Color-tunable liquid crystal device

Abstract

A color-tunable liquid crystal device, which is used for solving the problem of existing liquid crystal devices of being incapable of selecting the color of reflected light by changing the voltage. The color-tunable liquid crystal device comprises: two substrates, each electrically connected to a voltage source, a switchable electric field being formed between the two substrates, and the alignment direction of the two substrates being horizontal alignment; and a liquid crystal layer, located between the two substrates, wherein the liquid crystal layer reflects light of various wavelengths, the liquid crystal layer has a liquid crystal material, and the liquid crystal material comprises a negative nematic liquid crystal, a chiral molecule and a salt ion.

Description

Adjustable color liquid crystal element TECHNICAL FIELD

[0001] The present invention relates to an adjustable color liquid crystal element, in particular, an adjustable color liquid crystal element containing salt ions. BACKGROUND

[0002] Liquid crystal materials are an integral part of modern technology, not only applied in display technology, but also widely used in other fields, such as liquid crystal monitors, liquid crystal projection, liquid crystal televisions, liquid crystal microscopes, etc.

[0003] Among various liquid crystal materials, cholesteric liquid crystals are one of the liquid crystal materials that are being developed due to their wide operating temperature range and high stability. Cholesteric liquid crystals are usually formed by doping nematic liquid crystals with chiral molecules, and the distance of 360 degrees rotation of cholesteric liquid crystal molecules is defined as the pitch. The pitch of cholesteric liquid crystal molecules mainly determines the wavelength of light that can be reflected by the liquid crystal material, and therefore has a significant impact on color presentation.

[0004] The pitch of cholesteric liquid crystal materials is not easy to change after manufacturing, so it is difficult to achieve the effect of adjusting the color. In the prior art, high molecular materials or polymer materials must be added to the cholesteric liquid crystal material, and the proportions of the components must be carefully controlled, so that the cholesteric liquid crystal material can produce Helfrich deformation to change the pitch of the cholesteric liquid crystal molecules, thereby achieving the effect of changing color. TECHNICAL PROBLEM

[0005] However, adding high molecular materials to cholesteric liquid crystal materials will have at least the following two disadvantages: first, high molecular materials usually need to be polymerized and cured by irradiating ultraviolet (UV) light, which not only complicates the process steps, but also may affect the liquid crystal material; second, adding high molecular materials to the liquid crystal material will reduce the compatibility of the material with dichroic dyes, and during the polymerization of the high molecular material, the dichroic dyes will be degraded and lose their absorption properties, reducing the usability of the final product.

[0006] Therefore, it is necessary to develop a liquid crystal element that can solve the problem of having to add high molecular materials to adjust the color in the prior art. TECHNICAL SOLUTION

[0007] To solve the above problems, the main purpose of the present invention is to provide an adjustable color liquid crystal element, which can solve the problem that high molecular materials must be added to adjust the color in the prior art by providing the forces provided by the negative liquid crystal and the salt ions, respectively.

[0008] The quantity words "one" and "said" used in the elements and components of the present application throughout the specification and claims are intended to refer to one or at least one, unless otherwise indicated by context. The article "a" is intended to refer to one or at least one, unless otherwise indicated by context. The singular terms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0009] The tunable color liquid crystal element of the present application can include two substrates electrically connected to a voltage source respectively, a switchable electric field formed between the two substrates, wherein the alignment direction of the two substrates is horizontal alignment; a liquid crystal layer between the two substrates, reflecting light of various wavelengths, the liquid crystal layer having a liquid crystal material, and the liquid crystal material including a negative nematic liquid crystal, a chiral molecule and a salt ion.

[0010] Therefore, the tunable color liquid crystal element of the present application can generate Helmholtz deformation by the force provided by the negative liquid crystal and the salt ion respectively, thereby controlling the wavelength of the light reflected by the liquid crystal element to make the liquid crystal element display different colors, which is the effect of the present application.

[0011] The voltage source applies an alternating voltage to the two substrates, and the frequency of the alternating voltage is 60 Hz to 1000 Hz. In this way, the alternating voltage can affect the arrangement of the liquid crystal molecules, so that the liquid crystal layer is in a dynamic scattering state, and has the effect of switching the reflection of light of various wavelengths.

[0012] The concentration of the salt ion is between 0.01% and 1% by weight. In this way, the amount of voltage applied can be optimized by adjusting the concentration of the salt ion, thereby reducing the operating voltage.

[0013] The electric field gradually increases from zero, and the wavelength of the light reflected by the liquid crystal layer decreases accordingly. In this way, adjusting the voltage size can change the arrangement of the liquid crystal molecules to reflect light of different wavelength ranges, thereby having the effect of reflecting light of different colors.

[0014] The concentration of the salt ion is between 0.25 ppm and 100 ppm by weight. In this way, the wavelength distribution of the reflected light can be changed by adjusting the concentration of the salt ion, thereby having the effect of increasing the light adjustment function.

[0015] The electric field gradually increases from zero, and the spectral width of the light reflected by the liquid crystal layer increases accordingly. In this way, adjusting the voltage size can change the spectral width of the reflected light, thereby having the effect of controlling the reflection of monochromatic light or white light.

[0016] The liquid crystal layer switches to reflect light of various colors within a reaction time, and the reaction time is less than 200 milliseconds. In this way, the liquid crystal element can quickly switch the color change, thereby having the effects of reducing image delay and synchronizing vision and operation. Attached Figure Description

[0017] Figure 1: A perspective view of a preferred embodiment of the color-tunable liquid crystal element of the present invention;

[0018] Figure 2: Arrangement of liquid crystal molecules in negative cholesterol liquid crystal material under the action of an electric field;

[0019] Figure 3: The arrangement of liquid crystal molecules, including salt ions, under the influence of an electric field;

[0020] Figure 4: Reflectance spectra of the liquid crystal element of the present invention when different voltages are applied;

[0021] Figure 5: Relationship between peak reflectance wavelength and voltage for liquid crystal elements with different concentrations of salt ions according to the present invention;

[0022] Figure 6: Reflectance spectra of the low-concentration salt ion liquid crystal element of the present invention when different voltages are applied.

[0023] Explanation of reference numerals in the attached figures:

[0024] [This invention]

[0025] 1:Substrate

[0026] 2: Liquid Crystal Layer

[0027] 21: Liquid crystal molecules

[0028] E: Electric field

[0029] S1, S2, S3: Spectral curves

[0030] D1, D2, D3: Polylines. The best embodiment of the present invention

[0031] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments of the present invention are described below in detail with reference to the accompanying drawings.

[0032] Please refer to Figure 1, which is a preferred embodiment of the color-tunable liquid crystal element of the present invention. The color-tunable liquid crystal element includes two substrates 1 and a liquid crystal layer 2, which is located between the two substrates 1.

[0033] The two substrates 1 are separated from each other and arranged oppositely, and preferably arranged parallel to each other, so that the liquid crystal layer 2 has a uniform thickness. The two substrates 1 are preferably transparent composite materials, such as glass, acrylic, plastic, etc., so that light can pass through the two substrates. Each substrate can further include a transparent conductive material, such as indium tin oxide (ITO), nano-silver wire, transparent conductive metal, etc., for electrically connecting a voltage source (not shown) to apply an alternating voltage to the two substrates 1 to generate an electric field between the two substrates 1 and act on the liquid crystal material in the liquid crystal layer 2. The frequency of the alternating voltage is 60 Hz to 1000 Hz, and preferably 60 Hz.

[0034] The liquid crystal material in the liquid crystal layer 2 includes a negative nematic liquid crystal, a chiral molecule, and a salt ion mixed with each other, so that the liquid crystal material doped with the chiral molecule becomes a cholesteric liquid crystal (CLC). In this embodiment, the negative nematic liquid crystal refers to a liquid crystal material having a negative dielectric anisotropy. When an electric field acts on the negative nematic liquid crystal, the long axis (or director) of the negative nematic liquid crystal is perpendicular to the direction of the electric field. This property greatly contributes to the Helmholtz deformation of the liquid crystal material of the present application, which changes the pitch of the cholesteric liquid crystal molecules, thereby changing the wavelength of the reflected light to achieve the effect of changing the color.

[0035] In this embodiment, the salt ion can be a positive and negative ion decomposed from a salt dissolved in water or liquid crystal. The salt can be sodium chloride (NaCl), calcium sulfate (CaSO4), sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), potassium nitrate (KNO3), tetrabutylammonium bromide (TBAB), tetrabutylammonium hydrogensulfate (TBAHS), tetrabutylammonium chloride (TBACl), tetrabutylammonium hexafluorophosphate (TBAHFP), tetrabutylammonium tetrafluoroborate (TBATFB), etc., but the present application is not limited thereto.

[0036] In addition, the two substrates 1 act on the liquid crystal layer 2 with horizontal alignment, as shown in FIG. 1. When no electric field acts on the liquid crystal layer 2, the liquid crystal molecules 21 in the liquid crystal layer 2 are only affected by the alignment and are arranged horizontally relative to the two substrates 1.

[0037] Referring to FIG. 2, a schematic diagram of the negative cholesteric liquid crystal material under the effect of an electric field is shown. As previously described, when an electric field E is applied to the liquid crystal molecules 21 in the liquid crystal layer 2, the long axis (or director) of the liquid crystal molecules 21 is perpendicular to the direction of the electric field E. Thus, the negative liquid crystal property allows the liquid crystal molecules 21 to align parallel to the plane of the substrates 1 both in the absence and presence of an electric field.

[0038] Referring to FIG. 3, a schematic diagram of the tunable color liquid crystal element of the present application under the effect of an electric field is shown. The salt ions included in the liquid crystal molecules 21 cause the liquid crystal molecules 21 to be perturbed or rotated under the effect of the applied electric field E, a phenomenon known as the dynamic scattering effect. Thus, in the case of horizontal alignment of the two substrates 1, the effect of the added salt ions provides a force that causes the liquid crystal molecules to align "not parallel" to the plane of the substrates 1.

[0039] By the combined effect of the electric field and the alignment of the substrates, the liquid crystal material of the present application can exhibit a Helfrich distortion without the need for additional polymer material. In addition, the magnitude of the dynamic scattering effect can be adjusted by varying the voltage. Thus, the degree of Helfrich distortion can be varied by the voltage, thereby allowing the wavelength of the light reflected by the liquid crystal element to be controlled and the liquid crystal element to display different colors.

[0040] Referring to FIG. 4, a graph of the measured reflectance spectra of the tunable color liquid crystal element of the present application under different applied voltages is shown. In this example, the spectral curves SI, S2 and S3 represent the wavelength distribution for applied voltages of 0 V, 32 V and 60 V, respectively. When no voltage is applied to the liquid crystal element (i.e., 0 V), the reflectance peak of the spectral curve SI is approximately at 610 nm, which corresponds to the red light region, indicating that the liquid crystal element displays (reflects) red color when no voltage is applied. When a voltage of 32 V is applied to the liquid crystal element, the maximum reflectance peak of the spectral curve S2 is approximately at 545 nm, which corresponds to the green light region, indicating that the liquid crystal element displays green color at this time. When a voltage of 60 V is applied to the liquid crystal element, the maximum reflectance peak of the spectral curve S3 is approximately at 460 nm, which corresponds to the blue light region, indicating that the liquid crystal element displays blue color at this time.

[0041] From the above-mentioned embodiments, the liquid crystal element has a better reflectivity in the red to green light range during the color adjusting process, so that the light adjusting effect of red and green light is the best. However, the color-adjustable liquid crystal element of the present application is not limited to this. By adjusting the composition of the liquid crystal material and the salt ions, the reflection wavelength of the liquid crystal element under no applied voltage and the adjustable reflection wavelength range under applied voltage can be selected. For example, the liquid crystal element reflects infrared light at 0 V, and can reflect red light and yellow light as the voltage gradually increases. Similarly, the liquid crystal element can reflect green light at 0 V, and can reflect blue light and even ultraviolet light as the voltage gradually increases.

[0042] Next, please refer to Table 1, which shows the reaction time required for the color conversion between various reflected light colors in the present embodiment. The reaction time of each group of tests is within 200 milliseconds. The color-adjustable liquid crystal element of the present application can quickly switch the color, which has the effects of reducing image delay and avoiding operation and visual asynchronization.

[0043] Table 1, reaction time of each group of samples to be tested.

[0044]

[0045] Next, please refer to FIG. 5, which is a graph showing the relationship between the reflection peak wavelength and the voltage of the liquid crystal element of the present application with different concentrations of salt ions. The broken lines D1, D2 and D3 represent the ion concentration of 0%, 0.06% and 0.35% by weight, respectively. In the present embodiment, the salt used is tetrabutylammonium tetrafluoroborate, but the present application is not limited to this.

[0046] As shown by the broken line D1, when no salt ions are added to the liquid crystal element (i.e. the concentration is 0%), although the reflection peak wavelength may still fluctuate slightly as the voltage increases, this fluctuation has no significant pattern and does not continuously decrease as the voltage increases, which is not sufficient to make the liquid crystal element show different colors.

[0047] Next, please refer to the broken lines D2 and D3, as the concentration of salt ions increases, the same voltage can achieve a greater wavelength shift. In other words, increasing the concentration of salt ions can achieve equal wavelength shift with smaller voltage, so the liquid crystal element of the present application can display the same color with smaller voltage. However, too high concentration of salt ions will cause excessive ion accumulation, which will cause problems such as poor cholesteric liquid crystal arrangement and poor electrical properties of the element, therefore, the concentration of salt ions selected by the present application is preferably between 0.01% and 1% by weight.

[0048] Please refer to FIG. 6, which is a reflectance spectrum diagram of the tunable color liquid crystal element of the present application when different voltages are applied. The concentration of the salt ions is 0.34 ppm. When no voltage is applied to the liquid crystal element (i.e. 0 V), the wavelength range with reflectance of 25% or more is about 670 nm to 730 nm, which only corresponds to the red light section, indicating that the liquid crystal element displays (reflects) red color when no voltage is applied. When a voltage of 60 V is applied to the liquid crystal element, the wavelength range with reflectance of 25% or more is about 610 nm to 770 nm, the spectral width is increased and covers the orange light, red light and infrared light ranges. When a voltage of 120 V is applied to the liquid crystal element, the wavelength range with reflectance of 25% or more is about 500 nm to 800 nm, the spectral width is increased and covers the green light, yellow light, orange light, red light and infrared light ranges. When a voltage of 160 V is applied to the liquid crystal element, the wavelength range with reflectance of 25% or more is about 450 nm to 800 nm, the spectral width almost covers all the visible light bands, indicating that the liquid crystal element can display (reflect) white light.

[0049] From the above examples, it can be seen that the concentration of the salt ions of the liquid crystal element is less than 0.01%, especially between 0.25 ppm and 100 ppm by weight, and the spectral width of the reflected light can be widened with the increase of the applied voltage, i.e. the reflected light includes more color lights of different wavelengths, even all the visible light bands, so as to achieve the effect of reflecting white light.

[0050] In summary, the tunable color liquid crystal element of the present application generates Helmholtz deformation by the forces provided by the negative liquid crystal and the salt ions respectively, so as to control the wavelength of the reflected light of the liquid crystal element and make the liquid crystal element display different colors, which is the effect of the present application.

[0051] Although the present application has been disclosed by the above preferred embodiments, it is not intended to limit the present application, and various modifications and changes can be made to the above embodiments without departing from the spirit and scope of the present application, which still falls within the technical scope protected by the present application. Therefore, the protection scope of the present application should be defined by the claims.

Claims

1. An adjustable color liquid crystal cell, characterized by, The application relates to a liquid crystal display device, comprising: two substrates, each of which is electrically connected to a voltage source, and a switchable electric field is formed between the two substrates, wherein the alignment direction of the two substrates is horizontal alignment; a liquid crystal layer between the two substrates, which reflects light of various wavelengths, and the liquid crystal layer has a liquid crystal material, wherein the liquid crystal material comprises a negative nematic liquid crystal, a chiral molecule and a salt ion. The voltage source applies an alternating voltage to the two substrates, and the frequency of the alternating voltage is 60-1000 Hz.

2. The tunable color liquid crystal cell of claim 1, wherein, The concentration of the salt ion is between 0.01% and 1% in weight percentage.

3. The tunable color liquid crystal cell of claim 1, wherein, The electric field gradually increases from zero, and the wavelength of the light reflected by the liquid crystal layer gradually decreases.

4. An adjustable colour liquid crystal cell as claimed in claim 3, characterised in that, The concentration of the salt ion is between 0.25 ppm and 100 ppm in weight per million.

5. The tunable color liquid crystal cell of claim 1, wherein, The electric field gradually increases from zero, and the spectral width of the light reflected by the liquid crystal layer increases.

6. An adjustable colour liquid crystal cell as claimed in claim 5, characterised in that, The liquid crystal layer switches to reflect various colored light within a reaction time, and the reaction time is less than 200 ms.

7. The tunable color liquid crystal cell of claim 1, wherein, ​

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