Intelligent dimming film with low driving voltage and quick response

Abstract

The invention provides an intelligent dimming film with low driving voltage and quick response, and belongs to the technical field of liquid crystal dimming films.Ferroelectric nematic liquid crystals DIO, liquid crystal monomers RM257, non-liquid crystal monomers EHA and photoinitiators IRG 651 are evenly mixed according to a certain proportion, then the mixture is poured into a liquid crystal box with indium tin oxide electrodes at a certain temperature, and the liquid crystal box with the indium tin oxide electrodes is formed. Electrodes are connected through wires, an alternating current electric field with certain intensity is applied, meanwhile, ultraviolet radiation is adopted for polymerization till complete curing is achieved, and the intelligent thin film based on the polymer constraint ferroelectric nematic phase liquid crystal with ultralow driving voltage and high response speed can be obtained. The intelligent thin film is easy to prepare, high in yield, low in driving voltage and stable in performance, energy consumption of building materials can be greatly reduced, and use safety can be greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid crystal dimming films, and specifically relates to an intelligent dimming film with low driving voltage and fast response. Background Art

[0002] The liquid crystal dimming film is an intelligent device that can dynamically control light. Its core principle is to manipulate the orientation of liquid crystal molecules through an electric field, and then dynamically control the light transmittance of the film to achieve the switching of the film between transparent / opaque states. This device has broad application prospects in intelligent buildings and intelligent car windows, etc. However, existing liquid crystal dimming film devices still have key problems such as high driving voltage and slow response speed, which not only limit their application in occasions with high safety requirements, but also are difficult to meet the urgent needs of modern society for energy conservation and emission reduction. Based on this, the present invention proposes an intelligent dimming film with ultra-low driving voltage and fast response. Summary of the Invention

[0003] To solve the problem that the existing liquid crystal dimming film devices still have a high driving voltage, the present invention proposes an intelligent dimming film with low driving voltage and fast response. The preparation method of the intelligent dimming film of the present invention is: under the action of an electric field, a mixture composed of ferroelectric nematic liquid crystal, liquid crystal monomer, and non-liquid crystal monomer is polymerized by ultraviolet light. After the polymerization is completed, the molecular orientation of the ferroelectric nematic liquid crystal is restricted by the liquid crystal monomer polymer network arranged along the electric field and the non-liquid crystal monomer polymer network arranged randomly. The dielectric constant of the ferroelectric liquid crystal is very large, and in addition, the polymer network constraint has a pre-orientation effect on it. Therefore, the prepared polymer sample can realize the switching from the scattering state to the transparent state at a very low driving voltage, and the preparation of the ultra-low driving voltage intelligent dimming film is realized.

[0004] An intelligent dimming film with low driving voltage and fast response, its preparation method includes the following steps:

[0005] Step 1: Dissolve the ferroelectric nematic liquid crystal material DIO, liquid crystal monomer RM257, non-liquid crystal monomer EHA, and photoinitiator IRG 651 in a brown wide-mouth bottle containing dichloromethane solvent, and mix evenly; the structural formulas of DIO, RM257, EHA, and IRG 651 are as follows:

[0006]

[0007]

[0008] Step 2: Evaporate the mixed solution in Step 1 to obtain a liquid crystal mixture, and then heat and shake it to obtain a uniform liquid crystal mixture;

[0009] Step 4: Pour the liquid crystal mixture into the liquid crystal cell at a certain temperature, and then cool the temperature to make the liquid crystal mixture in the ferroelectric nematic phase;

[0010] Step 5: Apply a square-wave AC electric field to the liquid crystal cell, and at the same time perform ultraviolet light irradiation curing to complete the construction of the polymer network and obtain the intelligent dimming film.

[0011] Preferably, in the step 1, the mass ratio of DIO, RM257, EHA, and IRG 651 is 92:2.9:2.9:2.2.

[0012] Preferably, in the step 1, the way of mixing evenly is: seal it in a brown wide-mouth bottle, place it on a hot stage and heat it at 60°C - 70°C for 2 - 5 minutes, then transfer it to a vortex oscillator and shake it for 1 - 5 minutes, repeat heating and shaking for multiple times.

[0013] Preferably, the specific operation in the step 2 is: place the brown wide-mouth bottle on a hot stage, set the temperature to 70°C, and let it stand for 2 hours to obtain the liquid crystal mixture; subsequently, heat the liquid crystal mixture at 100 - 120°C for 5 - 10 minutes, and then shake it for 1 - 5 minutes to obtain a uniform liquid crystal mixture.

[0014] Preferably, the preparation method of the liquid crystal cell is: use an ultraviolet glue uniformly mixed with silica particles to bond two glass substrates with transparent indium tin oxide electrodes into a liquid crystal cell, and weld wires on the transparent indium tin oxide electrodes of each glass substrate respectively.

[0015] Preferably, the step 4 is specifically: pour the liquid crystal mixture into the liquid crystal cell prepared in the step 3 by capillary action at a high temperature of 120°C, and then cool the temperature to obtain the ferroelectric nematic phase. The specific cooling method is: cool it to 49 - 51°C at a speed of 5°C per minute, and keep it standing at 49 - 51°C for 5 - 10 minutes.

[0016] Preferably, the specific operation in the step 5 is: at 49 - 51°C, apply an AC square-wave electric field with an amplitude of 10vpp and a frequency of 1kHz to the liquid crystal cell in the step 4, and at the same time irradiate it with ultraviolet light with a power of 30mw / cm 2 and a wavelength of 365nm for 2 minutes to complete the curing and obtain the intelligent dimming film.

[0017] Beneficial effects:

[0018] (1) For the dimming film prepared by the present invention, while realizing the electric field switching between the transparent / scattering states, the driving voltage is greatly reduced. Among them, the threshold voltage is as low as 0.5V at the lowest, and the saturation voltage is as low as 9.0V at the lowest. The applied voltage is much lower than the human body safety voltage, greatly improving the safety of the product, and at the same time greatly reducing the energy consumption.

[0019] (2) The present invention can quickly realize the switching between the transparent and scattering states of the dimming film. The rise time of the light response waveform is about 0.25 ms at the shortest, and the fall time is about 0.4 ms at the shortest.

[0020] (3) The present invention has the advantages of low energy consumption, high safety, fast response speed, simple preparation, low cost, good stability, etc. Description of the Drawings

[0021] Figure 1 It is the chemical structural formula of the raw materials of the present invention, the schematic diagram of the process of the method of the present invention, and the schematic diagram of the molecular state in the dimming film with and without an electric field; among them, a is the chemical structural formula of DIO, RM257, EHA, and IRG 651, b is the schematic diagram of the preparation process of the dimming film, and c is the schematic diagram of the molecular state in the dimming film with and without an electric field.

[0022] Figure 2 It is the threshold voltage, saturation voltage, and contrast of the dimming film prepared in Example 1; among them, a is the threshold voltage and saturation voltage at different temperatures, and b is the contrast at different temperatures.

[0023] Figure 3 It is the response speed of the dimming film prepared in Example 1 tested at different voltages near room temperature.

[0024] Figure 4 It is the transmittance result of the dimming film prepared in Example 1 tested 3000 times under specific conditions.

[0025] Figure 5 It is the optical path diagram for testing the dimming film; from left to right in sequence are: a laser with a wavelength of 532 nm, a temperature-controlled hot stage (including a liquid crystal cell with a dimming film), and a photodetector. Detailed Embodiments

[0027] The technical solution of the present invention will be described in detail below through examples, but the protection scope of the present invention is not limited to the described examples.

[0028] In the embodiments of the present invention, the ferroelectric nematic liquid crystal material DIO is from Nanjing Shuxin Technology Co., Ltd., the liquid crystal monomer RM257 is from Nanjing Leyao Co., Ltd., the non-liquid crystal monomer EHA is from Shanghai Macklin Biochemical Co., Ltd., and the photoinitiator IRG 651 is from Nanjing Leyao Technology Co., Ltd. The chemical structural formulas of DIO, RM257, EHA, and IRG 651 are as Figure 1 shown.

[0029] Example 1

[0030] This embodiment provides an intelligent dimming film based on polymer-constrained ferroelectric nematic liquid crystal with low driving voltage and fast response. The preparation method of the intelligent dimming film is as follows: Figure 1 as shown in b of the following, and includes the following steps:

[0031] Step 1: Dissolve ferroelectric nematic liquid crystal material DIO, liquid crystal monomer RM257, non-liquid crystal monomer EHA, and photoinitiator IRG 651 in dichloromethane solvent according to the ratio of 92wt%: 2.9wt%: 2.9wt%: 2.2wt%, transfer it into a brown wide-mouth bottle and seal it, place it on a hot stage and heat it at 70°C for 2 minutes, then transfer it to a vortex oscillator and shake it for 1 minute. Repeat the above heating and shaking processes 5 times to make the solution evenly mixed.

[0032] Step 2: Place the brown wide-mouth bottle containing the mixed solution on the hot stage for evaporation, set the temperature to 70°C, and let it stand for 2 hours to obtain a liquid crystal mixture; subsequently, heat the liquid crystal mixture at 120°C for 5 minutes, and then shake it for 2 minutes to obtain a homogeneous liquid crystal mixture.

[0033] Step 3: Use ultraviolet glue uniformly mixed with silica particles with a diameter of 20μm to bond two glass substrates with transparent indium tin oxide electrodes into a liquid crystal cell, and make the thickness of the liquid crystal cell 20 ± 0.5μm. Use two wires to weld to the transparent indium tin oxide electrodes on both sides of the glass substrate respectively. (The two wires are connected to the electrodes and are used to apply the electricity to be applied to the electrodes through the wires).

[0034] Step 4: Pour the liquid crystal mixture into the liquid crystal cell prepared in Step 3 by capillary action at a high temperature of 120°C, and then cool the temperature to make the liquid crystal mixture in the ferroelectric nematic phase; the specific cooling method: cool it to 50°C at a speed of 5°C per minute, and keep it standing at 50°C for 5 minutes.

[0035] Step 5: Vertically apply a square-wave alternating current electric field to the liquid crystal cell, and at the same time immediately perform ultraviolet light irradiation curing to complete the construction of the polymer network, and then obtain the intelligent dimming film. The specific method is: at 50°C, apply an alternating square-wave electric field with an amplitude of 10vpp and a frequency of 1kHz to the liquid crystal cell in Step 4, and at the same time irradiate it with ultraviolet light with a power of 30mw / cm 2 and a wavelength of 365nm for 2 minutes to complete the curing. Schematic diagrams of the molecular states in the dimming film with and without an electric field are as shown in c of the following. In this step, vertical means perpendicular to the upper and lower glass substrates. Since the electrodes are attached to the glass substrates, the applied electric field is perpendicular to the glass substrates (liquid crystal cell). Figure 1 as shown in c of the following. In this step, vertical means perpendicular to the upper and lower glass substrates. Since the electrodes are attached to the glass substrates, the applied electric field is perpendicular to the glass substrates (liquid crystal cell).

[0036] In the following Embodiment 2 - Embodiment 5 of the present invention, the test optical path is as shown in Figure 5As shown. The dimming films used were all prepared according to the steps of Example 1. Since 50°C is the phase transition temperature of the dimming film prepared by the method of the present invention and its performance is unstable, the dimming film was not tested near 50°C. In the present invention, it is defined that the transmittance is the percentage obtained by dividing the transmitted intensity by the maximum transmitted light intensity, and the threshold voltage V th is the voltage corresponding to when the transmittance increases by 10% from the minimum value, and the saturation voltage V sat is the voltage corresponding to when the transmittance reaches 90% of the maximum value. The contrast ratio (CR) is the ratio of the maximum transmittance to the minimum transmittance. The rise time corresponds to the time required for the transmitted intensity to rise from 10% to 90% of the maximum value, and the fall time corresponds to the time required for the transmitted intensity to fall from 90% to 10% of the maximum value.

[0037] Example 2

[0038] In Example 2, the threshold voltage Vth, saturation voltage Vsat, and contrast ratio CR of the dimming film prepared in Example 1 were tested. The test process is as follows:

[0039] The liquid crystal cell with the dimming film was placed in the optical path as Figure 5 shown. A square wave electric field with a frequency of 10 Hz (low level is 0 V) was applied to the dimming film at 30°C, 35°C, 40°C, 45°C, 60°C, 70°C, 80°C, and 100°C respectively. The test results are as Figure 2 shown.

[0040] At low temperatures (below 50°C), the liquid crystal mixture constituting the dimming film is ferroelectric nematic, i.e., NF; at high temperatures (above 50°C), the liquid crystal mixture constituting the dimming film is nematic, i.e., N.

[0041] As Figure 2 shown, the maximum threshold voltage of the dimming film prepared in Example 1 is 1.6 V (appearing at 30°C), and the minimum is 0.5 V (appearing at 70°C and 80°C). As the temperature increases, the threshold voltage shows a downward trend; the maximum saturation voltage is 18.1 V (appearing at 100°C), and the minimum is 9.0 V (appearing at 35°C). As the temperature increases, the saturation voltage shows a trend of decreasing - increasing - decreasing - increasing; the maximum contrast ratio is 57.5 (appearing at 35°C), and the minimum is 2.5 (appearing at 80°C), indicating that at low temperatures, the transmittance of the dimming film changes greatly, while at high temperatures, the transmittance of the dimming film changes little.

[0042] Example 3

[0043] The same electric field was applied to the dimming film prepared in Example 1, and the influence on its response speed was tested at different temperatures, specifically reflected by the rise time and fall time. The process is as follows:

[0044] Place the liquid crystal cell with the dimming film in the optical path as shown in Figure 5 the figure. Apply a square wave electric field with a frequency of 10 Hz, and low and high levels of 0 V and 10 V respectively to the dimming film at 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 70 °C, 80 °C, 92 °C, and 100 °C. Test results: At low temperatures (i.e., in the N F phase), the shortest rise time is about 0.25 ms, and the shortest fall time is about 0.4 ms. As the temperature increases, the rise time first remains between 0.25 and 0.3 ms, and then rises to about 0.9 ms, while the fall time shows a downward trend. At high temperatures (i.e., in the N phase), the shortest rise time is about 0.25 ms, and the shortest fall time is about 1.5 ms. As the temperature increases, both the rise time and the fall time show a downward trend.

[0045] Example 4

[0046] Test the effect of voltage magnitude on the response speed of the dimming film prepared in Example 1 at near room temperature, specifically reflected by the rise time and the fall time. The process is as follows:

[0047] Place the liquid crystal cell with the dimming film in the optical path as shown in Figure 5 the figure. Set the experimental temperature to 40 °C and apply a square wave electric field with a frequency of 10 Hz to the dimming film. Fix the low level at 0 V and increase the high level from 2 V in increments of 2 V to 20 V. The test results are as shown in Figure 3 the figure. As the voltage increases, the rise time first decreases and then remains at about 0.3 ms, while the fall time stabilizes near 0.6 ms.

[0048] Example 5

[0049] Test the stability of the performance of the dimming film prepared in Example 1 at a fixed temperature and electric field. The process is as follows:

[0050] Place the liquid crystal cell with the dimming film in the optical path as shown in Figure 5 the figure. Set the experimental temperature to 40 °C and apply a square wave electric field with a frequency of 1 Hz, a low level of 0 V, and a high level of 10 V to the dimming film. The test results are as shown in Figure 4 the figure. After 3000 cycles of testing, the transmittance of the dimming film stably switches between 0 and 80%.

[0051] Comparative Example 1

[0052] 1) When the mass ratio of DIO, RM257, EHA, and IRG 651 is set to 92:4.8:1:2.2, and all other process step parameter methods are the same as those in Example 1, the light-scattering effect of the light-dimming film obtained is not obvious, and the contrast ratio CR is very low. This is because RM257 is affected by the vertical electric field and forms a vertically arranged polymer network after polymerization, while EHA is not affected by the electric field and forms a randomly arranged polymer network after polymerization. The more vertically arranged networks and the fewer randomly arranged networks, the more ordered the liquid crystal molecules. When an electric field is applied to such a light-dimming film, the improvement of the molecular order by the electric field is very small.

[0053] 2) When the mass ratio of DIO, RM257, EHA, and IRG 651 is set to 92:1:4.8:2.2, and all other process step parameter methods are the same as those in Example 1, the light-dimming film obtained has fewer vertically arranged networks and more randomly arranged networks, and the initial arrangement of the liquid crystal molecules is relatively disordered. Although the light-dimming film prepared in this way has a good scattering effect and a high contrast ratio, it requires a relatively large threshold voltage and saturation voltage.

[0054] 3) When the mass ratio of DIO, RM257, EHA, and IRG 651 is set to 96:0.9:0.9:2.2, and all other process step parameter methods are the same as those in Example 1, the content of the liquid crystal (DIO) is too high and the content of the polymers (RM257 EHA) is too low, resulting in poor film-forming properties of the light-dimming film.

[0055] 4) Steps four and five are set as follows: Step four, the liquid crystal mixture is filled into the liquid crystal cell prepared in step three by capillary action at a high temperature of 120 °C, and then the temperature is cooled to make the liquid crystal mixture in the ferroelectric nematic phase; the specific cooling method: cool it to 70 °C at a rate of 5 °C per minute and keep it standing at 70 °C for 5 minutes. When all other process step parameter methods are the same as those in Example 1, the light-dimming film obtained has an unclear light-scattering effect and a very low contrast ratio CR. At this time, the liquid crystal mixture is polymerized when it is in the nematic phase, and the molecules are already very ordered after polymerization. As a result, when an electric field is applied in step five, the improvement of the molecular order is very small.

[0056] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as a limitation of the present invention itself. Various changes can be made to it in form and detail without departing from the spirit and scope of the present invention.

Claims

1. A smart dimming film with low driving voltage and fast response, characterized in that: The preparation method of the smart dimming film is as follows: Step 1: Dissolve the ferroelectric nematic liquid crystal material DIO, liquid crystal monomer RM257, non-liquid crystal monomer EHA, and photoinitiator IRG651 in a brown wide-mouth bottle containing dichloromethane solvent and mix them evenly; the structural formulas of DIO, RM257, EHA, and IRG 651 are as follows: Step 2: evaporating the mixed solution in step 1 to obtain a liquid crystal mixture, and then heating and shaking to obtain a uniform liquid crystal mixture; Step 4: pouring the liquid crystal mixture into a liquid crystal box at a certain temperature, and then cooling the temperature to make the liquid crystal mixture in a ferroelectric nematic phase; Step 5: Apply a square wave AC electric field to the liquid crystal box and simultaneously perform UV light irradiation curing to complete the polymer network construction and obtain the smart dimming film.

2. The smart dimming film according to claim 1, characterized in that: In the step 1, the mass ratio of DIO, RM257, EHA, and IRG651 is 92:2.9:2.9:2.

2.

3. The smart dimming film according to claim 1, characterized in that: In the step 1, the mixing is carried out in the following manner: after sealing the brown wide-mouth bottle, heating it on a hot plate at 60° C. to 70° C. for 2 to 5 minutes, then transferring it to a vortex oscillator and shaking it for 1 to 5 minutes, and repeating the heating and shaking for multiple times.

4. The smart dimming film according to claim 1, characterized in that: The specific operations in step 2 are: The brown wide-mouth bottle was placed on a hot stage, the temperature was set to 70° C., and the liquid crystal mixture was obtained after standing for 2 hours; then, the liquid crystal mixture was heated at 100-120° C. for 5-10 minutes, and then shaken for 1-5 minutes to obtain a uniform liquid crystal mixture.

5. The smart dimming film according to claim 1, characterized in that: The preparation method of the liquid crystal box is as follows: Two glass substrates with transparent indium tin oxide electrodes are bonded into a liquid crystal box using ultraviolet glue uniformly mixed with silicon dioxide particles, and wires are welded to the transparent indium tin oxide electrodes on each glass substrate.

6. The smart dimming film according to claim 1, characterized in that: The step 4 is specifically as follows: The liquid crystal mixture is poured into the liquid crystal box prepared in step 3 by capillary action at a high temperature of 120°C, and then the temperature is cooled to obtain a ferroelectric nematic phase. The specific cooling method is: cool to 49-51°C at a rate of 5°C per minute, and maintain 49-51°C for 5-10 minutes.

7. The smart dimming film according to claim 1, characterized in that: The specific operation of step 5 is: At 49-51°C, an AC square wave electric field with an amplitude of 10 Vpp and a frequency of 1 kHz is applied to the liquid crystal box in step 4. At the same time, the power is 30 mW / cm 2 , irradiate under ultraviolet light with a wavelength of 365nm for 2 minutes to complete the curing to obtain the smart dimming film.

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