Light modulating materials comprising a liquid crystal phase dispersed in a birefringent polymeric phase

• US 4,994,204 A
• Filed: 03/20/1989
• Issued: 02/19/1991
• Est. Priority Date: 11/04/1988
• Status: Expired due to Term

• Current Assignee: Kent State University
• Original Assignee: Kent State University
• Inventors: West, John L., Doane, Joseph W.
• Primary Examiner(s): Maples, John S.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/324,051
• Time in Patent Office: 701 Days
• Field of Search: 428/1, 252/299.01, 252/299.5, 350/334, 350/347 E, 350/348, 350/347 R
• US Class Current: 252/299.01
• CPC Class Codes: C09K 19/38 Polymers
• 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: 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 haze-free light modulating polymer dispersed liquid crystal (PDLC) material is disclosed which comprises a polymer matrix which is birefringent and possesses anisotropic optical properties similar to those of the dispersed liquid crystal microdroplets such that the PDLC material in its transparent state exhibits a refractive index that is matched for all directions of incident light providing for an optically clear, scatter-free film for all angles of view. Electrooptic light shutters are possible from this material which are transparent in the field OFF-state and opaque in the field ON-state or vice versa, depending upon the microdroplet structure and configuration of the light shutter device.

Claims

1. A light modulating liquid crystal material comprising a liquid crystal phase interspersed with a birefringent, light transmissive polymer, the effective indices of refraction of the liquid crystal phase and the polymer being matched for all directions of incident light so that the material is transparent and haze-free in one of a field-ON state or a field-OFF state, and the effective indices of refraction are mismatched for all directions of incident light so that the material is opaque in the other of the field-ON state or field-OFF state.

2. The material of claim 1 wherein the liquid crystal phase has ordinary and extraordinary indices of refraction which are respectively matched to the ordinary and extraordinary indices of refraction of the polymer, the material being transparent and haze-free when the optical axes of the liquid crystal phase and the polymer are aligned and being opaque when the optical axes of the liquid crystal phase and the polymer are not aligned.

3. The material of claim 1 wherein the polymer is a liquid crystal polymer.

4. The material of claim 3 wherein the polymer comprises a liquid-crystal-side-group.

5. The material of claim 1 wherein the polymer comprises a liquid-crystal-side-group polymeric epoxy.

6. The material of claim 4 wherein at least one of the liquid-crystal-side-groups comprises a cyanobiphenyl.

7. The material of claim 1 wherein the liquid crystal phase exhibits a frequency dependent dielectric anisotropy.

15. A material according to claim 1 wherein the polymer comprises a polymer matrix and the liquid crystal phase comprises microdroplets of liquid crystal dispersed in the polymer matrix.

8. A light modulating liquid crystal material comprising a first optically birefringent phase dispersed in a second optically birefringent phase, one of said first and second birefringent phases comprising a polymer phase having mesogenic moieties with optical axes aligned relative to a surface of the material, the other of said first and second birefringent phases comprising a liquid crystal phase, and the ordinary and extraordinary indices of refraction of the first and second birefringent phases being matched, whereby the material is transparent and haze-free at all viewing angles when the optical axes of the liquid crystal phase and the mesogenic moieties are aligned, and the material is opaque when the optical axes of the liquid crystal phase and the mesogenic moieties are unaligned.

9. The material of claim 8 wherein the second birefringent phase consists essentially of a liquid-crystal-side-group polymer and the first birefringent phase consists essentially of a liquid crystal.

10. The material of claim 9 wherein the liquid-crystal-side-group polymer comprises liquid-crystal-side-groups having a labile moiety capable of cross-linking with another moiety identical to itself.

11. The material of claim 10 wherein the moieties are cross-linked to permanently align the liquid-crystal-side-groups.

16. A material according to claim 8 wherein the first birefringent phase is the liquid crystal phase and the second birefringent phase is the polymer phase.

12. A fail-safe, light modulating liquid crystal material comprising microdroplets of liquid crystal exhibiting negative dielectric anisotropy dispersed in a light transmissive, liquid-crystal-side-group polymeric synthetic resin matrix, the ordinary and extraordinary indices of refraction of the microdroplets being respectively matched to the ordinary and extraordinary refractive indices of the matrix, the liquid-crystal-side-groups exhibiting positive dielectric anisotropy, and the optical axes of the matrix and microdroplets being perpendicular to a viewing surface of the material, whereby the material is transparent in the absence of an applied field and is opaque in the presence of an applied field.

13. A fail-safe, light modulating liquid crystal material comprising a light transmissive, liquid crystal polymeric synthetic resin matrix containing microdroplets of liquid crystal, the ordinary and extraordinary indices of refraction of the microdroplets and the matrix being respectively matched, and the optical axes of the microdroplets and matrix being aligned parallel in a direction oblique to the viewing angle of incident light, and the microdroplets being responsive to an applied field to misalign the optical axes of the microdroplets and whereby the material is opaque in the ON-state.

14. A light modulating liquid crystal material comprising discrete quantities of liquid crystal contained in a birefringent solid, the discrete quantities of liquid crystal having ordinary and extraordinary indices of refraction which are respectively matched to ordinary and extraordinary indices of refraction of the matrix so that the material is light-transmissive when the optical axes of the microdroplets and matrix are aligned.

17. A light modulating liquid crystal material comprising a first optically birefringent phase dispersed in a second optically birefringent phase, one of said first and second birefringent phases comprising a polymer phase having mesogenic moieties and the other of said first and second birefringent phases comprising a liquid crystal phase;

ordinary and extraordinary indices of refraction of the liquid crystal phase and the mesogenic moieties being matched;

optical axes of the liquid crystal phase and the mesogenic moieties being aligned in the absence of an electric or magnetic field so that the effective indices of refraction of the liquid crystal phase and the mesogenic moieties for all directions of incident light are matched; and

said liquid crystal phase being responsive to an applied electric or magnetic field to reorient the optical axis of the liquid crystal out of alignment with the optical axis of the liquid crystalline polymer phase so that the material is less light transmissive in a field-on state than in a field-off state.