Color liquid crystal display consisting of polymer-dispersed chiral liquid crystal having negative dielectric anisotropy

• US 5,200,845 A
• Filed: 03/25/1992
• Issued: 04/06/1993
• Est. Priority Date: 10/31/1989
• Status: Expired due to Fees

• Current Assignee: University of Hawaii at Manoa
• Original Assignee: University of Hawaii at Manoa
• Inventors: Crooker, Peter P., Yang, Dengke
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Duong, Tai V.
• Application Number:
  US07/857,678
• Time in Patent Office: 377 Days
• Field of Search: 350/346, 350/350 S, 350/351, 350/350 R, 350/334, 350/336, 350/331 R
• US Class Current: 349/175
• 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 1/13476 in which at least one liquid crystal cell or layer assumes a scattering state
• CPC Class Codes: G02F 1/13718 based on a change of the texture state of a cholesteric liquid crystal
• CPC Class Codes: G02F 2201/343 cholesteric liquid crystal reflector
• CPC Class Codes: G02F 2203/02 reflective

Abstract

A color liquid crystal display and display material formed by microdroplets of chiral or cholesteric liquid crystal phase dispersed in a polymeric matrix. The liquid crystal in the microdroplets exhibits strong negative dielectric anisotropy so that in the presence of an electric field the helical planes of the chiral material align perpendicular to the field. Incident light is reflected at a selected wavelength depending upon the helical pitch. In the field-OFF state, the liquid crystal directors are configured or randomly oriented so as to scatter incident light.

Claims

1. A liquid crystal color display comprising at least one sheet of liquid crystal material formed by microdroplets of liquid crystal having a generally spherical shape and a diameter of about 1-20 μ

m dispersed in a polymeric matrix by phase separation, said liquid crystal being in the cholesteric phase and having negative dielectric anisotropy of at least -3, said material being further characterized in that;

the liquid crystal in said microdroplets has a liquid crystal director configuration or a random orientation in the absence of an electric field so that incident light is scattered, and

the application of an electric field is effective to cause the cholesteric liquid crystal in said microdroplets to align perpendicular to the direction of the field to form a planar helical texture having a helical pitch so as to selectively reflect light of a wavelength determined by the helical pitch of the chiral liquid crystal.

2. A display according to claim 1 incorporating at least two sheets of liquid crystal material, said sheets being stacked and each sheet reflecting a different primary color.

3. A display according to claim 1 or claim 2 including electrode means on outer sheet surfaces for establishing said field.

4. A liquid crystal color display comprising layers of liquid crystal material formed by microdroplets of chiral liquid crystal having a generally spherical shape and a diameter of about 1-20 μ

m dispersed in a polymeric matrix by phase separation, said chiral liquid crystal having negative dielectric anisotropy of at least -3, said material being further characterized in that;

the liquid crystal in said microdroplets has a liquid crystal director configuration or a random orientation in each layer in the absence of an electric field so that incident light is scattered,

the application of an electric field is effective to cause the chiral liquid crystal in said microdroplets to align perpendicular to the direction of the field to form a planar helical texture having a helical pitch so as to selectively reflect light of a wavelength determined by the helical pitch of the chiral liquid crystal,

a plurality of said layers have chiral liquid crystal of different helical pitches so that each layer will reflect a different color of light, said layer being vertically arranged to form a stacked array, and

means for selectively applying a voltage to each of said plurality of layers.

5. The display according to claim 4 wherein one of said layers reflects red light, another reflects green light and a third reflects blue light.

6. A display according to claim 4 or claim 5 wherein said device is operative in a reflecting mode to achieve a range of reflected colors by additive color mixing.

7. A display according to claim 4 or claim 5 which is operative in transmission to achieve a range of colors by subtractive color mixing.