubes and nanoparticles were produced by anodization rather than additionally employing other methods, providing low cost and great simplicity. Electrochemical impedance spectroscopy under AM 1.5 illumination indicates the construction of hybrid morphology has superior recombination characteristics and a longer electron lifetime than nanoparticulate systems. This enhancement with the incorporation of anodized titania nanoparticles with 1D architectures is unprecedented for solar cells. Owing to the better light harvesting efficiency, extended electron lifetime and desirable electron extraction, the short-circuit photocurrent density of solar cell is 18.89 mA cm(-2) with an overall power conversion efficiency of 8.80% and an incident photon-to-current conversion efficiency of 84.6% providing a very promising candidate for sustainable energy production with a high performance/cost ratio.

Carbon‐Nanotube/Silver Networks in Nitrile Butadiene Rubber for Highly Conductive Flexible Adhesives

An adhesive with high conductivity, flexibility, cyclability, oxidation resistance, and good adhesion is developed using microscale silver flakes, multiwalled carbon nanotubes decorated with nanoscale silver particles, and nitrile butadiene rubber. Light-emitting-diode chips are attached to the conductive, flexible adhesive pattern on a poly(ethylene terephthalate) substrate as a visual demonstration. The brightness is invariant during bending tests.

Flexible, transparent single-walled carbon nanotube transistors with graphene electrodes.

This paper reports a mechanically flexible, transparent thin film transistor that uses graphene as a conducting electrode and single-walled carbon nanotubes (SWNTs) as a semiconducting channel. These SWNTs and graphene films were printed on flexible plastic substrates using a printing method. The resulting devices exhibited a mobility of ∼ 2 cm(2) V(-1) s -1), On/Off ratio of ∼ 10(2), transmittance of ∼ 81% and excellent mechanical bendability.

Knitted Fabrics Made from Highly Conductive Stretchable Fibers

We report knitted fabrics made from highly conductive stretchable fibers. The maximum initial conductivity of fibers synthesized by wet spinning was 17460 S cm(-1) with a rupture tensile strain of 50%. The maximum strain could be increased to 490% by decreasing the conductivity to 236 S cm(-1). The knitted fabric was mechanically and electrically reversible up to 100% tensile strain when coated by poly(dimethylsiloxane). The normalized resistance of the poly(dimethylsiloxane)-coated fabric decreased to 0.65 at 100% strain.

Continuous extraction of highly pure metallic single-walled carbon nanotubes in a microfluidic channel

Highly pure metallic single-walled carbon nanotubes were continuously extracted from a mixture of semiconducting and metallic species using a nondestructive, scalable method. Two laminar streams were generated in an H-shaped microfluidic channel with two inlets and two outlets. The flow conditions were carefully controlled to minimize diffusive and convective transport across the boundary between the two flows. Dielectrophoretic force from the embedded electrode at the junction extracted metallic nanotubes from a stream of nanotube suspension toward the other stream of buffer solution without nanotubes. The highly pure metallic and enriched semiconducting nanotubes were obtained simultaneously at each outlet using this novel approach. Excellent selectivity was verified by electrical transport measurement, absorption, and Raman spectroscopic analysis.

The effects of interfacial bonding on mechanical properties of single-walled carbon nanotube reinforced copper matrix nanocomposites

The effects of interfacial bonding on mechanical properties of single-walled carbon nanotube reinforced copper matrix nanocomposites were investigated. The nanocomposites were fabricated by means of a powder metallurgy process, which consists of mixing carbon nanotubes with matrix powder followed by hot-pressing. The mixing process was carried out by ultrasonicating the nanotubes and copper powder in ethanol. The interfacial strength between the nanotubes and the copper matrix was improved by coating the nanotubes with nickel. The displacement rate of the nanotube reinforced nanocomposites was found to increase at 200 °C, whereas that of the nickel-coated nanotube reinforced nanocomposites significantly decreased. The incorporation of carbon nanotubes and nickel-coated carbon nanotubes in the copper matrix composites improved tribological properties compared with those of pure copper specimens.

In-pipe inspection robot system with active steering mechanism

We present a robot system for in-pipe inspection of underground urban gas pipelines. The robot is configured as an articulated structure like a snake with a tether cable. Two active driving vehicles are located in front and rear of the system, and passive modules such as a control module are chained between the active vehicles. The proposed robot has outstanding mobility offered by a new steering mechanism, called double active universal joint, which makes it possible to cope with complicated configurations of underground pipelines. Characteristic features of the system are described and the construction of the system is briefly outlined.

Silver-plated carbon nanotubes for silver/conducting polymer composites

Carbon nanotubes (CNTs) have advantages as conductive fillers due to their large aspect ratio and excellent conductivity. In this study, a novel silver/conducting polymer composite was developed by the incorporation of silver-plated CNTs. It is important to achieve a homogeneous dispersion of nanotubes and to improve the interfacial bonding to utilize the excellent properties of reinforcements in the matrix material. The homogeneous dispersion of nanotubes was achieved by an acid treatment process, and the interfacial contact was improved by electroless silver plating around nanotubes. The resistivity of the silver/conducting polymer composite was decreased by 83% by the addition of silver-plated single-walled carbon nanotubes. Conductive bumps were also screen-printed to demonstrate the capability of the composite as electrical interconnects for multi-layer printed circuit boards.