Katsunori Tsunoda

Dispersion and Purification of Single-Wall Carbon Nanotubes Using Carboxymethylcellulose

We have developed a novel method for the purification of single-wall carbon nanotubes (SWNTs) that involves annealing in air and dispersing the SWNTs in an aqueous solution of carboxymethylcellulose (CMC). The purity of the resulting SWNTs was evaluated by analytical techniques such as electron microscopy, Raman spectroscopy, and thermogravimetric analysis (TGA). As a result, it was revealed that CMC functioned as an effective dispersion reagent in the exfoliation of the SWNT bundles and thereby, SWNTs with appreciably high quality were prepared.

Characterization and modification of amorphous carbon films consisting of sp2 and sp3 bonds using magneto-plasma dynamic arc-jet

A magneto plasma dynamic arc-jet (MPD arc-jet) can introduce a large energy pulse to a source gas and enable synthesis amorphous carbon films consisting of sp2 and sp3 bonds (hybrid amorphous carbon). The process conditions which affect the structure and the properties of the synthesized films are described here. Homogeneous films were obtained using the MPD arc-jet technique. Films were also in-situ modified with modifier gases due to the excellent characteristics of the MPD arc-jet. A substrate temperature of 200°C and a bias potential of -200 V resulted in harder films. The hardness are related to the hydrogen content and chemical bond nature of the carbon in the films. Homogeneity in the deposition direction could be achieved by in-situ modification. The refractive index, hardness, and other properties of the films were controlled by this modification.

Characterization of water contribution to excimer laser ablation of collagen

Abstract In order to gain an obvious insight into the role of water in the mechanism of the excimer laser ablation of the cornea, we have macroscopically investigated the ablation behavior of collagen gel in the swelled state by direct photoetching using an ArF excimer laser with time-resolved photography, and furthermore, the thermal effects on the microscopic structures of the collagen molecules by FTIR–ATR spectroscopy. The hydrated collagen film (HF) has a smaller threshold fluence than the dried collagen film (DF). From the time-resolved photographs, the ejected materials were detected only for HF. It was predicted that the effect of bubble formation for HF contributes to the etching. The FTIR–ATR spectroscopic results revealed that the existence of the water suppressed the denaturation of the collagen to gelatin on the surface in the irradiated region. Overall, it was inferred that during the ablation process for HF, the laser energy would be mostly consumed as the latent heat of evaporation of water, that is, the water in the gel matrix would contribute to the suppression of the increment in the temperature in the irradiated region.

Purification of Single Wall Carbon Nanotubes Using Gelatin

We have developed a simple procedure for the purification of single wall carbon nanotubes (SWNTs) with gelatin as the dispersing reagent. The steps of this procedure were performed in the following order: annealing in air, sonication in an aqueous solution of gelatin, and soaking in hydrochloric acid solution. The advantage of using gelatin as a dispersing reagent is not only that it is useful for untangling the SWNT bundles, but also that the gelatin molecule and the metallic catalyst can be removed using HCl.

Characterization of materials ejected by excimer laser ablation of hydrated collagen gel

The materials ejected from the hydrated collagen gel by ArF laser (193 nm) ablation were investigated using time-resolved photography, atomic force microscopy (AFM), and FTIR attenuated total reflectance spectroscopy (FTIR-ATR). The time-resolved photography suggested that the characteristics of the ejected materials were affected by the laser fluence and the surface condition, and the driving force of the material ejection would be the cavitation bubble collapse. The AFM and FTIR-ATR measurements demonstrated that measurable-sized materials were ejected by the laser ablation and the structure of the collagen in the ejected materials was partially changed from the original. Some of the ejected materials were found to consist of low molecular weight polypeptides.

AFM study of excimer laser ablation of polythiophene films

Abstract Atomic force microscopy (AFM) was used to estimate the etching form on excimer laser ablation of polythiophene films. Electrochemically prepared polythiophene films were irradiated with ArF (193 nm) and KrF (248 nm) excimer lasers through a mask attached to the film. Single pulse irradiation of these lasers created a well-defined periodic structure on the irradiated region. The periodic structure was ascribed to Fresnel diffraction of the incident beam with the edge of the mask and was characteristic of non-fusible polythiophene films. The threshold fluences above which the etching occurs were determined to be approximately 30 and 50 mJ cm −2 for the 193 nm and 248 nm lasers respectively. The emission spectra from the plume suggested that the degree of fragmentation was higher for 193 nm irradiation than for 248 nm irradiation at the same fluence.

Reactions of radicals in filled rubber compounds : II. Generation and subsequent reactions of radicals upon deformation

Effect of stretching on oxidative crosslinking of a carbon black filled IR vulcanizate at a normal temperature was studied by means of ESR and crosslink density measurements. Upon deformation, ESR intensity increased and crosslink density decreased, indicating scission of load supporting bonds generating free radicals. Bond scission increased with increasing strain. Resting after deformation, the ESR intensity decayed steadily following simple combination of first order and second order kinetics. The decay was overwhelmingly caused by first order reactions, which were considered to be irrelevant to crosslinking. On the other hand, crosslink density increased during resting. The results strongly suggested that ESR observed the radicals at the surface of the carbon black filled rubber, while crosslink density evaluated the bulk property. The crosslink density increase during resting outweighed the reduction due to deformation. Deformation accompanied by radical generation apparently accelerated oxidative crosslinking.

Reactions of radicals in filled rubber compounds : I. Detection of free radicals in rubbers by ESR

ESR measurements were made with vulcanized rubbers of a gum, three carbon black filled and a silica filled compounds. The radicals in the filled rubbers were found to have long lives unlike the gum rubber. Carbon black was found to reduce the sensitivity of ESR due to shielding effect in the magnetic field. The degree of sensitivity reduction appeared to depend on the inter-aggregate distance. Upon exposure to toluene vapor, the ESR intensity of black filled rubbers increased for a short period as swelling widened the inter-aggregate distance and then decayed steadily with further exposure. Such a variation was not found with the gum and silica filled vulcanizates. The decay was faster with higher oxygen content of the environment. In a given environment, however, the decay could be dealt by simple kinetics. Diffusion of oxygen did not seem to play any part. It was inferred that ESR observes radicals only in a thin surface layer of the black filled rubber. The kinetic zero-time radical concentration, obtained by toluene vapor exposure in a nitrogen environment, was considered to be the surface radical concentration in the absence of the shielding effect. Among the rubbers of different black loadings, it showed an exponential relation with the value obtained by direct observation due to the difference in the shielding effect arising from difference in loadings. With the rubber of the same formulation, however, the radical concentration obtained by direct observation showed a linear relation with the kinetic zero-time value, suggesting possibility of quantitative comparison by ESR among the rubbers with the same carbon black content.

Studies of Porphyrin-fullerene dyads with oligoethylene glycols spacers in solution

Two novel Porphyrin-fullerene dyads (PFDs) were synthesized, in which flexible spacers of oligoethylene glycol chains were incorporated with different numbers of ethylene glycol moieties. And the emission and electrochemical properties were examined. From the estimations of the quantum yields and free energy, ΔG, for the electron transfer reaction in the excited state, our novel PFDs were suggested to have an efficient electron transfer capability required for compounds constituting artificial photosynthesis system.

Transient thermochromism during ArF excimer laser ablation of poly(3-dodecylthiophene) films

The photothermal effects involved in ArF (193 nm) laser ablation of poly(3-dodecylthiophene) (PDT) films, which have the characteristics of fusibility and thermochromism, were studied using atomic force microscopy and transient absorption spectroscopy. A molten layer was observed in the irradiated region of the PDT films. The behavior of the transient absorption spectra corresponding to the thermochromism showed a rapid increase in temperature during laser duration. A heating rate of approximately 5×109 deg/s was obtained. The obtained findings reveal that photothermal effects are significantly involved in the ablation process.