At&t Bell Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

American Telephone and Telegraph, Co.

Jayantilal S Patel

John W Goodby

Robert William Filas

Thomas M Leslie

Robert B Meyer

John M Geary

A liquid crystal device includes a liquid crystal material (30) in which the molecules (15) form a helix having its axis essentially parallel to the plates (13, 20) of the device. A suitable electric field (E), applied essentially perpendicular to the plates, causes planes of the directors (n) to rotate about the field direction to an acute angle .phi. with respect to the helix axis, thereby inducing alternating bands of splay and bend in the material. Such configurations, which have polar symmetry, give rise to the flexoelectric effect in which the polarization (P) of the molecules tends to be parallel to the applied field, and the magnitude of the field is linearly related to tan .phi.. The ability to rotate the directors means that the optical properties of the material can be changed.

Flexoelectric liquid crystal device

Excellent ordering in ferroelectric liquid crystal devices is obtained by utilizing a material having a smectic C phase and no higher temperature orthogonal smetic phases. Ordering is accomplished by the combination of (1) contacting the liquid crystal material in the smectic C phase with an ordering substance and (2) subjecting the liquid crystal material to a slowly varying electric field.

Ferroelectric liquid crystal devices

High-tilt (e.g., 5.degree.-85.degree.) can be achieved by chemical treatment of the interior surfaces of a liquid crystal device. Illustratively, the treatment entails applying a combination of surface coupling agents one of which alone would cause the LC director to make and angle .alpha..sub.1 (e.g., .alpha..sub.1 =0.degree.; homogeneous alignment) with the surface and another of which alone would yield .alpha..sub.2 (e.g., .alpha..sub.2 =90.degree., homeotropic alignment), but together they produce .alpha..sub.3 different from .alpha..sub.1 and .alpha..sub.2.

Liquid crystal device with chemically-induced high-tilt alignment coating

In a liquid crystal device one interior surface of the cell is coated with a polymer (e.g., a crystalline polymer such as PET) which, when rubbed, produces alignment of the liquid crystal molecules, and the opposite interior surface is coated with a material (e.g., an amorphous polymer, such as PMMA) which, even if rubbed, does not produce such alignment. Also described is a combination of an aligning polymer and a non-aligning, non-polymer (e.g., a silane surfactant or bare ITO). This technique is particularly useful in producing alignment of relatively thick, ferroelectric smectic liquid crystal cells.

Alignment technique for liquid crystal devices

The alignment of liquid crystal materials in cells utilized for devices is significantly enhanced through the use of materials such as polyamides, polyimides, nylons, and polyesters. This expedient for alignment of liquid crystal materials is useful for nematic and cholesteric liquid crystals, but finds particularly advantageous use for aligning smectic liquid crystals.

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Scotch Plains, NJ, United States of America

Jayantilal S Patel