Polymers for control of orientation and stability of liquid crystals

• US 7,179,509 B2
• Filed: 01/12/2004
• Issued: 02/20/2007
• Est. Priority Date: 04/05/2000
• Status: Expired due to Fees

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Kornfield, Julia A., Kempe, Michael D.
• Primary Examiner(s): Wu; Shean C.
• Application Number:
  US10/755,906
• Publication Number:
  US 20040142117A1
• Time in Patent Office: 1,135 Days
• Field of Search: 349/86, 349/88, 349/183, 252/299.01, 252/299.5, 428/1.1, 428/1.3
• US Class Current: 428/1.1
• CPC Class Codes: C09K 19/542 Macromolecular compounds
• CPC Class Codes: C09K 2323/00 Functional layers of liquid crystal optical display excluding electroactive liquid crystal layer characterised by chemical composition
• CPC Class Codes: C09K 2323/03 Viewing layer characterised by chemical composition
• CPC Class Codes: G02F 1/133703 by introducing organic surfactant additives into the liquid crystal material
• CPC Class Codes: G02F 1/13775 Polymer-stabilized liquid crystal layers

Abstract

An electro-optically active polymer gel material comprising a high molecular weight alignment polymer adapted to be homogeneously dispersed throughout a liquid crystal to control the alignment of the liquid crystal molecules and/or confer mechanical stability is provided. The electro-optically active polymer gel comprises a homogenous gel in which the polymer strands of the gel are provided in low concentration and are well solvated by the small molecule liquid crystal without producing unacceptable slowing of its electrooptic response. During formation of the gel, a desired orientation is locked into the gel by physical or chemical cross-linking of the polymer chains. The electro-optically active polymer is then utilized to direct the orientation in the liquid crystal gel in the “field off” state of a liquid crystal display. The electro-optically active polymer also provides a memory of the mesostructural arrangement of the liquid crystal and acts to suppress the formation of large scale deviations, such as, for example, fan-type defects in a FLC when subjected to a mechanical shock. A method of making an electro-optically active polymer gel material and an electrooptic device utilizing the electro-optically active polymer gel of the present invention is also provided.

Claims

1. An electrooptically active gel layer comprising:

a quantity of liquid crystal molecules; and

a polymer having at least one middle portion solvated by the liquid crystal molecules, the middle portion being incorporated between at least two end portions, the end portions being physically associated with each other.

2. The gel layer as described in claim 1, wherein the polymer is a block copolymer and the middle portion comprises at least one midblock and the end portions comprise at least two endblocks.

3. The gel layer as described in claim 1, wherein the polymer is telechelic, and wherein the end portions comprise at least two end groups.

4. The gel layer as described in claim 1, wherein the polymer middle portion comprises a mainchain polymer, and wherein a plurality of liquid crystal molecules are incorporated into the mainchain of the polymer.

5. The gel layer as described in claim 1, wherein the polymer middle portion comprises a plurality of sidegroups, and wherein a plurality of liquid crystal molecules are incorporated into the sidegroups of the polymer.

6. The gel layer as described in claim 1, wherein the polymer middle portion comprises a mixed side-chain/main-chain liquid crystal polymer.

7. The gel layer as described in claim 1, wherein the polymer dictates the alignment of the liquid crystal.

8. The gel layer as described in claim 1, wherein the polymer comprises less than 5% of the gel layer by mass.

9. The gel layer as described in claim 1, wherein the polymer comprises equal to or less than 2% of the gel layer by mass.

10. The gel layer as described in claim 1, wherein the polymer has a molecular weight of at least 2 million g/mol.

11. The gel layer as described in claim 1, wherein the polymer has a molecular weight of at least 1 million g/mol.

12. The gel layer as described in claim 1, wherein the polymer has a molecular weight of at least 100,000 g/mol.

13. The gel layer as described in claim 1, wherein the polymer comprises a fluorinated polymer.

14. The gel layer as described in claim 1, wherein the gel layer has a switching time of less than double the switching time of the liquid crystal molecules in the absence of the polymer.

15. The gel layer as described in claim 1, wherein the gel layer has a switching time of less than 10 times the switching time of the liquid crystal molecules in the absence of the polymer.

16. The gel layer as described in claim 1, wherein the end portion further comprises at least one linking portion, wherein the linking portion either physically or chemically cross-links with either the linking portion or end portion of another polymer.

17. The gel layer as described in claim 1, wherein the gel is thermoreversible.

18. The gel layer as described in claim 1, wherein the end portion is made crosslinkable with other end portions by application of either a photo or thermal initiating energy.

19. The gel layer as described in claim 18, wherein the photo initiating energy is selected from the group consisting of:

UV-light, X-ray, gamma-ray, and radiation with high-energy electrons or ions.

20. The gel layer as described in claim 1, wherein the liquid crystal molecules are aligned according to a geometry selected from the group consisting of:

uniaxial, twisted, supertwisted, tilted, chevron and bookshelf.

21. The gel layer as described in claim 1, wherein the polymer mechanically stabilizes the liquid crystal molecules.

22. The gel layer as described in claim 1, wherein the gel may be reversibly dissolved and gelled.

23. An electrooptic device comprising two substrates, which are provided with at least one electrode, and an electro-optically active gel layer which is located between the two substrates, wherein the electro-optically active gel layer includes a quantity of liquid crystal molecules and a polymer having at least one middle portion solvated by the liquid crystal molecules, the middle portion being incorporated between at least two end portions, the end portions being physically associated with each other.

24. The electrooptic device as described in claim 23, wherein the polymer is a block copolymer and the middle portion comprises at least one midblock and the end portions comprise at least two endblocks.

25. The electrooptic device as described in claim 23, wherein the polymer is telechelic, and wherein the end portions comprise at least two end groups.

26. The electrooptic device as described in claim 23, wherein the polymer middle portion comprises a mainchain polymer and wherein a plurality of liquid crystal molecules are incorporated into the mainchain of the polymer.

27. The electrooptic device as described in claim 23, wherein the polymer middle portion comprises a plurality of sidegroups, and wherein a plurality of liquid crystal molecules are incorporated into the mainchain of the polymer.

28. The electrooptic device as described in claim 23, wherein the polymer middle portion comprises a mixed side-chain/main-chain liquid crystal polymer.

29. The electrooptic device as described in claim 23, wherein the polymer dictates the alignment of the liquid crystal.

30. The electrooptic device as described in claim 23, wherein the polymer comprises less than 5% of the gel layer by mass.

31. The electrooptic device as described in claim 23, wherein the polymer comprises equal to or less than 2% of the gel layer by mass.

32. The electrooptic device as described in claim 23, wherein the polymer has a molecular weight of at least 2 million g/mol.

33. The electrooptic device as described in claim 23, wherein the device is a display device.

34. An electrooptically active gel layer comprising:

a quantity of liquid crystal molecules; and

a quantity of polymer molecules, the polymer molecules being homogeneously dispersed within the liquid crystal molecules, the liquid crystal molecules solvating at least a portion of each polymer molecule, each polymer molecule comprising at least one other portion physically associated with a corresponding portion of another polymer molecule.

35. The gel layer as described in claim 34, wherein the physically associated portions of the polymer molecules form crosslinks that produce a polymer network.

36. The gel layer as described in claim 34, wherein the physically associated portions of the polymer are insoluble in the liquid crystal molecules.

37. The gel layer as described in claim 34, wherein the physically associated portions of the polymer comprise covalently cross-linked functional groups.

38. The gel layer as described in claim 34, wherein the physically associated portions of the polymer are covalently cross-linked using photo intiating energy.

39. The gel layer as described in claim 34, wherein the physically associated portions of the polymer are covalently cross-linked using thermal initiating energy.