The effects of silica particle diameter on dispersion and aggregation behavior in water were analyzed, using alkoxidederived silica powders with particle diameters of 8 -260 nm. The present study focused on the relationships between the surface silanol structure and the interaction forces between solid surfaces in water. The surface silanol structure and interaction between particles were determined using Fourier transform infrared spectroscopy, Fourier transform nearinfrared spectroscopy, and atomic force microscopy. For relatively large particles (>30 nm in diameter), the surface silanols primarily were hydrogen-bonded silanols, and isolated silanols disappeared. The hydrogen-bonded silanols formed a hydrogen-bonded water layer on the particle surface; therefore, the additional hydration force was strong between these relatively large particles. In contrast, the surface density of isolated silanols increased as the particle diameter decreased to <30 nm, and the additional hydration force between ultrafine powders disappeared. The aggregation behaviors of alkoxidederived silica powders were dependent on the hydration force, which was changed by the surface silanol structure.

Two kinds of molecular reorientation processes in SSFLC cells were observed. One (a) is accompanied by the nucleation and growth of domains and the other (b) proceeds by uniform brightness change without any domain formation throughout a cell. In transmittance change, (a) and (b) are also explained by two-step and single-step switchings, respectively. The switching speed of the case (b) is one hundred times faster than that of the case (a) at a low electric field. The models for these switching processes are presented: an internal disclination model for case (a), and a cooperative director reorientation model for case (b).

Two configurations of the phase compensation method are presented to measure the cell gap of a filled twisted nematic liquid crystal display (TN-LCD). The twist angle of the TN-LCD can be any value between 0° and 360° and the pretilt angle can be any practical value. The cell gap measured by this method is the true TN cell gap, namely the thickness of the LC layer which is primarily responsible for the TN optics. Due to this reason, the phase compensation method can also be applied to measure the cell gap of a color TN cell. The measurement uncertainty of this method is within ±1%.

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