Electric control bistable dimming film based on ultraviolet distribution polymerization and preparation method thereof

Abstract

The invention discloses an electric control bistable dimming film based on ultraviolet distribution polymerization and a preparation method thereof, and the method comprises the following steps: 1, uniformly mixing a liquid crystal photopolymerizable monomer, a negative cholesteric liquid crystal mixture, a free radical type initiator and a photoinduced leaving type photoinitiator to obtain a composite system; 2, heating the composite system until the temperature is 2-10 DEG C higher than the clearing point of the composite system to obtain an isotropic liquid, pouring the isotropic liquid into a liquid crystal box or between two conductive films, extruding to form a film, placing the poured liquid crystal box or film in an environment of 2-10 DEG C higher than the clearing point of the composite system for 3-5 minutes, and placing the poured liquid crystal box or film at room temperature for 2-5 minutes to obtain the isotropic liquid film. The liquid crystal box or the film is filled with the composite system; and 3, at room temperature, the liquid crystal box or the thin film filled with the composite system is irradiated with 405nm light and 365nm light in sequence to obtain the electric control bistable state light adjusting film, the contrast ratio is high, the bistable state effect is good, the binding power is strong, the scattering state and the transparent state are adjustable under a low-frequency electric field, and the transmittance of visible light and near-infrared light is low.

Description

Technical Field

[0001] The invention relates to energy-saving materials, in particular to an electrically controlled bistable dimming film based on ultraviolet distributed polymerization and a preparation method thereof. Background Art

[0002] The electrically controlled bistable dimming film only needs to apply an electric field when switching between transparent and opaque states. After the electric field is removed, both states can be stably maintained. Compared with polymer dispersed liquid crystal (PDLC) and transverse electrically controlled dimming film, the electrically controlled bistable dimming film is more energy-efficient and can be used in multiple products such as smart windows, electronic paper, writing boards, electronic tags, displays, projectors, sensors and light valves.

[0003] Conventional electrically controlled bistable dimming film systems include dual-frequency driven cholesteric liquid crystal (D-ChLC) systems, ion-doped negative cholesteric liquid crystal (N-ChLC) systems, and polymer-stabilized dual-frequency driven cholesteric liquid crystal (PSD-ChLC) systems, wherein: the content of polymerizable monomers in the PSD-ChLC system is the lowest, only 3wt% to 6wt%; the D-ChLC system and the N-ChLC system lack polymer components, and the mechanical properties of the film are poor. Moreover, the light scattering state of the bistable electrically controlled liquid crystal dimming film based on the D-ChLC system needs to be maintained by applying a low-frequency electric field. At this time, the dielectric thermal effect causes the film to heat up severely, making the film easily damaged.

[0004] In recent years, polymer microsphere-filled liquid crystal systems and new flower or rod-shaped polymer-anchored cholesteric liquid crystal systems have emerged, among which: 1) the polymer microsphere-filled liquid crystal system contains a high content of polymer, and the polymer is dispersed in the continuous phase liquid crystal matrix in the form of microspheres, so that the adhesion of the film and the stability of the light scattering effect are significantly improved. The polymer systems used in the existing polymer microsphere-filled liquid crystal system are epoxy-thiol system and acrylate-thiol system. Among them, the epoxy-thiol system adopts a thermal curing method to synthesize an electrically controlled bistable dimming film, which has the problems of long curing time and high curing temperature. The acrylate-thiol system adopts a UV curing method to synthesize an electrically controlled bistable dimming film. Although the curing The method is simple, but the thiol molecules have poor solubility with the liquid crystal molecules. When the thiol content increases, the obtained sample produces phase separation, which affects the uniformity and contrast of the film; 2) Chinese invention patent CN202410719708.6 prepares a new flower or rod-shaped polymer anchored cholesteric liquid crystal system, which can be used to prepare a bistable electrically controlled dimming film by a single ultraviolet polymerization method. However, under a low-frequency electric field, the near-infrared light transmittance of the bistable electrically controlled dimming film is relatively high, and the heat blocking effect is not ideal. Moreover, a high-frequency electric field needs to be applied to achieve the regulation of the scattering state and the transparent state, which is not conducive to the subsequent combination with the TFT drive circuit, and is not conducive to the use of bistable products in the field of electronic paper display. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an electrically controlled bistable dimming film based on ultraviolet distributed polymerization and a preparation method thereof. The prepared electrically controlled bistable dimming film has the advantages of high contrast, good bistable effect, strong adhesion, low transmittance of visible light and near-infrared light under low-frequency electric fields, and the scattered state and transparent state can be controlled by different low-frequency electric fields.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing an electrically controlled bistable dimming film based on ultraviolet distributed polymerization comprises the following steps:

[0008] Step 1, weighing 6.0wt% to 36.0wt% of a liquid crystal photopolymerizable monomer, 64.0wt% to 94.0wt% of a negative cholesteric liquid crystal mixture, 0.5wt% to 4.0wt% of a free radical initiator based on the mass of the liquid crystal photopolymerizable monomer, and 1.0wt% to 8.0wt% of a photo-induced leaving photoinitiator based on the mass of the liquid crystal photopolymerizable monomer, mixing and stirring to obtain a composite system;

[0009] Step 2, first heating the composite system to a temperature 2 to 10°C higher than its clearing point to obtain an isotropic liquid, then pouring the isotropic liquid into a liquid crystal box or between two conductive films, extruding into a film, and then placing the poured liquid crystal box or film in an environment 2 to 10°C higher than the clearing point of the composite system for 3 to 5 minutes, and then placing it at room temperature for 2 to 5 minutes to obtain a liquid crystal box or film poured with the composite system;

[0010] Step 3. At room temperature, first use light with a wavelength of 405nm to irradiate the liquid crystal box or film infused with the composite system, so that part of the liquid crystal photopolymerizable monomers undergo polymerization reaction under the action of the photo-leaving photoinitiator and generate ionic compounds. Then use ultraviolet light with a wavelength of 365nm to irradiate the liquid crystal box or film infused with the composite system, so that the remaining liquid crystal photopolymerizable monomers are completely polymerized under the action of the free radical initiator to obtain an electrically controlled bistable dimming film.

[0011] Furthermore, the liquid crystal photopolymerizable monomer in step 1 is at least one of compound I, compound II, compound III and compound IV.

[0012]

[0013] Furthermore, the negative cholesteric liquid crystal mixture of step 1 is formed by mixing negative nematic liquid crystal and chiral compound, and the chiral compound accounts for 1.0% to 30.0% of the mass of the negative cholesteric liquid crystal mixture;

[0014] The chiral compound is at least one of chiral agents S811, R811, S1011, R1011, R2011, S5011 and R5011.

[0015] Furthermore, the maximum absorption cutoff wavelength of the free radical initiator in step 1 is less than 390 nm.

[0016] Furthermore, the free radical initiator is at least one of 3-methyl-4, phenylbenzophenone, 2-hydroxy-2-methyl-1-[4-(tert-butyl)phenyl]-1-propanone and benzil dimethyl ether.

[0017]

[0018] Furthermore, the photo-induced leaving type photoinitiator in step 1 is at least one of the compound NVOC-HA, the compound NPPOC-TMG, the compound NVOC-DEA, the compound NPPOC-DEA, the compound NVOC-TMG and the compound MNPPOC-TMG.

[0019]

[0020]

[0021] Furthermore, in step 2, the thickness of the liquid crystal box is controlled by a spacer with a thickness of 10 to 43 μm, and the distance between the two conductive films is controlled by a glass microsphere spacer with a diameter of 10 to 43 μm.

[0022] Furthermore, in step 3, the illumination intensity of the light with a wavelength of 405 nm is 5.5 to 40 mw / cm 2 , and the irradiation time is 20 to 90 minutes; the illumination intensity of ultraviolet light with a wavelength of 365nm is 0.10 to 2.12mw / cm 2 , and the irradiation time is 1 to 10 minutes.

[0023] An electrically controlled bistable dimming film, wherein the polymer network morphology presents a multi-level microscopic morphology structure combining a flower-like network and a porous structure.

[0024] Furthermore, the electrically controlled bistable dimming film has a transmittance of light in the wavelength range of 400 to 2500 nm under a low-frequency electric field of 5 Hz and 40 V, and an average transmittance of 1.98%. Under an electric field of 50 to 100 Hz and 60 V, the electrically controlled bistable dimming film is transparent.

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] 1) First, use light with a wavelength of 405nm to irradiate the liquid crystal box or film filled with the composite system, so that part of the liquid crystal photopolymerizable monomers undergo polymerization under the action of the photoinduced leaving photoinitiator and generate ionic compounds, which helps the negative cholesteric liquid crystal mixture in the sample to produce violent disturbances when a low-frequency electric field is applied, thereby reducing the light transmittance of the electrically controlled bistable dimming film in the visible light region and the near-infrared region under the low-frequency electric field. Then, use 365nm ultraviolet light to irradiate the liquid crystal box or film filled with the composite system to make the remaining liquid crystal photopolymerizable monomers undergo polymerization reaction. Under the action of the free radical initiator, the monomers are quickly and completely polymerized, so that the polymer presents a multi-level microscopic structure combining a flower-like network and a porous state, has good bistability and low near-infrared light transmittance, and at the same time gives the electrically-controlled bistable dimming film better adhesion performance; in short, the electrically-controlled bistable dimming film prepared by the present invention through step-by-step irradiation of ultraviolet rays of two wavelengths not only has a good bistability effect, but also has a lower near-infrared light transmittance under a low-frequency electric field of 1 to 10 Hz, and has good adhesion and high contrast.

[0027] 2) Since the liquid crystal photopolymerizable monomer and the negative cholesteric liquid crystal mixture have good mutual solubility, the electrically controlled bistable dimming film is endowed with good uniformity.

[0028] 3) The electrically controlled bistable dimming film prepared by the present invention can adjust the scattering state and the transparent state by a low-frequency AC electric field of 1 to 100 Hz, thereby adjusting the transmittance, which is beneficial to the subsequent combination with the TFT driving circuit. In particular, under a low-frequency electric field of 5 Hz and 40 V, the transmittance of visible light and near-infrared light in the wavelength range of 400 to 2500 nm is less than 5.4%, and the average transmittance is 1.98%. When used in building doors and windows, automobile windows and display fields, it has a significant energy-saving effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 : The actual effect diagram of the electrically controlled bistable dimming film prepared in Example 1 of the present invention under low-frequency electric fields of different frequencies and after the corresponding low-frequency electric field is removed for 20 days;

[0030] Figure 2 : Polarized microscope photos of the electrically controlled bistable dimming film prepared in Example 1 of the present invention under low-frequency electric fields of different frequencies and after the corresponding low-frequency electric field is removed for 20 days;

[0031] Figure 3 : Wavelength-transmittance curves of the electrically controlled bistable dimming films prepared in Example 1 of the present invention and Comparative Example 1 under low-frequency electric fields of different frequencies and after the corresponding low-frequency electric fields are removed for 100 days;

[0032] Figure 4 : SEM image of the electrically controlled bistable dimming film prepared in Comparative Example 1 of the present invention;

[0033] Figure 5 : SEM image of the electrically controlled bistable dimming film prepared in Example 1 of the present invention;

[0034] Figure 6 : SEM image of the electrically controlled bistable dimming film prepared in Comparative Example 2 of the present invention;

[0035] Figure 7 : Wavelength-transmittance curve of the electrically controlled bistable dimming film prepared in Comparative Example 2 of the present invention in low-frequency electric fields of different frequencies and after the corresponding low-frequency electric field is removed for 100 days;

[0036] Figure 8 : SEM image of the electrically controlled bistable dimming film prepared in Comparative Example 3 of the present invention;

[0037] Fig. 9 : Wavelength-transmittance curve of the electrically controlled bistable dimming film prepared in Comparative Example 3 of the present invention in low-frequency electric fields of different frequencies and after the corresponding low-frequency electric field is removed for 100 days;

[0038] Fig.10 : SEM image of the electrically controlled bistable dimming film prepared in Comparative Example 4 of the present invention;

[0039] Fig.11 : Wavelength-transmittance curves of the dimming film prepared in Comparative Example 4 of the present invention when no electric field is applied, low-frequency electric fields of different frequencies are applied, and the corresponding low-frequency electric field is removed for 100 days. DETAILED DESCRIPTION

[0040] The specific contents of the present invention are further explained in detail below in conjunction with embodiments.

[0041] The structural formulas of Compound I, Compound II, Compound III and Compound IV involved in Examples 1 to 5 of the present invention and Comparative Example 1 are as follows:

[0042]

[0043]

[0044] The maximum absorption cutoff wavelengths of 3-methyl-4-phenylbenzophenone, 2-hydroxy-2-methyl-1-[4-(tert-butyl)phenyl]-1-propanone and benzil dimethyl ether involved in Examples 1 to 5 of the present invention and Comparative Example 1 are all less than 390 nm, and their structural formulas are as follows:

[0045]

[0046] The structural formulas of the compounds NVOC-HA, NPPOC-TMG, NVOC-DEA, NPPOC-DEA, NVOC-TMG and MNPPOC-TMG involved in Examples 1 to 5 of the present invention and Comparative Example 1 are as follows:

[0047]

[0048]

[0049] The synthesis methods of the compounds NVOC-HA, NPPOC-TMG, NVOC-DEA, NPPOC-DEA, NVOC-TMG and MNPPOC-TMG can be found in the literature [Spatial and Temporal Control of Thiol-Michael Addition via Photocaged Superbase in Photopatterning and Two-Stage Polymer Networks Formation].

[0050] The negative nematic liquid crystals involved in Examples 1 to 5 of the present invention and Comparative Example 1 were purchased from Jiangsu Hecheng Display Technology Co., Ltd. and are numbered HNG756300-100 (T NI =126°C, Δn (589nm, 25°C) = 0.108, Δε (1KHz, 25°C) = -5.6).

[0051] The chiral agents S811, R811, S1011, R1011, R2011, S5011 and R5011 involved in Examples 1 to 5 of the present invention and Comparative Example 1 are all commercially available products.

[0052] Example 1

[0053] Step 1, weighing 21.0wt% of a liquid crystal photopolymerizable monomer, 79.0wt% of a negative cholesteric liquid crystal mixture, 2.5% of a free radical initiator based on the mass of the liquid crystal photopolymerizable monomer, and 4.5% of a photoinduced leaving photoinitiator based on the mass of the liquid crystal photopolymerizable monomer, mixing and stirring evenly to obtain a composite system, wherein: the liquid crystal photopolymerizable monomer is compound I; the negative cholesteric liquid crystal mixture is formed by mixing a negative nematic liquid crystal and a chiral agent R2011 in a mass ratio of 98:2; the free radical initiator is 3-methyl-4, phenylbenzophenone; the photoinduced leaving photoinitiator is formed by mixing a compound NVOC-HA and a compound NPPOC-TMG in any proportion;

[0054] Step 2, first heat the composite system to a temperature 6°C higher than its clearing point to obtain an isotropic liquid, then infuse the isotropic liquid into a liquid crystal box, the thickness of the liquid crystal box is controlled by a spacer with a thickness of 16 μm, then place the infused liquid crystal box in an environment 6°C higher than the clearing point of the composite system for 4 minutes to make the composite system evenly distributed in the liquid crystal box, and then place it at room temperature for 4 minutes to obtain a liquid crystal box infused with the composite system;

[0055] Step 3: At room temperature, use a wavelength of 405 nm and a light intensity of 13.6 mw / cm 2 The liquid crystal box filled with the composite system was irradiated with light for 30 minutes, so that part of the liquid crystal photopolymerizable monomers were polymerized under the action of the photo-leaving photoinitiator to generate ionic compounds. Then, the light with a wavelength of 365nm and an intensity of 0.49mw / cm 2 The liquid crystal box filled with the composite system is irradiated with ultraviolet light for 5 minutes, so that the remaining liquid crystal photopolymerizable monomers are completely polymerized under the action of the free radical initiator to obtain an electrically controlled bistable dimming film.

[0056] Figure 1 This is a real-life effect diagram of the electrically controlled bistable dimming film prepared in Example 1, wherein: Figure 1 (a) is a photo of the electrically controlled bistable dimming film under a low-frequency electric field of 5 Hz and 40 V; Figure 1 (b) is a photo of the electrically controlled bistable dimming film after the 5 Hz, 40 V low-frequency electric field was removed for 20 days; Figure 1 (c) is a photo of the electrically controlled bistable dimming film under a low-frequency electric field of 100 Hz and 60 V; Figure 1 (d) is a photo of the electrically controlled bistable dimming film after the 100 Hz, 60 V low-frequency electric field was removed for 20 days;

[0057] By comparison Figure 1 (a)~ Figure 1 (b) It can be seen that after removing the 5Hz, 40V low-frequency electric field for 20 days, the light transmittance of the dimming film is low and presents a scattered state; by comparison Figure 1 (c)~ Figure 1 (d) It can be seen that after 20 days of removal of the 100 Hz, 60 V low-frequency electric field, the light transmittance of the dimming film is high, the sample appears transparent, and the word "bistable" can be seen on the background behind it.

[0058] Figure 2 Polarized light microscope photos of the electrically controlled bistable dimming film prepared in Example 1 in different states, wherein: Figure 2 (a) is a polarizing microscope photo of the electrically controlled bistable dimming film under a low-frequency electric field of 5 Hz and 40 V; Figure 2 (b) is a polarizing microscope photo of the electrically controlled bistable dimming film after the 5 Hz, 40 V low-frequency electric field was removed for 20 days; Figure 2 (c) is a polarizing microscope photo of the electrically controlled bistable dimming film under a low-frequency electric field of 100 Hz and 60 V; Figure 2 (d) is a polarizing microscope photo of the electrically controlled bistable dimming film after the 100 Hz, 60 V low-frequency electric field was removed for 20 days;

[0059] By observation Figure 2 (a) It can be seen that under the low-frequency electric field of 5Hz and 40V, a black field is presented in the transmission mode of the polarizing microscope lens, indicating that the light transmittance of the dimming film is low, indicating that almost no light is transmitted; Figure 2 (b) It can be seen that after 20 days of removing the 5 Hz, 40 V low-frequency electric field, the sample exhibits a focal conic texture. It is well known that when a low-frequency electric field is applied, liquid crystal will undergo dynamic scattering and be in a focal conic texture. After 20 days of turning off the low-frequency electric field, the focal conic texture still exists, indicating that the dimming film prepared in Example 1 is very stable. By observing Figure 2 (c)~ Figure 2 (d) shows that when the 100 Hz, 60 V low-frequency electric field is applied and when the 100 Hz, 60 V low-frequency electric field is removed, the dimming film has a planar texture. Figure 2 (d) It proves that Example 1 successfully prepared the electrically controlled bistable dimming film.

[0060] from Figure 5 It can be seen that the polymer network of the electrically controlled bistable dimming film prepared in Example 1 presents a multi-level microstructure combining a flower-like network and a porous structure. This structure is beneficial to reducing the light transmittance in the near-infrared region under a low-frequency electric field, so that the sample maintains good bistable performance.

[0061] Example 2

[0062] Step 1, weighing 6.0wt% of liquid crystal photopolymerizable monomer, 94.0wt% of negative cholesteric liquid crystal mixture, 4.0% of free radical initiator based on the mass of liquid crystal photopolymerizable monomer and 1.0% of photoinduced leaving photoinitiator based on the mass of liquid crystal photopolymerizable monomer, mixing and stirring evenly to obtain a composite system, wherein: the liquid crystal photopolymerizable monomer is formed by mixing compound I and compound III in a ratio of 1:1; the negative cholesteric liquid crystal mixture is formed by mixing negative nematic liquid crystal and chiral agent R5011 in a mass ratio of 99:1; the free radical initiator is formed by mixing 3-methyl-4, phenyl dibenzophenone and 2-hydroxy-2-methyl-1-[4-(tert-butyl)phenyl]-1-propanone in any proportion; the photoinduced leaving photoinitiator is formed by mixing compound NPPOC-TMG, compound NVOC-DEA and compound NPPOC-DEA in any proportion;

[0063] Step 2, first heat the composite system to a temperature 2°C higher than its clearing point to obtain an isotropic liquid, then infuse the isotropic liquid into a liquid crystal box, the thickness of the liquid crystal box is controlled by a spacer with a thickness of 20 μm, then place the infused liquid crystal box in an environment 2°C higher than the clearing point of the composite system for 5 minutes to make the composite system evenly distributed in the liquid crystal box, and then place it at room temperature for 2 minutes to obtain a liquid crystal box infused with the composite system;

[0064] Step 3: At room temperature, use a wavelength of 405 nm and a light intensity of 5.5 mw / cm 2 The liquid crystal box filled with the composite system was irradiated with light for 90 minutes, so that part of the liquid crystal photopolymerizable monomers were polymerized under the action of the photo-leaving photoinitiator to generate ionic compounds. Then, the light with a wavelength of 365nm and an intensity of 0.10mw / cm 2 The liquid crystal box filled with the composite system is irradiated with ultraviolet light for 10 minutes, so that the remaining liquid crystal photopolymerizable monomers are completely polymerized under the action of the free radical initiator to obtain an electrically controlled bistable dimming film.

[0065] Example 3

[0066] Step 1, weighing 36.0wt% of a liquid crystal photopolymerizable monomer, 64.0wt% of a negative cholesteric liquid crystal mixture, 0.5% of a free radical initiator based on the mass of the liquid crystal photopolymerizable monomer, and 8.0% of a photoinduced leaving photoinitiator based on the mass of the liquid crystal photopolymerizable monomer, mixing and stirring evenly to obtain a composite system, wherein: the liquid crystal photopolymerizable monomer is formed by mixing compound I and compound IV in a ratio of 40:60; the negative cholesteric liquid crystal mixture is formed by mixing a negative nematic liquid crystal and a chiral agent S811 in a mass ratio of 92:8; the free radical initiator is formed by mixing 2-hydroxy-2-methyl-1-[4-(tert-butyl)phenyl]-1-propanone and benzil dimethyl ether in any proportion; the photoinduced leaving photoinitiator is formed by mixing compound NVOC-TMG and compound MNPPOC-TMG in any proportion;

[0067] Step 2, first heat the composite system to a temperature 10°C higher than its clearing point to obtain an isotropic liquid, then infuse the isotropic liquid into a liquid crystal box, the thickness of the liquid crystal box is controlled by a spacer with a thickness of 30 μm, and then place the infused liquid crystal box in an environment 10°C higher than the clearing point of the composite system for 3 minutes to make the composite system evenly distributed in the liquid crystal box, and then place it at room temperature for 5 minutes to obtain a liquid crystal box infused with the composite system;

[0068] Step 3: At room temperature, use a wavelength of 405 nm and a light intensity of 40 mw / cm 2 The liquid crystal box filled with the composite system was irradiated with light for 20 minutes, so that part of the liquid crystal photopolymerizable monomers were polymerized under the action of the photo-leaving photoinitiator to generate ionic compounds. Then, the light with a wavelength of 365nm and an intensity of 2.12mw / cm 2 The liquid crystal box filled with the composite system is irradiated with ultraviolet light for 1 minute, so that the remaining liquid crystal photopolymerizable monomers are completely polymerized under the action of the free radical initiator to obtain an electrically controlled bistable dimming film.

[0069] Example 4

[0070] Step 1, weighing 25.0wt% of a liquid crystal photopolymerizable monomer, 75.0wt% of a negative cholesteric liquid crystal mixture, 1.5% of a free radical initiator based on the mass of the liquid crystal photopolymerizable monomer, and 6.0% of a photoinduced leaving photoinitiator based on the mass of the liquid crystal photopolymerizable monomer, mixing and stirring evenly to obtain a composite system, wherein: the liquid crystal photopolymerizable monomer is compound IV; the negative cholesteric liquid crystal mixture is formed by mixing a negative nematic liquid crystal and a chiral compound in a mass ratio of 78:22, and the chiral compound is formed by mixing chiral agents S1011, R1011 and S5011 in any proportion; the free radical initiator is 2-hydroxy-2-methyl-1-[4-(tert-butyl)phenyl]-1-propanone; and the photoinduced leaving photoinitiator is compound NVOC-TMG;

[0071] Step 2, firstly heat the composite system to a temperature higher than 8°C of its clearing point to obtain an isotropic liquid, then pour the isotropic liquid between two conductive films and extrude them into a film, wherein the distance between the two conductive films is controlled by a glass microsphere spacer having a diameter of 43 μm, and then place the poured film in an environment 8°C higher than the clearing point of the composite system for 4 minutes to make the composite system evenly distributed in the liquid crystal box, and then place it at room temperature for 3 minutes to obtain a liquid crystal box poured with the composite system;

[0072] Step 3: At room temperature, use a wavelength of 405 nm and a light intensity of 23 mw / cm 2 The liquid crystal box filled with the composite system was irradiated with light for 60 minutes, so that part of the liquid crystal photopolymerizable monomers were polymerized under the action of the photo-leaving photoinitiator to generate ionic compounds. Then, the light with a wavelength of 365nm and an intensity of 1.11mw / cm 2 The liquid crystal box filled with the composite system was irradiated with ultraviolet light for 8 minutes, so that the remaining liquid crystal photopolymerizable monomers were completely polymerized under the action of the free radical initiator to obtain an electrically controlled bistable dimming film.

[0073] Example 5

[0074] Step 1, weighing 15.0wt% of a liquid crystal photopolymerizable monomer, 85.0wt% of a negative cholesteric liquid crystal mixture, a free radical initiator accounting for 3.0% of the mass of the liquid crystal photopolymerizable monomer, and a photoinduced leaving photoinitiator accounting for 2.5% of the mass of the liquid crystal photopolymerizable monomer, mixing and stirring evenly to obtain a composite system, wherein: the liquid crystal photopolymerizable monomer is formed by mixing compound I and compound IV in a mass ratio of 80:20; the negative cholesteric liquid crystal mixture is formed by mixing a negative nematic liquid crystal and a chiral agent R811 in a mass ratio of 70:30; the free radical initiator is formed by mixing 3-methyl-4, phenyl benzophenone and benzil dimethyl ether; the photoinduced leaving photoinitiator is formed by mixing compound NVOC-HA and compound NVOC-TMG in any proportion;

[0075] Step 2, firstly heat the composite system to a temperature 4°C higher than its clearing point to obtain an isotropic liquid, then pour the isotropic liquid between two conductive films and extrude them into a film, wherein the distance between the two conductive films is controlled by a glass microsphere spacer with a diameter of 10 μm, and then place the poured film in an environment 4°C higher than the clearing point of the composite system for 3 minutes to make the composite system evenly distributed in the liquid crystal box, and then place it at room temperature for 5 minutes to obtain a liquid crystal box poured with the composite system;

[0076] Step 3: At room temperature, use a wavelength of 405 nm and a light intensity of 30 mw / cm 2 The liquid crystal box filled with the composite system was irradiated with light for 40 minutes, so that part of the liquid crystal photopolymerizable monomers were polymerized under the action of the photo-leaving photoinitiator to generate ionic compounds. Then, the light with a wavelength of 365nm and an intensity of 1.60mw / cm 2 The liquid crystal box filled with the composite system is irradiated with ultraviolet light for 3 minutes, so that the remaining liquid crystal photopolymerizable monomers are completely polymerized under the action of the free radical initiator to obtain an electrically controlled bistable dimming film.

[0077] Comparative Example 1

[0078] Step 1, weighing 21.0wt% of a liquid crystal photopolymerizable monomer, 79.0wt% of a negative cholesteric liquid crystal mixture, 2.5% of a free radical initiator based on the mass of the liquid crystal photopolymerizable monomer, and 4.5% of a photoinduced leaving photoinitiator based on the mass of the liquid crystal photopolymerizable monomer, mixing and stirring evenly to obtain a composite system, wherein: the liquid crystal photopolymerizable monomer is compound I; the negative cholesteric liquid crystal mixture is formed by mixing a negative nematic liquid crystal and a chiral agent R2011 in a mass ratio of 98:2; the free radical initiator is 3-methyl-4, phenylbenzophenone; the photoinduced leaving photoinitiator is formed by mixing a compound NVOC-HA and a compound NPPOC-TMG in any proportion;

[0079] Step 2, first heat the composite system to a temperature 6°C higher than its clearing point to obtain an isotropic liquid, then infuse the isotropic liquid into a liquid crystal box, the thickness of the liquid crystal box is controlled by a spacer with a thickness of 16 μm, then place the infused liquid crystal box in an environment 6°C higher than the clearing point of the composite system for 4 minutes to make the composite system evenly distributed in the liquid crystal box, and then place it at room temperature for 4 minutes to obtain a liquid crystal box infused with the composite system;

[0080] Step 3: At room temperature, use a wavelength of 405 nm and a light intensity of 13.6 mw / cm 2 The liquid crystal box infused with the composite system was irradiated with light for 30 minutes to obtain an electrically controlled bistable dimming film.

[0081] Figure 3 The wavelength-transmittance curves of the electrically controlled bistable dimming films prepared in Example 1 and Comparative Example 1 are as follows: Figure 3 (a) is a wavelength-transmittance curve of the electrically controlled bistable dimming films prepared in Example 1 and Comparative Example 1 under a low-frequency electric field of 5 Hz and 40 V; Figure 3 (b) is a wavelength-transmittance curve of the electrically controlled bistable dimming films prepared in Example 1 and Comparative Example 1 after the 5 Hz, 40 V low-frequency electric field is removed for 100 days; Figure 3 (c) is a wavelength-transmittance curve of the electrically controlled bistable dimming films prepared in Example 1 and Comparative Example 1 under a low-frequency electric field of 100 Hz and 60 V; Figure 3 (d) is a wavelength-transmittance curve of the electrically controlled bistable dimming films prepared in Example 1 and Comparative Example 1 after the 100 Hz, 60 V low-frequency electric field is removed for 100 days;

[0082] from Figure 3(a) It can be seen that under a low-frequency electric field of 5 Hz and 40 V, the electrically controlled bistable dimming film prepared by step-by-step polymerization under irradiation with light of different wavelengths in Example 1 has a significantly lower transmittance of light in the wavelength range of 1000 to 2500 nm than the electrically controlled bistable dimming film prepared by one-step polymerization in Comparative Example 1; Figure 3 (b) It can be seen that after the 5 Hz, 40 V low-frequency electric field is removed for 100 days, the light transmittance of the electrically controlled bistable dimming film prepared in Example 1 in the wavelength range of 400 to 2500 nm is significantly lower than the light transmittance of the electrically controlled bistable dimming film prepared in Comparative Example 1 under the same conditions; Figure 3 (c)~ Figure 3 (d) It can be seen that the transmittance of the electrically controlled bistable dimming film prepared in Example 1 in the wavelength range of 400-2500 nm is relatively high, whether under the low-frequency electric field of 100 Hz and 60 V or after the low-frequency electric field of 100 Hz and 60 V is removed.

[0083] In addition, from Figure 3 (a)~ Figure 3 (b) It can be seen that under a low-frequency electric field of 5 Hz and 40 V, the light transmittance of the dimming film prepared in Example 1 is lower than 5.4% in the wavelength range of 400 to 2500 nm. After calculation, its average transmittance is 1.98%, while the electrically-controlled bistable dimming film prepared in Comparative Example 1 has an average transmittance of 19.21% under the same conditions, indicating that the light transmittance of the bistable electrically-controlled dimming film prepared in Example 1 in the near-infrared region is very low.

[0084] from Figure 4 It can be seen that the electrically-controlled bistable dimming film prepared in Comparative Example 1 is in the shape of a single flower flake, has a relatively simple microstructure, lacks a porous structure, and has poor light scattering and absorption effects, so its transmittance is relatively high. In contrast, the electrically-controlled bistable dimming film prepared in Example 1 not only presents a flower flake network, but also is rich in micropores and layers. The rich porous structure and layers promote the scattering and absorption of light inside the dimming film, thereby reducing the light transmittance.

[0085] Comparative Example 2

[0086] Step 1, weighing 21.0wt% of a liquid crystal photopolymerizable monomer, 79.0wt% of a negative cholesteric liquid crystal mixture, 2.5% of a free radical initiator based on the mass of the liquid crystal photopolymerizable monomer, and 4.5% of a photoinduced leaving photoinitiator based on the mass of the liquid crystal photopolymerizable monomer, mixing and stirring evenly to obtain a composite system, wherein: the liquid crystal photopolymerizable monomer is compound I; the negative cholesteric liquid crystal mixture is formed by mixing a negative nematic liquid crystal and a chiral agent R2011 in a mass ratio of 98:2; the free radical initiator is 3-methyl-4, phenylbenzophenone; the photoinduced leaving photoinitiator is formed by mixing a compound NVOC-HA and a compound NPPOC-TMG in any proportion;

[0087] Step 2, first heat the composite system to a temperature 6°C higher than its clearing point to obtain an isotropic liquid, then infuse the isotropic liquid into a liquid crystal box, the thickness of the liquid crystal box is controlled by a spacer with a thickness of 16 μm, then place the infused liquid crystal box in an environment 6°C higher than the clearing point of the composite system for 4 minutes to make the composite system evenly distributed in the liquid crystal box, and then place it at room temperature for 4 minutes to obtain a liquid crystal box infused with the composite system;

[0088] Step 3: At room temperature, use a wavelength of 365 nm and a light intensity of 0.49 mw / cm 2 The liquid crystal box filled with the composite system was irradiated with ultraviolet light for 5 minutes, and then a wavelength of 405nm and a light intensity of 13.6mw / cm 2 The liquid crystal box infused with the composite system was irradiated with light for 30 minutes to obtain an electrically controlled bistable dimming film.

[0089] from Figure 6 It can be seen that the electrically controlled bistable dimming film prepared in Comparative Example 2 is mainly a porous structure with less petal-shaped structures.

[0090] from Figure 7 (a) It can be seen that under a low-frequency electric field of 5 Hz and 40 V, the electrically controlled bistable dimming film prepared by polymerization by sequentially irradiating light with wavelengths of 365 nm and 405 nm in Comparative Example 2 has an average transmittance of 22.69% in the wavelength range of 400-2500 nm, which is significantly higher than the average transmittance of 1.98% of the electrically controlled bistable dimming film under the same conditions in Example 1. After removing the low-frequency electric field of 5 Hz and 40 V for 100 days, the transmittance in the wavelength range of 400-2500 nm is also higher than the transmittance of the electrically controlled bistable dimming film prepared in Example 1, indicating that the order of irradiation of light of different wavelengths has an important influence on the transmittance of the electrically controlled bistable dimming film; Figure 7(b) It can be seen that the transmittance of the electrically controlled bistable dimming film prepared in Comparative Example 2 in the wavelength range of 400 to 2500 nm is relatively high, whether under a 100 Hz, 60 V low-frequency electric field or 100 days after the 100 Hz, 60 V electric field is removed.

[0091] Comparative Example 3

[0092] Step 1, weighing 21.0wt% of a liquid crystal photopolymerizable monomer, 79.0wt% of a negative cholesteric liquid crystal mixture, 2.5% of a free radical initiator based on the mass of the liquid crystal photopolymerizable monomer, and 4.5% of a photoinduced leaving photoinitiator based on the mass of the liquid crystal photopolymerizable monomer, mixing and stirring evenly to obtain a composite system, wherein: the liquid crystal photopolymerizable monomer is compound I; the negative cholesteric liquid crystal mixture is formed by mixing a negative nematic liquid crystal and a chiral agent R2011 in a mass ratio of 98:2; the free radical initiator is 3-methyl-4, phenylbenzophenone; the photoinduced leaving photoinitiator is formed by mixing a compound NVOC-HA and a compound NPPOC-TMG in any proportion;

[0093] Step 2, first heat the composite system to a temperature 6°C higher than its clearing point to obtain an isotropic liquid, then infuse the isotropic liquid into a liquid crystal box, the thickness of the liquid crystal box is controlled by a spacer with a thickness of 16 μm, then place the infused liquid crystal box in an environment 6°C higher than the clearing point of the composite system for 4 minutes to make the composite system evenly distributed in the liquid crystal box, and then place it at room temperature for 4 minutes to obtain a liquid crystal box infused with the composite system;

[0094] Step 3: At room temperature, use a wavelength of 365 nm and a light intensity of 0.49 mw / cm 2 The liquid crystal box infused with the composite system was irradiated with ultraviolet light for 5 minutes to obtain an electrically controlled bistable dimming film.

[0095] from Figure 8 It can be seen that the electrically controlled bistable dimming film prepared in Comparative Example 3 is mainly a porous structure with very few petal-shaped structures, and has a poor light scattering effect.

[0096] from Fig. 9 (a) It can be seen that the electrically controlled bistable dimming film prepared by one-step polymerization with a wavelength of 365nm in Comparative Example 3 has an average transmittance of 23.53% in the wavelength range of 400-2500nm under a low-frequency electric field of 5Hz and 40V, which is significantly higher than the average transmittance of the electrically controlled bistable dimming film prepared in Example 1 under the same conditions. After removing the low-frequency electric field of 5Hz and 40V for 100 days, the transmittance in the wavelength range of 400-2500nm is also higher than the transmittance of the electrically controlled bistable dimming film prepared in Example 1; Fig. 9(b) It can be seen that the transmittance of the electrically controlled bistable dimming film prepared in Comparative Example 3 in the wavelength range of 400 to 2500 nm is relatively high, whether under a low-frequency electric field of 100 Hz and 60 V or 100 days after the electric field of 100 Hz and 60 V is removed.

[0097] Comparative Example 4

[0098] Step 1, weighing 21.0wt% of a liquid crystal photopolymerizable monomer, 79.0wt% of a negative cholesteric liquid crystal mixture, 2.5% of a free radical initiator based on the mass of the liquid crystal photopolymerizable monomer, and 4.5% of a photoinduced leaving photoinitiator based on the mass of the liquid crystal photopolymerizable monomer, mixing and stirring evenly to obtain a composite system, wherein: the liquid crystal photopolymerizable monomer is compound I; the negative cholesteric liquid crystal mixture is formed by mixing a negative nematic liquid crystal and a chiral agent R2011 in a mass ratio of 98:2; the free radical initiator is 3-methyl-4, phenylbenzophenone; the photoinduced leaving photoinitiator is formed by mixing a compound NVOC-HA and a compound NPPOC-TMG in any proportion;

[0099] Step 2, first heat the composite system to a temperature 6°C higher than its clearing point to obtain an isotropic liquid, then infuse the isotropic liquid into a liquid crystal box, the thickness of the liquid crystal box is controlled by a spacer with a thickness of 16 μm, then place the infused liquid crystal box in an environment 6°C higher than the clearing point of the composite system for 4 minutes to make the composite system evenly distributed in the liquid crystal box, and then place it at room temperature for 4 minutes to obtain a liquid crystal box infused with the composite system;

[0100] Step 3: At room temperature, use a wavelength of 365 nm and a light intensity of 2.85 mw / cm 2 The liquid crystal box filled with the composite system was irradiated with ultraviolet light for 5 minutes to obtain a dimming film.

[0101] from Fig.10 It can be seen that the electrically controlled bistable dimming film prepared in Comparative Example 4 is mainly a dense polymer network without a petal-like structure.

[0102] from Fig.11 It can be seen that the dimming film prepared in Comparative Example 4 has no response characteristics to the low-frequency electric field and does not have a bistable characteristic.

Claims

1. A method for preparing an electrically controlled bistable dimming film based on ultraviolet distributed polymerization, characterized in that: The steps include: Step 1, weighing 6.0wt% to 36.0wt% of a liquid crystal photopolymerizable monomer, 64.0wt% to 94.0wt% of a negative cholesteric liquid crystal mixture, 0.5wt% to 4.0wt% of a free radical initiator based on the mass of the liquid crystal photopolymerizable monomer, and 1.0wt% to 8.0wt% of a photo-induced leaving photoinitiator based on the mass of the liquid crystal photopolymerizable monomer, mixing and stirring to obtain a composite system; Step 2, first heating the composite system to a temperature 2 to 10°C higher than its clearing point to obtain an isotropic liquid, then pouring the isotropic liquid into a liquid crystal box or between two conductive films, extruding into a film, and then placing the poured liquid crystal box or film in an environment 2 to 10°C higher than the clearing point of the composite system for 3 to 5 minutes, and then placing it at room temperature for 2 to 5 minutes to obtain a liquid crystal box or film poured with the composite system; Step 3. At room temperature, first use light with a wavelength of 405nm to irradiate the liquid crystal box or film infused with the composite system, so that part of the liquid crystal photopolymerizable monomers undergo polymerization reaction under the action of the photo-leaving photoinitiator and generate ionic compounds. Then use ultraviolet light with a wavelength of 365nm to irradiate the liquid crystal box or film infused with the composite system, so that the remaining liquid crystal photopolymerizable monomers are completely polymerized under the action of the free radical initiator to obtain an electrically controlled bistable dimming film.

2. The method for preparing an electrically controlled bistable dimming film based on ultraviolet distributed polymerization according to claim 1, characterized in that: The liquid crystal photopolymerizable monomer in step 1 is at least one of compound I, compound II, compound III and compound IV.

3. The method for preparing an electrically controlled bistable dimming film based on ultraviolet distributed polymerization according to claim 1, characterized in that: The negative cholesteric liquid crystal mixture in step 1 is formed by mixing negative nematic liquid crystal and chiral compounds, and the chiral compounds account for 1.0% to 30.0% of the mass of the negative cholesteric liquid crystal mixture; The chiral compound is at least one of chiral agents S811, R811, S1011, R1011, R2011, S5011 and R5011.

4. The method for preparing an electrically controlled bistable dimming film based on ultraviolet distributed polymerization according to claim 1, characterized in that: The maximum absorption cutoff wavelength of the free radical initiator in step 1 is less than 390 nm.

5. The method for preparing an electrically controlled bistable dimming film based on ultraviolet distributed polymerization according to claim 4, characterized in that: The free radical initiator is at least one of 3-methyl-4, phenyl benzophenone, 2-hydroxy-2-methyl-1-[4-(tert-butyl)phenyl]-1-propanone and benzil dimethyl ether.

6. The method for preparing an electrically controlled bistable dimming film based on ultraviolet distributed polymerization according to claim 1, characterized in that: The photo-induced leaving type photoinitiator in step 1 is at least one of the compound NVOC-HA, the compound NPPOC-TMG, the compound NVOC-DEA, the compound NPPOC-DEA, the compound NVOC-TMG and the compound MNPPOC-TMG.

7. The method for preparing an electrically controlled bistable dimming film based on ultraviolet distributed polymerization according to claim 1, characterized in that: In the step 2, the thickness of the liquid crystal box is controlled by a spacer with a thickness of 10 to 43 μm, and the distance between the two conductive films is controlled by a glass microsphere spacer with a diameter of 10 to 43 μm.

8. The method for preparing an electrically controlled bistable dimming film based on ultraviolet distributed polymerization according to claim 1, characterized in that: In step 3, the light intensity of the light with a wavelength of 405 nm is 5.5 to 40 mw / cm 2 , and the irradiation time is 20 to 90 minutes; the illumination intensity of ultraviolet light with a wavelength of 365nm is 0.10 to 2.12mw / cm 2 , and the irradiation time is 1 to 10 minutes.

9. The electrically controlled bistable dimming film prepared according to the method according to any one of claims 1 to 8, characterized in that: The polymer network morphology of the electrically controlled bistable dimming film presents a multi-level microstructure that combines a flower-like network and a porous structure.

10. The electrically controlled bistable dimming film according to claim 9, characterized in that: Under a low-frequency electric field of 5Hz and 40V, the transmittance of light in the wavelength range of 400-2500nm is less than 5.4%, and the average transmittance is 1.98%. Under a low-frequency electric field of 50-100Hz and 60V, the electrically controlled bistable dimming film is transparent.

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