A method for preparing a liquid crystal / polymer thin film

Abstract

A method for preparing a liquid crystal / polymer thin film, the method comprising: uniformly mixing the following components and stirring to form an isotropic liquid: 40.0-80.0% of a mixed crystal material, 5.0-40.0% of a liquid crystal monomer, 10.0-40.0% of a thiol polymerizable monomer, 1.0-25.0% of an olefin polymerizable monomer, 1.0-25.0% of a crosslinking agent, 0.5-2.0% of a photoinitiator, and the side group of the liquid crystal monomer being a fluorine-containing substituent or other substituent; uniformly coating the mixed liquid on a pre-prepared substrate, or filling it into a pre-prepared liquid crystal cell, placing it under an ultraviolet lamp for polymerization reaction, and taking out the cured product on the substrate or in the liquid crystal cell to obtain the liquid crystal / polymer thin film. By changing the types of the thiol polymerizable monomer, acrylate polymerizable monomer, olefin polymerizable monomer or nanoparticles, or by changing the type or incorporation ratio of the liquid crystal monomer, the preparation method of the present invention can prepare liquid crystal / polymer thin films with different optical properties and viewing angles.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material preparation, and particularly relates to a method for preparing a liquid crystal / polymer thin film. Background Art

[0002] Due to its unique ordered structure, the macroscopic physical properties of liquid crystal materials are neither the same as those of isotropic liquids nor those of highly ordered crystals. Therefore, they exhibit anisotropy in aspects such as optics and electricity, and have broad application prospects. Among liquid crystal materials, the most promising one is the polymer dispersed liquid crystal (PDLC) thin film. The PDLC thin film is a new type of liquid crystal functional film material, which has the advantages of high contrast, simple preparation, and no need for polarizers. Therefore, the PDLC thin film shows great application prospects in large-size flexible display devices, nonlinear optical materials, electro-controlled smart glass, selective permeable membranes, thermal sensors, liquid crystal gratings, holographic thin films, optical switches, etc. The PDLC material is very attractive in both the development of application devices and the research of basic principles, and thus has become a very active research frontier in the field of liquid crystal materials.

[0003] As a liquid crystal / polymer composite material, the PDLC thin film can be used as optical thin films such as anti-peeping films and diffusion films. The viewing angle and transmittance are important performance indicators of the thin film, and the key factor determining them is the refractive index matching of the liquid crystal material and the polymer matrix. However, the current PDLC thin films have single optical properties and viewing angles and cannot be specifically adjusted according to actual needs, that is, their applications are greatly limited. Summary of the Invention

[0004] Based on this, the present invention provides a method for preparing a liquid crystal / polymer thin film to solve the technical problem that the existing PDLC thin film has single optical properties and viewing angles and cannot be specifically adjusted according to actual needs.

[0005] To achieve the above object, the present invention provides a method for preparing a liquid crystal / polymer thin film, which comprises the following steps:

[0006] (1) Mix the following components evenly by mass percentage and stir to form an isotropic liquid:

[0007]

[0008] Among them: the side group of the liquid crystal monomer is a fluorine-containing substituent;

[0009] (2) Uniformly coat the above-mentioned mixed liquid on a pre-prepared substrate, or fill it into a pre-prepared liquid crystal cell, place it under an ultraviolet lamp for polymerization reaction, and take out the cured product on the substrate or in the liquid crystal cell to obtain the liquid crystal / polymer thin film.

[0010] As a further preferred technical solution of the present invention, the liquid crystal monomer includes one or more of 4”-ethyl-2',3,4,5-tetrafluoro-1,1':4',1”-terphenyl, 2',3,4,5-tetrafluoro-4”-propyl-1,1':4',1”-terphenyl, and 2',3,4,5-tetrafluoro-4”-pentyl-1,1':4',1”-terphenyl.

[0011] As a further preferred technical solution of the present invention, the thiol polymerizable monomer includes one or more of ethylene glycol bis(3-mercaptopropionate), 1,4-butanediol bis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), trimethylolpropane tris(mercaptoacetate), pentaerythritol tetra(3-mercaptopropionate), pentaerythritol tetra(3-mercaptoacetate) ester, inositol hexakis(mercapto propionate), Capcure 3-800, Capcure 3830-81, Capcure 40secHV, Capcure WR-6, Epomate QX-lO, EPomate qx-40, MP-gg90, and EH-316.

[0012] As a further preferred technical solution of the present invention, 1.0 to 10.0% of an acrylate polymerizable monomer is further added in step (1), and the acrylate polymerizable monomer includes one or more of diethylene glycol diacrylate, 3-(trimethoxysilyl)propyl acrylate, isopropyl methacrylate, 1,4-butanediol diacrylate, polyethylene glycol diacrylate 600, and polyethylene glycol diacrylate 800.

[0013] As a further preferred technical solution of the present invention, the ethylenically polymerizable monomer is a bisphenol A type, a vinyl ether monomer, or an allyl ether monomer, and includes one or more of 2,2-bis(allyloxymethyl)-1-butanol (E1), diallyl ether, α,α-diallyl glycerol ether, and bisphenol A diallyl ether.

[0014] As a further preferred technical solution of the present invention, 0 to 2.0% of nanoparticles are further added in step (1), and the nanoparticles are one or more of SiO2, ITO, Cs x WO3, and W-VO2

[0015] As a further preferred technical solution of the present invention, the crosslinking agent includes one or more of 1,3,5-triallyl cyanurate and triallyl isocyanurate.

[0016] As a further preferred technical solution of the present invention, the photoinitiator is a benzoin type initiator, and the benzoin type initiator includes benzoin dimethyl ether Irgacure 651.

[0017] As a further preferred technical solution of the present invention, the polymerization reaction conditions are as follows: the intensity of ultraviolet light is 0.5-15 mW / cm 2 , and the temperature ranges from room temperature to 100 °C.

[0018] As a further preferred technical solution of the present invention, in step (1), by changing the types of thiol polymerizable monomers, acrylate polymerizable monomers, vinyl polymerizable monomers or nanoparticles, or by changing the types or incorporation ratios of liquid crystal monomers, liquid crystal / polymer thin films with different optical properties and viewing angles can be prepared.

[0019] The preparation method of the liquid crystal / polymer thin film of the present invention can achieve the following beneficial effects by adopting the above technical solutions:

[0020] (1) Introducing nanoparticles of inorganic components with a relatively high molar refraction, and through increasing or decreasing their contents, the refractive index (n p ) of the polymer matrix (thiol polymerizable monomer, acrylate polymerizable monomer, vinyl polymerizable monomer) can be bidirectionally adjusted;

[0021] (2) By adding fluorine-substituted liquid crystal monomers to the mixed crystal material, the ordinary light refractive index (n o ) and birefringence (Δn) of the liquid crystal monomers can be effectively regulated;

[0022] (3) Through the bidirectional adjustment of the polymer matrix and the regulation of the ordinary light refractive index (n o ) and birefringence (Δn) of the crystal monomers, liquid crystal / polymer thin films with different optical properties and viewing angles can be prepared according to requirements;

[0023] (4) The preparation method of the present invention is simple, the reaction is mild, pollution-free, and the prepared liquid crystal / polymer thin film has excellent mechanical properties, good electro-optical properties, longer service life, and good optical properties. Description of the Drawings

[0024] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0025] Figure 1 are the molecular structural formulas of the thiol polymerizable monomer, vinyl polymerizable monomer, crosslinking agent, and photoinitiator used in Examples 1-3 provided by the present invention;

[0026] Figure 2 is the scanning electron micrograph of the polymer network prepared in Example 1 of the present invention;

[0027] Figure 3 is the light diffusion ability curve in Example 2 of the present invention;

[0028] Figure 4 It is the light diffusion ability curve in Example 3.

[0029] The realization of the object, functional features, and advantages of the present invention will be further described in conjunction with the embodiments and with reference to the accompanying drawings. Detailed implementation manners

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation manners. Terms such as "upper", "lower", "left", "right", "middle", and "one" cited in the preferred embodiments are only for the sake of clarity in narration and are not used to limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships shall also be regarded as the scope of implementation of the present invention without substantial changes in the technical content.

[0031] In order to solve the technical problems that the current PDLC film has single optical performance and viewing angle and cannot be specifically adjusted according to actual needs, that is, its application is greatly restricted, the inventors of the present application have obtained a method for preparing a liquid crystal / polymer film through creative labor. This method can prepare liquid crystal / polymer films with different optical performances and viewing angles by changing the types of thiol polymerizable monomers, acrylate polymerizable monomers, vinyl polymerizable monomers, or nanoparticles, or by changing the types or incorporation ratios of liquid crystal monomers. The method specifically includes the following steps:

[0032] (1) Mix the following components evenly by mass percentage and stir to form an isotropic liquid under the condition of 60 - 100 °C:

[0033]

[0034]

[0035] (2) Uniformly coat the above-mentioned mixed liquid on a pre-prepared substrate or fill it into a pre-prepared liquid crystal cell, and place it under an ultraviolet lamp with a light intensity range of 0.5 - 15 mW / cm 2 , and carry out a polymerization reaction at a temperature from room temperature to 100 °C. After the polymerization reaction is completed, take out the cured product on the substrate or in the liquid crystal cell to obtain the liquid crystal / polymer film.

[0036] In specific implementation, in order to prepare liquid crystal / polymer films with different optical performances and viewing angles, it is achieved by precisely controlling the raw materials and their ratios in step (1). Specifically: change the types of thiol polymerizable monomers, acrylate polymerizable monomers, vinyl polymerizable monomers, or nanoparticles to control the refractive index of the polymer network matrix, or change the types or incorporation ratios of liquid crystal monomers to control the birefringence and dielectric constant of the liquid crystal monomer material.

[0037] The specific materials used for preparing the liquid crystal / polymer film are as follows:

[0038] The liquid crystal monomers include side-chain fluorine-substituted materials such as NF1 (4”-ethyl-2',3,4,5-tetrafluoro-1,1':4',1”-terphenyl), NF2 (2',3,4,5-tetrafluoro-4”-propyl-1,1':4',1”-terphenyl), and NF3 (2',3,4,5-tetrafluoro-4”-pentyl-1,1':4',1”-terphenyl).

[0039] The thiol polymerizable monomer is one or more of small molecule thiol polymerizable monomers or macromolecule thiol polymerizable monomers. Among them, the small molecule thiol polymerizable monomers include ethylene glycol bis(3-mercaptopropionate), 1,4-butanediol bis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), trimethylolpropane tris(mercaptoacetate), pentaerythritol tetra(3-mercaptopropionate) (TTMP), pentaerythritol tetra(mercaptoacetate) (PTMP), and inositol hexakis(mercaptoacetate) (DHMP); the small and large molecule thiol polymerizable monomers include, for example, Capcure 3-800, Capcure 3830-81, Capcure 40secHV in the United States, or CaptureLOF, Capcure WR-6 in Germany, or Epomate QX-lO, EPomate qx-40, MP-gg90, EH-316 in Japan.

[0040] The acrylate polymerizable monomer is one or more of small molecule acrylate polymerizable monomers or macromolecule acrylate polymerizable monomers. Among them, the small molecule acrylate polymerizable monomers include diethylene glycol diacrylate, 3-(trimethoxysilyl)propyl acrylate, isopropyl methacrylate, and 1,4-butanediol diacrylate; the macromolecule acrylate polymerizable monomers include polyethylene glycol diacrylate 600 (PEGDA600) and polyethylene glycol diacrylate 800 (PEGDA800).

[0041] The vinyl polymerizable monomers are bisphenol A type, vinyl ether monomers, and allyl ether monomers, including 2,2-bis(allyloxymethyl)-1-butanol (E1), diallyl ether, α,α-diallyl glycerol ether, and bisphenol A diallyl ether.

[0042] The crosslinking agents include 1,3,5-triallyl cyanurate (TAC) and triallyl isocyanurate.

[0043] The photoinitiator is a benzoin type initiator including benzoin dimethyl ether Irgacure 651 (Irg 651).

[0044] The nanoparticles are inorganic nanoparticles, including SiO2, ITO, Cs x WO3, W-VO2.

[0045] The material system used in the preparation method of the present invention is a liquid crystal / polymer composite system. Nanoparticles of inorganic components with relatively high molar refraction are introduced into the system. By increasing or decreasing their content, the refractive index (n p ) of the polymer matrix (mercaptan polymerizable monomer, acrylate polymerizable monomer, olefin polymerizable monomer) can be adjusted bidirectionally. The refractive index matching between the liquid crystal monomer and the polymer matrix is crucial for optical properties. That is, when the refractive index (n p ) of the polymer matrix is close to the ordinary light refractive index (n o ) of the liquid crystal monomer, the light transmittance of the liquid crystal / polymer thin film is the largest, and its viewing angle is also related thereto. In addition, by adding a fluorine-substituted liquid crystal monomer to the mixed crystal material, the ordinary light refractive index (n o ) and birefringence (Δn) of the liquid crystal monomer can be effectively regulated. Based on the above principles, bidirectional adjustment of the refractive indices of the polymer matrix and the liquid crystal monomer can be achieved, thereby improving the optical properties and viewing angle of the liquid crystal / polymer thin film.

[0046] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments.

[0047] The chemical structures of the mercaptan polymerizable monomer, olefin polymerizable monomer, crosslinking agent, and photoinitiator used in the following Examples 1-3 are as Figure 1 shown.

[0048] Example 1

[0049] The types and ratios of the selected liquid crystal monomer, mercaptan polymerizable monomer, acrylate polymerizable monomer, olefin polymerizable monomer, crosslinking agent, and photoinitiator are listed in Table 1, where E8 is a mixed crystal material. The raw materials in Table 1 were stirred at 80 °C to form an isotropic liquid, mixed evenly, coated on a clean glass substrate, and then placed under an ultraviolet lamp with a light intensity of 5 mW / cm 2 for 300 s of curing; after the curing was completed, the prepared liquid crystal / polymer thin film sample was immersed in a sample bottle filled with cyclohexane for 2 weeks, and the cyclohexane was replaced regularly to better remove the liquid crystal molecules in the sample; finally, the immersed sample was placed in a vacuum oven and dried for 24 h. After sputtering gold on its surface, the network morphology of the sample could be observed by SEM, and the results are as Figure 2 shown.

[0050] Table 1. Materials and ratio table used in Example 1 (by wt.%)

[0051]

[0052] Note: The liquid crystal monomer NF in the ingredients used in Table 1 is prepared by mixing NF1, NF2, and NF3 in a ratio of 1:1:1.

[0053] Example 2

[0054] The selected liquid crystal monomers, thiol polymerizable monomers, vinyl polymerizable monomers, crosslinking agents, photoinitiator materials and their ratios are listed in Table 2, where E8 is a mixed crystal material. Table 2 provides a total of six groups of ingredients X1-6, and six groups of samples X1-5 are prepared respectively according to the following steps. The preparation steps for each sample are as follows: Stir the raw materials in the table at 80 °C to form an isotropic liquid, mix evenly, coat it on a clean glass substrate, and cure it under ultraviolet light to obtain a liquid crystal / polymer thin film sample.

[0055] The viewing angles of samples X1-6 were measured using the angular light intensity distribution as follows: Place the prepared sample on the stage. The distance between the sample and the plane light source is 40 mm, and the distance between the photodetector and the sample is 20 cm. The sample and the light source rotate simultaneously, and the rotation angle ranges from -90° to 90°. At each rotation of a certain angle, the light intensity detector PR655 will record the corresponding light intensity in real time. The effective size of all samples in the test is 40×40 mm 2 , and the results are as Figure 3 shown. In samples X1-6, the refractive index (n p ) of the polymer matrix and the birefringence (Δn) of the liquid crystal monomer used were measured separately using an Abbe refractometer, and the results are shown in Table 2.

[0056] Table 2. Materials and ratio table used in Example 2 (by wt.%)

[0057]

[0058] Note: The content of the photoinitiator Irg 651 in the ingredients used in Table 2 is 1 wt.%, and the liquid crystal monomer NF is prepared by mixing NF1, NF2, and NF3 in a ratio of 1:1:1.

[0059] Analysis of Table 2 shows that when using Capucure 3-800 thiol polymerizable monomer to replace TTMP in the system, since the molecular weight of Capcure3-800 is relatively large, the content of sulfur element in the sample decreases, and the refractive index of the polymer matrix gradually decreases, realizing the adjustment of the refractive index np of the polymer matrix. The polymer refractive index and liquid crystal refractive index of sample X6 have the best matching, so its viewing angle is wider and the maximum transmittance is higher.

[0060] Example 3

[0061] The names and ratios of the selected liquid crystal monomers, thiol-polymerizable monomers, olefin-polymerizable monomers, crosslinking agents, and photoinitiators are listed in Table 3, where E8 is a mixed crystal material. Table 3 provides a total of five groups of ingredients, namely Y1 - 5. Five groups of samples, Y1 - 5, can be prepared respectively according to the following steps. The preparation steps for each sample are as follows: Stir the raw materials in the table at 80 °C to form an isotropic liquid, mix them evenly, coat them on a clean glass substrate, and cure them under ultraviolet light to obtain liquid crystal / polymer thin film samples.

[0062] Use an angular light intensity distribution tester to measure the viewing angles of samples Y1 - 5 respectively, as follows: Place the prepared sample on the stage. The distance between the sample and the planar light source is 40 mm, and the distance between the light detector and the sample is 20 cm. The sample and the light source rotate simultaneously, and the rotation angle ranges from -90° to 90°. Every time a certain angle is rotated, the light intensity detector PR655 will record the corresponding light intensity in real time. The effective size of all samples in the test is 40×40 mm 2 , and the results are as Figure 4 shown. For samples Y1 - 5, use an Abbe refractometer to measure the refractive index (n p ) of the polymer matrix and the birefringence (Δn) of the used liquid crystal monomers respectively. The results are shown in Table 2.

[0063] Table 3. Materials and Ratio Table Used in Example 3 (by wt.%)

[0064]

[0065]

[0066] Note: The content of the photoinitiator Irg 651 in the ingredients used in Table 3 is 1 wt.%, and the liquid crystal monomer NF is composed of NF1, NF2, and NF3 in a ratio of 1:1:1.

[0067] Analyzing Table 3 shows that when keeping the content of non-liquid crystal polymerizable monomers unchanged, using the liquid crystal material NF to regulate the birefringence of the mixed crystal E8, as the content of the fluorinated liquid crystal monomer increases, the ordinary light refractive index n o of the mixed crystal gradually increases. When n o matches the refractive index n p of the polymer matrix most closely, that is, sample Y3, at this time, the viewing angle of the thin film is wider and the maximum transmittance is higher.

[0068] Example 4

[0069] Adopt the same material system as in Example 3, and only configure the liquid crystal monomer NF with any one of NF1, NF2, and NF3. Use an Abbe refractometer to measure the refractive index (n p) and the birefringence (Δn) of the liquid crystal monomers used, it is found that as the content of the fluorinated liquid crystal monomer increases, the ordinary light refractive index n of the mixed crystal o gradually increases.

[0070] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only examples, and various changes or modifications can be made to this embodiment without departing from the principle and essence of the present invention. The protection scope of the present invention is only defined by the appended claims.

Claims

1. A method for preparing a liquid crystal / polymer thin film, characterized in that, It includes the following steps: (1) Mix the following components evenly by mass percentage and stir to form an isotropic liquid: The thiol polymerizable monomers are 13.75 wt.% of TTMP and 13.75 wt.% of Capcure 3-800, and their structural formulas are as follows: ； The ethylenically polymerizable monomer is 13.25 wt.% of E1, and its structural formula is as follows: ； The crosslinking agent is 13.25 wt.% of TAC, and its structural formula is as follows: ； The photoinitiator is 1 wt.% of Irgacure 651; The mixed crystal material is E8, which is prepared by mixing the compounds 3OCB, 5OCB, 8OCB, 5CB, and 5CT shown by the following structures: ； The liquid crystal monomer is prepared by mixing NF1, NF2, and NF3 shown by the following structures in a ratio of 1:1:1: ； Wherein: when the mixed crystal material is 40.50 wt.%, the liquid crystal monomer is 4.50 wt.%; when the mixed crystal material is 36.00 wt.%, the liquid crystal monomer is 9.00 wt.%; when the mixed crystal material is 31.50 wt.%, the liquid crystal monomer is 13.50 wt.%; (2) Uniformly coat the above-mentioned mixed liquid on a pre-prepared substrate, or fill it into a pre-prepared liquid crystal cell, place it under an ultraviolet lamp for polymerization reaction, take out the cured product on the substrate or in the liquid crystal cell, and obtain a liquid crystal / polymer thin film.

2. The preparation method of the liquid crystal / polymer thin film according to claim 1, characterized in that, In step (2), the polymerization reaction conditions are as follows: the intensity of ultraviolet light is 0.5 - 15 mW / cm 2 , and the temperature ranges from room temperature to 100 °C.

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