Akiko Kawai

Encapsulation of hemoglobin in mesoporous silica (FSM)- : Enhanced thermal stability and resistance to denaturants

Hemoblogin (Hb), which is a typical oligomeric protein, was introduced into the pores of mesoporous silica (FSM: folded‐sheet mesoporous material) that had a diameter of 7.5 nm. Soret CD spectra of Hb–FSM‐7.5 conjugates showed a peak that was identical to that of free Hb. This suggests that Hb retained its highly ordered structure in the mesoporous silica. In addition, the UV‐visible absorption spectrum showed that Hb had an increased resistance to heat denaturation in the silica. Even after heat treatment at 85 °C, Hb–FSM‐7.5 retained its ligand‐binding activity. The stability of Hb–FSM‐7.5 was examined further by measuring its peroxidase‐like activity. Encapsulation of Hb resulted in the retention of activity in the presence of high NaCl or Gdn‐HCl levels. This suggests that encapsulation prevented dissociation and denaturing. Thus, it seems that the mesopores created a favorable environment for the oligomeric protein to perform its function, even under harsh conditions.

Layered Hybrid Perovskites with Micropores Created by Alkylammonium Functional Silsesquioxane Interlayers

Layered organic-inorganic hybrid perovskites that consist of metal halides and organic interlayers are a class of low-dimensional materials. Here, we report the fabrication of layered hybrid perovskites using metal halides and silsesquioxane with a cage-like structure. We used a silsesquioxane as an interlayer to produce a rigid structure and improve the functionality of perovskite layers. Propylammonium-functionalized silsesquioxane and metal halide salts (CuCl2, PdCl2, PbCl2, and MnCl2) were self-assembled to form rigid layered perovskite structures with high crystallinity. The rigid silsesquioxane structure produces micropores between the perovskite layers that can potentially be filled with different molecules to tune the dielectric constants of the interlayers. The obtained silsesquioxane-metal halide hybrid perovskites exhibit some characteristic properties of layered perovskites including magnetic ordering (CuCl4(2-) and MnCl4(2-)) and excitonic absorption/emission (PbCl4(2-)). Our results indicate that inserting silsesquioxane interlayers into hybrid perovskites retains and enhances the low-dimensional properties of the materials.

THE ROLE OF INTERFACIAL POLARIZATION IN THE ELECTRORHEOLOGICAL EFFECTS

The conductive, dielectric and surface properties of severl water-free polymer or inorganic material based ER fluids, as well as their response times, are investigated to elucidate the physical ground of the electrorheological effect. It is found that the slow polarization, especially the interfacial polarization rather than the Debye polarization, should be responsible for the observed phenomena. Combining with the recent achievements (both theoretical and experimental) in the electrorheological field, we argue that is the interfacial polarization that does play a central role in electrorheological response. The particle re-orientation process is actually resulted from the large interfacial polarization.

Effect of adsorbed water contained in heat-treated silica particles on electrorheology

Electrorheology (ER) of heat-treated monodispersed silica particles in silicon oil was investigated using a rotational viscometer. The effect of adsorbed water contained in the silica particles on the ER effect was clarified. The silica particles were prepared by hydrolyzing tetraethylorthosilicate (TEOS). The silica particles were heated at various temperatures and suspended in silicon oil, followed by measuring the ER effect in the silicon oil at room temperature. The heat treatment temperature ranged from 25 to 700°C. The adsorbed water was characterized by thermogravimetry and IR spectroscopy. The ER effect became maximum at some heat treatment temperature between room temperature and 200°C. Physically adsorbed water on silica which was removed with heat treatment below 200°C affected the ER effect. A large quantity of physically adsorbed water, however, decreased the ER effect. The ER effect became negligibly small with heat treatment above 200°C. A proper quantity of physically adsorbed water was found to be necessary for an appreciable ER effect. The effect of adsorbed water on the ER is discussed.

Controlled Formation of Silica Structures Using Siloxane/Block Copolymer Complexes Prepared in Various Solvent Mixtures

Block copolymers exhibit regularly patterned structures induced by microphase separation. Here we present a method for preparing various particulate silica (SiO2) nanostructures by controlling the microphase separation of block copolymers. In this method, siloxane, a SiO2 precursor, is adsorbed onto poly(4-vinylpyridine) blocks of polystyrene-block-poly(4-vinylpyridine) in solvent mixtures. After siloxane/polymer complexes are coprecipitated via further siloxane polycondensation, the resulting precipitates are heated to remove the polymer. The results of scanning electron microscopy revealed that SiO2 formed various structures including cylindrical, spherical, and lamellar. Different SiO2 nanostructures formed via the microphase separation of siloxane/polymer complexes are prepared simply by varying solvent mixtures without changing the polymer chain. The structural change is interpreted in terms of polymer-solvent interactions and volume fractions in siloxane/polymer complexes.

EFFECTS OF SHAPE AND SIZE OF DISPERSOID ON ELECTRORHEOLOGY

The effects of shape and size of dispersoids on electrorheology were investigated. In order to study the effect of shape on electrorheology, three kinds of hydroxy-zinc complexes were used for dispersoids. Hydroxy-zinc complexes were Zn5(OH)8Cl2 · H2O(1), Zn5(OH)8(NO3)2 · 2H2O(2), and Zn5(OH)8(CH3COO)2 · 2H2O(3). Shapes of (1) and (2) are plate. The shape of (3) is rod. The ER fluid containing (3) showed the lowest permittivity and the lowest ER effect. The ER phenomena containing dispersoids with different shapes were independent of their shapes and were explained by their dielectric properties. Zinc oxides prepared by the heat treatment of (1), (2), and (3) were used for studying the effect of size on electrorheology. The particle size influenced their dielectric property and influenced their electrorheology. The dielectric properties were responsible for the ER effect.

Effect of dielectric properties on electrorheology of BaTiO3 suspensions

Abstract The effect of dielectric properties on electrorheological (ER) phenomena in barium titanate (BaTiCO3) suspensions was studied, changing the size of BaTiO3 particles prepared by oxalate-based coprecipitation. The size of BaTiO3 particles significantly affected the dielectric property of BaTiO3 suspensions, changing the ER effect. ER phenomena are explained well by the dielectric property model we propose.

The effect of surface characteristics of silica particles on electrorheology

The effect of the surface characteristics of silica particles on electrorheology (ER) was investigated with a suspension that contained monodispersed silica particles in a silicon oil. Two types of adsorbed water exist at the silica surface; one is dehydrated below 200°C (free water) and the other above 200°C (bound water). It was found that the free water was essential for the ER effect and there was an appropriate amount of free water for an optimum ER effect. The silica surface was treated with cetanol. Cetanol-treated silica has less bound water than untreated silica. The amount of free water on the cetanol-treated silica was controlled by vacuum drying and exposure to saturated water vapor. The cetanol treatment of silica lowered the ER effect. With less bound water on the cetanol-treated silica, the control of free water did not change the ER effect. A direct relationship was not found between the ER effect and current density.

Chemically assisted dry comminution of an inorganic powder

Chemically assisted dry comminution (CADC) of an inorganic powder was conducted in order to obtain fine powder with large specific surface area. Soda glass powder was comminuted with lithium nitrate under dry conditions. The interaction of lithium nitrate with soda glass powder during the comminution assisted the soda glass powder in being comminuted. Soda glass powder of about 180 m2/g was prepared by CADC, whereas the specific surface area in ordinary dry comminution (DC) of soda glass powder was only 3.8 m2/g. Zirconia content as a contaminant was lower in CADC than in ordinary DC. The prevention of agglomeration of the comminuted soda glass by lithium nitrate and the ion-exchange between lithium and sodium ions in the soda glass powder during CADC were thought to help the comminution.

Ordered Ag nano-particle arrays derived from Ag nano-stripes

The preparation of the Ag nano-stripes made from a Ag aerosol of less than 5 nm diameter in the presence of a surfactant (dodecanethiol) at ca. 150 ◦C was previously described [1]. The slight heating (from 150 to 175 ◦C) of the prepared Ag nano-stripes produced an ordered Ag nano-particle array, which consisted of uniform 3– 4 nm Ag nano-particles with the two-dimensional array of 8 × 6 particles per 50 nm square. This method of preparing ordered uniform nano-particle arrays is totally different from the conventional ones, most of which have applied the technique of self-assembly of particles or lithography. Nano-structures such as twoor three-dimensional ordered arrays consisting of uniform nano-particles have a potential for the exhibition of quantum effects leading to the possibility of light-emitting diodes and quantum dot lasers [2, 3], because these devices require a very large number of very faint quantum effect signals emitted from ordered uniform nano-particles. In addition, such nano-structures can also be used for the future development of high-density storage targets of the order of 1 terabits per square inch, which would require fabrications on a nanometer scale [4, 5]. A variety of different methods such as the selfassembly of particles or photo-lithography have been used in attempts to prepare such nano-structures; however, the self-assembly has not produced well-defined enough particle arrangements to exhibit quantum effects in terms of the orientation and regularity of nanoparticles [6]. This is probably an intrinsic tendency because the method of self-assembly is a mere assembly of particles based on an interfacial phenomenon between nano-particles and solvent liquid during the evaporation of solvent [7–10]. This property of self-assembly might give limitations to the applications. On the other hand, the method of photo-lithography gives well-defined particle patterns [11]; however, the degree of precision obtained using this technique is now of the order of sub-micron (0.1–1 μm), not nano-meter as desired [12]. A novel method to overcome these drawbacks is described here, which is totally different from the conventional ones such as self-assembly. The procedure is illustrated in Fig. 1a, which is based on the breakdown of Ag nano-stripes into equal-sized pieces probably due to the thermal force of the dodecanethiol molecule. The pattern of the Ag nano-stripes made from a very small aerosol of less than ca. 5 nm probably consists of alternate nano-sized stripes of Ag and dodecanethiol surfactant as shown in Fig. 1b, details of which are described elsewhere [1]. The thiol functional group (-SH) in the dodecanethiol stripes is presumed to link with the silver in the Ag stripes. In addition, dodecanethiol is an oily liquid having a boiling point of ca. 200 ◦C, indicating that dodecanethiol is subject to thermal effects with increasing temperatures close to the boiling point. Consequently, in this case, a slight increase from 150 ◦C to 175 ◦C for the nano-Ag stripes caused a significant change in the breakdown of Ag nano-stripes into approximately homogeneous sized particles. Based on this consideration, this process could be called a kind of self-organization. Fig. 2 shows a TEM micrograph of the prepared ordered Ag nano-particles array, which exhibits some unique properties that are different from those obtained by conventional methods. First, a closer examination of Fig. 2 shows that the prepared nano-particles are 3–4 nm in size, uniform, and not round but wedge-shaped, suggesting that the Ag nano-stripes could have been broken into particles by certain external forces resulting from the thermal effect of the dodecanethiol molecules linked to the Ag stripes. Second, they form a certain directional array, that is to say, an isolated linear (onedimensional) array of nano-particles as shown in Fig. 2. Third, they show an accurate two-dimensional particle array of 8 × 6 particles per 50 nm square, which is not isotropic probably due to anisotropy of the Ag nanostripes. In contrast, the major conventional method of self-assembly does not produce any specific directional array. The electron diffraction analysis of the prepared nano-particles array shows a halo, Fig. 2, indicating that the nano-particles are amorphous. The elemental analysis (EDX) was described in the previous paper [1]. In addition, this result turns our attention to the transition process from the Ag nano-stripes to the ordered Ag nano-particles array. Fig. 3 shows a TEM micrograph of the transition process from the nano-stripes to the ordered nano-particle array, in the top-left part of which the early stage of the production process can be seen. This micrograph demonstrates that the present method is totally different from conventional ones. In conclusion, a novel method to fabricate an ordered Ag nano-particle array is described, which is different from the conventional ones such as selfassembly. This method features a slight additional heating from 150 ◦C to 175 ◦C of Ag nano-stripes derived from a nano-sized Ag aerosol in the presence of dodecanethiol. The prepared ordered particle array consists of uniform Ag nano-particles with a 3–4 nm size and