Liquid crystalline light modulating device and material

• US 5,437,811 A
• Filed: 10/30/1992
• Issued: 08/01/1995
• 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): TUCKER, PHILIP C
• Application Number:
  US07/969,093
• Time in Patent Office: 1,005 Days
• Field of Search: 359/51, 359/52, 359/91, 252/299.01, 252/299.5
• US Class Current: 252/299.01
• 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 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 having a pitch length effective to reflect light outside the visible spectrum, the polymer being distributed in phase separated domains in the 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, and wherein said phase separated domains are formed in the presence of a field such that a proportion of the liquid crystal in the vicinity of the domains is characterized by preferential homeotropic alignment in the absence of a field, and the surrounding regions of liquid crystal are characterized by a light scattering focal conic texture in the absence of a field and an 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 wherein the pitch length of the chiral nematic liquid crystal is in a range of from about 1.0 to about 4.0 microns.

4. The cell as claimed in claim 1 wherein the pitch length of the chiral nematic liquid crystal is in a range of from about 0.5 to about 1.0 microns.

5. The cell as claimed in claim 1, 2, 3 or 4 wherein the chiral nematic liquid crystal contains from about 1 to about 16% by weight chiral material based in the combined weight of nematic liquid crystal and chiral material.

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

7. The cell as claimed in claim 1, 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.

20. The cell as claimed in claim 1 wherein the polymer is present in an amount of less than 10% by weight based on the total weight of polymer and liquid crystal in the cell.

8. 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 focal conic and 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 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, 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.

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

10. The cell as claimed in claim 8 wherein the pitch length of the chiral nematic liquid crystal is in a range of from about 1.0 to about 4.0 microns.

11. The cell as claimed in claim 8 wherein the pitch length of the chiral nematic liquid crystal is in a range of from about 0.5 to about 1.0 microns.

12. The cell as claimed in claim 8, 9, 10 or 11 wherein the chiral nematic liquid crystal contains from about 1 to about 16% by weight chiral material based in the combined weight of nematic liquid crystal and chiral material.

13. The cell as claimed in claim 8, 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.

14. The cell as claimed in claim 8 wherein the polymer is present in an amount of less than 10% by weight based on the total weight of polymer and liquid crystal in the cell.

15. 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 focal conic and twisted planar textures having a pitch length that reflects light in the visible spectrum, the polymer being distributed in phase separated domains in the 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, and wherein the liquid crystal exhibits a stable light reflecting twisted planar structure in a field-OFF condition following removal of a high field-ON condition sufficient to homeotropically align the liquid crystal, and at least a portion of the liquid crystal exhibits a stable light scattering focal conic texture in a field-OFF condition following removal of a low field-ON condition below that which will homeotropically align the liquid crystal.

16. The cell as claimed in claim 15 wherein the pitch length of the chiral nematic liquid crystal is in a range of from about 0.25 to about 0.44 microns.

17. The cell as claimed in claim 15 wherein the chiral nematic liquid crystal contains from about 27 to about 66% chiral material based on the combined weight of nematic liquid crystal and chiral material.

18. The cell as claimed in claim 15, including cell wall structure treated to align the liquid crystal molecules.

19. The cell as claimed in claim 15, 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.

21. The cell as claimed in claim 15 wherein the polymer is present in an amount of less than 10% by weight based on the total weight of polymer and liquid crystal in the cell.