Directly formed polymer dispersed liquid crystal light shutter displays

• US 5,270,843 A
• Filed: 08/31/1992
• Issued: 12/14/1993
• Est. Priority Date: 08/31/1992
• Status: Expired due to Term

• Current Assignee: Jiansheng Wang
• Original Assignee: Jiansheng Wang
• Inventors: Wang, Jiansheng
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MAI, HUY KIM
• Application Number:
  US07/938,881
• Time in Patent Office: 470 Days
• Field of Search: 359/51, 359/52, 359/103, 359/106
• US Class Current: 349/90
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 1/13347 working in reverse mode, i.e. clear in the off-state and scattering in the on-state

Abstract

A polymer dispersed liquid crystal display device is provided comprising a copolymer formed from monomers having significantly different reactivities. A reverse mode device is provided consisting of negative liquid crystal microdroplets dispersed in a non-homogeneous polymer matrix consisting of a monomer having a high reactivity and a high surface free energy and another monomer having a low reactivity and has a low surface free energy. The surface active monomer is preferentially distributed at the surface of microdroplets formed by phase separation, causing homeotropic alignment of the liquid crystals.

Claims

1. A polymer-dispersed liquid crystal light shutter device for transmitting and scattering light comprising:

a non-homogeneous light transmissive copolymer matrix; and

droplets of liquid crystal material dispersed in the copolymer matrix.

2. The device of claim 1 wherein the copolymer matrix is comprised of at least two monomers having differing reactivities and the droplets of liquid crystal material are spontaneously formed from solution during solidification of the film.

3. The device of claim 1 wherein the refractive index around the droplets continuously varies with composition of the copolymer and the copolymer composition continuously varies with distance from the surface of the droplets, so as to provide a wider viewing angle of the device.

4. The device of claim 1 wherein the refractive index of the copolymer adjacent to the surface of the droplets is substantially matched with the refractive index of the liquid crystal material formed from solution, so as to provide a wider viewing angle of the device.

5. The device of claim 2 wherein the monomer having higher reactivity is a normal monomer and the monomer having lower reactivity is a surface active monomer, the liquid crystal material is negative type, and the ratio of normal monomer to surface active monomer is selected to produce a homeotropic alignment, the device being reverse mode.

6. The device of claim 2 wherein the monomers are normal monomers and the liquid crystal material is positive type and the display device is normal mode.

7. The device of claim 2 wherein the monomer having higher reactivity has a comb-shaped structure.

8. The device of claim 2 wherein the monomer having lower reactivity has a comb-shaped structure.

9. The device of claim 2 wherein the monomer having lower reactivity has a liquid crystalline structure.

10. The device of claim 2 wherein the copolymer comprises an acrylic or an epoxy resin.

11. The device of claim 2 wherein the monomer having highest reactivity is a normal monomer and at least two monomers having lower reactivity comprise a surface active monomer, the liquid crystal material is negative type, and the ratio of normal monomer to surface active monomer is selected to produce a weak homeotropic alignment, the liquid crystal material being aligned so as to produce less haze in the display.

12. The device of claim 5 wherein the surface-active monomer is comprised of silicon-containing or fluorine-containing groups.

13. The device of claim 5 wherein the surface active monomer is comprised of an acrylic group, amine group, or epoxy group.

14. The device of claim 8 wherein the side chains of the comb-shaped polymer are comprised of silicon or fluorine, so as to align liquid crystal material in the droplets substantially perpendicular to the surface of the film.

15. The device of claim 8 wherein the comb-shaped polymer is comprised of a linking group and a group selected from a group consisting of spacer, mesogenic and tail groups.

16. The device of claim 8 wherein the linking group of the comb-shaped polymer is selected from a group consisting of acrylic, amine and epoxy groups.

17. The device of claim 8 wherein the comb-shaped polymer is comprised of linking, mesogenic and tail groups and the tail group is a long chain comprising silicon or fluorine.

18. A method of forming a polymer-dispersed liquid crystal light shutter device for transmitting and scattering light comprising:

mixing a higher reactivity monomer, a lower reactivity monomer and a liquid crystal material to form a homogeneous solution; and

curing the copolymer.

19. The method of claim 18 wherein the higher reactivity monomer is a normal monomer, the lower reactivity monomer is a surface active monomer and the liquid crystal material is negative type, wherein the ratio of normal monomer to surface active monomer is varied to select an effective composition producing a homeotropic alignment of liquid crystals in the droplets and a reverse mode.

20. The method of claim 18 wherein the monomers are normal monomers and the liquid crystal material is of the positive type, the device produced being normal mode.

21. The method of claim 18 wherein one of the monomers has a comb-shaped structure.

22. The method of claim 19 wherein the surface active monomer is comprised of a silicon-containing or fluorine-containing group.

23. A method for flattening microdroplets of negative liquid crystal material dispersed in a polymer comprising:

applying an electric field to the polymer during the time the microdroplets are spontaneously forming from solution and the liquid crystal material is in an anisotropic state.