Cholesteric liquid crystal with light / heat / electric response, preparation and application thereof

Abstract

The present invention discloses a cholesteric liquid crystal with light / heat / electric response, its preparation and application. The cholesteric liquid crystal is obtained by mixing a non-responsive chiral dopant, a light / heat responsive chiral azobenzene dopant, and a liquid crystal host; and the cholesteric liquid crystal is planar oriented in a liquid crystal cell oriented by horizontal friction of polyvinyl alcohol; the concentration of the chiral azobenzene molecule dopant is 3.4-3.8wt%. The cholesteric liquid crystal can respond to changes in light, temperature, and voltage, and can adjust the photonic band gap of the cholesteric liquid crystal by changing the irradiation time and heating temperature, or by changing the content of the chiral dopant and the heating temperature. The reversible electrical response pattern of the cholesteric liquid crystal can also be prepared by applying a voltage.

Description

Technical Field

[0001] The present invention relates to the technical field of light / heat / electric response of cholesteric liquid crystals, and more specifically to a cholesteric liquid crystal with light / heat / electric response, its preparation and application. Background Art

[0002] Typically, cholesteric liquid crystals (CLCs) spontaneously assemble into supramolecular helical structures with periodic pitches (p) in the range of several hundred nanometers, exhibiting a one-dimensional photonic band gap (PBG) and resulting in the reflection of circularly polarized light. CLCs have yielded promising applications in sensors, polarizers, reflectors, filters, tunable lasers, and beam steering devices. Importantly, the cholesteric helical p and its reflected color can be easily and dynamically modulated by light, temperature, humidity, magnetic fields, voltage, and mechanical stress, offering important applications in next-generation communications engineering and integrated optical devices.

[0003] Among various stimuli-responsive chiral dopants for fabricating CLCs, light-driven chiral molecules have recently emerged as excellent candidates due to the steric advantages of light for both remote and local manipulation. As a prominent light-driven chiral molecule, axially chiral azobenzene molecules (chiral azobenzenes) with two azo bonds undergo reversible trans-to-cis photoisomerization of the azo configuration, yielding two other isomers containing one or two cis configurations. The three isomers are characterized by the following isomerization sequence: (trans, trans)-configuration → (trans, cis)-configuration → (cis, cis)-configuration. The (cis, cis)-configuration → (cis, trans)-configuration → (trans, trans)-configuration can be induced by visible light irradiation. Incorporating chiral azobenzene molecules into host liquid crystals (LCs) can induce the formation of CLCs, resulting in large changes in the helical torsional force (HTP, β) value. However, since azobenzene compounds are typical photochromic materials, research on CLCs triggered by chiral azobenzene molecules has mainly focused on photoresponse. For example, Professor Yu Yanlei's team has developed rewritable photonic paper that can write, erase and adjust local colors by light-driven CLCs. CLCs are doped with chiral azobenzene molecules connected to chiral centers, with a self-organized helical superstructure, with two structural elements with light-adjustable pitch p (for color adjustment) and a reconfigurable helical axis (for writing and erasing). Few studies have analyzed the changes in the reflective color of CLCs caused by the temperature response of azobenzene molecules. These studies are very important for providing additional optical information for potential applications. Summary of the Invention

[0004] In light of the above-mentioned drawbacks, the first object of the present invention is to provide a cholesteric liquid crystal with photo- / thermal- / electrical response. This cholesteric liquid crystal can respond to changes in light, temperature, and voltage. The photonic band gap of the cholesteric liquid crystal can be adjusted by varying the irradiation time and heating temperature, or by varying the content of the chiral dopant and the heating temperature. Both approaches can achieve a red shift in the reflected color of the cholesteric liquid crystal. A reversible electrical response pattern of the cholesteric liquid crystal can also be prepared by applying a voltage.

[0005] The second object of the present invention is to provide a method for preparing the cholesteric liquid crystal as described above.

[0006] The third object of the present invention is to provide a method for adjusting the photonic band gap of cholesteric liquid crystals by varying the irradiation time and the heating temperature.

[0007] A fourth object of the present invention is to provide a method for adjusting the photonic band gap of cholesteric liquid crystals by varying the content of a chiral dopant and the heating temperature.

[0008] A fifth object of the present invention is to provide a method for preparing a reversible electrical response pattern of cholesteric liquid crystal, wherein the method achieves erasure and visualization of the pattern by adjusting the voltage applied to the cholesteric liquid crystal.

[0009] A sixth object of the present invention is to provide an application of the above-mentioned cholesteric liquid crystal in the field of photon patterning or anti-counterfeiting.

[0010] In order to achieve the above first object, the present invention adopts the following technical solutions:

[0011] The present invention discloses a cholesteric liquid crystal with light / heat / electric response, wherein the cholesteric liquid crystal is obtained by mixing a non-responsive chiral dopant, a light / heat responsive chiral azobenzene dopant, and a liquid crystal host;

[0012] The cholesteric liquid crystal is in a planar orientation in a liquid crystal cell oriented by horizontal rubbing of polyvinyl alcohol;

[0013] The concentration of the chiral azobenzene dopant is 3.4-3.8 wt %.

[0014] In the present invention, the chiral azobenzene dopant selected has both chirality induction and light conversion, and is also temperature-responsive, giving the cholesteric liquid crystal a good light / heat response effect. The cholesteric liquid crystal can respond to changes in light, temperature, and voltage, and can adjust the photonic band gap of the cholesteric liquid crystal by changing the irradiation time and heating temperature, or by adjusting the content of the chiral azobenzene dopant or the non-responsive chiral dopant and the heating temperature. The photonic band gap of the cholesteric liquid crystal can be adjusted. Both approaches can achieve a red shift in the reflected color of the cholesteric liquid crystal, and the erasure and appearance of the pattern can be achieved by adjusting the voltage applied to the cholesteric liquid crystal. In addition, the provided cholesteric liquid crystal can achieve a wide range of visible light band gap adjustment within a narrow adjustment range of the chiral dopant concentration (or proportion), which is beneficial to the practical application of pattern display and anti-counterfeiting.

[0015] The cholesteric liquid crystal of the present invention uses a light-patterned mask. UV irradiation is performed at varying times or chiral dopant concentrations to adjust the photonic band gap of the pattern color. The entire liquid crystal cell is then heated again. Compared to existing methods that only adjust the photonic band gap of the pattern color, this method allows for adjustment of both the background and pattern color photonic band gaps. The results show that different irradiation times result in different trans-cis isomerization rates of the light-driven chiral azobenzene, resulting in different reflected color patterns. After heating the entire liquid crystal cell again, the background and pattern colors are brought to the same color at a certain temperature, thereby concealing the pattern.

[0016] For another adjustment method, the photonic band gap is adjusted by using a change in chiral dopant and temperature, and the cholesteric liquid crystal of the present invention also shows RGB colors that are sensitive to temperature. The color change of the temperature-driven sample may be due to the spiral that unfolds as the thermal energy increases, which leads to a decrease in the HTP value of the chiral azobenzene molecule. By changing the concentration of the chiral azobenzene or non-responsive chiral dopant (such as S5011) respectively, the reflection wavelength shifts from blue to red as the concentration of the chiral azobenzene molecule or the non-responsive chiral dopant decreases. And by selecting a chiral azobenzene molecule or a non-responsive chiral dopant with a certain concentration ratio, after raising the temperature, precise control can be achieved in a wider visible light region within a narrower concentration or ratio adjustment range, and the reflection band gap of the sample changes from blue to red, which provides a prerequisite for patterned display and pattern hiding and encryption.

[0017] The design idea for the reversible electrical response pattern is to control the orientation state of cholesteric liquid crystal molecules by controlling the change of voltage, thereby achieving the display and erasure of the image.

[0018] Furthermore, the initial band gap of the cholesteric liquid crystal is 441-481 nm.

[0019] Furthermore, the non-responsive chiral dopant is selected from one or both of S5011 and S811.

[0020] Furthermore, in the raw material, the concentration of the non-responsive chiral dopant is 1.0-1.4 wt %.

[0021] Furthermore, the liquid crystal host is selected from one or more of E7, SLC1717, and 5CB.

[0022] Furthermore, based on 100 parts by mass of the total raw materials, the raw materials include: 1.0-1.4 parts of a non-responsive chiral dopant, 3.4-3.8 parts of a light / heat responsive chiral azobenzene dopant, and 95.6-94.8 parts of a liquid crystal host.

[0023] In order to achieve the above second purpose, the present invention adopts the following technical solutions:

[0024] The present invention discloses a method for preparing the cholesteric liquid crystal as described above, comprising the following steps:

[0025] uniformly mixing a non-responsive chiral dopant, a light / heat responsive chiral azobenzene dopant, and a liquid crystal host to obtain a cholesteric liquid crystal mixture;

[0026] The cholesteric liquid crystal mixture is poured into a liquid crystal box rubbed and aligned with polyvinyl alcohol to obtain the cholesteric liquid crystal with planar alignment.

[0027] Furthermore, the preparation method of the cholesteric liquid crystal mixture is:

[0028] A non-responsive chiral dopant, a light / heat responsive chiral azobenzene dopant, and a liquid crystal host are dissolved in dichloromethane and placed in an oven at 40-60° C. until the dichloromethane is completely evaporated, thereby preparing a CLC mixture reflecting blue.

[0029] Furthermore, the preparation method of the planar-oriented cholesteric liquid crystal is as follows:

[0030] The cholesteric liquid crystal mixture is heated to its clearing point, and the isotropic phase is poured into a liquid crystal cell oriented by polyvinyl alcohol rubbing through capillary action, and then cooled to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0031] Furthermore, a polyvinyl alcohol aqueous solution was prepared as the planar alignment layer by adding commercially available white solid particles of polyvinyl alcohol into deionized water, placing the mixture on a heating table, stirring, heating and dissolving the mixture.

[0032] Furthermore, the glass substrate used for the polyvinyl alcohol planar alignment layer is cleaned by ultrasonic cleaning with a neutral detergent, cleaning with tap water, ultrasonic cleaning with deionized water, ultrasonic cleaning with ethanol, and then placed in a drying oven for drying before use.

[0033] Furthermore, a polyvinyl alcohol planar orientation layer is prepared. Using a desktop coating machine, a clean glass substrate is spin-coated with a polyvinyl alcohol aqueous solution, thereby completing the preparation of the polyvinyl alcohol orientation layer. Furthermore, before using the desktop coating machine to spin-coat the polyvinyl alcohol aqueous solution, it is best to first apply a thin layer of polyvinyl alcohol aqueous solution to the glass substrate using a plastic dropper. The glass substrate coated with the polyvinyl alcohol aqueous solution is then placed in an oven for heating and drying. The polyvinyl alcohol thin coating is rubbed in the same direction with a rayon cloth to perform an orientation treatment. The rubbed and oriented polyvinyl alcohol thin coating is then ultrasonically cleaned with ethanol and finally blown dry with nitrogen.

[0034] Furthermore, a planar-oriented liquid crystal box is prepared. The first step is to prepare a spacer. The spacer used to prepare the liquid crystal box is made of polyethylene terephthalate (PET) plastic film. Use scissors to cut the PET plastic film into strips. The second step is to encapsulate the liquid crystal box. Take two planar-oriented glass substrates and place one side of the polyvinyl alcohol orientation layer parallel to each other along the orientation direction. Use a PET plastic film spacer to control the spacing between the two glass substrates (the box spacing of the liquid crystal box). That is, the strip is placed at the edge of the long axis of the planar-oriented glass substrate and then covered with another planar-oriented glass substrate. Then, use a paper clip to dip a small amount of 502 glue and apply it to both sides of the glass substrate for edge sealing. Finally, use a dovetail clamp to clamp both sides of the glass substrate and place it at room temperature to cure the 502 glue, thereby completing the preparation of the blank liquid crystal box.

[0035] In order to achieve the third object, the present invention adopts the following technical solutions:

[0036] The present invention discloses a method for adjusting the photonic band gap of cholesteric liquid crystal, comprising the following steps:

[0037] Adjust the irradiation time and heating temperature to keep the composition of cholesteric liquid crystal unchanged:

[0038] The cholesteric liquid crystal as described above is irradiated with a 365 nm light source;

[0039] The cholesteric liquid crystals irradiated for different irradiation times are heated again to adjust the photonic band gap;

[0040] Furthermore, the heating temperature range is 25-52°C.

[0041] Furthermore, after the cholesteric liquid crystal is irradiated with a 365 nm light source for 0.2 s, 0.5 s, 0.8 s, 1.6 s, 1.8 s, 2.0 s, or 2.3 s, the cholesteric liquid crystal is placed on a heating table and heated to adjust the photonic band gap.

[0042] In order to achieve the fourth purpose above, the present invention adopts the following technical solutions:

[0043] The present invention discloses a method for adjusting the photonic band gap of cholesteric liquid crystal, comprising the following steps:

[0044] Adjust the content of chiral dopant in cholesteric liquid crystal and heating temperature, and fix the irradiation time:

[0045] The cholesteric liquid crystal as described above is irradiated with a 365 nm light source;

[0046] The cholesteric liquid crystal irradiated by a 365nm light source is heated again to adjust the photonic band gap.

[0047] Furthermore, the heating temperature range is 25-52°C.

[0048] In order to achieve the fifth purpose, the present invention adopts the following technical solutions:

[0049] The present invention discloses a method for preparing a reversible electrical response pattern of cholesteric liquid crystal, comprising the following steps:

[0050] Adjust the voltage applied to the cholesteric liquid crystal and fix the content of the chiral dopant, temperature, and irradiation time:

[0051] The cholesteric liquid crystal as described above is irradiated with a 365 nm light source;

[0052] Applying voltage to the cholesteric liquid crystal after irradiation with a 365nm light source and adjusting the voltage to achieve the preparation of a reversible electrical response pattern;

[0053] Furthermore, the applied voltage is within a range of 0-65V.

[0054] In order to achieve the sixth objective, the present invention discloses an application of the above-mentioned cholesteric liquid crystal in the field of photon patterning or anti-counterfeiting.

[0055] The beneficial effects of the present invention are as follows:

[0056] The present invention discloses a cholesteric liquid crystal with light / thermal / electrical response, its preparation, and its application. The cholesteric liquid crystal is obtained by mixing a non-responsive chiral dopant, a light / thermal responsive chiral azobenzene dopant, and a liquid crystal host, and has the following advantages:

[0057] 1. The cholesteric liquid crystal of the present invention can cause a change in the photonic band gap of the cholesteric liquid crystal when irradiated with light, heated, or when the chiral dopant changes, thereby achieving a red shift in the reflection color of the cholesteric liquid crystal.

[0058] 2. The cholesteric liquid crystal of the present invention utilizes a light-patterned mask. Upon exposure to a 365nm light source, the photoresponsive chiral azobenzene transforms from a trans configuration to a cis configuration. Different irradiation times induce different conversion rates of trans-to-cis isomerization, resulting in different helical twisting forces in the chiral azobenzene molecules after irradiation, thus displaying red, green, and blue reflected colors. Furthermore, when the cholesteric liquid crystal, after irradiation with a 365nm light source, is heated again, both the background color and the pattern color change with temperature.

[0059] 3. The cholesteric liquid crystal of the present invention also exhibits temperature-sensitive RGB color. When the concentration of chiral azobenzene changes from 3.8wt% to 3.4wt% while the concentration of the non-responsive chiral dopant remains unchanged, or when the concentration of the non-responsive chiral dopant changes from 1.4wt% to 1.0wt% while the concentration of the chiral azobenzene remains unchanged, the reflection wavelength shifts from blue to red as the concentration of the chiral dopant decreases. By selecting a certain concentration ratio of chiral azobenzene and a non-responsive chiral dopant, when the temperature is increased, precise control can be achieved within a narrow adjustment range of concentration or ratio over a wide visible range, and the reflection band gap of the sample shifts from blue to red.

[0060] 4. The cholesteric liquid crystals of the present invention exhibit reversible electrical response behavior under voltage. An image with a blue background and a green "apple" pattern remains unchanged below 30V. As the voltage increases, the image slowly erases. The image is completely erased when the voltage reaches 65V. After the voltage is removed, the image can be revisited under pressure.

[0061] 5. The method for preparing the cholesteric liquid crystal provided by the present invention is simple, low-cost, and suitable for large-scale preparation, and can be used in the field of photon patterning or anti-counterfeiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0063] Figure 1 The results show that the photonic band gap of cholesteric liquid crystal can be adjusted by changing the concentration of the chiral dopant and the temperature.

[0064] Figure 2 It shows that the photonic band gap of the cholesteric liquid crystal of the present invention is adjusted when the irradiation time and temperature change.

[0065] Figure 3The light / heat dual-response patterned anti-counterfeiting design of the cholesteric liquid crystal of the present invention is shown.

[0066] Figure 4 The effect of changing the reversible electric response pattern of the cholesteric liquid crystal of the present invention is shown. DETAILED DESCRIPTION

[0067] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and drawings. Those skilled in the art should understand that the following specific description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0068] According to a specific embodiment of the present invention, there is provided a cholesteric liquid crystal having optical / thermal / electrical response, wherein the cholesteric liquid crystal is planarly aligned in a liquid crystal cell made of a glass sheet coated with a polyvinyl alcohol alignment layer;

[0069] The cholesteric liquid crystal is obtained by mixing a non-responsive chiral dopant, a light / heat responsive chiral azobenzene dopant, and a liquid crystal host; the concentration of the chiral azobenzene dopant is 3.4-3.8 wt %.

[0070] Cholesteric liquid crystals are typically prepared by doping a chiral compound into an achiral nematic liquid crystal host. The resulting mixture self-organizes into a helical superstructure that exhibits selective reflection of circularly polarized light of a certain wavelength and a specific handedness, depending on its helical pitch, p, and the twist direction of the director. The ability of a chiral dopant to transform an achiral nematic liquid crystal into a cholesteric liquid crystal is characterized by its helical twisting power (HTP, β), which is related to the helical pitch, p, of the helical superstructure, as β = 1 / cp, where "c" is the concentration of the chiral dopant.

[0071] In order to make the initial reflection band gap of the cholesteric liquid crystal mixture be in the blue range, the concentration of the light / thermo-responsive chiral azobenzene dopant is selected to be 3.4-3.8 wt %, and the concentration of the non-responsive chiral dopant is selected to be 1.0-1.4 wt %.

[0072] For example, a photo- / thermo-responsive chiral azobenzene dopant needs to possess three functions. First, it must act as a photoresponsive molecule, undergoing rod-shaped trans-to-bent cis isomerization upon UV light irradiation, resulting in cholesteric liquid crystals with varying helical pitches p depending on the azobenzene molecule's configuration. Second, it must act as a chiral dopant. Due to its chiral group, the chiral dopant can induce nematic liquid crystals to form cholesteric liquid crystals, inducing a helical arrangement of liquid crystal molecules. Third, it must be temperature-responsive, enabling both background and pattern colors to change with temperature.

[0073] In this embodiment, a light pattern mask is used, and the cholesteric liquid crystal presents different reflective colors after UV irradiation for different times, and the different irradiation times are selected from one of 0.2s, 0.5s, 0.8s, 1.6s, 1.8s, 2.0s or 2.3s.

[0074] Specifically, using a light pattern mask, after being irradiated for 0.2s, 0.5s, 0.8s, 1.6s, 1.8s, 2.0s or 2.3s, the pattern area of ​​the cholesteric liquid crystal respectively presents one of aquamarine (523.70nm), turquoise (542.86nm), spring green (559.58nm), yellow-green (596.85nm), yellow-orange (623.69nm), red-orange (641.00nm) and red (662.19nm).

[0075] In a preferred example, the non-responsive chiral dopant is selected from one or both of S5011 and S811. The chiral dopant is doped into the liquid crystal host to induce the nematic liquid crystal to twist and then form a cholesteric liquid crystal.

[0076] Doping chiral azobenzene into nematic liquid crystals can induce the nematic liquid crystals to twist and form cholesteric liquid crystals, but the helical twisting force is low. A large amount of chiral azobenzene needs to be doped to make the reflection wavelength within the visible light range. Too high a concentration of chiral azobenzene will cause the physical properties of the liquid crystal matrix to change, and may even lead to a decrease in the performance of the liquid crystal. A left-handed chiral dopant S5011 having the same chirality as the chiral azobenzene molecule and a high helical twisting force is doped into the system to reduce the content of chiral azobenzene. The overall mass fraction of the chiral dopant in the raw material is selected to be 4.4-5.2wt%. For example, the chiral azobenzene molecules suitable for this embodiment include but are not limited to the compounds shown in the following structural formula:

[0077]

[0078] In another preferred example, the liquid crystal host is selected from one or more of E7, SLC1717, and 5CB; and the liquid crystal host is in a liquid crystal state at room temperature.

[0079] In another preferred example, the raw materials include: 1.0-1.4 parts of a non-responsive chiral dopant, 3.4-3.8 parts of a light / heat responsive chiral azobenzene dopant, and 95.6-94.8 parts of a liquid crystal host, wherein the total amount of the aforementioned components is 100 parts by mass.

[0080] Another specific embodiment of the present invention provides a method for preparing the cholesteric liquid crystal as described above, comprising the following steps:

[0081] uniformly mixing a non-responsive chiral dopant, a light / heat responsive chiral azobenzene dopant, and a liquid crystal host to obtain a cholesteric liquid crystal mixture;

[0082] pouring the cholesteric liquid crystal mixture into a liquid crystal cell rubbed and aligned with polyvinyl alcohol to obtain the cholesteric liquid crystal with planar alignment;

[0083] In a preferred example, the method for uniform mixing is: dissolving a non-responsive chiral dopant, a light / heat responsive chiral azobenzene dopant, and a liquid crystal host in dichloromethane, and placing the mixture in an oven at 40-60°C until the dichloromethane is completely evaporated, thereby preparing a CLC mixture reflecting blue.

[0084] In a preferred example, the method for preparing the planar alignment layer comprises the following steps:

[0085] (1) Preparation of polyvinyl alcohol aqueous solution as a planar alignment layer:

[0086] 3 g of commercially available white solid particles of polyvinyl alcohol were added to 97 mL of deionized water, and the mixture was placed on a heating table at 200° C. and stirred and heated to dissolve for 5 h to obtain a 3 wt % aqueous solution of polyvinyl alcohol.

[0087] (2) Cleaning method of glass substrate used for polyvinyl alcohol planar alignment layer:

[0088] (a) Ultrasonic cleaning with neutral detergent for 30 minutes

[0089] (b) Clean with tap water for 30 minutes

[0090] (c) Ultrasonic cleaning with deionized water for 30 min

[0091] (d) Ethanol ultrasonic cleaning for 30 min

[0092] (e) Place in a drying oven at 80°C for drying and set aside.

[0093] (3) Preparation method of polyvinyl alcohol planar alignment layer:

[0094] (a) Using a benchtop spin coater, spin coat a clean glass substrate with a 3 wt% aqueous solution of polyvinyl alcohol at 400-800 rpm for 10-20 seconds, and then at 2000-4000 rpm for 20-40 seconds, thereby forming a polyvinyl alcohol alignment layer. Prior to spin coating the polyvinyl alcohol solution using the benchtop spin coater, it is best to apply a thin layer of the polyvinyl alcohol solution to the glass substrate using a plastic dropper.

[0095] (b) The glass substrate coated with the polyvinyl alcohol aqueous solution was placed in an oven at 80°C for 1 hour and dried. The polyvinyl alcohol thin coating was rubbed 10-20 times in the same direction with a rayon cloth to achieve alignment. The rubbed and aligned polyvinyl alcohol thin coating was then ultrasonically washed with ethanol for 10 minutes and finally dried with nitrogen.

[0096] In a preferred example, the method for preparing the liquid crystal cell includes the following steps:

[0097] (1) Preparation of spacer pads:

[0098] The spacers used in preparing the liquid crystal cell are made of a polyethylene terephthalate (PET) plastic film with a thickness of 15 μm. The PET plastic film is cut into strips of 1 mm*3 cm using scissors.

[0099] (2) Packaging of liquid crystal box:

[0100] Take two planar-oriented glass substrates and place them opposite each other with one side of the polyvinyl alcohol orientation layer parallel to the orientation direction. Use a 15μm thick PET plastic film spacer to control the spacing between the two glass substrates (the cell spacing of the liquid crystal box). That is, the strip is placed at the edge of the long axis of the planar-oriented glass substrate, and then covered with another planar-oriented glass substrate. Then, use a paper clip to dip a small amount of 502 glue and apply it to both sides of the glass substrate for edge sealing. Finally, use a dovetail clamp to clamp both sides of the glass substrate and place it at room temperature to cure the 502 glue. The curing time is about 10 minutes, thus completing the preparation of the blank liquid crystal box.

[0101] In a preferred example, the method for producing a planar-oriented cholesteric liquid crystal comprises the following steps:

[0102] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the blank liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0103] Another embodiment of the present invention provides a method for adjusting the photonic band gap of cholesteric liquid crystal by changing the concentration of a chiral dopant and the temperature, comprising the following steps:

[0104] A cholesteric liquid crystal with a planar orientation and an initial blue color is placed on a heating table and heated to obtain a cholesteric liquid crystal with a reflection color in the visible light region.

[0105] In a preferred example, the cholesteric liquid crystal has an initial color of blue, the concentration of the chiral azobenzene or the concentration of the non-responsive chiral dopant is fixed, and the concentration of the other chiral dopant is adjusted, wherein the concentration of the chiral azobenzene molecules is 3.4-3.8 wt %, and the concentration of the non-responsive chiral dopant is 1.0-1.4 wt %;

[0106] In a preferred example, the temperature range of the heated cholesteric liquid crystal is 25-52°C;

[0107] In a preferred example, the photonic band gap of the heated cholesteric liquid crystal can be adjusted to a range of 441-685 nm.

[0108] Another specific embodiment of the present invention provides a method for adjusting the photonic band gap of cholesteric liquid crystal by changing irradiation time and temperature, comprising the following steps:

[0109] The cholesteric liquid crystal with a planar orientation and an initial blue color is irradiated for different times using a photomask to obtain a photon pattern in which the color of the irradiated area is in the visible light region and the non-irradiated area is a blue background. The liquid crystal is then heated again to adjust the photonic band gap.

[0110] In a preferred example, the cholesteric liquid crystal with an initial color of blue has a concentration of chiral azobenzene molecules of 3.5 wt %, a concentration of the non-responsive chiral dopant of 1.4 wt %, and an initial band gap of 463.45 nm.

[0111] In a preferred example, a photomask is used to irradiate the sample for different times, which are 0.2, 0.5, 0.8, 1.6, 1.8, 2.0 and 2.3 seconds.

[0112] In a preferred example, the temperature range of the heated cholesteric liquid crystal is 25-52°C;

[0113] In a preferred example, the pattern colors of the exposed area are aquamarine (523.70 nm), turquoise (542.86 nm), spring green (559.58 nm), yellow-green (596.85 nm), yellow-orange (623.69 nm), red-orange (641.00 nm), and red (662.19 nm).

[0114] In a preferred example, a photomask is used to irradiate the sample for 0.2 seconds, and then the entire liquid crystal cell is heated. The photonic bandgap of the background color can be adjusted to a range of 463.45-679.41 nm, and the photonic bandgap of the pattern color can be adjusted to a range of 523.70-648.86 nm.

[0115] Another embodiment of the present invention provides a method for preparing a reversible electrical response pattern of cholesteric liquid crystal, comprising the following steps:

[0116] A cholesteric liquid crystal with a planar orientation and an initial blue color was irradiated with a photomask for 0.8 seconds, obtaining a photon pattern with a spring green color in the irradiated area and a blue background in the non-irradiated area. Then, voltage was applied again to achieve reversible erasure and appearance of the photon pattern.

[0117] In a preferred example, the cholesteric liquid crystal with an initial color of blue has a concentration of chiral azobenzene molecules of 3.5 wt %, a concentration of non-responsive chiral dopant of 1.4 wt %, and an initial band gap of 463.45 nm;

[0118] In a preferred example, a photomask is used to irradiate the sample, the irradiation time is 0.8s, and the color of the irradiated area is spring green;

[0119] In a preferred example, the voltage applied to the cholesteric liquid crystal is in the range of 0-65 V. When the threshold voltage of 65 V is reached, the pattern and background are completely erased. After the voltage is removed, the pattern and background reappear when a finger presses the sample.

[0120] In another embodiment of the present invention, there is provided an application of the cholesteric liquid crystal as described above in the field of photon patterning or anti-counterfeiting.

[0121] Since cholesteric liquid crystals exhibit different colors after being irradiated with UV for different times, when the liquid crystal box is heated again, both the background color and the pattern color change, making it well suited for applications in the field of patterned anti-counterfeiting.

[0122] The technical solution of the present invention is described below with reference to some specific embodiments:

[0123] Example 1

[0124] 1. Preparation of liquid crystal cell with polyvinyl alcohol planar alignment layer

[0125] 3g of commercially available white solid polyvinyl alcohol (PVA) particles were added to 97mL of deionized water and heated on a 200°C heating plate for 5 hours with stirring to dissolve. This yielded a 3wt% aqueous solution of PVA. Using a benchtop spin coater, a clean glass substrate was spin-coated with the 3wt% PVA solution at 400 rpm for 10 seconds and then at 3500 rpm for 30 seconds. This completed the preparation of the PVA alignment layer. Before spin-coating the PVA solution using the benchtop spin coater, it is best to apply a thin layer of PVA solution to the glass substrate using a plastic dropper. The PVA-coated glass substrate was then heated in an 80°C oven for 1 hour and dried. The oriented PVA coating was then rubbed 10 times with a rayon cloth in the same direction. The rubbed oriented PVA coating was then ultrasonically cleaned with ethanol for 10 minutes and then dried with nitrogen. The spacer used to prepare the liquid crystal box is made of polyethylene terephthalate (PET) plastic film with a thickness of 15μm. Use scissors to cut the PET plastic film into 1mm*3cm strips. Take two planar-oriented glass substrates and place one side of the polyvinyl alcohol orientation layer parallel to each other along the orientation direction. Use a 15μm thick PET plastic film spacer to control the spacing between the two glass substrates (the box spacing of the liquid crystal box). That is, the strip is placed at the edge of the long axis of the planar-oriented glass substrate and then covered with another planar-oriented glass substrate. Then, use a paper clip to dip a small amount of 502 glue and apply it to both sides of the glass substrate for edge sealing. Finally, use a dovetail clamp to clamp both sides of the glass substrate and place it at room temperature to cure the 502 glue for about 10 minutes, thereby completing the preparation of the blank liquid crystal box.

[0126] 2. Preparation of CLC mixture reflecting blue

[0127] Dissolve 1 part of a non-responsive chiral dopant, 3.5 parts of a photo- or thermo-responsive chiral azobenzene, and 95.5 parts of a liquid crystal host in dichloromethane. Stir evenly on a 40°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0128] 3. Preparation of cholesteric liquid crystals with planar orientation

[0129] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 45°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0130] Example 2

[0131] 1. Preparation of polyvinyl alcohol orientation layer is the same as in Example 1

[0132] 2. Preparation of CLC mixture reflecting blue

[0133] Dissolve 1.1 parts of a non-responsive chiral dopant, 3.5 parts of a photo- or thermo-responsive chiral azobenzene, and 95.4 parts of a liquid crystal host in dichloromethane. Stir evenly on a 44°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0134] 3. Preparation of cholesteric liquid crystals with planar orientation

[0135] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 35°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0136] Example 3

[0137] 1. Preparation of polyvinyl alcohol orientation layer is the same as in Example 1

[0138] 2. Preparation of CLC mixture reflecting blue

[0139] Dissolve 1.2 parts of a non-responsive chiral dopant, 3.5 parts of a photo- or thermo-responsive chiral azobenzene, and 95.3 parts of a liquid crystal host in dichloromethane. Stir evenly on a 43°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0140] 3. Preparation of cholesteric liquid crystals with planar orientation

[0141] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 40°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0142] Example 4

[0143] 1. Preparation of polyvinyl alcohol orientation layer is the same as in Example 1

[0144] 2. Preparation of CLC mixture reflecting blue

[0145] Dissolve 1.3 parts of a non-responsive chiral dopant, 3.5 parts of a photo- or thermo-responsive chiral azobenzene, and 95.2 parts of a liquid crystal host in dichloromethane. Stir evenly on a 42°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0146] 3. Preparation of cholesteric liquid crystals with planar orientation

[0147] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 40°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0148] Example 5

[0149] 1. Preparation of polyvinyl alcohol orientation layer is the same as in Example 1

[0150] 2. Preparation of CLC mixture reflecting blue

[0151] Dissolve 1.4 parts of a non-responsive chiral dopant, 3.5 parts of a photo- or thermo-responsive chiral azobenzene, and 95.1 parts of a liquid crystal host in dichloromethane. Stir evenly on a 40°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0152] 3. Preparation of cholesteric liquid crystals with planar orientation

[0153] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 41°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0154] Example 6

[0155] 1. Preparation of polyvinyl alcohol orientation layer is the same as in Example 1

[0156] 2. Preparation of CLC mixture reflecting blue

[0157] Dissolve 1.0 part of a non-responsive chiral dopant, 3.4 parts of a photo- / thermo-responsive chiral azobenzene, and 95.6 parts of a liquid crystal host in dichloromethane. Stir evenly on a 46°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0158] 3. Preparation of cholesteric liquid crystals with planar orientation

[0159] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 50°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0160] Example 7

[0161] 1. Preparation of polyvinyl alcohol orientation layer is the same as in Example 1

[0162] 2. Preparation of CLC mixture reflecting blue

[0163] Dissolve 1.0 part of a non-responsive chiral dopant, 3.6 parts of a photo- / thermo-responsive chiral azobenzene, and 95.4 parts of a liquid crystal host in dichloromethane. Stir evenly on a 40°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0164] 3. Preparation of cholesteric liquid crystals with planar orientation

[0165] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 47°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0166] Example 8

[0167] 1. Preparation of polyvinyl alcohol orientation layer is the same as in Example 1

[0168] 2. Preparation of CLC mixture reflecting blue

[0169] Dissolve 1.0 part of a non-responsive chiral dopant, 3.7 parts of a photo- or thermo-responsive chiral azobenzene, and 95.3 parts of a liquid crystal host in dichloromethane. Stir evenly on a 40°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0170] 3. Preparation of cholesteric liquid crystals with planar orientation

[0171] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 48°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0172] Example 9

[0173] 1. Preparation of polyvinyl alcohol orientation layer is the same as in Example 1

[0174] 2. Preparation of CLC mixture reflecting blue

[0175] Dissolve 1.0 part of a non-responsive chiral dopant, 3.8 parts of a photo- or thermo-responsive chiral azobenzene, and 95.2 parts of a liquid crystal host in dichloromethane. Stir evenly on a 40°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0176] 3. Preparation of cholesteric liquid crystals with planar orientation

[0177] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 49°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0178] Example 10

[0179] 1. Preparation of polyvinyl alcohol orientation layer is the same as in Example 1

[0180] 2. Preparation of CLC mixture reflecting blue

[0181] Dissolve 1.05 parts of a non-responsive chiral dopant, 3.5 parts of a photo- / thermo-responsive chiral azobenzene, and 95.45 parts of a liquid crystal host in dichloromethane. Stir evenly on a 40°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0182] 3. Preparation of cholesteric liquid crystals with planar orientation

[0183] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 44.5°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the blank liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0184] Example 11

[0185] 1. Preparation of polyvinyl alcohol orientation layer is the same as in Example 1

[0186] 2. Preparation of CLC mixture reflecting blue

[0187] Dissolve 1.15 parts of a non-responsive chiral dopant, 3.5 parts of a photo- or thermo-responsive chiral azobenzene, and 95.35 parts of a liquid crystal host in dichloromethane. Stir evenly on a 40°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0188] 3. Preparation of cholesteric liquid crystals with planar orientation

[0189] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 43.5°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0190] Example 12

[0191] 1. Preparation of polyvinyl alcohol orientation layer is the same as in Example 1

[0192] 2. Preparation of CLC mixture reflecting blue

[0193] Dissolve 1.25 parts of a non-responsive chiral dopant, 3.5 parts of a photo- or thermo-responsive chiral azobenzene, and 95.25 parts of a liquid crystal host in dichloromethane. Stir evenly on a 40°C heating plate until the dichloromethane evaporates completely. This creates a blue-reflecting CLC mixture.

[0194] 3. Preparation of cholesteric liquid crystals with planar orientation

[0195] Take a blank liquid crystal box, heat the configured cholesteric liquid crystal mixture to 42.5°C to an isotropic state, and pour the cholesteric liquid crystal mixture in the isotropic phase into the liquid crystal box through capillary action. Then cool it to the cholesteric liquid crystal temperature to obtain cholesteric liquid crystal with planar orientation.

[0196] Example 13

[0197] Effects of Chiral Dopant Concentration and Temperature on the Photonic Band Gap of Cholesteric Liquid Crystals

[0198] Polarization optical microscope and fiber spectrometer were used to monitor the change of reflection color and photonic band gap position of cholesteric liquid crystal in real time. Cholesteric liquid crystal reflecting blue was selected as the starting sample for testing. The liquid crystal box filled with cholesteric liquid crystal mixture was placed on a hot stage with a black substrate, and the light-driven CLC showed temperature-driven red, green and blue reflection colors. When the concentration of chiral azobenzene was changed from 3.8wt% to 3.4wt%, and the concentration of non-responsive chiral dopant S5011 was kept constant at 1.0wt%; or when the concentration of non-responsive chiral dopant S5011 was changed from 1.4wt% to 1.0wt%, and the concentration of chiral azobenzene was kept constant at 3.5wt%, the reflection wavelength shifted from blue to red as the concentration of chiral dopant decreased ( Figure 1 A and 1B). Typically, when the concentration of S5011 is 1.4wt%, the concentration of chiral azobenzene is 3.5wt%, and the concentration of E7 is 95.1wt%, at 25°C, the initial reflection color of CLCs is blue, and the initial reflection wavelength is 463.45nm. When heated to 35°C, a cyan color with a reflection center at 488.02nm appears. When heated to 40°C, it produces a yellow-green color with a reflection center at 526nm. When the temperature reaches 50°C, a red color with a photonic band gap position at 678.63nm is produced ( Figure 1 C) The temperature-driven change in reflective color may be due to the helical expansion with the increase of thermal energy, which leads to a decrease in the HTP of chiral azobenzene. The effect of changes in chiral dopant concentration and temperature on the photonic band gap of cholesteric liquid crystals is shown in Figure 2. Figure 1 shown.

[0199] Example 14

[0200] Modulation of the Photonic Band Gap of Cholesteric Liquid Crystals by Varying Irradiation Time and Temperature

[0201] Polarization optical microscopy and fiber optic spectrometer were used to monitor the changes in the reflective color and photonic band gap position of cholesteric liquid crystals in real time. Cholesteric liquid crystals reflecting blue were selected as the starting sample for testing. The liquid crystal box filled with the cholesteric liquid crystal mixture was placed on a hot stage with a black substrate. In order to adjust the reflection band to the visible light region, the composition of the CLCs mixture was modulated to 3.5wt% chiral azobenzene molecules, 1.4wt% S5011 and 95.1wt% E7. Utilizing the temperature response based on chiral azobenzene molecules, thermochromic dynamic color patterns were created by ultraviolet pre-irradiation writing using a photomask with an apple shape ( Figure 2 A). That is, the light / heat dual-responsive CLC achieves dynamic color regulation through two steps (first step: irradiation, second step: heating). The color is modulated by changing the irradiation time and subsequent temperature. The exposed pattern color and the unexposed background color show the characteristic of color red shift due to the controllable temperature. In order to study the relationship between temperature and reflection band, the reflection spectrum of the CLCs mixture was measured at different temperatures ( Figure 2 C). At 25°C, the CLC mixture is in the cholesteric phase and blue relative to the background color. Above 51°C, the CLC mixture is transparent due to its isotropic phase. Between 25 and 51°C, the reflection band is consistent with the color of a digital photograph. Upon heating, the reflection band gap is centered at approximately 463.45 nm at 25°C and red-shifts to 679.41 nm at 51°C. Thus, the visible light region can be fully covered within the temperature range of 25 to 51°C. This tunable reflection band gap in response to temperature changes is caused by the helical expansion of the CLC with increasing thermal energy, which gradually increases the helical pitch of the CLC and causes the reflection band gap to red-shift during heating from 25°C to 51°C. Therefore, this CLC mixture exhibits excellent thermochromic properties. For the pattern colors, when the CLCs were irradiated for 0.2s, 0.5s, 0.8s, 1.6s, 1.8s, 2.0s, or 2.3s, the “apple” pattern in the exposed area showed aquamarine (523.70nm), turquoise (542.86nm), spring green (559.58nm), yellow-green (596.85nm), yellow-orange (623.69nm), red-orange (641.00nm), and red (662.19nm), respectively. Figure 2 B) Subsequently, the color of the "apple" pattern irradiated for different times undergoes a red shift as the temperature increases.

[0202] Thermochromism provides a reversible color response to a specific temperature that can be observed with the naked eye. However, visual detection of thermochromism only roughly interprets the temperature. Therefore, CLCs based on temperature-responsive chiral azobenzene molecules should be integrated with a suitable readout platform to convert the temperature-induced color into a numerical value. Typically, fiber optic spectrometers are used to measure the reflected wavelength. Although fiber optic spectrometers provide precise analysis of wavelength shifts, the benchtop equipment involved is bulky, expensive, and inconvenient for outdoor use. The use of smartphones in analytical methods has increasingly attracted attention for color quantification. Because smartphones are equipped with built-in high-resolution cameras, color data can be collected from samples as digital images and then converted to specific values. For smartphone-based color analysis to be effective, various image parameters need to be considered. The hue (H), saturation (S), and value (V) color space is derived from RGB data. Each of the three parameters can be interpreted as follows: Hue (H), with a value between 0 and 360, is the dominant wavelength color, while saturation (S) refers to the color intensity. As saturation increases, the color appears increasingly pure. Value (V) refers to the lightness or darkness of the color. H is a good alternative parameter because the color represented by a single numerical value closely matches the perceived color represented by the wavelength. Therefore, the color analysis of a series of "apple" patterns based on temperature-responsive chiral azobenzene molecules under UV pre-irradiation for different times was studied. Photo images of the "apple" pattern containing RGB data were processed to extract the H parameter. The reflected color images of the thermochromic samples were captured using the built-in camera (HUAWEI nova 9). The camera application was set to automatic mode, and the background of the subject was defined as a black substrate to obtain brighter structural colors. The image was imported into a color application (Pipettestefan TrostMedia) and the H parameter value was obtained from the central area of ​​the sample. The effects of irradiation time and temperature on the perceived color were studied by changing the UV pre-irradiation time and temperature ( Figure 2 D1 and Figure 2 D2) During each UV pre-irradiation time, the H parameter of the exposed pattern area decreases with increasing temperature before the CLCs reach the clearing point. This can be attributed to the decrease in the order of CLCs with increasing temperature. The effect of changing the irradiation time and temperature on the photonic band gap of cholesteric liquid crystals is shown in Figure 2. Figure 2 shown.

[0203] Example 15

[0204] Light / heat dual-responsive patterned anti-counterfeiting design

[0205] Polarization optical microscopy and fiber optic spectrometer were used to monitor the changes in the reflective color and photonic band gap position of cholesteric liquid crystals in real time. A cholesteric liquid crystal reflecting blue was selected as the starting sample for testing. The liquid crystal cell filled with the cholesteric liquid crystal mixture was placed on a hot stage with a black substrate. Compared with single-response materials, dual-response photonic CLCs have greater potential in the development of anti-counterfeiting pattern applications and can provide users with additional useful information. Typically, these patterns are formed by a single irradiation step in a single liquid crystal cell in a predefined template using photomask technology. Here, we propose a simple method to design anti-counterfeiting patterns in which the background color and the "apple" pattern color change with increasing temperature. Compared with conventional CLCs that only display static and fixed color patterns, our CLCs system contains both light and heat driving sources, which can accurately adjust the dynamic colors in the pattern. In an exemplary manner, the "apple" pattern was generated at 18.6 mW cm at 25 °C. -2 The UV intensity was exposed to UV light for 0.2s, which fixed the 523.70nm reflection band gap in this area to aquamarine color ( Figure 3 B1). The sample is then heated to 46°C, causing the color of the unexposed area (background color) to change from blue to light green, and the reflection wavelength to change from 463.45 nm to 566.73 nm ( Figure 3 A1). At the same time, the "apple" pattern area is fixed to green-yellow, and the reflection band gap is 565.94nm ( Figure 3 B1). In this way, the photonic band gap positions of the background color and the pattern color tend to be the same ( Figure 3 C1 and 3C2, green dotted circles). Therefore, the "apple" pattern is well hidden. Then, at 47℃, the green-yellow background color turns to golden yellow, and the reflection band gap is 601.60nm ( Figure 3 A1 and Figure 3 A2), the “apple” pattern reappears and changes to chocolate color with a reflection band gap of 611.08nm ( Figure 3 B1 and Figure 3 B2). At 50°C, slightly below the isotropic transition temperature, the background color and pattern color show different shades of brown. When the isotropic temperature reaches 52°C, the background color and pattern color mostly become colorless. Figure 3 shown.

[0206] Example 16

[0207] Effect of changes in the reversible electrical response pattern of cholesteric liquid crystals

[0208] By applying a voltage, the spatially patterned image can be gradually erased ( Figure 4A). Specifically, below 30V, the image color remains unchanged, i.e., the background is blue and the "apple" pattern is spring green. At 40V, a local area of ​​the image is erased. Subsequently, as the voltage increases from 40V to 60V, the area of ​​the image where it is erased gradually increases. At 60V, the "apple" pattern is completely erased, while a small area of ​​blue background is left at the bottom of the image. Finally, when the voltage reaches 65V (1Hz), the background color and pattern color of the image are completely erased due to the helical axis switching from an ordered planar state to a randomly arranged scattered focal conic state. After the voltage is removed, the "apple" pattern reappears, but the background remains colorless. Interestingly, due to the orientation effect caused by shear flow, the image is completely restored under pressure.

[0209] One advantage of the photo-thermal dual-responsive CLC system is its potential to provide full-color tunability of background and pattern, as well as the ability to electrically switchable imaging. Figure 4 As shown in B. Under 365nm light irradiation at 25℃, a spring green "apple" pattern was written into the sample through a photomask ( Figure 4 B1). After reaching the isotropic temperature of 52°C, the image becomes colorless ( Figure 4 B2), which is attributed to the helical axis changing from a planar state with ordered orientation ( Figure 4 C1, 4C'1, bottom) changes to an isotropic state ( Figure 4 C2, 4C'2, bottom). The color reappears with cooling in the isotropic state. At 25 °C, a spring green "apple" pattern and a blue background are observed ( Figure 4 B3). Once again, the patterned image can be hidden by applying a voltage. After applying a voltage of 65V, the background and the reflected color of the light-written pattern are erased ( Figure 4 B4), which is due to the change of the helical axis from a planar state with ordered orientation ( Figure 4 C3, 4C'3, bottom) changes to a randomly oriented scattering focal conic state ( Figure 4 C4, 4C'4, bottom). Simply apply pressure to recover the hidden image ( Figure 4 B5). It is worth noting that this image does not require expensive driving circuits or complex ITO patterns on the substrate surface, as only two simple unpatterned transparent electrodes are used. The CLC texture initially formed is a planar texture ( Figure 4 C1, 4C'1, top), because the parallel alignment layer provides a strong anchoring, a single domain texture is generated. The helical axis in the domain is perpendicular to the substrate surface, and Bragg reflection can be obtained. When a voltage of 65 V is applied, the texture is converted to a focal conic texture ( Figure 4 C4, 4C'4, top), a scattering state in which the helical axes are randomly arranged ( Figure 4C4, 4C'4, bottom). The scattered light effectively hides the image written by UV irradiation. When mechanical force is applied to the sample, the planar orientation effect induced by shear flow ( Figure 4 C5, 4C'5, bottom), the planar texture appears ( Figure 4 C5, 4C'5, top), original image restored. This result provides new insights into the development of light / thermal / electrically driven CLC systems for practical applications.

[0210] The above performance tests were repeatedly performed using the cholesteric liquid crystals prepared in Examples 1-16, and the results were the same as above.

[0211] Comparative Example 1

[0212] We also prepared CLCs with other concentration ratios and used them to study the effect of the chiral dopant concentration ratio on the band gap shift under heating. Two parts of a non-responsive chiral dopant, two parts of a photo- / thermo-responsive chiral azobenzene, and 96 parts of a liquid crystal host were dissolved in dichloromethane and stirred on a 45°C hotplate until the dichloromethane evaporated completely, yielding a CLC mixture that reflected blue. A blank liquid crystal cell was prepared and the prepared cholesteric liquid crystal mixture was heated to 50°C until it became isotropic. The isotropic cholesteric liquid crystal mixture was then poured into the cell via capillary action. The cell was then cooled to the cholesteric liquid crystal temperature, yielding a planar, blue-reflecting cholesteric liquid crystal. The cell was heated on a hotplate. As the temperature increased from 20°C to 50°C, the sample's reflectance shifted from blue (480 nm) to green (523 nm), ultimately returning to colorless in the isotropic state. The band gap shifted slightly in the visible region, suggesting that further optimization of the chiral dopant concentration ratio is needed.

[0213] Using the same sample preparation method, CLCs with varying chiral dopant concentrations were prepared. Maintaining the S5011 concentration at 1wt%, the chiral azobenzene dopant concentrations were 1wt%, 1.5wt%, 2wt%, 2.5wt%, and 3wt%, respectively. The corresponding initial band gaps of the CLCs were 619nm, 590nm, 560nm, 531nm, and 501nm, respectively. The initial reflected color was red or green. Subsequent heating resulted in a redshift of the CLC band gap to the near-infrared region, making the color invisible to the naked eye. Therefore, the chiral dopant concentrations described above do not meet the requirements for tunability in the visible light region.

[0214] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A cholesteric liquid crystal with light / thermal / electrical response, characterized in that: The cholesteric liquid crystal is obtained by mixing a non-responsive chiral dopant, a light / heat responsive chiral azobenzene dopant, and a liquid crystal host; The cholesteric liquid crystal is in a planar orientation in a liquid crystal cell oriented by horizontal rubbing of polyvinyl alcohol; The concentration of the chiral azobenzene dopant is 3.4-3.8 wt %; The non-responsive chiral dopant is selected from S5011; The liquid crystal host is selected from E7; The chiral azobenzene dopant is selected from one of the following structures: C 46 H 50 N4O2; C 50 H 58 N4O2; C 54 H 66 N4O2; C 58 H 74 N4O2.

2. The cholesteric liquid crystal according to claim 1, wherein The initial band gap of the cholesteric liquid crystal is 441-481 nm.

3. The cholesteric liquid crystal according to claim 1, wherein In the raw materials, the concentration of the non-responsive chiral dopant is 1.0-1.4 wt %.

4. The cholesteric liquid crystal according to claim 1, wherein Based on 100 parts by mass of the total raw materials, the raw materials include: 1.0-1.4 parts of a non-responsive chiral dopant, 3.4-3.8 parts of a light / heat responsive chiral azobenzene dopant, and 95.6-94.8 parts of a liquid crystal host.

5. The method for preparing cholesteric liquid crystal according to any one of claims 1 to 4, wherein: The steps include: uniformly mixing a non-responsive chiral dopant, a light / heat responsive chiral azobenzene dopant, and a liquid crystal host to obtain a cholesteric liquid crystal mixture; The cholesteric liquid crystal mixture is poured into a liquid crystal box rubbed and aligned with polyvinyl alcohol to obtain the cholesteric liquid crystal with planar alignment.

6. A method for adjusting the photonic band gap of cholesteric liquid crystal, characterized in that: The steps include: Adjust the irradiation time and heating temperature to keep the composition of cholesteric liquid crystal unchanged: irradiating the cholesteric liquid crystal according to any one of claims 1 to 4 with a 365 nm light source; The cholesteric liquid crystals irradiated with a 365nm light source for different periods of time were heated again to adjust the photonic band gap.

7. The method according to claim 6, characterized in that The heating temperature range is 25-52°C.

8. The method according to claim 6, characterized in that After irradiating the cholesteric liquid crystal with a 365 nm light source for 0.2 s, 0.5 s, 0.8 s, 1.6 s, 1.8 s, 2.0 s, or 2.3 s, the cholesteric liquid crystal is placed on a heating table and heated to adjust the photonic band gap.

9. A method for adjusting the photonic band gap of cholesteric liquid crystal, characterized in that: The steps include: Adjust the content of chiral dopant in cholesteric liquid crystal and heating temperature, and fix the irradiation time: irradiating the cholesteric liquid crystal according to any one of claims 1 to 4 with a 365 nm light source; The cholesteric liquid crystal irradiated by a 365nm light source is heated again to adjust the photonic band gap.

10. The method according to claim 9, characterized in that The heating temperature range is 25-52°C.

11. A method for preparing a reversible electrical response pattern of cholesteric liquid crystal, characterized in that: The steps include: Adjust the voltage applied to the cholesteric liquid crystal and fix the content of the chiral dopant, heating temperature and irradiation time: irradiating the cholesteric liquid crystal according to any one of claims 1 to 4 with a 365 nm light source; A voltage is applied to the cholesteric liquid crystal after being irradiated by a 365nm light source, and the voltage is adjusted to achieve the preparation of a reversible electrical response pattern.

12. The preparation method according to claim 11, characterized in that The applied voltage ranges from 0 to 65V.

13. Use of the cholesteric liquid crystal according to any one of claims 1 to 4 in the field of photon patterning or anti-counterfeiting.

Images