Search

Mechanical and electrical properties of porous composites consisting of spring-shape carbon microcoils (CMCs) and silicone-rubber were investigated. The CMC/rubber porous composites having 71–81% porosity had compressive elastic moduli of 0.04–0.1 MPa which were 2–4% of a composite having the same ingredients without pores. The porous structure gave the composites not only the flexibility but a unique piezoresistivity in a wide compressive strain range. Resistivities of the porous composites increased over 104 times with a compressive strain up to 80%, while those of other porous composites including fibrous or particulate carbon fillers decreased only several tens of percent. CMC/rubber porous composites having such a unique piezoresistivity enabled us to develop a new tactile sensor system.

Spring-shaped carbon microcoils (CMCs) were embedded in silicone–rubber to form CMC/silicone–rubber composites. The electrical and mechanical properties of the composites were examined and compared with those of the composites involving straight carbon nanofibers and carbon blacks as a conductor. The electrical resistivity of the CMC/silicone–rubber composites decreased dramatically by increasing the CMC content and was as low as 100 Ω cm at 10% CMC volume content. With a compressive or tensile strain, the resistivity increased sharply much more than that of the other composites. The high resistive sensitivity of the composites is ascribed to an easy-to-deform configuration of the CMCs in the composites under an applied stress.

Spring-shaped carbon microcoils (CMCs) were embedded in epoxy resins to form CMC/epoxy resin composites. The mechanical properties of the composites were examined and compared with those of conventional straight carbon fiber (CF) /epoxy resin composites. CMCs were found to be more effective than CFs as a reinforcing material for the epoxy resin having a low Young’s modulus (0.54 MPa). SEM images of the fractured cross-sections of the composite revealed that CMCs were not pulled out from the resin matrix but fractured with the matrix. This could be ascribed to the unique conformations of CMCs.

Fifty eight inclusion crystals of cholamide (CAM) with aliphatic alcohols have been systematically investigated by X-ray crystallography. The host frameworks of the inclusion crystals can be categorized into three structural types: bilayer, herringbone, and crossing structures. Most of the guests are included in bilayer structures, which can be further divided into four sub-types. The host frameworks isomerize depending on the size and shape of the guest molecules. This dependence is clearly evaluated by the relationship between the volume of the guest molecules and the packing coefficient of the void space in the host frameworks. Although the host frameworks with the cavities and the structural isomerization are very similar to those of the inclusion crystals of cholic acid (CA), the inclusion behavior of aliphatic alcohols in the two hosts is completely different: fifty four alcohols can be included in the bilayer-type structures of CAM, but only two in those of CA. This is attributed to their different functional groups, which lead to different hydrogen-bond networks with the guest alcohols. The result in the two hosts is a good example to understand the effect of host–guest hydrogen bonds on guest inclusion in cavities that are identical in size and shape. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Magnetic nanoparticles consisted of nickel zinc ferrite (NZF) were chemically synthesized by co-precipitation and simultaneously coated onto carbon microcoils (CMC), and their structure and magnetic properties were investigated. The samples were prepared at various mass ratios of CMC : NZF ranging from 1 : 5 to 5 : 1. According to X-ray diffraction (XRD) measurements, all the samples synthesized in this study exhibit peaks associated with the spinel ferrite structure of NZF nanoparticles along with a fairly broad peak due to the amorphous structure of CMC. The sample synthesized at CMC: NZF = 1 : 1 gives the highest crystallinity and the largest magnetization at 300 K for NZF according to XRD and magnetization measurement using a superconducting quantum interference device magnetometer. Microstructural analysis of the CMC-NZF assemblies using scanning electron microscopy shows that the use of oleic acid and oleylamine improves the coverage of NZF on CMC and that the assembly made at CMC: NZF = 2 : 1 yields the highest coverage of NZF nanoparticles onto the CMC surface.

Helical TiO2/CMC (carbon microcoils) microtubes and helical TiO2 microtubes were obtained by making TiO2 layer coatings on the surface of CMC templates using a sol-gel and chemical vapor deposition (CVD) processes. The preparation conditions, morphologies and some properties were examined. Uniform TiO2 (anatase) layers were obtained on the CMC templates by a CVD process using vapor phase hydrolysis of titanium tetra-isopropoxide at 300°C followed by heat treatment in N2 or by calcination in air at 500–;650°C. The helical TiO2/CMC microtubes showed good photocatalytic activity. It was considered that the helical structure activated and enhanced the photocatalytic activity of TiO2, probably caused by the generation of inductive microelectric current induced by the irradiation of UV light, resulting in the generation of micromagnetic fields around the tubes.

Hydrogen was adsorbed on carbon coils under 10 MPa hydrogen gas at liquid nitrogen temperature. The equilibrium pressure of hydrogen desorbed from the as-grown carbon coils with an amorphous structure was three to four times greater than those of multiwall carbon nanotubes (MWNT) and active carbons (AC). The heat treatment of the carbon coils at 850 °C contributed to an increase in hydrogen adsorption by 20% compared to the as-grown carbon coils. On the other hand, the adsorption of hydrogen gas on the carbon coils decreased significantly after heat treatment at a temperature higher than 1000 °C due to formation of capsule-like carbon composed of 10–20 layers on the surface of the carbon coils.

The electromagnetic (EM) wave absorption properties in the gigahertz region (12–110 GHz) of carbon microcoils (CMCs) with a three-dimensional-helical/spiral chiral structure (1–10 μm coil diameter and 0.1–10 mm coil length) were examined using the open space method. It was found that the target value of reflection loss, over −20 dB (above 99% absorptivity) necessitated for commercial applications, could be obtained for EM absorption composites of only 1–2 wt % addition of CMCs in a polyurethane matrix for the 30–35, 50–55, 75–80, and 95–100 GHz bands. A CMCs addition of more than 3 wt % resulted in a decrease of the EM wave absorptivity, because of the increase in the reflection of the EM waves. Multilayer absorption composites showed a higher EM absorptivity than that of single-layer composites. The longer the coil length, the higher the absorptivity could be obtained. The absorption mechanism of the EM waves by CMCs is discussed.

Novel TiO 2 microcoils were obtained by coating TiO 2 layers on the carbon microcoil templates by using a sol–gel process. The preparation conditions, morphologies, microstructure, and some properties were examined. It was found that helical TiO 2 fibers, including TiO 2 microcoils (TMCs) or TiO 2 microtubes with negative coiling patterns on the surface (TMCNCs) were obtained, depending on the coating conditions. TMCNCs were formed when used low concentrations of titanium tetra-isopropoxide in ethanol, while TMCs were formed when used high concentrations.

The carbon micro-coils were prepared by the catalytic pyrolysis of acetylene at 770–775 °C using Ni, Nb, Ta and their oxides with the superimposed application of an electromagnetic field (AC, DC) from both the outer and inner sides of the reaction tube as well as with application of a bias voltage to the substrate. The effect of the electromagnetic field on the coil yield and morphology were examined. The coil yield increased by 1.1–1.2 times with the superimposed application of the AC or DC electromagnetic field. It was found that the superimposed application of the outer and inner electric magnetic fields resulted in the strong influence on the morphology of the grown carbon coils. The effect of the non-inductive zero magnetic field obtained with a counter magnetic field on the growth of the carbon coils was also examined. The maximum coil yield of 30–32.5 mg/cm2-substrate was obtained with the application of both the outer and inner DC–EM fields or non-inductive EM field.

The temperature dependence of the electric resistance and the magnetoresistance for both the as-grown carbon micro-coil obtained by chemical vapor deposition and those annealed at various temperatures up to 3000 °C were measured in the temperature range from 5 to 300 K. The activation energy estimated from resistance vs. temperature curves decreases essentially with the raise of the annealing temperature, which seems to show that coils annealed at higher temperature are graphitized with a higher degree of crystallization. Annealing temperature dependence of magnetresistance at 5 K is also thought to be due to the difference of graphitization degree. Field direction dependence of the room temperature magnetoresistance in the highly graphitized coils is consistent with the assumptions that the current flows helically along the fiber constituting the coil and that the increase of the resistance under magnetic field is due to the perpendicular component of the field to the current direction.

Temperature dependence of the electric resistance and the magnetoresistance for both the as-grown carbon micro-coil obtained by chemical vapor deposition and those annealed at various temperatures up to 3000°C were measured in the range from 5 to 300 K. The resistivity and the activation energy decreases with increase in the annealing temperature, which seems to show that coils annealed at higher temperature are more highly graphitized. All annealed coils show negative magnetoresistance at least at low temperature and under low magnetic field, and the positive part of the magnetoresistance becomes predominant under high magnetic field and at high temperatures in highly graphitized coils annealed at temperatures higher than 2500°C. This annealing temperature dependence of the magnetoresistance is assumed to be due to the difference of the carrier concentration by graphitization. The as-grown coil shows no magnetoresistance. The field direction dependence of the magnetoresistance suggests that the current flows helically along the fiber constituting the coil.

Carbon nanocoils with a coil diameter of 50–450 nm were prepared by the catalytic pyrolysis of acetylene, and the preparation conditions and morphology were examined. To clarify the growth mechanism, the carbon nanocoils were also heat treated at 2500 °C for 8 h in a N2 atmosphere, then partially oxidized in air at 600 °C for 15 min. The carbon nanocoils could be grown at 740–770 °C either by applying a magnetic field to the reaction zone or by using sputtered thin films of Au or Au/Ni as a catalyst. Carbon nanocoils are generally single coils, while carbon microcoils are generally double coils. There are two kinds of nanocoils with differing microstructures. One is formed from a carbon fiber with a double microstructure of thin core fiber and clad, while the other is formed from a fiber with a “herring-bone” structure.

The carbon micro-coils were prepared by a ultrasonic wave CVD process, in which ultrasonic waves of 23–65 kHz were irradiated in the growing atmosphere of the carbon micro-coils. The irradiation effects of the ultrasonic waves on the growth, morphology and some properties of the carbon micro-coils were examined. With ultrasonic wave irradiation, the coil yield and the thickness of the coil layers increased by about 1.5 times and 1.3 times higher than that without irradiation, respectively. The coil diameter increased from 3–5 μm without irradiation to 5–9 μm with irradiation. The density increased from 1.8 g/cm3 without irradiation to 2.0 g/cm3 with irradiation by a 23 kHz ultrasonic wave.

N-Methyldeoxycholamide (1) was recrystallized from over one hundred organic substances in a search for inclusion compounds. Only ethylene glycol (EG) was included into host assemblies together with...

Chiral compounds, N-methyl-, N-ethyl-, and N-n-propylcholamides, form crystalline inclusion compounds with water or small organic substances. The compounds were analyzed by X-ray diffraction methods. It was found that the crystals have bilayered structures accumulated by chiral molecular sheets. The chiral molecules associate in a unique head-to-head/tail-to-tail and right-to-left motif to give chiral and amphiphilic sheets. Such sheets stack by adhesions between the hydrophilic sides and between the lipophilic sides. The alkyl groups of the amides prompt the formation of a hydrogen-bonding network between the tails instead of a cyclic one between the head and tail. The guest molecules are accommodated into small cavities between the steroidal side chains. Chirality 10:600–618, 1998. © 1998 Wiley-Liss, Inc.

TiO2/C composite microcoils and TiO2 hollow microcoils were obtained by coating the surface of carbon microcoil (CMC) templates with TiO2 layers using chemical vapor deposition. Uniform TiO2 (anatase) layers were formed on the CMC templates by the vapor phase hydrolysis of titanium tetraisopropoxide at 300°C, followed by heat treatment in N2 or by calcination in air at 500–800°C. It was found that the TiO2/C composited microcoils had a good photocatalytic activity. It was also found that the TiO2 hollowed microcoils as well as the TiO2/C composite microcoils can effectively absorb the electromagnetic waves in the GHz region.

N-Methyldeoxycholanamide specifically includes water instead of organic substances, which is in contrast to deoxycholic acid and deoxycholanamide. Such a specific inclusion behaviour is reasonably explained by the crystal structure of the hemihydrate. The N-methyl group induces a ladder-like hydrogen bonding scheme involving water, The resulting molecular arrangement inhibits an inclusion of organic guests.

A hydroxybenzaldehyde derivative which has isobutenyl linkage reacts with a variety of diamines to efficiently result in a 2∶2 macrocyclic compound.

not Available.

A combinatorial library approach enables us to find new low molecular-weight organogelators composed of a bile acid–alkylamine salt; the gel phenomena are investigated by FT-IR spectroscopy, SEM, and X-ray crystallography.

A hydroxybenzaldehyde derivative which has isobutenyl linkage reacts with a variety of diamines to efficiently result in a 2∶2 macrocyclic compound.

The substitution of lithocholic acid (1) to lithocholamide (4) led to the finding of the formation of channel-type inclusion compounds with a limited range of organic substances, such as alcohols, ketones and so on. The inclusion behavior of 4 is greatly different from those of the known hosts of bile acids and their derivatives.

N-Isopropylcholamide afforded three kinds of matters in organic solvents; organogels, inclusion crystals, and guest-free crystals. The gelation occurred in aromatic liquids in the presence of methanol as a good solvent, while the inclusion crystals were formed when adding ethanol, 1-propanol, or acetone as a good solvent. The guest-free crystals were obtained in benzene when using 2-butanone, 2-pentanone, or 3-pentanone. Electron microscopic image of the organogel exhibited that the network was formed by gathering of many colloidal particles of several hundreds nanometers in diameter.

Addition of water enables deoxycholamide to form a triangular pillar-like assembly with a core involving water and a surface involving organic compounds.