Cholesteric liquid crystal and viologen composite color electrochromic display device and preparation method thereof

Abstract

The invention discloses a cholesteric liquid crystal and viologen compound type color electrochromic display device, which is characterized in that a viologen color-changing material and cholesteric liquid crystal are vertically overlapped in space, the space between a bottom layer ITO (Indium Tin Oxide) and a middle layer ITO is filled with the viologen color-changing material, and the space between the middle layer ITO and a top layer ITO is filled with a cholesteric liquid crystal material, so that the cholesteric liquid crystal and the cholesteric liquid crystal compound type color electrochromic display device is obtained. And a layer of birefringence film is attached to the top layer ITO. According to the color-changing material layer and the liquid crystal layer, gradient changes of displayed colors can be achieved by changing the concentration of a chiral agent, the magnitude of applied voltage and the rotation angle. The invention overcomes the defects of few color types, low saturation and slow response speed in the existing colorized display technology, and has the advantages of rich color types, high color saturation, diversified regulation and control modes, high response speed and capability of realizing color gradient change.

Description

Technical Field

[0001] The invention belongs to the field of electrochromic display, and in particular relates to a cholesteric liquid crystal and viologen composite color electrochromic display device and a preparation method thereof. Background Art

[0002] At present, the technical solutions for realizing color display mainly include redox electrochromism, cholesteric liquid crystal display, and electrophoretic electronic paper technology. Redox electrochromism mainly uses the color change of the color-changing material under the applied voltage to display different colors. It has the disadvantages of few color types and low color saturation. Cholesteric liquid crystal display mainly uses the selective reflection characteristics of the double helix structure of liquid crystal molecules to a specific band, and achieves different color display effects by adjusting the pitch change. However, cholesteric liquid crystal can only switch between three states of transparency, coloring and scattering under external field voltage, and cannot achieve gradient color changes of a single device. Moreover, cholesteric liquid crystal only completely reflects or transmits circularly polarized light, so the reflectivity for natural light is at most 50%. Electrophoretic electronic paper mainly uses the directional movement of charged positive and negative particles of different colors under the electric field to achieve color changes, but it has the disadvantages of slow response speed, few colors that can be displayed, and clustering of positive and negative particles for a long time. Summary of the invention

[0003] In view of the problems existing in the above-mentioned color display technology, such as the small number of color types, low saturation, slow response speed, etc., the present invention proposes a cholesteric liquid crystal and violacein composite color electrochromic display device, which controls the color of the color-changing material layer and the color of the liquid crystal layer to be displayed collaboratively or independently by applying voltage to the color-changing material layer and the liquid crystal layer and changing the rotation angle respectively, and realizes more colorful color changes of the composite device based on the mechanism of color superposition.

[0004] The technical scheme of the present invention is: a method for preparing a cholesteric liquid crystal and viologen composite color electrochromic display device, the display device comprises a bottom ITO glass, an intermediate ITO glass and a top ITO glass, the intermediate ITO glass is a double-sided ITO conductive glass, a viologen color-changing material is filled between the bottom ITO glass and the intermediate ITO glass, a cholesteric liquid crystal material is filled between the intermediate ITO glass and the top ITO glass, and a birefringent film is attached to the outward side of the top ITO glass;

[0005] The steps of the method for preparing the display device are as follows:

[0006] 1) Synthesis of cholesteric liquid crystal: adding a left-handed or right-handed chiral agent to a nematic liquid crystal and stirring to obtain a cholesteric liquid crystal material;

[0007] 2) Spin-coating a photo-orientation agent on one side of a top layer of ITO conductive glass and an intermediate layer of ITO conductive glass, and after drying on a hot plate, fixing the ITO conductive glass coated with the photo-orientation agent into an ITO box, irradiating the ITO box with linearly polarized light to achieve uniform orientation of the orientation layer, and then filling the prepared cholesteric liquid crystal material into the ITO box by siphoning;

[0008] 3) fixing the bottom layer ITO conductive glass on the other side of the middle layer ITO conductive glass to form an ITO box; filling the violet color-changing material into the ITO box by siphoning;

[0009] 4) The birefringent film is attached to the outward surface of the top ITO glass to prepare the cholesteric liquid crystal and viologen composite color electrochromic display device.

[0010] Wherein, the chiral agent in step 1) is a commonly used chiral agent material on the market, including but not limited to: S811, R811, S5011, R5011.

[0011] Wherein, the nematic liquid crystal in step 1) is a nematic liquid crystal material commonly used in the market, including but not limited to: E7, RM257, HMS-100.

[0012] Wherein, the photo-alignment agent in step 2) is a common photo-alignment agent on the market, such as SD1.

[0013] Preferably, the hot plate drying in step 2) is drying on a hot plate at 100-150° C. for 40-80 minutes. More preferably, the drying time is 50-60 minutes.

[0014] Preferably, in step 2), the fixed ITO box is irradiated with linearly polarized light for 10-15 minutes. More preferably, the irradiation time is 10 minutes.

[0015] Preferably, the preparation of the viologen color-changing material in step 3) is as follows: 10-200 mg of viologen hexafluorophosphate and 0.1-2 g of polymethyl methacrylate or polyvinyl alcohol are dissolved in 1-100 ml of acetonitrile solution or water to obtain a gel-like viologen color-changing material.

[0016] Preferably, the viologen hexafluorophosphate is at least any one of diethyl viologen hexafluorophosphate, diphenyl viologen hexafluorophosphate, and diheptyl viologen hexafluorophosphate with different substitution groups.

[0017] Preferably, the viologen color-changing material may also include 10-100 mg ferrocene.

[0018] Preferably, in step 4), the thickness of the birefringent film is 10-50 μm.

[0019] Preferably, in step 2), the ITO conductive glass coated with the photo-alignment agent is fixed into an ITO box using a double-sided adhesive having a thickness of 5-50 μm.

[0020] Preferably, in step 3), the bottom layer of ITO conductive glass is fixed on the other side of the middle layer of ITO conductive glass using a double-sided adhesive having a thickness of 10-500 μm to form an ITO box.

[0021] In the present invention, ITO, ITO glass and ITO conductive glass have the same meaning, and all refer to liquid crystal display ITO conductive glass which is processed by coating a layer of indium tin oxide (commonly known as ITO) film on a soda-lime-based or silicon boron-based substrate glass by various methods such as sputtering and evaporation.

[0022] Viologen color-changing materials can display different colors by different material ratios, and RGB colors can be displayed by adjusting the types of viologen compounds and different material combinations. For example, dioctyl viologen diiodide DOV(I)2 and polyvinyl alcohol (PVA) dissolved in deionized water can generate a red viologen color-changing gel, while diethyl viologen hexafluorophosphate DEV((PF)6)2 and ferrocene (DMFc) and polymethyl methacrylate (PMMA) dissolved in acetonitrile solution can generate a blue viologen color-changing gel.

[0023] Viologen color-changing materials and cholesteric liquid crystals are vertically superimposed in space. Based on the principle of color superposition, by applying voltage to the vioogen color-changing layer and the cholesteric liquid crystal layer respectively, or changing the rotation angle, the color changes of the two can be controlled collaboratively or independently. Changing the magnitude of the applied voltage and the rotation angle can respectively achieve gradient changes in the colors of the vioogen and liquid crystal layers, thereby superimposing to produce more colorful color changes. Among them, the vioogen material can switch between the transparent and colored states under positive and negative alternating electric fields, and the cholesteric liquid crystal material can achieve gradient changes in color under changing electric fields and changing rotation angles. The central reflection wavelength of the cholesteric liquid crystal is regulated by changing the concentration of the chiral agent. The specific formula is as follows:

[0024]

[0025] Wherein, λ is the central reflection wavelength, n is the refractive index of the liquid crystal material, HTP is the helical twisting force constant of the liquid crystal, and C is the concentration of the chiral agent.

[0026] Figure 2 The effect of the mass ratio of the chiral agent and the magnitude of the applied voltage on the color of the device is shown. Under five chiral agent concentrations, the device displays different colors by changing the applied voltage. Figure 3 The reflectance spectra and device display colors of the devices corresponding to different weight ratios of chiral agents are shown.

[0027] The present invention introduces a birefringent film, and linearly polarized incident light is converted into circularly polarized light after passing through the birefringent film, thereby being completely reflected by the cholesteric liquid crystal. By changing the angle between the linearly polarized light and the birefringent film, different degrees of circularly polarized light can be achieved, thereby achieving a gradient change in the color of the cholesteric liquid crystal. The change in the rotation angle can cause a change in the color displayed by the device. Figure 4 The corresponding spectral changes of the device at different rotation angles are shown. Figure 5 Shows the color change of the same device at different angles.

[0028] The color of the cholesteric liquid crystal and viologen composite color electrochromic display device of the present invention can be changed with the concentration of the chiral agent, the magnitude of the applied voltage, and the rotation angle.

[0029] The present invention can realize gradient changes in the colors of viologens and liquid crystal layers respectively by changing the concentration of the chiral agent, the magnitude of the applied voltage, and the rotation angle, thereby superimposing and producing colorful color changes, realizing gradient changes in the colors of a single device, and being able to display a variety of colors. The present invention overcomes the defects of the existing color display technology, such as a small number of color types, low saturation, and slow response speed, and has the advantages of rich color types, high color saturation, various control modes, fast response speed, and the ability to realize color gradient changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The schematic diagram of the structure of the cholesteric liquid crystal and viologen composite device of the present invention is shown, which is: birefringent film, top ITO glass, cholesteric liquid crystal layer, middle double-sided ITO glass, viologen color-changing layer, bottom ITO glass.

[0031] Figure 2 The effect of the mass ratio of the chiral agent and the magnitude of the applied voltage on the device color is shown.

[0032] Figure 3 The reflectance spectra and device colors of devices corresponding to different weight ratios of chiral agents are shown.

[0033] Figure 4 The corresponding spectral changes of the device at different rotation angles are shown.

[0034] Figure 5 Shows the color change of the same device at different angles.

[0035] Figure 6 is the spectrum of the display device prepared in Example 1

[0036] Figure 7 is the spectrum of the display device prepared in Example 2 DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to these embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0038] Embodiment 1:

[0039] 1) Synthesis of cholesteric liquid crystal: 2 mg of chiral agent S5011 was added to 0.5 g of nematic liquid crystal E7 and stirred to obtain a cholesteric liquid crystal material;

[0040] 2) Spin-coat the photo-orientation agent SD1 on two pieces of 2cmx2.5cm ITO conductive glass, one of which has double-sided ITO, i.e. the middle layer ITO conductive glass, and the single-sided ITO glass is the top layer ITO. After spin coating, dry it on a hot plate at 100°C for 60 minutes, fix the middle layer ITO glass and the top layer ITO glass coated with the orientation agent into an ITO box with a double-sided tape of 5μm thickness, irradiate the fixed ITO box with 403nm wavelength linear polarized light for 10 minutes to achieve uniform orientation of the orientation layer, and then use the siphon effect to fill the prepared cholesteric liquid crystal material into the ITO box to form a cholesteric liquid crystal layer;

[0041] 3) Use 80 μm thick double-sided tape to stick to the four corners of the other side of the middle layer of double-sided ITO conductive glass, and fix a piece of ITO glass on it to form an ITO box composed of the middle layer ITO glass and the bottom layer ITO glass, which is used to fill the viologen color-changing material. Dissolve 40 mg of dioctyl viologen diiodide DOV(I)2 and 0.2 g of polyvinyl alcohol (PVA) in deionized water to generate a red viologen color-changing gel, and use the siphon effect to fill the red viologen color-changing gel into the ITO box to form a viologen color-changing layer.

[0042] 4) A birefringent film with a thickness of 10 μm is attached to the outward side of the top ITO glass. Thus, the preparation of the composite display device based on cholesteric liquid crystal and viologen is completed.

[0043] The structure of the cholesteric liquid crystal and viologen composite display device is as follows Figure 1 As shown, the display device includes a bottom ITO glass, an intermediate ITO glass and a top ITO glass, wherein the intermediate ITO glass is a double-sided ITO conductive glass, a violet color-changing layer formed by a violet color-changing material is filled between the intermediate ITO glass and the bottom ITO glass, a cholesteric liquid crystal layer formed by a cholesteric liquid crystal material is filled between the intermediate ITO glass and the top ITO glass, and a birefringent film is attached to the other side (i.e., the side facing outward) of the top ITO glass.

[0044] Figure 6 The spectrum test data of the composite device of dioctyl viologen diiodide color-changing gel and cholesteric liquid crystal prepared in Example 1. The color of the CLC layer can be adjusted by changing the weight ratio of the chiral agent in the CLC. By applying different gradients of coloring voltage to the viologen color-changing gel layer, gradually increasing from 0V to -2.2V, the transmittance of the device spectrum gradually decreases, such as Figure 6 The positions of the spectral valleys of the devices corresponding to different chiral agent concentrations are different, which is reflected in the color difference. As the voltage increases, the transmittance of the CLC and viologen compound composite device in the wavelength range of 400-800nm ​​gradually decreases, and the color gamut coordinate changes of the device correspond to Figure 6 b, d, f, h, j. Under five different chiral agent concentrations, the applied voltage is changed, and the actual device displays colors such as Figure 6 As shown in Figure k.

[0045] Embodiment 2:

[0046] 1) Synthesis of cholesteric liquid crystal: 3 mg of chiral agent S5011 was added to 0.5 g of nematic liquid crystal E7 and stirred to obtain a cholesteric liquid crystal material;

[0047] 2) Spin-coat the photo-alignment agent SD1 on two pieces of 2cmx2.5cm ITO conductive glass, one of which has double-sided ITO, i.e., the middle layer ITO conductive glass. After coating, dry it on a hot plate at 100°C for 60 minutes, fix the two pieces of ITO glass coated with the alignment agent with a double-sided tape with a thickness of 5μm to form an ITO box, irradiate the fixed ITO box with 403nm wavelength linear polarized light for 10 minutes to achieve uniform orientation of the alignment layer, and fill the prepared cholesteric liquid crystal material into the ITO box by siphoning to form a cholesteric liquid crystal layer;

[0048] 3) Use 80 μm thick double-sided tape to stick to the four corners of the other side of the middle layer ITO glass, and fix a piece of ITO glass on it to make an ITO box for filling with viologen color-changing material; 40 mg of diethyl viologen hexafluorophosphate DEV((PF)6)2, 10 mg of ferrocene (DMFc), and 0.4 g of polymethyl methacrylate (PMMA) are dissolved in 2 ml of acetonitrile solution to obtain a blue viologen color-changing gel, and the blue viologen color-changing gel is filled into the ITO box by siphoning to form a viologen color-changing layer.

[0049] 4) A birefringent film with a thickness of 10 μm is attached to the outward side of the top ITO glass. Thus, the preparation of the composite display device based on cholesteric liquid crystal and viologen is completed.

[0050] Figure 7The spectrum test data of the composite device of diphenyl viologen hexafluorophosphate color-changing gel and cholesteric liquid crystal is shown in Example 2. The color of the CLC layer can be adjusted by changing the weight ratio of the chiral agent in the CLC. By applying different gradient coloring voltages to the viologen color-changing gel layer, gradually increasing from 0V to -1.5V, the transmittance of the device spectrum gradually decreases, such as Figure 7 The positions of the spectral valleys of the devices corresponding to different chiral agent concentrations are different, which is reflected in the color difference. As the voltage increases, the transmittance of the CLC and viologen compound composite device in the wavelength range of 400-800nm ​​gradually decreases, and the color gamut coordinate changes of the device correspond to Figure 7 b, d, f, h, j. Under five different chiral agent concentrations, the applied voltage is changed, and the device photos are as follows Figure 7 As shown in Figure k.

[0051] The present invention realizes the gradient change of the color of a single device and can display a variety of colors. By changing the magnitude of the applied voltage and changing the rotation angle, the gradient change of the color of the violet and liquid crystal layer can be realized respectively, thereby superimposing and producing colorful color changes.

[0052] The above-described embodiments are only some preferred solutions of the present invention, but they are not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for preparing a cholesteric liquid crystal and viologen composite color electrochromic display device, characterized in that: The display device comprises a bottom ITO glass, an intermediate ITO glass and a top ITO glass, wherein the intermediate ITO glass is a double-sided ITO conductive glass, a violet color-changing material is filled between the bottom ITO glass and the intermediate ITO glass, a cholesteric liquid crystal material is filled between the intermediate ITO glass and the top ITO glass, and a birefringent film is attached to the outward side of the top ITO glass; The steps of the method for preparing the display device are as follows: 1) Synthesis of cholesteric liquid crystal: adding a left-handed or right-handed chiral agent to a nematic liquid crystal and stirring to obtain a cholesteric liquid crystal material; 2) Spin-coating a photo-orientation agent on one side of a top layer of ITO glass and an intermediate layer of ITO glass, and after drying on a hot plate, fixing the ITO glass coated with the photo-orientation agent into an ITO box, irradiating the ITO box with linearly polarized light to achieve uniform orientation of the orientation layer, and then filling the prepared cholesteric liquid crystal material into the ITO box by siphoning; 3) fixing the bottom ITO glass on the other side of the middle ITO glass to form an ITO box; filling the violet color-changing material into the ITO box by siphoning; 4) The birefringent film is attached to the outward surface of the top ITO glass to prepare the cholesteric liquid crystal and viologen composite color electrochromic display device.

2. The method for preparing the cholesteric liquid crystal and viologen composite color electrochromic display device according to claim 1, characterized in that: The hot plate drying in step 2) is drying on a hot plate at 100-150° C. for 40-80 minutes.

3. The method for preparing the cholesteric liquid crystal and viologen composite color electrochromic display device according to claim 1, characterized in that: In step 2), the fixed ITO box is irradiated with linearly polarized light for 10-15 minutes.

4. The method for preparing the cholesteric liquid crystal and viologen composite color electrochromic display device according to claim 1, characterized in that: Step 3) The preparation of the viologen color-changing material is as follows: 10-200 mg of viologen hexafluorophosphate and 0.1-2 g of polymethyl methacrylate or polyvinyl alcohol are dissolved in 1-100 ml of acetonitrile solution or water to obtain a gel-like viologen color-changing material.

5. The method for preparing the cholesteric liquid crystal and viologen composite color electrochromic display device according to claim 4, characterized in that: The viologen hexafluorophosphate is at least any one of diethyl viologen hexafluorophosphate, diphenyl viologen hexafluorophosphate and diheptyl viologen hexafluorophosphate with different substitution groups.

6. The method for preparing the cholesteric liquid crystal and viologen composite color electrochromic display device according to claim 4, characterized in that: The viologen color-changing material may also include 10-100 mg ferrocene.

7. The method for preparing the cholesteric liquid crystal and viologen composite color electrochromic display device according to claim 1, characterized in that: In step 4), the thickness of the birefringent film is 10-50 μm.

8. A cholesteric liquid crystal and viologen composite color electrochromic display device, characterized in that: The display device comprises a bottom layer of ITO glass, an intermediate layer of ITO glass and a top layer of ITO glass, wherein the intermediate layer of ITO glass is a double-sided ITO glass, a violet change layer formed by a violet color-changing material is filled between the intermediate layer of ITO glass and the bottom layer of ITO glass, a cholesteric liquid crystal layer formed by a cholesteric liquid crystal material is filled between the intermediate layer of ITO glass and the top layer of ITO glass, and a birefringent film is attached to the outward side of the top layer of ITO glass; the cholesteric liquid crystal and violet composite color electrochromic display device is prepared by the method described in any one of claims 1 to 7.

9. The cholesteric liquid crystal and viologen composite color electrochromic display device according to claim 6, characterized in that: The viologen color-changing material and the cholesteric liquid crystal material are respectively filled between the bottom layer ITO glass and the middle layer ITO glass, and between the middle layer ITO glass and the top layer ITO glass in a spatial vertical stacking manner.

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