Fabrication of Transparent,Tough, and Conductive Shape‐Memory Polyurethane Films by Incorporating a Small Amount of High‐Quality Graphene

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 μm²), 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.     

Kink formation and motion in carbon nanotubes at high temperatures

We report that kink motion is a universal plastic deformation mode in all carbon nanotubes when being tensile loaded at high temperatures. The kink motion, observed inside a high-resolution transmission electron microscope, is reminiscent of dislocation motion in crystalline materials: namely, it dissociates and multiplies. The kinks are nucleated from vacancy creation and aggregation, and propagate in either a longitudinal or a spiral path along the nanotube walls. The kink motion is related to dislocation glide and climb influenced by external stress and high temperatures in carbon nanotubes.     

Internal energy content of n-butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two-photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd.     

Raman scattering in Europium chalcogenides near magnetic phase transitions

The inelastic light scattering spectra of the europium chalcogenides are analyzed in terms of a one phonon-one spin Raman process. Calculations are presented for the temperature dependence of the integrated intensity of the “spin-disorder” spectrum of EuS and compared with experiment. The observed temperature dependence of the Raman spectrum of EuSe in the two-sublattice antiferromagnetic phase is presented and examined in terms of the one phonon-one spin mechanism. Experiments are suggested in which the Raman spectra can be used to measure the magnetic field dependence of the order parameter exponent β in EuTe.     

Infrared and Raman spectroscopy of graphite-ferric chloride

We present the first detailed study of the stage dependence of the IR- and Raman-active optic graphitic modes in a graphite acceptor intercalation compound. The general frequency upshift observed with increasing FeCl₃ concentration for all optic modes is interpreted to indicate an in-plane compression within the graphitic layers. An identification of the IR-active modes with bounding and interior graphite layers is made. A lineshape analysis of the IR spectra implies IR dipole moments corresponding to ～70% of the effective charge in the graphite bounding layers, independent of stage, and ～30% distributed among the graphite interior layers for stage n?3 compounds.     

Sodium chloride-catalyzed oxidation of multiwalled carbon nanotubes for environmental benefit

A sodium chloride (NaCl) catalyst (0.1 w/w %) lowers the oxidation temperature of graphitized multiwalled carbon nanotubes: MWCNT-20 (diameter: 20-70 nm) and MWCNT-80 (diameter: 80-150 nm). The analysis of the reaction kinetics indicates that the oxidation of MWCNT-20 and MWCNT-80 mixed with no NaCl exhibits single reaction processes with activation energies of E(a) = 159 and 152 kJ mol(-1), respectively. The oxidation reaction in the presence of NaCl is shown to consist of two different reaction processes, that is, a first reaction and a second reaction process. The first reaction process is dominant at a low temperature of around 600 degrees C, while the second reaction process becomes more dominant than the first one in a higher temperature region. The activation energies of the first reaction processes (MWCNT-20: E(a1) = 35.7 kJ mol(-1); MWCNT-80: E(a1) = 43.5 kJ mol(-1)) are much smaller than those of the second reaction processes (MWCNT-20: E(a2) = 170 kJ mol(-1); MWCNT-80: E(a2) = 171 kJ mol(-1)). The comparison of the kinetic parameters and the results of the spectroscopic and microscopic analyses imply that the lowering of the oxidation temperature in the presence of NaCl results from the introduction of disorder into the graphitized MWCNTs (during the first reaction process), thus increasing the facility of the oxidation reaction of the disorder-induced nanotubes (in the second reaction process). It is found that the larger nanopits and cracks on the outer graphitic layers are caused by the catalytic effect of NaCl. Therefore, the NaCl-mixed samples showed more rapid and stronger oxidation compared with that of the nonmixed samples at the same residual quantity.     

Clifford Fourier Transformation and Uncertainty Principle for the Clifford Geometric Algebra Cl 3,0

First, the basic concept of the vector derivative in geometric algebra is introduced. Second, beginning with the Fourier transform on a scalar function we generalize to a real Fourier transform on Clifford multivector-valued functions Third, we show a set of important properties of the Clifford Fourier transform on Cl_3,0 such as differentiation properties, and the Plancherel theorem. Finally, we apply the Clifford Fourier transform properties for proving an uncertainty principle for Cl_3,0 multivector functions.     

Generating suspended single-walled carbon nanotubes across a large surface area via patterning self-assembled catalyst-containing block copolymer thin films

Using self-assembled block copolymers as templates, catalytically active nanostructures with controlled size and space have been produced. A self-assembled polystyrene-b-polyferrocenylsilane thin film and monolayer of surface micelles of cobalt-complexed polystyrene-b-poly(2-vinylpyridine) are fully compatible with novolac-based conventional photoresists. Combining bottom-up self-assembly of catalyst-containing block copolymers with top-down microfabrication processing, plateaus covered with arrays of catalytically active nanostructures have been generated. Spatially selective growth of suspended single-walled carbon nanotubes over a large surface area has been achieved. Greatly enhanced Raman signals have been detected from the suspended tubes. This facile method of creating highly ordered catalyst nanostructures on top of posts enables the rational synthesis of suspended carbon nanotubes, thus facilitating the study of CNT properties by optical methods and enabling the fabrication of devices based on suspended CNTs.     

High-performance electric double-layer capacitors using mass-produced multi-walled carbon nanotubes

Mass-produced multi-walled carbon nanotubes (MWNTs, which have the trademark VGNF®) have been investigated for their potential for use in electric double-layer capacitors (EDLCs). The variation aspects of these MWNTs by KOH activation showed quite interesting features. The gravimetric capacitance enhancement and specific surface area on KOH activation increased linearly. However, the capacitance per unit surface area has a maximum at 200 wt.?% of KOH addition. The VGNF-KOH 500 sample exhibits a capacitance enhancement as much as 13 times greater (28.3 F/g) than that of the as-grown materials (2.2 F/g), under the conditions of charging up to 3.5 V and discharging at a current density of 10 mA/cm². Interestingly, for this MWNT (VGNF®), selective attack on its amorphous carbon impurity has also been observed, as demonstrated from both scanning electron microscopy observations and Raman spectra. Consequently, the results of this study will provide insight into the potentiality of using MWNTs for EDLC electrodes, which would enable the cheapest production cost among the various types of carbon nanotubes.     

Low-dimensional thermoelectric materials

The promise of low dimensional thermoelectric materials for enhanced performance is reviewed, with particular attention given to quantum wells and quantum wires. The high potential of bismuth as a low-dimensional thermoelectric material is discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 755–758 (May 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.