Light modulating materials comprising a liquid crystal microdroplets dispersed in a birefringent polymeric matri method of making light modulating materials

• US 5,240,636 A
• Filed: 03/30/1992
• Issued: 08/31/1993
• Est. Priority Date: 04/11/1988
• 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): Stoll, Robert L.
• Assistant Examiner(s): WU, SHEAN CHIU
• Application Number:
  US07/860,114
• Time in Patent Office: 519 Days
• Field of Search: 252/299.01, 252/299.5, 428/1, 359/103, 359/104, 359/93, 359/94, 359/246, 359/251, 359/256, 359/283
• 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: 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 which is birefringent and possesses anisotropic optical properties similar to those of the dispersed liquid crystal 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 liquid crystal phase structure and configuration of the light shutter device.

Claims

1. A method of making a light modulating liquid crystal material having the characteristic of displaying haze-free transparency for all directions of incident light comprising the steps of forming a liquid crystal phase interspersed with a birefringent, light transmissive polymeric phase, the liquid crystal phase and polymer phase having matched ordinary and extraordinary indices of refraction and aligning the optical axis of the polymer phase relative to a surface of the material, whereby haze-free transparency is obtained by aligning the optical axis of the liquid crystal phase parallel to the optical axis of the polymer phase, and the material is rendered opaque by mismatching the effective refractive indices of the liquid crystal phase and polymer phase.

2. The method of claim 1 wherein the step of aligning the optical axis of the polymer phase is carried out so that the optical axis of the polymer phase is normal to a viewing surface of the material.

3. The method of claim 1 wherein the step of aligning the optical axis of the polymer phase is carried out by applying an electric or magnetic field to the material.

4. The method of claim 3 including the step of fixing the alignment of the optical axis of the polymer phase so that it is maintained when the electric or magnetic field is removed.

5. The method of claim 4 wherein the step of fixing is carried out by cross-linking the polymer phase.

6. A method of making a liquid crystal light modulating material comprising the steps of forming a solution of liquid crystal, curing agent, and uncured synthetic resin, one of the curing agent or resin having mesogenic units, and thereafter curing the solution to induce spontaneous formation of a liquid crystal phase interspersed with a liquid-crystal-side-group polymeric synthetic resin phase, the step of curing the solution being carried out in an electric or magnetic field effective to align the liquid-crystal side-groups and the liquid crystal phase and the mesogenic units being selected to have matching ordinary and extraordinary indices of refraction after the resin is cured to provide haze-free transparency in one of a field-ON or field-OFF condition.

7. The method of claim 6 including the step of cross-linking the liquid-crystal-side-groups to cause permanent alignment relative to a surface of the material.

8. The method of claim 7 wherein the step of cross-linking is carried out by photochemical, thermal, free radical, or x-ray inducement.

9. A method of making a liquid crystal light modulating material comprising the steps of forming a solution of liquid crystal, mesogenic synthetic resin, and a solvent, and thereafter removing the solvent to induce spontaneous formation of a liquid crystal phase interspersed with a liquid-crystal-side-group polymeric synthetic resin phase, the step of removing the solvent being carried out in an external electric or magnetic field effective to align liquid-crystal-side-groups of the polymeric phase and the liquid crystal phase and the polymeric phase having matched ordinary and extraordinary indices of refraction to provide haze-free transparency in one of a field-ON or field-OFF condition.

10. The method of claim 9 including a step of cross-linking a liquid-crystal-side-group of the polymeric phase to cause permanent alignment relative to a surface of the material.

11. The method of claim 10 wherein the step of cross-linking is carried out by photochemical, thermal, free radical, or x-ray inducement.

12. A method of making a liquid crystal light modulating material comprising the steps of heating a mixture of liquid crystal and a birefringent synthetic liquid-crystalline-side-group resin to form a homogeneous solution of the liquid crystal and resin, and thereafter cooling the solution to induce spontaneous formation of a liquid crystal phase interspersed with a polymer phase having liquid-crystalline-side-groups, the step of cooling the solution being carried out in an external electric or magnetic field effective to align the liquid-crystal-side-groups and the liquid crystal phase and the liquid-crystalline-side-groups having matching ordinary and extraordinary indices of refraction to provide haze-free transparency in one of a field-ON or field-OFF condition.

13. The method of claim 12 including the step of cross-linking the liquid-crystal-side-groups to cause permanent alignment relative to a surface of the material.

14. The method of claim 13 wherein the step of cross-linking is carried out by photochemical, thermal, free radical, or x-ray inducement.

15. The method of claim 14 wherein the birefringent synthetic liquid-crystalline-side-group resin is formed from an optically isotropic synthetic resin and a mesogenic curing agent the step of thermal inducement of cross-linking is carried out at a temperature above a curing temperature at which the synthetic resin was cured with the mesogenic curing agent.