The influence of particle size (0. 019-0.24μm) of TiO2 on UV-ray-shielding capability was studied. UV-ray-shielding capability of TiO2 depended on the wavelength. That is, the smaller the primary particle size was, the greater its shielding capability against around300nm of UV-B range was. On the contrary, for the shielding capability against around 350nm of UV-A range, an optimum primary particle size was found.
The relationship between rheological properties and texture of a smectic-A liquid crystal, 4-cyano-4'-octylibiphenyl (8CB), was studied. The rheological measurements were carried out using the Rheometrics Fluids Spectrometer (RFSII) with a cone and plate geometry. We measured rheological properies such as steady shear viscosity, stress growth, and strage and loss moduli, G' and G” after various flow histories and observed the change of the texture under steady shear. For the measurements without pre-shearing just after cooling from its isotropic phase, G' and G” showed the frequency dependence in the low frequency region. However, with applying pre-shearing after cooling, G' was almost constant irrespective of frequency, and the sample became turbid. With increasing shear rate, the value of G' increased, and the opacity became much higher. It is thought that the defects in the smectic structure are formed with applying shear and caused the light scattering. The heterogeneous structure with defects is responsible for the elastic behaviour. At higher shear rate, the denser defective structure was obtained. For each shear rate, there was the intrinsic equilibrium state containing corresponding quantities of defects. The shear induced structure was affected only by the external stimulation.
Monodispersed crystalline hexagonal germanium (IV) oxide particles with an average size of 2.0, μm were prepared by cooling from 50 to 10°C an ethanolic mixed solution (30% by volume) of 8.4 x 10-2 mol dm-3 germanium (IV) and 1.7 mol dm-3 hydrochloric acid, for example. A fraction of soluble germanium (IV) species in a supernatant solution finally reached 0.36 at 10°C after 325h. A rate-determining step of the particle growth was revealed to be a polynuclear layers mechanism as judged from the fractional change of the germanium (IV) species. Uniform cuboidal particles of crystalline germanium (IV) oxide were also prepared by oxidizing at 100°C a mixed solution of 0.11 mol dm-3 tris (oxalato) germanate (IV) complex, 4.0 mol dm-3 sulfuric acid, and ethanol of 13% by volume with 2.2 mol dm-3 hydrogen peroxide. Additionally, uniform tetrahedral particles of Na2Ge3O, ? 7H2O were obtained at 100°C and pHi 8.5 from an ethanolic solution (50% by volume) of 3.5 x 10-2 mol dm-3 8-quinolinolatogermanium (IV) complex in the presence of sodium ions.