Liquid crystal elastomers

• US 6,312,770 B1
• Filed: 04/12/1999
• Issued: 11/06/2001
• Est. Priority Date: 01/04/1996
• Status: Expired due to Fees

• Current Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Original Assignee: Defence Research Agency, The secretary of state for defence in her Britannic Majesty's Government of the United Kingdom of Great Britain And Northern Ireland
• Inventors: Coates, David, Verrall, Mark A, Blackwood, Keith M, Sage, Ian C, Jones, Michelle
• Primary Examiner(s): WU, SHEAN CHIU
• Application Number:
  US09/091,746
• Time in Patent Office: 939 Days
• Field of Search: 252/299.01, 428/1.1, 428/1.3
• US Class Current: 428/1.1
• CPC Class Codes: C09K 19/38 Polymers
• CPC Class Codes: C09K 19/3857 containing at least one asymmetric carbon atom
• 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 1/133365 Cells in which the active layer comprises a liquid crystalline polymer

Abstract

This invention describes a method for the loading and alignment of elastomers in electro-optic and electro-active devices. It comprises the in-situ polymerization between substrates of liquid crystal monomers in the presence of cross-linking reagents. It also describes the production of free-standing elastomer films.

Claims

1. A method of making an electro-optic device comprising a layer of a thin elastomer film having an aligned chiral smectic C phase, the method comprising the steps of:

(a) forming a cell comprising two cell walls spaced apart, the walls'"'"' inner surfaces having formed thereon electrode structures;

(b) providing a mixture comprising a smectic liquid crystal monomer material and cross-linking agent;

(c) introducing the mixture of step (b) between the cell walls, and thereafter

(d) polymerizing the mixture such that an amount of elastomer is formed.

2. The method according to claim 1 wherein at least one wall is surface treated to provide liquid crystal alignment.

3. The method according to claim 1 wherein the mixture additionally contains a photoinitiator.

4. The method according to claim 1 wherein the polymerization is carried out under UV light.

5. The method according to claim 4 wherein the polymerization is carried out with the addition of heat.

6. The method according to claim 1 wherein the mixture additionally contains a thermal initiator.

7. The method according to claim 1 comprising the additional step of aligning the smectic liquid crystal monomer material by heating to the isotropic phase and cooling slowly to a liquid crystalline phase.

8. The method according to claim 1 comprising the additional step of aligning the smectic liquid crystal monomer material by heating to a liquid crystal phase and cooling slowly to another liquid crystalline phase.

9. The method according to claim 1 wherein during the polymerization process the monomer material is maintained in an aligned state in a liquid crystal phase.

10. The method according to claim 1 wherein the polymerized mixture is aligned.

11. The method according to claim 7 or 8 wherein the polymerized mixture is aligned.

12. The method according to claim 1 wherein at least one of the cell walls is flexible.

14. The method according to claim 1 or claim 13 wherein during the polymerization of the mixture either a DC or AC bias is applied or a thermal bias is applied across the cell.

15. The method according to claim 1 or claim 13 wherein during polymerization of the mixture any combination of DC, AC and thermal bias is applied across the cell.

13. A method of making a thin layer of elastomer film comprising an aligned chiral smectic C phase, the method comprising the steps of:

(a) forming a cell comprising two cell walls of which at least one of the cell walls is flexible, said cell walls being spaced apart;

(b) providing a mixture comprising a smectic liquid crystal monomer material and cross-linking reagent;

(c) introducing the mixture between the cell walls;

(d) polymerizing the mixture; and

(e) removing the elastomer film from between the cell walls.

16. The method according to claim 13 wherein at least one wall is surface treated to provide liquid crystal alignment.

17. A device comprising two spaced cell walls of which at least one of the cell walls is flexible, said cell walls being spaced apart, and a layer of a liquid crystal elastomer comprising an aligned chiral smectic phase enclosed between the cell walls.

18. A method of making an electro-active device comprising a thin elastomer film having a smectic liquid crystal, said process comprising the steps of:

(a) forming a cell comprising two cell walls spaced apart, the walls inner surfaces having formed thereon electrode structure

(b) providing a mixture comprising a smectic liquid crystal monomer material and cross linking agent;

(c) introducing the mixture between the cell walls; and

(d) polymerizing the mixture such that an amount of elastomer is formed.

19. The method according to claim 18 wherein the electro-active device is a sensor.

20. The method according to claim 19 wherein the sensor is either a pyroelectric or piezoelectric device.

21. The method according to claims 18, 19 or 20 wherein during the polymerization of the mixture either a DC or AC bias is applied or a thermal bias is applied across the cell.

22. The method according to claim 18, 19 or 20 wherein during the polymerization of the mixture any combination of DC, AC and thermal bias is applied across the cell.

23. A device comprising a cell wall, said cell wall having deposited thereon a layer of a liquid crystal elastomer comprising an aligned chiral sectic phase.

24. A device according to claim 23 wherein an electrode structure is sandwiched between the liquid crystal elastomer and the cell wall.

25. A device according to either of claims 23 or 24 wherein a conductive layer is deposited on the exposed elastomer layer.