Strain Sensing Characteristics of Rubbery Carbon Nanotube Composite for Flexible Sensors.

In this study, the piezoresistive properties of CNT (Carbon Nanotube)/EPDM composite are characterized for the applications of a flexible sensor. The CNT/EPDM composites were prepared by using a Brabender mixer with MWCNT (Multi-walled Carbon Nanotube) and organoclay. The static and quasi-dynamic voltage output responses of the composite sensor were also experimentally studied and were compared with those of a conventional foil strain gage. The voltage output by using a signal processing system was fairly stable and it shows somehow linear responses at both of loading and unloading cases with hysteresis. The voltage output was distorted under a quasi-dynamic test due to its unsymmetrical piezoresistive characteristics. The CNT/EPDM sensor showed quite tardy response to its settling time test under static deflections and that would be a hurdle for its real time applications. Furthermore, since the CNT/EPDM sensor does not have directional voltage output to tension and compression, it only could be utilized as a mono-directional force sensor such as a compressive touch sensor.

Freeze-drying-induced changes in the properties of graphene oxides.

We have characterized and evaluated changes in graphene oxide (GO) induced by means of freeze-drying. In order to evaluate these changes, we investigated the effects of freeze-drying and chemical reduction processes on the structure, morphology, chemical composition, and Raman properties of GO and reduced GO. The freeze-dried GO had a pore structure, maintaining a pored morphology even after thermal annealing. The freeze-dried samples were composed of a single folded nanosheet or a few nanosheets stacked and folded. The oxygen-containing functional groups were removed not only during the freeze-drying but also during the reduction processes, with an accompanying decrease in the average size of the sp(2) carbon domain (i.e. an increase in the ID/IG value).

Evidence of Ostwald ripening during evolution of micro-scale solid carbon spheres.

Ostwald ripening is an evolutionary mechanism that results in micro-scale carbon spheres from nano-scale spheres. Vapor-phase carbon elements from small carbon nanoparticles are transported to the surface of submicron-scale carbon spheres, eventually leading to their evolution to micro-scale spheres via well-known growth mechanisms, including the layer-by-layer, island, and mixed growth modes. The results obtained from this work will pave the way to the disclosure of the evolutionary mechanism of micro-scale carbon spheres and open a new avenue for practical applications.

Synthesis and characterization of single- and few-layer mica nanosheets by the microwave-assisted solvothermal approach.

We have successfully fabricated single- and few-layer mica nanosheets, by means of using a solvothermal method in conjunction with a microwave irradiated expansion process. In the solvothermal process, dissolved potassium ions were intercalated onto the interlayer space of the mica. Following this, microwave irradiation facilitates the exfoliation of individual nanosheets. The synthesized products were characterized by field emission scanning electron microscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray diffraction, x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy measurements. AFM and TEM studies claimed the existence of single-layer mica. High-resolution TEM (HR-TEM) investigations revealed that the exfoliated product corresponded to a crystalline mica structure, being comprised of Si, Al, O, and K elements. XPS spectra exhibited the major constituent peaks, including O 1s, Si 2p, Al 2p, and K 2p. In addition, C atomic concentration has been slightly increased by the contamination during exfoliation, presumably due to the increase of the exposed mica surface. The C 1s XPS spectra revealed that the C-C bonding in organic surface contaminants was broken, whereas the Si-C bonding was enhanced, by the exfoliation process. The O 1s XPS spectra revealed that the Si-O bonding in mica was broken, generating the O-Si-C bonding. This study paves the way towards the fabrication of single- or few-layer inorganic nanosheets of desired materials, via a convenient and efficient route.

Catalyst-free fabrication of graphene nanosheets without substrates using multiwalled carbon nanotubes and a spark plasma sintering process.

Catalyst-free graphene nanosheets without substrates were synthesized using pure solid carbon sources of multiwalled carbon nanotubes (MWCNTs) and a spark plasma sintering (SPS) process. Single and few-hundred-nanometer graphene nanosheets were formed from gas-phase carbon atoms which were directly evaporated from MWCNTs at a local high temperature.

Fabrication of single-phase titanium carbide layers from MWCNTs using high DC pulse.

Single-phase layered titanium carbide (TiC) was successfully synthesized by reacting carbon nanotubes (CNTs) and titanium dioxide (TiO2) under a high direct current (DC) pulse. Single-phase TiC layer fabrication is confirmed as the transformation of multi-layered graphene from MWCNTs. Therefore its thickness and width is almost identical to those of transformed graphene layers. This is the first report on the formation of single-phase layered nano-TiC. Scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HR-TEM) were used for the characteristic analysis of single-phase layered TiC structures.