Switchable volume hologram materials and devices

• US 20040091787A1
• Filed: 10/24/2003
• Published: 05/13/2004
• Est. Priority Date: 07/12/1996
• Status: Abandoned Application

• Current Assignee: Science Applications International Corporation
• Original Assignee: Science Applications International Corporation
• Inventors: Bunning, Timothy J., Tondiglia, Vince P., Natarajan, Lalquidi V., Sutehrland, Richard L.
• Application Number:
  US10/691,593
• Publication Number:
  US 20040091787A1
• Time in Patent Office: Days
• US Class Current: 430/1
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• 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 1/13342 Holographic polymer dispersed liquid crystals
• CPC Class Codes: G03F 7/001 Phase modulating patterns, e.g. refractive index patterns
• CPC Class Codes: G03F 7/031 Organic compounds not covered by group G03F7/029
• CPC Class Codes: G03H 1/02 Details of features involved during the holographic process; Replication of holograms without interference recording
• CPC Class Codes: G03H 1/0248 Volume holograms
• CPC Class Codes: G03H 2001/026 Recording materials or recording processes G03H2226/11 takes precedence; corresponding details, see subgroups of G03H2260/00
• CPC Class Codes: G03H 2260/12 Photopolymer
• CPC Class Codes: G03H 2260/33 Having dispersed compound
• CPC Class Codes: Y10T 428/24802 Discontinuous or differential coating, impregnation or bond [e.g., artwork, printing, retouched photograph, etc.]

Abstract

A new photopolymerizable material allows single-step, fast recording of volume holograms with properties that can be electrically controlled. Polymer-dispersed liquid crystals (PDLCs) in accordance with the invention preferably comprise a homogeneous mixture of a nematic liquid crystal and a multifunctional pentaacrylate monomer, in combination with photoinitiator, coinitiator and cross-linking agent. Optionally, a surfactant such as octanoic acid may also be added. The PDLC material is exposed to coherent light to produce an interference pattern inside the material. Photopolymerization of the new PDLC material produces a hologram of clearly separated liquid crystal domains and cured polymer domains. Volume transmission gratings made with the new PDLC material can be electrically switched between nearly 100% diffraction efficiency and nearly 0% diffraction efficiency. By increasing the frequency of the switching voltage, switching voltages in the range of 50 Vrms can be achieved. The optional use of surfactant allows low switching voltages at lower frequencies than without surfactant. In an alternative embodiment, a PDLC material in accordance with the invention can be utilized to form reflection gratings, including switchable reflection gratings. In still further embodiments, a PDLC material in accordance with the invention can be used to form switchable subwavelength gratings. By further processing, static transmission reflection, and subwavelength PDLC materials can be formed.

Claims

1. A slanted hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure:

(a) a polymerizable monomer;

(b) a liquid crystal;

(c) a cross-linking monomer;

(d) a coinitiator; and

(e) a photoinitiator dye;

wherein the hologram has opposing surfaces and a plurality of polymer regions having a first refractive index and polymer-dispersed liquid crystal regions having a second refractive index disposed at an angle to the opposing surfaces of the hologram whereby the symmetry axis of the liquid crystal is disposed at an angle to the opposing surfaces of the hologram.

2. The slanted hologram of claim 1, wherein the polymerizable monomer comprises dipentaerythritol hydroxypentaacrylate.

3. The slanted hologram of claim 1, wherein the polymer-dispersed liquid crystal material further comprises, before exposure, a surfactant.

4. The slanted hologram of claim 1, wherein:

(a) the liquid crystal comprises 10-40% by total weight of the polymer-dispersed liquid crystal material;

(b) the cross-linking monomer comprises 5-15% by total weight of the polymer-dispersed liquid crystal material;

(c) the amount of coinitiator is 10<sup>−

3</sup> to 10<sup>−

4</sup> gram moles; and

(d) the amount of photoinitiator dye is 10<sup>−

5</sup> to 10<sup>−

6</sup> gram moles.

5. The slanted hologram of claim 1, wherein:

(a) the liquid crystal comprises 10-40% by total weight of the polymer-dispersed liquid crystal material;

(b) the cross-linking monomer comprises 10-18% by total weight of the polymer-dispersed liquid crystal material;

(c) the coinitiator comprises 2-3% by total weight of the polymer-dispersed liquid crystal material; and

(d) the photoinitiator dye comprises 0.2-0.4% by total weight of the polymer-dispersed liquid crystal material.

6. The slanted hologram of claim 2, wherein the surfactant comprises about 6% by total weight of the polymer-dispersed liquid crystal material.

7. The slanted hologram of claim 2, wherein the surfactant comprises about 5-10% by total weight of the polymer-dispersed liquid crystal material.

8. The slanted hologram of claim 2, wherein the liquid crystal includes a mixture of cyano biphenyls.

9. The slanted hologram of claim 1, wherein the cross-linking monomer comprises N-vinylpyrrolidone.

10. The slanted hologram of claim 1, wherein the coinitiator comprises N-phenylglycine.

11. The slanted hologram of claim 1, wherein the photoinitiator dye comprises rose bengal ester.

12. The slanted hologram of claim 3, wherein the surfactant comprises octanoic acid.

13. The slanted hologram of claim 4, wherein the polymer-dispersed liquid crystal material further comprises, before exposure, a surfactant.

14. The slanted hologram of claim 5, wherein the polymer-dispersed liquid crystal material further comprises, before exposure, a surfactant.

15. The slanted hologram of claim 4, wherein the polymerizable monomer comprises dipentarythritol hydroxypentaacrylate.

16. The slanted hologram of claim 5, wherein the polymerizable monomer comprises dipentarythritol hydroxypentaacrylate.

17. A slanted hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure:

(a) a polymerizable monomer;

(b) a liquid crystal;

(c) a cross-linking monomer;

(d) a coinitiator; and

(e) a photoinitiator dye;

wherein the hologram has opposing surfaces and a plurality of alternative planes of polymer channels having a first refractive index and polymer-dispersed liquid crystal channels having a second refractive index disposed at an angle to the opposing surfaces of the hologram whereby the symmetry axis of the liquid crystal is disposed at an angle to the opposing surfaces of the hologram.

18. The slanted hologram of claim 17, wherein the polymerizable monomer comprises dipentarythritol hydroxypentaacrylate.

19. The slanted hologram of claim 17, wherein the polymer-dispersed liquid crystal material further comprises, before exposure, a surfactant.

20. The slanted hologram of claim 17, wherein:

(a) the liquid crystal comprises 10-40% by total weight of the polymer-dispersed liquid crystal material;

(b) the cross-linking monomer comprises 5-15% by total weight of the polymer-dispersed liquid crystal material;

(c) the amount of coinitiator is 10<sup>−

3</sup> to 10<sup>−

4</sup> gram moles; and

(d) the amount of photoinitiator dye is 10<sup>−

5</sup> to 10<sup>−

6</sup> gram moles.

21. The slanted hologram of claim 17, wherein:

(a) the liquid crystal comprises 10-40% by total weight of the polymer-dispersed liquid crystal material;

(b) the cross-linking monomer comprises 10-18% by total weight of the polymer-dispersed liquid crystal material;

(c) the coinitiator comprises 2-3% by total weight of the polymer-dispersed liquid crystal material; and

(d) the photoinitiator dye comprises 0.2-0.4% by total weight of the polymer-dispersed liquid crystal material.

22. The slanted hologram of claim 18, wherein the surfactant comprises about 6% by total weight of the polymer-dispersed liquid crystal material.

23. The slanted hologram of claim 18, wherein the surfactant comprises about 5-10% by total weight of the polymer-dispersed liquid crystal material.

24. The slanted hologram of claim 18, wherein the liquid crystal includes a mixture of cyano biphenyls.

25. The slanted hologram of claim 17, wherein the cross linking monomer comprises N-vinylpyrrolidone.

26. The slanted hologram of claim 17, wherein the coinitiator comprises N-phenylglycine.

27. The slanted hologram of claim 17, wherein the photoinitiator dye comprises rose bengal ester.

28. The slanted hologram of claim 19, wherein the surfactant comprises octanoic acid.

29. The slanted hologram of claim 20, wherein the polymer-dispersed liquid crystal material further comprises, before exposure, a surfactant.

30. The slanted hologram of claim 21, wherein the polymer-dispersed liquid crystal material further comprises, before exposure, a surfactant.

31. The slanted hologram of claim 20, wherein the polymerizable monomer comprises dipentarythritol hydroxypentaacrylate.

32. The slanted hologram of claim 21, wherein the polymerizable monomer comprises dipentarythritol hydroxypentaacrylate.

33. A static hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure:

(a) a polymerizable monomer;

(b) a liquid crystal;

(c) a cross-linking monomer;

(d) a coinitiator; and

(e) a photoinitiator dye;

wherein the hologram has a plurality of polymer regions having a first refractive index and polymer-dispersed liquid crystal regions having a second refractive index wherein at least a portion of the liquid crystal in the polymer-dispersed liquid crystal regions has been removed.

34. A static hologram made by exposing an interference pattern inside a polymer-dispersed liquid crystal material, the polymer-dispersed liquid crystal material comprising, before exposure:

(a) a polymerizable monomer;

(b) a liquid crystal;

(c) a cross-linking monomer;

(d) a coinitiator; and

(e) a photoinitiator dye;

wherein the hologram has a plurality of alternating planes of polymer channels having a first refractive index and polymer-dispersed liquid crystal channels having a second refractive index wherein at least a portion of the liquid crystal in the polymer-dispersed liquid crystal channels has been removed.

35. A method for preparing static hologram, comprising:

disposing a polymer-dispersed liquid crystal material between transparent plates;

exposing an interference pattern inside the polymer-dispersed liquid crystal material thereby forming a hologram having polymer regions having a first refractive index and polymer-dispersed liquid crystal regions having a second refractive index; and

removing at least a portion of the liquid crystal in the polymer-dispersed liquid crystal channels.

37. The method of claims 35 or 36, wherein a portion of the liquid crystal in the polymer-dispersed liquid crystal channels is removed by disposing the hologram in a solvent.

36. A method for preparing a static hologram, comprising:

disposing a polymer-dispersed liquid crystal material between transparent plates;

exposing an interference pattern inside the polymerdispersed liquid crystal material thereby forming a hologram having alternating planes of polymer channels having a first refractive index and polymer-dispersed liquid crystal channels having a second refractive index; and

removing at least a portion of the liquid crystal in the polymer-dispersed liquid crystal channels.