Liquid crystal light valve method and apparatus using right and left-handed twist cholesteric liquid crystal

• US 4,688,901 A
• Filed: 06/11/1984
• Issued: 08/25/1987
• Est. Priority Date: 06/11/1984
• Status: Expired due to Fees

• Current Assignee: Molecular Control Corporation
• Original Assignee: Johnson Light Valve Incorporated
• Inventors: Albert, Richard
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/619,576
• Time in Patent Office: 1,170 Days
• Field of Search: 350/350 R, 350/351
• US Class Current: 349/86
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: F24S 50/80 for controlling collection or absorption of solar radiation
• CPC Class Codes: G02B 5/3016 involving passive liquid crystal elements optical properties of liquid crystals G02F1/0063; polarising elements associated with active liquid crystal devices G02F1/133528
• CPC Class Codes: G02F 1/132 Thermal activation of liquid crystals exhibiting a thermo-optic effect
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: Y02E 10/40 Solar thermal energy, e.g. solar towers
• CPC Class Codes: Y10S 359/90 Methods

Abstract

A liquid crystal light valve is provided which either reflects or transmits all wavelengths of light. Micron size cholesteric liquid crystal micelles are formed by adding a chiral molecule dopant to a nematic liquid and dispersing into a polymeric solution. The chiral dopant twists the micelle into a helical planar order along a helical axis. The interior structure of the micelle is a series of concentric spheres, the distance between the envelopes of which is the pitch. The pitch of the helical planar order of the micelles is adjusted by varying the concentration of chiral molecules which have been added to the nematic liquid. The sense of the helical planar order of the micelles is controlled and the micelles are dispensed in an inert polymeric binder forming a film which may be applied to a surface for controlling the light applied thereto either passing or reflecting the light depending on the temperature of the film. The light valve is controlled in one way by controlling the right and left hand sense of the helical planar order of the micelles by adding equal amounts of chiral dopants which have right and left handed orders.

Claims

1. The method of making a light valve which reflects or transmits all wavelengths of light comprising the steps of:

forming micron sized cholesteric liquid crystal micelles by adding a chiral molecule dopant to a nematic liquid dispersion which twists the micelle into a helical planar order along a helical axis,

adjusting the pitch of the helical planar order of the micelles by varying the concentration of chiral molecules,

controlling the sense of the helical planar order of said micelles,

dispensing said micelles in an inert polymeric binder forming a film which may be applied to a surface to which light to be controlled is applied for controlling the reflection or transmission of said light depending on the temperature of said film,

applying said film between a quarter wave plate and a plastic polarizer in which the optical axis of the polarizer is at 45% to optical axis of the quarter wave plate whereby no light passes above the transition temperature of said film.

2. The method of making a light valve which reflects or transmits all wavelengths of light comprising the steps of:

forming micron sized cholesteric liquid crystal micelles by adding a chiral molecule dopant to a nematic liquid dispersion which twists the micelle into a helical planar order along a helical axis,

adjusting the pitch of the helical planar order of the micelles by varying the concentration of chiral molecules,

controlling the sense of the helical planar order of said micelles,

dispensing said micelles in an inert polymeric binder forming a film which may be applied to a surface to which light to be controlled is applied for controlling the reflection or transmission of said light depending on the temperature of said film,

controlling the helical planar order of said micelles comprises adding equal amounts of right-handed and left-handed sense chiral dopant to said nematic liquid, and

coating the front and back surfaces of a half-wave plate with said film.

3. A light valve for transmitting and reflecting light in accordance with temperature comprising:

a polymeric film having micelles of liquid crystal material containing chiral dopants dispersed therein,

said micelles formed in groups which reflect light from 400 to 600 nanometers in 20 nanometer increments with each group repeated twice to reflect both left and right circularly polarized light,

said light valve being turned on when a phase transition temperature brings the micelles from a smectic to the cholesteric state.

4. The light valve as claimed in claim 3 wherein a first series of micelle groups are formed of CE2 to E-8 with the weight of CE2 in a range of 15 to 24% in increments of 0.8% and a second series of micelles formed with the optical enantioner of CE2 over the same composition range as said first series.

6. The light valve as claimed in claim 3 having a third group of micelles varied to provide a helical pitch in said film in a range of 8 to 15 microns whereby light applied to said film is reflected in the range of 8 to 15 microns below 20°

C. while being transmitted above that temperature.

5. A light valve for transmitting or reflecting on a broad band basis light applied thereto in accordance with the ambient temperature comprising:

a polymeric film having micelles of liquid crystal material dispersed therein,

said micelles being formed in a liquid crystalline material with said chiral additives in the form of an optically active molecule, said micelles having a diameter in the range of 2-10μ and

having the same direction sense,

a quarter wave plate having said polymeric film mounted to the back surface thereof,

a polarizer mounted on the front surface of said quarter wave plate, said polarizer having an optical axis making a 45°

angle with the optical axis of said quarter wave plate whereby light applied to said valve passes below the transition temperature of said cholesteric material in said film and is extinguished above the transition temperature.

7. A light valve for transmitting and reflecting light in accordance with temperature comprising:

a polymeric film having micelles of liquid crystalline material having chiral dopants dispersed therein,

said micelles formed in groups with the chiral dopants having the same sense which groups reflect light from 400 to 600 nanometers in 20 nanometer increments,

a half wave plate coated on the front and back surfaces with said polymeric film whereby light applied to the front surface of said half wave plate has its circular polarization reversed and is reflected from the back surface below the transition temperature of said film.

8. The method of making a light valve which reflects or transmits substantially 100% of incident light at all or selected wavelengths comprising the steps of:

preparing cholesteric liquid crystal compositions by varying the concentration of chiral molecules in order to scatter the desired wavelength and polarization by preparing two cholesteric liquid crystal compositions for each selected wavelength, one with right-handed chirality and the other with left-handed chirality,

dispensing separately for each wavelength and polarization said cholesteric liquid crystal compositions into an inert binder in which the liquid crystalline material remains undissolved and exists as a discontinuous phase within the continuous phase of the inert binder, and

mixing the dispersions of liquid crystalline material for forming a system of dispersed liquid crystalline material which contains equal concentrations of dispersed bodies of opposite chirality for each wavelength.

9. The method of claimed in claim 8, in which said dispersed bodies are micelles and the mixing step is performed such that said micelles are combined with little agitation such that each micelle maintains its own chiral identity.

10. The method of making a light valve which reflects or transmits substantially 100% of incident light at all or selected wavelengths comprising the steps of:

preparing cholesteric liquid crystal compositions by varying the concentration of chiral molecules in order to scatter the desired wavelength and polarization by preparing two cholesteric liquid crystal compositions for each selected wavelength, one with right-handed chirality and the other with left-handed chirality,

dispensing separately for each wavelength and polarization said cholesteric liquid crystal compositions into an inert polymeric binder in which the liquid crystalline material remains undissolved and exists as a discontinuous phase within the continuous phase of the inert polymeric binder,

mixing the dispersions of liquid crystalline material for forming a system of dispersed liquid crystalline material which contains unequal concentrations of micelles of left-handed and right-handed chiral bodies for selected wavelengths, and includes cholesteric material which scatters light in the 3 to 15 micrometer/region, the visible and near infrared region and includes compositions which scatter light of non-contiguous regions of the spectrum.