In this study, the soft embossing method is proposed to fabricate periodical microgrooved structure on polyimide surfaces. These microgrooved polyimide surfaces are assembled to form liquid-crystal cells. It is found that the director of liquid crystals uniformly aligns along the groove direction even when the groove width is as high as 3 microm. The anchoring energy of these microgrooved polyimide surfaces is higher than that of the typical rubbed surfaces. The pretilt angle of liquid crystals is adjusted by tuning the surface polarity of the polyimide alignment layer, which is identified by the advancing contact angle of water. The surface polarity of polyimide alignment layers is manipulated by simply mixing two kinds of polyimide: a more hydrophilic one and a more hydrophobic one. It is found that the pretilt angle of liquid crystals increases along with the advancing contact angle of water on the alignment layer under the condition of a fixed surface topography.

Density, viscosity, and refractive index for the binary systems water + 2-butoxyethanol and water + 2-(2-butoxyethoxy)ethanol have been measured at the temperatures ranging from (283.15 to 323.15) K at atmospheric pressure. The excess molar volume and deviations of viscosity and refractive index from a mole fraction average of these binary mixtures were correlated by the Redlich-Kister equation.

The square-wave grating silica surfaces are fabricated by soft embossing silica sol-gel precursor on glass substrates with an elastomeric polydimethylsiloxane mold. The patterned silica surface could induce the planar alignment of liquid crystal 4-n-pentyl-4Ј-cyanobiphenyl ͑5CB͒ along the direction of microgrooves but with no pretilt angle. The pretilt angle of 5CBs is adjusted from 0°to 90°by the further deposition of organosilane self-assembled monolayers with different functional end-groups on the patterned silica surfaces.

Liquid crystal alignment was investigated on the microgrooved silica surfaces modified by organosilanes. In this study, the microgrooved silica surfaces were fabricated by the soft embossing method followed by forming self-assembled monolayers (SAMs) of organosilanes on these microgrooved silica surfaces. The surface topography effect on the liquid crystal alignment is extensively discussed by using different microgrooved-patterned silica surfaces. The surface chemical nature effect on the liquid crystal alignment, as well as its pretilt angle, is also carefully examined by the SAM modifications to adjust the surface chemical property (hydrophobicity) under the condition of a fixed surface topography and liquid crystal type. The advancing contact angle of water is applied as an index of the surface hydrophobicity. The pretilt angle of the liquid crystal is successfully adjusted over the whole range from 0° to 90° continuously by simply tuning the surface hydrophobicity. The pretilt angle of the liquid crystal monotonically increases along with an increase in the advancing contact angle of water. That is, the pretilt angle of the liquid crystal is indeed only subject to the surface hydrophobicity under the condition of a fixed surface topography and liquid crystal type.

No abstract