Steady-flow and dynamic viscoelastic properties were measured with a cone-and-plate geometry on a rheometer controlled by stress (TA Instruments Co., Ltd. AR-1000N). The cone diameter was 40 mm and the gap angle between the cone and
plate was 4◦. The shear rates were from 0.01 to 500 s−1 in
steady-flow measurements. The angular frequencies were from
0.12 to 62.8 s−1 and the stress amplitude was 0.1 Pa in dynamic
measurements. The measuring temperature was 25 ◦C.
Adsorption of polyether-modified silicones on the particles surface was measured for 35 wt% suspensions. To determine the concentration of nonadsorbed dispersant, the suspensions were separated by centrifugation at 370,000g and the suspension medium was volatilized at 120 ◦C for 2 h from the supernatant solutions. Ultimately, the amount of adsorbed dispersants is calculated from the residual weights.
Ultraviolet–visible light transmittances were measured by a spectrophotometer (U-3500, Hitachi). The suspensions were diluted with decamethylcyclopentahexane and the 5 wt% suspensions were spread onto a piece of quartz plate (50 × 50 × 5 mm)
at a thickness of 10 µm by the use of an applicator (Yahata
Seiki Seisakusyo). The light transmittances were measured in the range from wavelength 280 to 700 nm. The transmittances at wavelengths from 280 to 320 nm are considered as the UVB protection ability.
Floc size distributions were measured by a particle size analyzer (Microtrac UPA 150, Nikkiso Co., Ltd.), which is based on the dynamic light-scattering method. The suspensions were also diluted with decamethylcyclopentahexane to a concentra- tion of 1.0 wt%.