Liquid crystalline light modulating device and material

• US 5,695,682 A
• Filed: 02/24/1997
• Issued: 12/09/1997
• Est. Priority Date: 05/02/1991
• Status: Expired due to Term

• Current Assignee: Kent State University
• Original Assignee: Kent State University
• Inventors: Yang, Deng-ke, Chien, Liang-Chy, Doane, J. William
• Primary Examiner(s): TUCKER, PHILIP C
• Application Number:
  US08/803,838
• Time in Patent Office: 288 Days
• Field of Search: 252/299.01, 252/299.5, 349/169
• US Class Current: 252/299.01
• CPC Class Codes: C09K 19/02 characterised by optical, electrical or physical properties of the components, in general
• CPC Class Codes: C09K 19/542 Macromolecular compounds
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: C09K 19/586 Optically active dopants; chiral dopants
• CPC Class Codes: G02F 1/0131 based on photo-elastic effects, e.g. mechanically induced birefringence
• CPC Class Codes: G02F 1/13345 Network or three-dimensional gels
• CPC Class Codes: G02F 1/13347 working in reverse mode, i.e. clear in the off-state and scattering in the on-state
• CPC Class Codes: G02F 1/13718 based on a change of the texture state of a cholesteric liquid crystal
• CPC Class Codes: G02F 1/13775 Polymer-stabilized liquid crystal layers

Abstract

A new liquid crystalline light modulating cell and material are characterized by liquid crystalline light modulating material of liquid crystal and polymer, the liquid crystal being a chiral nematic liquid crystal having positive dielectric anisotropy and including chiral material in an amount effective to form focal conic and twisted planar textures, the polymer being distributed in phase separated domains in the liquid crystal cell in an amount that stabilizes the focal conic and twisted planar textures in the absence of a field and permits the liquid crystal to change textures upon the application of a field. In one embodiment, the material is light scattering in a field-OFF condition and optically clear in a field-ON condition, while in another embodiment, the material is optically clear in a field-OFF condition and light scattering in a field-ON condition. In still another embodiment, the material exhibits stability at zero field in a colored, light reflecting state, a light scattering state and multiple stable reflecting state therebetween, as well as being optically clear in the presence of a field.

Claims

1. A method of selectively adjusting the intensity of reflection of colored light from a light modulating material of chiral nematic liquid crystal and polymer, between a maximum and a minimum intensity comprising subjecting said material to varying electric field pulses of sufficient duration and voltage to cause a first proportion of said chiral nematic material to exhibit a first optical state and a second proportion of said chiral nematic material to exhibit a second optical state, whereby said material will continuously reflect a selected intensity between said maximum and minimum that is proportional to the magnitude of the electric field pulse wherein said chiral nematic material in said first optical state exhibits a reflective planar texture and said chiral nematic material in said second optical state exhibits a transparent focal conic texture wherein both optical states are stable in the absence of a field.

2. The method according to claim 1 comprising applying square A.C. voltage pulses.

3. The method according to claim 2 comprising applying A.C. voltage pulses at a magnitude below that which will switch said material from said first optical state to said second optical state.

4. A method of addressing a light modulating cell comprising polymer and chiral nematic liquid crystalline light modulating material having positive dielectric anisotropy and a pitch length effective to reflect light in the visible spectrum, cell wall structure cooperating with said liquid crystal to form focal conic and twisted planar textures that are stable in the absence of a field, and means for addressing said liquid crystal material, said method comprising selectively applying voltage pulses to said material of a magnitude effective to transform at least a portion of said liquid crystal from a transparent light scattering focal conic texture to a light reflecting twisted planar texture, or to transform at least a portion of said liquid crystal from a light reflecting twisted planar texture to a transparent light scattering focal conic texture, whereby the amount of transformation is dependent on the magnitude of the voltage pulse and wherein both focal conic and twisted planar textures are simultaneously stable in the absence of a field.

5. The method according to claim 4 comprising selectively switching said material to a light reflecting twisted planar structure following the sudden removal of a voltage pulse effective to homeotropically align the liquid crystal, and a light scattering focal conic texture following removal of a voltage pulse below that which will homeotropically align the liquid crystal.

6. The method according to claim 4 comprising applying square A.C. voltage pulses.