Shingo Katayama

Electrorheological properties of silica suspensions

Monodisperse silica particles were formed by hydrolyzing tetraethylorthosilicate in an ethanol solution. For silica suspensions in a silicone oil, the steady‐shear viscosity and dynamic viscoelasticity were measured under electric fields up to 3.0 kV mm−1. At low shear rates and high field strength, the flow curve shows a plateau, showing development of a yield stress. The yield stress is proportional to the volume fraction of particles (Φ) and to the square of the electric field (E) for Φ<0.3. The number of chains linearly increases with volume fraction. At higher volume fractions it varies with (ΦE)2.4. The larger value of the exponent may be attributed to the crosslinking of chains. The scaling on Mason number is not applicable to the viscosity behavior in steady shear. This implies that the electric polarization forces are much stronger than predicted by the bulk polarization theory. The interparticle forces due to polarization are closely related to conditions at the surfaces of the particles, rather...

Effect of adsorbed water on the electrorheology of silica suspensions

Abstract Monodisperse silica particles were formed by hydrolyzing tetraethylorthosilicate in an ethanol solution and the silica suspensions dispersed in a silicone oil were prepared by a different procedure. The effects of adsorbed water on the electrorheological (ER) behavior were studied under oscillatory shear. The amounts of adsorbed water and surface silanol groups were determined by thermogravimetric analysis. The magnitude of the complex viscosity, |η∗|, increases with the application of electric fields. The physically adsorbed water is primarily responsible for the ER effect. However, the fluids containing large amounts of adsorbed water do not always show excellent ER performance. The surface silanol groups have an important role in promoting the ER effect. Not only the amount but also the situation of silanol groups determines the ER activity of adsorbed water.

Formation Behavior and Optical Properties of Transparent Inorganic-Organic Hybrids Prepared from Metal Alkoxides and Polydimethylsiloxane

The formation behavior of the transparent inorganic-organic hybrids prepared from silanol-terminated polydimethylsiloxane (PDMS) and metal alkoxides of Al (III), Ti (IV), Zr (IV), Nb (V) and Ta (V) chemically modified with ethyl acetoacetate (EAcAc) has been investigated. EAcAc bonded to metal alkoxides remained in hydrolyzed solutions and gels to prevent the rapid growth of large inorganic particles. It is speculated that extremely small inorganic clusters are dispersed uniformly in PDMS, resulting in the transparent hybrids. The upper limit of M(OR)n/PDMS ratio to obtain transparent hybrids was influenced by the inorganic source. As the number of remaining alkoxy groups in the modified alkoxide M(OR)n − x(EAcAc)x increased, the fabrication of transparent hybrids became difficult. The refractive index depended on the inorganic sources reflecting the difference in polarizability of the incorporated metallic ion and the molar volume of the hybrid. The refractive index increased in the order Al (III) < Zr (IV) ≦ Ti (IV) < Ta(V) ≦ Nb (V).

Synthesis and dynamic mechanical behaviour of inorganic-organic hybrids containing various inorganic components

Inorganic–organic hybrids containing various inorganic components have been successfully synthesized from silanol-terminated poly(dimethylsiloxane) (PDMS) and three different inorganic sources, Al(OBu s ) 3 , Ti(OEt) 4 and Ta(OEt) 5 , by using a sol–gel process. Inorganic components as well as the process conditions were found to affect the structure and properties of metal-O-PDMS hybrids from dynamic mechanical measurements and FTIR studies. The storage modulus increased and the peak height of the tan δ curve decreased in the order of Al-O-PDMS, Ti-O-PDMS and Ta-O-PDMS hybrids, which may result from the difference in valence and atomic mass of the metallic element constituting the inorganic component.

Processing and optical properties of patternable inorganic–organic hybrid films

Patternable inorganic–organic hybrid films were synthesized from diethoxydimethlysilane and Ti(OC2H5)4 modified with ethyl acetoacetate (EAcAc). Optical properties and patterning of the hybrid film were studied. The films showed the refractive index of 1.62–1.67 and small in-plane scattering. The hybrid films were patterned by the irradiation of ultraviolet (UV) light at 254 nm. Fourier-transform infrared study revealed that the chelate complex of Ti(OC2H5)4 and EAcAc in the hybrid films was decomposed by UV light. The decomposition of the chelate complex caused the structure change of the hybrid film, leading to the solubility difference between UV irradiated and unirradiated regions. The change of solubility by the UV irradiation makes it possible to fabricate patterned hybrid films.

Synthesis of inorganic-organic hybrids by incorporation of inorganic components into organic polymer using metal alkoxides

Inorganic-organic hybrids have been synthesized by incorporation of the inorganic component of Ti(OC2H5)4 into the organic polymer of ethyl cellulose. The inorganic-organic hybrids did not dissolve in toluene used as a solvent for the starting materials. The ethanol was formed as a by-product of the alcoholysis condensation reaction between Ti(OC2H5)4 and ethyl cellulose. These results suggest that ethoxy groups of Ti(OC2H5)4 react with hydroxy groups of ethyl cellulose to form cross-linking bonds of −O−Ti−O−. The reaction of Ti(OC2H5)4 with ethyl cellulose was further investigated by Fourier transform infrared (FT-IR) spectroscopy. The FT-IR spectroscopic experiments revealed that the Ti−O bond state of Ti(OC2H5)4 was changed by refluxing a toluene solution of Ti(OC2H5)4 with ethyl cellulose. The inorganic-organic hybrids have an interesting dielectric property; their dielectric constant is higher than that of ethyl cellulose and that of a simple mixture of TiO2 and ethyl cellulose.

Surface properties of polydimethylsiloxane-based inorganic/organic hybrid films deposited on polyimide sheets by the sol-gel method

Polydimethylsiloxane (PDMS)-based inorganic/organic hybrids films were prepared on polyimide sheets by the sol-gel method using silanol-terminated PDMS and titanium tetraisopropoxide as starting materials. The effect of heat-treatment temperature on the surface property of the hybrid films was examined in terms of contact angle of water and Tapping-Mode Atomic Force Microscopy (AFM). AFM phase images showed the presence of domains, 200–500 nm in size, on the surface of these films after heat-treatment below 300°C. These regions were more hydrophilic than the rest of the area. The domains disappeared at 300°C and the surface became homogeneous surface of the peak to valley value, about 10 nm. It is also uniformly hydrophobic and a maximum contact angle (about 115°C) was obtained.

Synthesis and thermoelectric characterization of polycrystalline Ni1−xCaxCo2O4 (x=0–0.05) spinel materials

Ca doped NiCo2O4 spinel materials were synthesized by conventional solid state reactions at 900 °C. Thermoelectric properties of polycrystalline products were characterized at high temperature range of ∼800 °C in air. d.c. conductivity of the prepared polycrystalline 5 mol % Ca doped NiCo2O4 was about 60 S m−1 at 300 °C. The value of d.c. conductivity was increased with the temperature increasing. Thermoelectric voltage of polycrystalline Ni1−xCaxCo2O4 (x=0–0.05) was positive at 300–800 °C, this showed p-type thermoelectric properties. The Seebeck coefficient of 5 mol % Ca doped NiCo2O4 was ca. 300 μV/K at 600 °C. The value of the Seebeck coefficient of Ni1−xCaxCo2O4 polycrystalline products decreased with the increasing temperature. Thermal conductivity of 5 mol % Ca doped NiCo2O4 was ca. 2.2 W m−1 K−1 at 600 °C. The estimated thermoelectric figure-of-merit, Z, of 5 mol % Ca doped NiCo2O4 spinel polycrystalline product was about 3.5×10−5 K−1 at 600 °C.

Effect of Metal Alkoxide Complexes on Condensation Reactions of Hydrolyzed Phenyltriethoxysilane

Metal alkoxide complexes, in which alkoxy groups were substituted with ethyl acetoacetate (EAcAc), were found to accelerate condensation reactions of hydrolyzed phenyltriethoxysilane (PTES) and affect the structure of phenylsiloxane networks. The 29Si NMR study revealed that the acceleration effect increased in the order Al(O-sec-C4H9)3−x(EAcAc)x < Ta(OC2H5)5−x(EAcAc)x < Ti(OC2H5)4−x(EAcAc)x. However, the GPC study revealed that the solution contained the high molecular weight species in the order Al(O-sec-C4H9)3−x(EAcAc)x < Ti(OC2H5)4−x(EAcAc)x < Ta(OC2H5)5−x(EAcAc)x. In the case of Ti(OC2H5)4−x(EAcAc)x, the smaller size of phenylsiloxane networks with a low content of silanol groups was formed in the solution. In the case of Ta(OC2H5)5−x(EAcAc)x, the larger size of phenylsiloxane networks with a high content of silanol groups was formed in the solution. In the case of Al(O-sec-C4H9)3−x(EAcAc)x, the small size of phenylsiloxane networks with a high content of silanol groups was formed in the solution. During gelation, the catalytic effect of the metal alkoxide complexes on the development of phenylsiloxane networks was also found. However, the average molecular weight of the gels increased in the order Ta(OC2H5)5−x(EAcAc)x < Ti(OC2H5)4−x(EAcAc)x ≤ Al(O-sec-C4H9)3−x(EAcAc)x. The metal alkoxide complexes were hydrolyzed and finally incorporated into the phenylsiloxane networks of gels to form M—O—Si bonds, which were indicated by the results of FT-IR analysis.

PROCESSING AND PROPERTIES OF INORGANIC-ORGANIC HYBRIDS CONTAINING VARIOUS INORGANIC COMPONENTS

Inorganic-organic hybrids containing various inorganic components have been synthesized from silanol-terminated polydimethylsiloxane (PDMS) and three different inorganic components: Al(O-sec-C4H9)3, Ti(OC2H5)4 and Ta(OC2H5)5. The hybrids obtained were transparent and flexible. Dynamic mechanical measurements and stress-strain experiments were carried out in order to study the effect of inorganic component on the properties of the Metal-O-PDMS hybrids. The storage modulus at around room temperature increased in the order Al-O-PDMS, Ti-O-PDMS, Ta-O-PDMS hybrids, indicating that the three-dimensional network structure became denser in this order. The tensile strength increased in the order Al-O-PDMS, Ta-O-PDMS, Ti-O-PDMS hybrids. The difference in tensile strength is considered to be related to the strength of the interaction between the inorganic component and PDMS. The elongation at failure also depended on the inorganic component. Ti-O-PDMS hybrid exhibited the largest elongation of all the samples (more than 200%).