Characterization of Porous ß-Type Tricalcium Phosphate Ceramics Formed via Physical Foaming with Freeze-Drying.

Porous ß-tricalcium phosphate (Ca3(PO4)2; ß-TCP) was prepared via freeze-drying and the effects of this process on pore shapes and sizes were investigated. Various samples were prepared by freezing ß-TCP slurries above a liquid nitrogen surface at -180 °C with subsequent immersion in liquid nitrogen at -196 °C. These materials were then dried under reduced pressure in a freeze-dryer, after which they were sintered with heating. Compared with conventional heat-based drying, the resulting pores were more spherical, which increased both the mechanical strength and porosity of the ß-TCP. These materials had a wide range of pore sizes from 50 to 200 µm, with the mean and median values both approximately 100 µm regardless of the freeze-drying conditions. Mercury porosimetry data showed that the samples contained small, interconnected pores with sizes of 1.24 ± 0.25 µm and macroscopic, interconnected pores of 25.8 ± 4.7 µm in size. The effects of nonionic surfactants having different hydrophilic/lipophilic balance (HLB) values on foaming and pore size were also investigated. Materials made with surfactants having lower HLB values exhibited smaller pores and lower porosity, whereas higher HLB surfactants gave higher porosity and slightly larger macropores. Even so, the pore diameter could not be readily controlled solely by adjusting the HLB value. The findings of this work indicated that high porosity (>75%) and good compressive strength (>2 MPa) can both be obtained in the same porous material and that foaming agents with HLB values between 12.0 and 13.5 were optimal.

Effect of Silicon Dioxide Nanoparticles on the Sintering Properties of Beta-Tricalcium Phosphate Composites.

Composite sintered bodies comprising silicon dioxide (SiO2) nanoparticles dispersed in ß-tricalcium phosphate (ß-TCP) were prepared. The addition of nano-sized colloidal SiO2 to the ß-TCP produced well-dispersed secondary phase nanoparticles that promoted densification by suppressing grain growth and increasing linear shrinkage of the sintered bodies. The SiO2 was found not to react with the ß-TCP at 1120 °C and the substitution of silicon for phosphorous to produce a solid solution did not occur. This lack of a reaction is ascribed to the absence of available calcium ions to compensate for the increase in charge associated with this substitution. The SiO2 nanoparticles were found to be present near the intersections of grain boundaries in the ß-TCP. ß-TCP composite sintered body containing 2.0 and 4.0 wt% SiO2 exhibited a bending strength comparable to that of cortical bone and hence could potentially be used as a bone filling material.

Preparation and Photocatalytic Activity of Hexagonal Plate-like ZnO Particles Using Anionic Surfactants.

Hexagonal plate-like ZnO particles with a high degree of c-face orientation have been synthesized using hydrothermal method in the presence of various anionic surfactants bearing different hydrocarbon chains. The c-face of the ZnO particles increased upon increasing the surfactant alkyl chain length. The photocatalytic activity of the as-obtained hexagonal plate-like ZnO particles was evaluated using the degradation of methylene blue (MB). Although the specific surface area of hexagonal rod-like particles is higher than that of hexagonal plate-like particles, the amount of MB adsorption on the ZnO particle surface was different for the hexagonal plate-like and rod-like particles. In addition, the hexagonal plate-like ZnO particles showed a significantly higher decrease in the MB concentration with the duration of ultraviolet light irradiation when compared to the hexagonal rod-like ZnO particles obtained in the absence of a surfactant. These results indicate that crystal-face-controlled ZnO with a high degree of c-face orientation exhibits high photocatalytic activity.

Synthesis and Photocatalytic Activity of Hexagonal Plate-like Shaped Au Nanoparticles/ZnO Composite Particles under Visible-light Irradiation.

We synthesized Au nanoparticle (AuNP)/ZnO composite particles in presence of an anionic surfactant and evaluated their photocatalytic activity under visible-light irradiation. AuNPs synthesized from HAuCl4 in the presence of amylase and the precursor solutions of ZnO were mixed, followed by a hydrothermal process, to synthesize crystal face-controlled AuNP/ZnO composite particles. X-ray diffraction (XRD) patterns and ultraviolet-visible (UV-Vis) spectra confirmed the formation of AuNP/ZnO composite particles. Furthermore, different Au to Zn concentration ratios in the precursor solutions resulted in different amounts of AuNPs in the composite particles. In addition, the average size of the AuNP/ZnO composite particles decreased with increasing Au to Zn concentration ratio. We believe AuNPs act as the nuclei for ZnO particle formation. The photocatalytic activity of the AuNP/ZnO composite particles was evaluated by the photodegradation of methylene blue (MB) under visible-light irradiation. The photodegradation rate of MB was higher with AuNP/ZnO composite particles compared to that with the ZnO particles synthesized in the absence of AuNPs. The AuNP/ZnO composite particles exhibit photocatalytic activity under visible-light irradiation owing to the enhanced charge separation efficiency and the localized surface plasmon resonance effect.

Effect of Anionic Amphiphiles on the Morphology of Hexagonal Plate-like ZnO Particles.

Zinc oxide (ZnO) particles were synthesized in the presence of anionic surfactants (ASs). The effect of ASs on the morphology of the ZnO particles was investigated by using ASs with various alkyl chain lengths and changing the molar ratio of AS/ZnSO4. Hexagonal plate-like ZnO particles were formed in the presence of ASs. Adsorption of the AS on the c face of the ZnO crystals inhibited (promoted) crystal growth along the c-axis (ab-axis) direction. Increasing the molar ratio of AS/ZnSO4 decreased the particle thickness, owing to the resulting increase in the coverage of the c face with AS. The particle diameter of the hexagonal plate-like ZnO particles (the diagonal length of the hexagonal plate) increased with increasing alkyl chain length of AS as a result of the van der Waals interactions between the alkyl chains. The data indicate that the particle diameter and thickness can be controlled by fine-tuning the van der Waals interactions between the alkyl chains and the coverage of the c face of the ZnO particles with AS.

Preparation of Hexagonal Plate-like ZnO Single-crystal Particles in the Presence of Anionic Amphiphiles.

In this study, we synthesized ZnO particles using anionic amphiphiles as an additive. While the single-crystal particles prepared in the absence of such amphiphiles had a hexagonal rod-like shape, those fabricated using anionic amphiphilic molecules had a hexagonal plate-like shape. The anionic amphiphiles inhibited crystal growth in the c-axis direction of ZnO. This demonstrated that the anionic surfactants served as crystal-growth-directing agents, controlling the shape of the ZnO particles.

Immobilization of DNA on Quartz Crystal Microbalance Sensor Modified with Self-Assembled Monolayer of Thiol Derivative.

In this study, we investigated the direct detection of DNA, without pretreatment, using a quartz crystal microbalance (QCM) sensor. This sensor is modified by a self-assembled monolayer of a thiol derivative that has an amino group as the terminal functional group. Contact angle values and the attenuated total reflectance Fourier transform infrared (ATR/FT-IR) spectra of the QCM sensors after immersion into an ethanol solution of thiol derivatives clearly showed that self-assembled monolayers of the derivatives were formed on the QCM sensors. Although QCM measurements using unmodified and carboxylic group-modified sensors could not detect DNA-Na salt, the sensor modified with amino groups could detect the DNA. This system can be used for the analysis of the interaction between DNA and DNAbinding proteins.

Fabrication and Functionalization of Inorganic Materials Using Amphiphilic Molecules.

In this review, the synthesis of inorganic materials with various properties using amphiphilic molecules is examined. Amphiphilic molecules are used for the formation of highly ordered mesostructures and the surface modification. Two examples of the mesostructures are crystalline mesoporous titania (TiO2) and the novel visible light responsive mesostuructured titania modified with dye in the pores, which can be fabricated using the molecular self-assemblies of amphiphiles as templates. Surface modification using amphiphilic molecules enables the construction of self-assembled arrays of silica particles and the preparation of a film that can control adsorption/desorption behavior of bovine serum albumin (BSA) by light irradiation.

Creation of giant two-dimensional crystal of zinc oxide nanodisk by method of single-particle layer of organo-modified inorganic fine particles.

In this study, the formation and structure of a single-particle layer of organo-zinc oxide are investigated using surface-pressure-area (π-A) isotherms, out-of-plane X-ray diffraction (XRD) analysis, and atomic force microscopy (AFM). Further, techniques for achieving the solubilization of inorganic fine particles in general solvents have been proposed, and a single-particle layer has been formed using such an inorganic solution as a "spreading solution" for an interfacial film. Surface modification of ZnO is performed using a long-chain carboxylic acid. Accordingly, a regular arrangement of ZnO can be easily achieved in order to overcome the relatively weak van der Walls interactions between inorganic materials. A condensed Langmuir monolayer of these particles is also formed. A multiparticle layered structure is constructed by the Langmuir-Blodgett (LB) technique. Out-of-plane XRD measurement results for a single-particle layer of organo-ZnO clearly show a sharp peak at 42 Å. This peak is attributed to the distance between ZnO layers. The AFM image of this single-particle layer of organo-ZnO shows a particle assembly with a uniform height of 60 nm. These aggregated particles form large two-dimensional crystals. In other words, a regular periodic structure along the c-axis and a condensed single-particle layer had been fabricated using Langmuir and LB techniques.

Fabrication and BSA adsorption/desorption properties of titania/silica composite films modified with silane coupling agents.

In this study, we successfully prepared titania/silica composite films modified with silane coupling agents having amino groups and investigated their bovine serum albumin (BSA) adsorption/desorption behavior under light irradiation. XRD patterns and ATR/FT-IR spectra of the films revealed the formation of titania/silica composite films modified with silane coupling agents. In these films, the adsorption and desorption of BSA could be controlled by light irradiation, through the locally photoinduced superhydrophilic titania surface.

Triggered J-aggregation in mixed Langmuir-Blodgett films of amphiphilic spiropyran having a methoxy group at the 5' position and an azobenzene derivative.

Here, we describe the formation of J-aggregates triggered by isomerization of an azobenzene derivative, N-[p-[(p-dodecylphenylazo)phenyloxy]dodecylpyridinium bromide (AzP), in mixed Langmuir-Blodgett (LB) films that contain an amphiphilic spiropyran with a methoxy group at the 5' position, MeO-SP1822. Pure LB films of MeO-SP1822 consist of multilayer domains embedded in a monolayer. UV irradiation of the films causes the isomerization of MeO-SP1822 to its merocyanine form, MeO-MC1822. Pure LB films of AzP comprise finger-like domains and granular domains. Irradiating mixed films of MeO-SP1822 and AzP with alternating UV and visible light causes J-aggregation of MeO-MC1822, with the amount of J-aggregates reaching a maximum at a 1:1 molar ratio. J-aggregation occurs in flat finger-like structures originating in the AzP-rich granular domains that are located on top of the MeO-MC1822-rich multilayer domains. J-aggregates are also present under the AzP-rich granular domains, though these domains do not serve as nucleation sites for the finger-like structures. We propose that granular domains serving as nucleation sites are partially buried in the multilayer domains, whereas those triggering the J-aggregation of MeO-MC1822 under the granular domains are situated on top of the multilayer domains.

Structures of langmuir-gibbs films consisting of long-chain fatty acid and water-soluble surfactants.

The structures of Langmuir-Gibbs (LG) films at the air-solution interface were studied using surface tensiometry, Brewster angle microscopy (BAM), and infrared external reflection spectroscopy (IR-ERS). The LG films were fabricated by forming Langmuir films of deuterated arachidic acid (D19A) and then injecting a water-soluble surfactant, sodium dodecyl sulfate or octaethylene glycol monododecyl ether, into the subphase. The presence of the LG films at the air-solution interface affected the surface tension of water. BAM observations revealed the formation of phase-separated monolayers consisting of D19A monolayers and expanded monolayers of water-soluble surfactant at low concentrations of the water-soluble surfactant. The presence of phase-separated structures was supported by the IR-ERS results. At high concentrations, the water-soluble surfactants adsorbed to the domains of D19A monolayers, forming bilayers under the monolayers. The IR-ERS results suggest the penetration of the water-soluble surfactants into the domains of D19A monolayers and the diffusion of D19A molecules into the bilayer regions of the water-soluble surfactants. At concentrations greater than the critical aggregate concentration and/or critical micelle concentration, D19A molecules were solubilized in the solution. In some cases, the multilayers were kinetically stabilized and were present even 24 h after the injection of the water-soluble surfactants into the subphase.

Patterning of J-aggregated dyes using directed self-assembly on micro- and nanopatterned templates fabricated from phase-separated mixed Langmuir-Blodgett films.

We report a useful technique for the deposition of dyes in the form of J-aggregates using directed self-assembly on the micro- and nanopatterned templates fabricated from the phase-separated mixed Langmuir-Blodgett (LB) films. The patterns of the mixed LB films can be tuned by adjusting the intermolecular interactions between the film-forming molecules. We used the mixed LB films containing silane coupling agent for the fabrication of micro- and nanopatterned templates, taking advantage of the difference between the surface free energy of the patterned regions and that of the self-assembled monolayers of the silane coupling agent. Atomic force microscopy showed that dyes were deposited by casting, spin-coating and the LB technique in accordance with the patterns of the original mixed LB films. Emission spectroscopy revealed that J-aggregates were formed in the patterned films. We succeeded in obtaining nanopatterns of a cyanine dye in the form of J-aggregates on the templates.

Phase-separated structures of mixed Langmuir-Blodgett films of fatty acid and hybrid carboxylic acid.

Phase separation often occurs in mixed Langmuir-Blodgett (LB) films. Usually circular domains at the micrometer length scale form in the LB films. The size and shape of the domains are governed by a compromise between two competing interactions of line tension and dipole-dipole interaction. An attempt was made to control the line tension by varying systematically the hydrophobic moieties of the film-forming molecules. Phase-separated structures of two-component mixed LB films of fatty acid [C(k)H(2k+1)COOH (HkA)] and hybrid carboxylic acid [C(m)F(2m+1)C(n)H(2n)COOH (FmHnA)] were investigated. IR spectra of the mixed LB films of H17A and F8H10A revealed that the alkyl chains were in an all-trans conformation and that the molecular orientation remained unchanged when the two components were mixed. Nanowires formed in the mixed LB films of HkA and F8H10A. The width of the nanowires increased with an increase in k. Domain size and shape in the mixed LB films of H17A and FmHnA depended strongly on the values of m and n. Circular domains at the micrometer length scale formed in the region m + n < 16. In contrast, domains at the nanometer length scale formed in the region m + n > or = 16 except for F6H10A. These results were explained by using a lattice model that considers the effect of the hydrophobic moieties of fatty acid and hybrid carboxylic acid on the line tension.

Formation mechanism for hexagonal-structured self-assemblies of nanocrystalline titania templated by cetyltrimethylammonium bromide.

Hexagonal-structured self-assemblies of nanocrystalline (anatase) titania templated by cetyltrimethylammonium bromide (C(16)H(33)N(CH(3))(3)Br; CTAB) (Hex-ncTiO(2)/CTAB Nanoskeleton) were formed after mixing of aqueous solutions containing CTAB spherical micelles and titanium oxysulfate acid hydrate (TiOSO(4).xH(2)SO(4).xH(2)O) as a titania precursor in the absence of any other additives. Formation mechanism of the Hex-ncTiO(2)/CTAB Nanoskeleton was examined in terms of the reaction temperature, titania precursor/CTAB mixing ratio, surfactant type, electrostatic interaction, micelle formation and molecular component. We found that crystal growth of crystalline (anatase) titania (polymorphic crystallization) was promoted with higher temperature and lower titania precursor content in aqueous solutions. In addition, we revealed that the crystalline (anatase) titania was formed in polycation, poly(allylamine hydrochloride ([CH(2)CH(CH(2)NH(2))HCl](n); PAH), and formamide (HCONH(2)) solutions. On the other hand, no titania formation was observed in anionic systems such as sodium dodecyl sulfate (CH(3)(CH(2))(11)OSO(3)Na; SDS) and poly(sodium 4-styrenesulfonate ([C(8)H(7)SO(3)Na](n); PSSS). This indicates that hydrolysis reaction of the titania precursor is initiated by not only cations but also nitrogen atoms in molecules and polymers. Hexagonally structure was formed in only cationic surfactant micellar solutions but not in polycation solutions and formamide.

Micro- and nanopatterned copper structures using directed self-assembly on templates fabricated from phase-separated mixed Langmuir-Blodgett films.

We report a versatile method to confine metal thin films in micro- and nanopatterns using directed self-assembly on the templates fabricated from phase-separated mixed Langmuir-Blodgett (LB) films. The pattern of the mixed LB films can be tuned by adjusting intermolecular interaction between the film-forming molecules in the LB films and by varying the fabrication conditions of the films such as the mixing ratio, subphase temperature, and surface pressure. We use the patterned LB films for templates to confine metal in patterned regions, taking advantage of the difference between the surface free energy of the patterned regions and that of the self-assembled monolayer of the silane coupling agent. Au nanoparticles are confined onto the patterned films as a catalyst for the succeeding Cu electroless deposition. The atomic force microscopic images, Auger electron spectra, and scanning Auger electron maps of a Cu-deposited film show that Cu is selectively deposited on the patterns of phase separation of the original mixed LB films.

Preparation of highly dispersed core/shell-type titania nanocapsules containing a single Ag nanoparticle.

Core/shell-type titania nanocapsules containing a single Ag nanoparticle were prepared. Ag nanoparticles were prepared using the reduction of silver nitrate with hydrazine in the presence of cetyltrimethylammonium bromide (CTAB) as protective agent. The sol-gel reaction of titanium tetraisopropoxide (TTIP) was used to prepare core/shell-type titania nanocapsules with CTAB-coated Ag nanoparticles as the core. TEM observations revealed that the size of the core (Ag particle) and the thickness of the shell (titania) of the core/shell particles obtained are about 10 nm and 5-10 nm, respectively. In addition, the nanocapsules were found to be dispersed in the medium as individual particles without aggregation. Moreover, titania coating caused the surface plasmon absorption of Ag nanoparticles to shift toward the longer wavelength side.

Direct synthesis of mesoporous titania particles having a crystalline wall.

In this study, we demonstrate a novel method for preparing crystallized mesoporous titania by using a low-temperature synthesis technique in the presence of cationic surfactant. XRD patterns showed that the titania particles obtained had both hexagonal structure and a wall with anatase crystalline structure. Transmission electron microscopy (TEM) observation and corresponding electron diffraction pattern confirmed that the calcined particles are crystallized mesoporous titania.