Generator for charged nanodroplets with sonic-jet ionizer was developed. The size distributions of ions and nanodroplets were measured as well as the electrical currents generated by ions and charged nanodroplets. The sonic-jet ionizer produced O^-₂(H₂O)_n ions with high density of 10⁹-10¹⁰cm^-3. When tetraethylorthosilicate (TEOS) and H₂O vapors were added in the oxygen gas, the generator formed negatively charged nanodroplets with average diameter of 1.3-1.8 and 1.3nm, respectively. SiO₂ nanoparticles synthesized from the charged TEOS nanodroplets were non-agglomerated. The size distributions measured at various furnace temperatures indicated that the formation mechanism of nanoparticles was ion-induced nucleation. In order to investigate the sterilization effects of negatively charged H₂O nanodroplets, yeast fungi were exposed to the gas flow from the charged nanodroplet generator. Survival rates of yeast were clearly reduced by the discharge.

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For crystallization in a solution that is one of the fabrication processes of functional particles, methods of altering particle shape with additives which are known as habit modifiers have attracted attention. The crystal habit is complicated in applications because there are many controlling parameters, such as supersaturation, concentration, types of additives. Therefore, it is necessary to clarify the mechanisms of crystal growth in order to control the crystal shape. In the present work, the influence of additives on crystal growth has been studied by experiments and simulations. In the experiment, a differential scanning calorimeter (DSC) was used for measuring the properties of clusters formed with various habit modifiers. The number of clusters increased with the concentration of habit modifiers. The formation of clusters was also investigated by molecular dynamics (MD) simulation. The simulation result agreed with the experiment result, and the formation of clusters that assembled around the additives was well demonstrated by the simulation.

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We prepared Au/γ-Fe₂O₃ and Au/Fe₃O₄ composite nanoparticles by sonochemically reducing Au (III) ions in an aqueous solution to form and stabilize gold nanoparticles on the surface of magnetic iron oxide particles. The aqueous dispersion of the particles exhibited a reddish color that is characteristic of nanosized gold particles. The color of the solution was segregated by a magnet, which proved that the composite nanoparticles of magnetic oxide and gold were formed. The composite nanoparticles showed a significant affinity to glutathione, which is a tripeptide with mercapto group. Because the present gold particles are sonochemically prepared and immediately supported on the magnetic oxide without using any stabilizer which blocks their surface, they are naked and active having affinity to glutathione even after composite formation.

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Synthesis of BST (Ba_0.5Sr_0.5TiO₃) spherical particles by polymer templating method was investigated. N-Vinylpyrrolidone-co-styrene polymer was used for polymer templates. Macromolecular metal-complex of Ba, Sr and Ti was selected as BST precursor. BST precursor was introduced to the polymer templates by an ultrasonic mixing technique. Templates filled with BST precursor were heated at 600, 700, 800, and 900°C in the air. Crystalline phase, particle size and morphology of BST particles were characterized by FE-SEM and XRD. FE-SEM and XRD analysis showed the formation of spherical particles composed of Ba_0.5Sr_0.5TiO₃ crystalline in cubic phase. When BST precursor was heated without templates, BST particles were irregular in shape.
By using this method, spherical BST particles having lower crystallization temperature and higher homogeneity in composition were successfully synthesized in a simple process.

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This paper focuses on the size effect of lead zirconate titanate. Pb(Zr_0.4Ti_0.6)O₃ (PZT40) nanoparticles with different sizes were prepared by a sol-gel method. The crystal size and structure were determined by X-ray diffraction. As a result, the c/a ratio or tetragonality approached unity with decreasing particle size. Raman spectra of PZT40 nano-particles with various sizes were observed and we found that there is a decrease in the soft mode at around 35nm, suggesting the existence of critical size for the PZT40 particles. The temperature dependence of Raman spectra clearly revealed that Tc for PZT40 nano-particles shifted toward lower temperatures due to the size effect. The intrinsic dielectric constants of PZT40 nano-particles calculated by LST relation increased with decreasing the particle size. These results prove that the Raman scattering is a powerful tool to investigate the ferroelectric materials.

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Wet dispersion mechanism of manometer-sized silica powder was investigated in a verticaltype beads mill using fine zirconium oxide (zirconia) beads. Zirconia beads of various sizes were used to disperse coagulated silica powders in nanometer size. The dispersed particles were measured by TEM and a dynamic light scattering technique and the contamination during the dispersion was also evaluated. Fine beads with the average diameters of 20μm and 50μm were found to be very effective for suppressing contamination from the beads as well as for achieving its homodispersity. 300μm-zirconia beads used in the present work had a very rough surface, which resulted in the silica powder contamination with zirconia in the level of 3250ppm. On the contrary, the surface of 20μm-beads was smooth and zirconia-contamination in the silica powder was decreased to 240ppm. The observation of bead surface and the amount of zirconia (impurity) suggested that the surface of large bead is easily worn away due to the collisions between the beads compared to smaller beads. The coagulated silica powder can be dispersed homogeneously using the beads with size smaller than 50μm, whereas coagulated silica particles were observed using the beads with size larger than 100μm. For coagulates of nanoparticles, main dispersion mechanism with large beads is pulverization while that with small beads is deflocculation. It is important not to give excessive energy to the coagulated particles for preventing the recoagulation and the contamination from the beads. Smaller beads (below 100μm) is suitable in this case.

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This paper presents the effect of frictional force between colloidal particles and a solid substrate on the formation of particle monolayer by a numerical simulation. Discrete Element Method is employed to simulate the dynamics of colloidal particles trapped in a liquid film. Forces such as capillary immersion force, contact force, van der Waals force and frictional force are included in the simulation model. Isotropic ordering factor and non-dimensional boundary length are introduced to quantify the structures of colloidal particles. In the case where the diameter of colloidal particles ranges from 100nm to 1000nm, the monolayer structures depend strongly on the frictional constant between a particle and a solid substrate. On the other hand, in the case where the diameter is about 10nm, large domains of hexagonal close-packed structures are formed because of the Brownian force.

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