Polymer stabilized liquid crystalline light modulating device and material

• US 5,691,795 A
• Filed: 04/20/1995
• Issued: 11/25/1997
• Est. Priority Date: 05/02/1991
• Status: Expired due to Term

• Current Assignee: Kent State University
• Original Assignee: Kent State University
• Inventors: Chien, Liang-Chy, Doane, J. William, Yang, Deng-Ke
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MILLER, CHARLES LELAND
• Application Number:
  US08/425,289
• Time in Patent Office: 950 Days
• Field of Search: 349/88, 349/115, 349/169, 349/176
• US Class Current: 349/169
• CPC Class Codes: C09K 19/02 characterised by optical, electrical or physical properties of the components, in general
• CPC Class Codes: C09K 19/542 Macromolecular compounds
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: C09K 19/586 Optically active dopants; chiral dopants
• CPC Class Codes: G02F 1/0131 based on photo-elastic effects, e.g. mechanically induced birefringence
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 1/13345 Network or three-dimensional gels
• CPC Class Codes: G02F 1/13347 working in reverse mode, i.e. clear in the off-state and scattering in the on-state
• CPC Class Codes: G02F 1/13718 based on a change of the texture state of a cholesteric liquid crystal
• CPC Class Codes: G02F 1/13775 Polymer-stabilized liquid crystal layers

Abstract

A new liquid crystalline light modulating cell and material are characterized by liquid crystalline light modulating material of liquid crystal and polymer, the liquid crystal being a chiral nematic liquid crystal having positive dielectric anisotropy and including chiral material in an amount effective to form focal conic and twisted planar textures, the polymer being distributed in phase separated domains in the liquid crystal cell in an amount that stabilizes the focal conic and twisted planar textures in the absence of a field and permits the liquid crystal to change textures upon the application of a field. In one embodiment, the material is light scattering in a field-OFF condition and optically clear in a field-ON condition, while in another embodiment, the material is optically clear in a field-OFF condition and light scattering in a field-ON condition. In still another embodiment, the material exhibits stability at zero field in a colored, light reflecting state, a light scattering state and multiple stable reflecting state therebetween, as well as being optically clear in the presence of a field.

Claims

1. A light modulating cell comprising liquid crystalline light modulating material of liquid crystal and phase-separated domains of polymer which form a cell wall structure, the liquid crystal being a chiral nematic liquid crystal having positive dielectric anisotropy and including chiral material in an amount effective to form a focal conic texture having a pitch length effective to reflect light outside the visible spectrum, said cell wall structure and liquid crystal cooperating to form a stable focal conic texture in the absence of a field, and to permit the liquid crystal to change textures upon the application of a field, and wherein said phase separated domains are formed in the presence of a field effective to homeotropically align the liquid crystal such that a portion of the liquid crystal in the vicinity of the domains is characterized by a preferential homeotropic alignment in the absence of a field, the resulting material being characterized by light scattering focal conic texture in the absence of a field and optically clear homeotropic alignment in a field-ON condition.

2. The cell as claimed in claim 1 wherein the chiral nematic liquid crystal has a pitch length that reflects light in the infra-red spectrum.

3. The cell as claimed in claim 1 including cell wall structure treated to align the liquid crystal molecules.

4. The cell as claimed in claim 1 wherein the polymer is present in an amount of from about 1.2 to about 40% based on the total weight of polymer and liquid crystal in the cell.

5. The cell as claimed in claim 1 wherein the polymer is present in an amount of from about 1.2 to about 10% based on the total weight of polymer and liquid crystal in the cell.

6. The cell as claimed in claim 1 wherein said liquid crystal consists essentially of chiral nematic liquid crystal having positive dielectric anisotropy.

7. A light modulating cell comprising liquid crystalline light modulating material of liquid crystal and polymer, the liquid crystal being a chiral nematic liquid crystal having positive dielectric anisotropy and including chiral material in an amount effective to form twisted planar textures having a pitch length effective to reflect light outside the visible spectrum and cell wall structure treated to align the liquid crystal, the polymer being distributed in phase separated domains in the cell in an amount that stabilizes the twisted planar textures in the absence of a field and permits the liquid crystal to change textures upon the application of a field, and wherein the liquid crystal is characterized by an optically clear twisted planar texture in the absence of a field and by a light scattering focal conic texture in a field-ON condition.

8. The cell as claimed in claim 7 wherein the chiral nematic liquid crystal has a pitch length that reflects light in the infra-red spectrum.

9. The cell as claimed in claim 7, wherein the polymer is present in an amount of from about 1.5 to about 40% based on the total weight of polymer and liquid crystal in the cell.

10. The cell as claimed in claim 7, wherein the polymer is present in an amount of from about 1.0 to about 10% based on the total weight of polymer and liquid crystal in the cell.

11. A light modulating device comprising cell wall structure and a polymer containing chiral nematic liquid crystalline light modulating material having positive dielectric anisotropy, said cell wall structure and liquid crystal cooperating to form focal conic and twisted planar textures that are stable in the absence of a field, wherein a first portion of said material exhibits a twisted planar texture in the absence of a field and a second portion of said material simultaneously exhibits a focal conic texture in the absence of a field, and means for establishing an electrical field through said material, said means adapted to provide electric field pulses of varying magnitude sufficient to selectively change the proportion of said material in said focal conic and twisted planar textures, whereby the intensity of light reflected may be selectively adjusted.

12. The device according to claim 11 wherein said cell wall structure is treated to align the liquid crystal.

13. The device according to claim 11, wherein said means for establishing a field through said material is adapted to provide an AC pulse.

14. The device according to claim 11 wherein said liquid crystal has a pitch length effective to reflect light outside the visible spectrum.

15. The device according to claim 11 wherein said liquid crystal has a pitch length effective to reflect light in the visible spectrum.

16. A light modulating reflective cell comprising cell wall structure and a polymer containing chiral nematic liquid crystal light modulating material having positive dielectric anisotropy and a pitch length effective to reflect light in the visible spectrum, said cell wall structure and liquid crystal cooperating to form focal conic and twisted planar textures that are stable in the absence of a field, and means for addressing said liquid crystal material, said means adapted to selectively establish a first voltage pulse of a magnitude effective to transform at least a portion of said liquid crystal from a focal conic texture to a light reflecting twisted planar texture, and a second voltage pulse of a magnitude effective to transform at least a portion of said liquid crystal from a light reflecting twisted planar texture to a focal conic texture.

17. The cell as claimed in claim 16 wherein the liquid crystal exhibits a stable light reflecting twisted planar texture following sudden removal of a voltage pulse effective to homeotropically align the liquid crystal, and a stable light scattering focal conic texture following removal of a voltage pulse below that which will homeotropically align the liquid crystal.

18. The device according to claim 16 including cell wall structure treated to align the liquid crystal.

19. The device according to claim 16 wherein said cell wall structure is treated to homeotropically align said liquid crystal.

20. The device according to claim 16, wherein said means for establishing a field through said material is adapted to provide an AC pulse.

21. The device according to claim 16 wherein said polymer is present in an amount of from about 1.0 to about 10% by weight based on the weight of the liquid crystal and polymer.