Pisith Singjai

Stretchable and flexible high-strain sensors made using carbon nanotubes and graphite films on natural rubber.

Conventional metallic strain sensors are flexible, but they can sustain maximum strains of only ∼5%, so there is a need for sensors that can bear high strains for multifunctional applications. In this study, we report stretchable and flexible high-strain sensors that consist of entangled and randomly distributed multiwall carbon nanotubes or graphite flakes on a natural rubber substrate. Carbon nanotubes/graphite flakes were sandwiched in natural rubber to produce these high-strain sensors. Using field emission scanning electron microscopy, the morphology of the films for both the carbon nanotube and graphite sensors were assessed under different strain conditions (0% and 400% strain). As the strain was increased, the films fractured, resulting in an increase in the electrical resistance of the sensor; this change was reversible. Strains of up to 246% (graphite sensor) and 620% (carbon nanotube sensor) were measured; these values are respectively ∼50 and ∼120 times greater than those of conventional metallic strain sensors.

Gel-carbon nanotube materials: the relationship between nanotube network connectivity and conductivity

The electrical resistance of carbon nanotube networks (NNs) prepared from combinations of gellan gum, xanthan gum, Triton X-100, SWNT and MWNT is reported. It is demonstrated that the NN conductivity can be obtained by analysing the resistance of two overlapping NN as a function of their overlap distance. Unexpectedly, the connectivity between two overlapping NN was found to scale with the electrical conductivity over 4 orders of magnitude. Insights into the dependence of inter-NN contact on applied pressure were obtained.

Joining carbon nanotubes

To fully exploit the exceptional electronic and mechanical properties of carbon nanotubes in real-world applications, it is desirable to create carbon nanotube networks in which separate, multiple nanotubes are joined so that as many as possible of the properties of single nanotubes are conserved. In this review we summarize the progress made towards this goal, covering techniques including electron and ion beam irradiation, Joule heating and spark plasma sintering.

Microstructure and Characterizations of Portland-Carbon Nanotubes Pastes

This research studied microstructure and characterizations of Portland cement with carbon nanotubes (CNTs) which were used as an additive material at 0 %, 0.5 % and 1 % by weight of cement. The compressive and flexural strength tests of mixes were conducted using water/cement ratios (w/c) of 0.5. Samples of mixes were selected for SEM analysis and then ground for TGA analysis. The results show that the compressive strength and flexural strength at all aging time of Portland-CNTs cement composites was higher than that of control mix. Microstructure results show that CNTs was filled in pores between matrix phases to show denser phase and TGA graphs show similar phases to PC mix.

Electrochemical energy-storage performances of nickel oxide films prepared by a sparking method

In this work, nickel oxide (NiO) films have been prepared by a sparking method on flexible chromium/gold coated polyethylene terephthalate substrates and investigated for electrochemical energy-storage applications. Structural characterizations by scanning/transmission electron microscopies, X-ray diffraction, X-ray photoelectron spectroscopy and a UV-vis spectrophotometer reveal that the film comprises polycrstalline NiO nanoparticles with diameters in the range of 3.0–6.0 nm loosely agglomerated into a porous foam-like network. The nanoporous sparked NiO films, exhibit remarkable energy-storage behavior with a high average specific charge capacity of 402.75 C g−1 at a discharge current of 1 A g−1 and a good capacity retention of 88% after 1000 cycles at a high discharge current of 40 A g−1. Thus, the sparking method is a promising alternative route for the preparation of high-performance electrochemical energy-storage devices.

Direct nanomaterial-DNA contact effects on DNA and mutation induction

The toxicity of nanomaterials has been well known, but mechanisms involved have been little known. This study was aimed at looking at direct interaction between nanomaterials and naked DNA for some fundamental understanding. Two different types of nanomaterials, carbon nanotubes (CNTs) and tungsten trioxide (WO₃) nanoplates, were simply mixed with naked DNA plasmid, respectively, in two different contact modes, dry or wet (in solution), for varied time periods. DNA topological forms were analyzed for changes using gel electrophoresis and fluoro-spectrometry. The nanomaterial-contacted DNA was transferred into bacteria Escherichia coli (E. coli) cells for mutation observation. Certain types and degrees of DNA damage were observed, such as single strand break and double strand break, and bacterial mutation was confirmed. The DNA damage increased with the contacting time in an exponential manner and increased more rapidly in the initial stage for the wet contact. The nanomaterials-contacted DNA transferred bacteria had about less than 10% survival but almost 100% mutation for the surviving cells. The CNTs were more offensive than the metal oxide nanomaterials. The mutation spectrum from the DNA sequencing analysis showed that DNA point mutation was dominated by transversion, which was dominated by guanine changes in the wet contact condition while by cytosine changes in the dry contact condition. The point mutation occurrence in the wet contact was more than in the dry contact, confirming the wet contact more active and thus dangerous than dry contact. This experiment, although as a model study, revealed that direct simple contacts between nanomaterials and DNA could cause DNA changes and thus induce mutations which might potentially lead to cancers, diseases and genetic changes. This could be a mechanism for nanomaterial genotoxicity to the cells and also provided a caution to applications in using nanomaterials for DNA delivery.

Synthesis of CNTs via ethanol decomposition over ball-milled Fe2O3 coated copper sheets

Carbon nanotubes (CNTs) were synthesized on ball-milled Fe2O3 coated copper sheets by the catalytic decomposition of ethanol vapor at 650°C. TEM, SEM, and EDX revealed the presence of 30–50 nm diameter multiwalled carbon nanotubes with catalytic particles at their tips. CNTs, α-Fe, and Fe3C were detected by XRD. Raman and TG analyses show that the product is CNTs with less than 10 wt % residues. The carbon yield was the maximum at 354 wt %.

Carbon Nanotube-SnO2 Composite Gas Sensor Prepared by Electron beam Evaporation

Carbon nanotube (CNT) is a useful material for gas sensing applications because of its high surface to volume ratio structure. In this work, multi-wall CNTs are incorporated into tin oxide thin film by the means of powder mixing and electron beam evaporation and the enhancement of gas-sensing properties is presented. The CNTs were combined with SnO2 powder with varying concentration in the range of 0.25-5% by weight and electron beam evaporated onto glass substrates. From AFM and TEM characterization, CNT inclusion in SnO2 thin film results in the production of circular cone protrusions of CNT clusters or single tube coated with SnO2 layer. Experimental results indicate that the sensitivity to ethanol of SnO2 thin film increases by the factors of 3-6. However, if the CNT concentration is too high, the sensitivity is decreased. Moreover, the CNT doped film can operate with good sensitivity and stability at a relatively low temperature of 250-300 degC. The improved gas-sensing properties should be attributed to the increasing of metal oxide surface adsorption area produced by CNT protrusion

Highly stretchable and sensitive strain sensors using nano-graphene coated natural rubber

ABSTRACT Flexible, stretchable and wearable sensors are needed for the human motion detection. Here, a highly stretchable and sensitive strain sensor is fabricated based on the coating of nano-graphene platelets on natural rubber by simple dry coating process. The gauge factors are adjustable in the ranges of 0.78–52.53 depended on the preparation conditions and strain state. The sensors showed a high stretchability up to 750% and high durability of 1500 stretching–releasing cycles. The stretchable strain sensors are capable of detecting a bending fingers and the pulse of radial artery on the wrist. In addition, a smart glove made form five independent strain sensors was created. The data of the glove finger motions are used to control an avatar robotic hand.

Synthesis of Silicon Carbide Nanowires Doped with Al2O3

Synthesis of silicon carbide nanowires (SiC NWs) from an alumina doped silica-graphite rod is reported. The rod was gradually heated up to a growth temperature by passing current through it under constant flowing argon at atmospheric pressure. The as-grown layers, deposited on the rod surface were separated from the inner core and characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, selected area electron diffraction, X-ray diffraction and Raman spectroscopy. A non-uniform layer thickness of alumina coating on SiC NWs was clearly observed when the doping was increased from 1 to 2 and 3 wt.%.