# US 10,871,694 B2 · Bistable cholesteric liquid crystal switchable window

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- Number: US 10,871,694 B2
- Document ID: US10871694B2
- Status: Granted
- Kind: B2
- Application number: 16/332,107
- Filed: 2017-09-11
- Published: 2019-11-28
- Granted: 2020-12-22
- Earliest claimed: 2016-09-09
- Assignees: Kent State University
- Applicants: Kent State University
- Inventors: Deng-Ke Yang; Meina Yu
- Web page: https://patentgrep.com/patent/US10871694B2

## CPC

- G02F 1/13718: {based on a change of the texture state of a cholesteric liquid crystal}
- C09K 19/586: {Optically active dopants; chiral dopants}
- E06B 9/24: Screens or other constructions affording protection against light, especially against sunshine; Similar screens for privacy or appearance; {Slat blinds}(operating, guiding or securing devices or arrangements for roll-type closures E06B9/56; free-hanging flexible screens A47H23/00)
- G02F 1/1343: Electrodes {(reflective electrodes G02F1/133553)}
- C09K 2019/0444: {characterized by a linking chain between rings or ring systems, a bridging chain between extensive mesogenic moieties or an end chain group}
- E06B 2009/2464: {featuring transparency control by applying voltage, e.g. LCD, electrochromic panels}
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- C09K: MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- E06B: FIXED OR MOVABLE CLOSURES FOR OPENINGS IN BUILDINGS, VEHICLES, FENCES OR LIKE ENCLOSURES IN GENERAL, e.g. DOORS, WINDOWS, BLINDS, GATES (shades or blinds for greenhouses A01G9/22; curtains A47H; lids for car boots or bonnets B62D25/10; skylights E04B7/18; sunshades, awnings E04F10/00)

## Abstract

A bistable cholesteric liquid crystal switchable window has two stable states in the absence of an applied voltage. A first stable state is a planar state which is transparent or reflective for visible light. A second stable state is a focal conic state which is opaque for visible light. The window can be switched from the first stable state to the second stable state via a first voltage pulse and from the second stable state to the first stable state via a second voltage pulse. The first voltage pulse and the second voltage pulse may have the same frequency.

## Claims

### Claim 1

A bistable cholesteric liquid crystal switchable window having:
two stable states in the absence of an applied voltage;
wherein a first stable state is a planar state which is transparent or reflective for visible light;
wherein a second stable state is a focal conic state which is opaque for visible light;
wherein the bistable window can be switched from the first stable state to the second stable state by a first voltage pulse;
wherein the bistable window can be switched from the second stable state to the first stable state by a second voltage pulse;
wherein the first voltage pulse has a first frequency, the second voltage pulse has a second frequency, and an absolute value of the difference between the first frequency and the second frequency is less than 2000 Hz; and
wherein the first voltage pulse has a first pulse width, the second voltage pulse has a second pulse width, and the first pulse width and the second pulse width are independently within the range of about 0.1 to about 1 seconds.

### Claim 2 (depends on 1)

The bistable cholesteric liquid crystal switchable window of claim 1, comprising:
a liquid crystal layer between two electrodes, wherein the liquid crystal layer comprises a liquid crystal.

### Claim 3 (depends on 2)

The bistable cholesteric liquid crystal switchable window of claim 2, wherein the two electrodes are indium tin oxide electrodes.

### Claim 4 (depends on 2)

The bistable cholesteric liquid crystal switchable window of claim 2, wherein the liquid crystal has twist and bend elastic constants which have a relative difference of less than 30%.

### Claim 5 (depends on 2)

The bistable cholesteric liquid crystal switchable window of claim 2, wherein the liquid crystal layer further comprises an elastic constant adjuster and a chiral dopant.

### Claim 6 (depends on 5)

The bistable cholesteric liquid crystal switchable window of claim 5, wherein the elastic constant adjuster is a dimer.

### Claim 7 (depends on 6)

The bistable cholesteric liquid crystal switchable window of claim 6, wherein the dimer is 1″ 7″-bis(4-cyanobiphenyl-4′-yl) heptane.

### Claim 8 (depends on 5)

The bistable cholesteric liquid crystal switchable window of claim 5, wherein the elastic constant adjuster and the chiral dopant control the transmittance of the scattering focal conic state.

### Claim 9 (depends on 5)

The bistable cholesteric liquid crystal switchable window of claim 5, wherein the elastic constant adjuster has a small bend elastic constant of less than 130% of the twist elastic constant.

### Claim 10 (depends on 5)

The bistable cholesteric liquid crystal switchable window of claim 5, wherein the elastic constant adjuster is a liquid crystal with a bent molecular shape.

### Claim 11 (depends on 5)

The bistable cholesteric liquid crystal switchable window of claim 5, wherein the elastic constant adjuster and the chiral dopant control the transmittance of the transparent planar state.

### Claim 12 (depends on 2)

The bistable cholesteric liquid crystal switchable window of claim 2, further comprising alignment layers between the two electrodes and the liquid crystal layer.

### Claim 13 (depends on 12)

The bistable cholesteric liquid crystal switchable window of claim 12, wherein the alignment layers comprise a polyimide.

### Claim 14 (depends on 1)

The bistable cholesteric liquid crystal switchable window of claim 1, wherein the first pulse width and the second pulse width are the same.

### Claim 15 (depends on 14)

The bistable cholesteric liquid crystal switchable window of claim 14, wherein the pulse width is about 0.5 seconds.

### Claim 16 (depends on 2)

The bistable cholesteric liquid crystal switchable window of claim 2, wherein the liquid crystal layer comprises from about 45 wt % to about 65 wt % of the liquid crystal, from about 20 wt % to about 40 wt % of a dimer, and from about 5 wt % to about 25 wt % of a chiral dopant.

### Claim 17 (depends on 2)

The bistable cholesteric liquid crystal switchable window of claim 2, wherein the liquid crystal layer comprises from about 50 wt % to about 60 wt % of the liquid crystal, from about 25 wt % to about 35 wt % of a dimer, and from about 10 wt % to about 20 wt % of a chiral dopant.

### Claim 18 (depends on 2)

The bistable cholesteric liquid crystal switchable window of claim 2, wherein the liquid crystal layer comprises about 55 wt % of the liquid crystal, about 29 wt % of a dimer, and about 15 wt % of a chiral dopant.

### Claim 19 (depends on 1)

The bistable cholesteric liquid crystal switchable window of claim 1, wherein the first voltage pulse and the second voltage pulse have different pulse widths.

### Claim 20

A method for operating a bistable cholesteric liquid crystal switchable window comprising:
applying a first voltage to the window;
wherein the application of the first voltage changes the window from a first transparent or reflective state to an opaque state;
turning off the first voltage; and
applying a second voltage to the window;
wherein the application of the second voltage changes the window from the opaque state to a second transparent or reflective state;
wherein the first voltage and the second voltage are the same or different;
wherein the first voltage is applied at a first frequency;
wherein the second voltage is applied at a second frequency; and wherein an absolute value of the difference between the first frequency and the second frequency is less than 2000 Hz; and
wherein the first voltage has a first pulse width, the second voltage has a second pulse width, and the first pulse width and the second pulse width are independently within the range of about 0.1 to about 1 seconds.