Polymer-stabilized thermotropic liquid crystal device

• US 20110234944A1
• Filed: 03/29/2011
• Published: 09/29/2011
• Est. Priority Date: 03/29/2010
• Status: Active Grant

• Current Assignee: Ravenbrick, LLC
• Original Assignee: Ravenbrick, LLC
• Inventors: Kish, Matthew B., Pickford, Michael, Cramer, Neil B., LaFrate, Andrew L., Caldwell, Christopher M., Powers, Richard M., McCarthy, Wil
• Granted Patent: US 8,828,176 B2
• Time in Patent Office: Days
• US Class Current: 349/86
• CPC Class Codes: B32B 2310/0831 using UV radiation
• CPC Class Codes: B32B 2457/202 LCD, i.e. liquid crystal displays
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: C09K 2019/548 stabilizing the alignment; Polymer stabilized alignment
• CPC Class Codes: G02F 1/132 Thermal activation of liquid crystals exhibiting a thermo-optic effect
• CPC Class Codes: G02F 1/133305 Flexible substrates, e.g. plastics, organic film
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 1/13392 spacers dispersed on the cell substrate, e.g. spherical particles, microfibres
• CPC Class Codes: G02F 1/13725 based on guest-host interaction G02F1/13762, G02F1/13737, take precedence
• CPC Class Codes: G02F 1/13775 Polymer-stabilized liquid crystal layers
• CPC Class Codes: Y10T 156/10 Methods of surface bonding and/or assembly therefor
• CPC Class Codes: Y10T 156/1052 with cutting, punching, tearing or severing

Abstract

A resizable polymer-stabilized, thermotropic liquid crystal device formulation is used in passive or active light-regulating and temperature-regulating films, materials and devices, including construction materials. Implementations of the device may be composed of five basic elements: one or more transparent substrates, a transparent surface treatment, a liquid crystal mixture, a stabilizing polymer, and spacer beads. The polymer-stabilized liquid crystal is coated and cured on at least one substrate. The transparent surface treatment and the stabilizing polymer network are selected to provide phase separation, curing, and adhesion within the LC mixture. The substrate or substrates may be polarizing or nonpolarizing.

Claims

1. A resizable polymer-stabilized, thermotropic liquid crystal device comprising

a transparent substrate;

a mixture of liquid crystal components coating the substrate and having a clearing point within a typical range of atmospheric temperatures and a freezing point below an expected minimum atmospheric temperature;

a means of defining a thickness of the coating of the mixture of liquid crystal components; and

a stabilizing polymer provided in conjunction with the mixture of liquid crystal components on the substrate that cures under the influence of an external stimulus.

2. The device of claim 1 further comprising a surface treatment provided on the substrate that promotes polymer adhesion with the substrate and that is wholly or partially transparent or translucent to one or more wavelength bands.

3. The device of claim 1, wherein the stabilizing polymer adheres to the substrate, the surface treatment, or both.

4. The device of claim 1, wherein the means of defining the thickness comprises a plurality of micro-scale spacers distributed within the mixture of liquid crystal components.

5. The device of claim 1 further comprising

a transparent opposing substrate;

and

a surface treatment provided on the substrate and the transparent opposing substrate that promotes polymer adhesion with the substrate and the transparent opposing substrate and that is wholly or partially transparent or translucent to one or more wavelength bands;

wherein

the means of defining the thickness comprises a plurality of micro-scale spacers distributed within the mixture of liquid crystal components; and

the opposing substrate is placed over the mixture of liquid crystal components, the micro-scale spacers, and the stabilizing polymer on the substrate and adhered to the stabilizing polymer.

6. The device of claim 2, wherein the surface treatment functions as an alignment layer for the mixture of liquid crystal components.

7. The device of claim 2, wherein the surface treatment is an integral feature of the substrate.

8. The device of claim 2, wherein the surface treatment comprises an application of one or more of the following materials to the substrate:

ethyl cyanoacrylates, methyl cyanoacrylates, thiol-ene adhesives, diacrylates, triacrylates, methacrylates, urethane acrylates, acrylated epoxies, polyimides, polystyrenes, vinyl polymers, fluoropolymers, ionenes, polyalkenes, nylons, and polyesters.

9. The device of claim 1, wherein the stabilizing polymer is distributed throughout the mixture of liquid crystal components.

10. The device of claim 1, wherein the stabilizing polymer is formed in a pattern on the substrate.

11. The device of claim 9, wherein the mixture of liquid crystal components is miscible with the stabilizing polymer and the stabilizing polymer forms a matrix within which the mixture of liquid crystal components is retained.

12. The device of claim 1, wherein the stabilizing polymer is phase separated from the mixture of liquid crystal components.

13. The device of claim 5, wherein the stabilizing polymer is positioned about an outer perimeter of the mixture of liquid crystal components and seals an outer edge between the substrate and the opposing substrate.

14. The device of claim 1, wherein the means for defining the thickness comprises patterned protrusions on a surface of the substrate.

15. The device of claim 1, wherein the external stimulus comprises one or more of light, heat, or ultraviolet radiation.

16. The device of claim 1, wherein the mixture of liquid crystal components is stable upon exposure to ultraviolet radiation.

17. The device of claim 5, wherein the stabilizing polymer network provides partial or total retention of the mixture of liquid crystal components within the substrate and the opposing substrate.

18. The device of claim 1, wherein the mixture of liquid crystal components is suitable for use in twisted nematic devices.

19. The device of claim 1, wherein the mixture of liquid crystal components is suitable for use in guest-host devices.

20. The device of claim 1, wherein the mixture of liquid crystal components has a clearing point between 0°

C. and 50°

C.

21. The device of claim 1, wherein the stabilizing polymer includes a photoinitiator or a thermal initiator.

22. A method for manufacturing a resizable polymer-stabilized, thermotropic liquid crystal device comprising

providing a transparent substrate;

coating the substrate with a mixture of liquid crystal components having a clearing point within a typical range of atmospheric temperatures and a freezing point below an expected minimum atmospheric temperature;

defining and maintaining a thickness of the mixture of liquid crystal components;

applying a stabilizing polymer to the substrate in conjunction with the mixture of liquid crystal components; and

curing the stabilizing polymer with an external stimulus to adhere the stabilizing polymer.

23. The method of claim 22 further comprising

treating a surface of the substrate with a material that is wholly or partially transparent or translucent to one or more wavelength bands and that promotes polymer adhesion with the substrate.

24. The method of claim 22, wherein the defining and maintaining operations further comprise distributing a plurality of micro-scale spacers within the mixture of liquid crystal components.

25. The method of claim 22 further comprising

providing a transparent opposing substrate;

treating a surface of the substrate and the opposing substrate with a wholly or partially transparent or translucent material that promotes polymer adhesion with the opposing substrate;

distributing a plurality of micro-scale spacers within the mixture of liquid crystal components as part of the defining and maintaining operations;

placing the opposing substrate over the mixture of liquid crystal components, the micro-scale spacers, and the stabilizing polymer on the substrate; and

adhering the opposing substrate with the surface treatment material to the stabilizing polymer.

26. The method of claim 25 further comprising cutting the resizable polymer-stabilized, thermotropic liquid crystal device with negligible or no leakage of the mixture of liquid crystal components from between the substrate and the opposing substrate.

27. The method of claim 22 further comprising removing the transparent substrate from the mixture of liquid crystal components and the stabilizing polymer after curing the stabilizing polymer.

28. The method of claim 22 further comprising applying the external stimulus uniformly across the device.

29. The method of claim 22 further comprising applying the external stimulus non-uniformly to produce a deliberate pattern of the stabilizing polymer across the device.

30. The method of claim 22, wherein the applying operation further comprises applying the stabilizing polymer in a pattern across the substrate.

31. The method of claim 22, wherein the mixture of liquid crystal components is miscible with the stabilizing polymer and the curing operation creates a matrix of the stabilizing polymer within which the mixture of liquid crystal components is retained.

32. The method of claim 25, wherein the applying operation further comprises applying the stabilizing polymer about an outer perimeter of the mixture of liquid crystal components and sealing an outer edge between the substrate and the opposing substrate.

33. The method of claim 22, wherein the curing operation comprises one of the following:

solidifying the stabilizing polymer, melting and re-solidifying the stabilizing polymer, or cross-linking the stabilizing polymer.

34. The method of claim 22, wherein the curing operation comprises one of the following actions with respect to the stabilizing polymer:

heating, photo-initiation, visible light exposure, ultraviolet exposure, electron beam, epoxy curing, application of water, changing solvent concentration, or providing a chemical accelerant.

35. The method of claim 23 further comprising including a photoinitiator or a thermal initiator in the transparent or translucent surface treatment material.

36. The method of claim 22 further comprising selecting a formulation for the mixture of liquid crystal components with an index of refraction that is substantially the same as an index of refraction of the stabilizing polymer or vice versa.

37. The method of claim 22 further comprising modifying the clearing point to be higher or lower than the typical range of atmospheric temperatures, such that thermotropic properties of the mixture of liquid crystal components are effected at operating temperatures expected in non-atmospheric temperature environments.