Holographic polymer dispersed liquid crystal mixed material, volume holographic grating and preparation method

Abstract

The invention discloses a holographic polymer dispersed liquid crystal mixed material, a preparation method of the holographic polymer dispersed liquid crystal mixed material, a preparation method of a volume holographic grating, the volume holographic grating, a volume holographic optical waveguide and holographic equipment. The preparation method of the mixed material comprises the following steps: providing polymerizable liquid crystal, a polymerizable monomer, a photoinitiator and a cross-linking agent; and uniformly mixing the polymerizable liquid crystal, a polymerizable monomer, a photoinitiator and a cross-linking agent to obtain the holographic polymer dispersed liquid crystal mixed material. In this way, the volume holographic grating with high stability and high refractive index modulation capability can be prepared from the mixed material.

Description

Technical Field

[0001] The present application relates to the technical field of holographic optical devices, and in particular to a holographic polymer dispersed liquid crystal hybrid material, a method for preparing a holographic polymer dispersed liquid crystal hybrid material, a method for preparing a volume holographic grating, a volume holographic grating, a volume holographic optical waveguide and a holographic device. Background Art

[0002] Holographic Polymer Dispersed Liquid Crystal (H-PDLC), with its unique structure and working mechanism, has broad application prospects in the optoelectronic field. Although H-PDLC technology has many advantages, it still faces some challenges in practical applications: First, the operating temperature of small molecule liquid crystal is relatively narrow, and even within the operating temperature range, its refractive index will fluctuate significantly with temperature changes, limiting the uniformity and stability of device operation; second, insufficient sealing of device packaging will cause small molecule liquid crystal to flow out of the device, resulting in loss of device performance and deterioration of liquid crystal molecules. Summary of the invention

[0003] Based on this, the present application provides a holographic polymer dispersed liquid crystal hybrid material, a method for preparing a holographic polymer dispersed liquid crystal hybrid material, a method for preparing a volume holographic grating, a volume holographic grating, a volume holographic optical waveguide and a holographic device, which can provide material support for the preparation of a volume holographic grating with high stability and high refractive index modulation capability.

[0004] In a first aspect, the present application provides a holographic polymer dispersed liquid crystal hybrid material, wherein the holographic polymer dispersed liquid crystal hybrid material comprises a polymerizable liquid crystal, a polymerizable monomer, a photoinitiator, and a cross-linking agent.

[0005] In a second aspect, the present application provides a method for preparing a holographic polymer dispersed liquid crystal hybrid material, the method comprising:

[0006] Providing polymerizable liquid crystal, polymerizable monomer, photoinitiator and cross-linking agent;

[0007] The polymerizable liquid crystal, polymerizable monomer, photoinitiator and cross-linking agent are mixed evenly to obtain the holographic polymer dispersed liquid crystal mixed material.

[0008] In a third aspect, the present application provides a method for preparing a volume holographic grating, the method comprising:

[0009] Providing a holographic polymer dispersed liquid crystal mixed material, wherein the holographic polymer dispersed liquid crystal mixed material is the holographic polymer dispersed liquid crystal mixed material as described above;

[0010] uniformly distributing the holographic polymer dispersed liquid crystal mixed material on the surface of the substrate;

[0011] A light beam is used to irradiate the surface of a substrate on which the holographic polymer dispersed liquid crystal hybrid material is uniformly distributed, so that the polymerizable monomers in the first area of ​​the holographic polymer dispersed liquid crystal hybrid material irradiated by the light undergo a first polymerization reaction, and the polymerizable liquid crystals in the second area of ​​the holographic polymer dispersed liquid crystal hybrid material irradiated by the light undergo a second polymerization reaction, thereby obtaining the volume holographic grating.

[0012] In a fourth aspect, the present application provides a volume holographic grating, which is prepared by the method for preparing a volume holographic grating as described above.

[0013] In a fifth aspect, the present application provides a volume holographic optical waveguide, wherein the volume holographic optical waveguide comprises the volume holographic grating as described above.

[0014] In a sixth aspect, the present application provides a holographic device, wherein the holographic device comprises the volume holographic optical waveguide as described above.

[0015] The embodiments of the present application provide a holographic polymer dispersed liquid crystal hybrid material, a preparation method of the holographic polymer dispersed liquid crystal hybrid material, a preparation method of a volume holographic grating, a volume holographic grating, a volume holographic optical waveguide and a holographic device. The holographic polymer dispersed liquid crystal hybrid material includes a polymerizable liquid crystal, a polymerizable monomer, a photoinitiator and a cross-linking agent. First, since the polymerizable liquid crystal can be polymerized, it can form a closer bond with the polymer matrix during the photopolymerization reaction, so its anti-aging, heat resistance, chemical corrosion resistance and other properties are significantly improved, thereby extending the service life of H-PDLC and significantly improving the stability and durability of H-PDLC. Moreover, since the polymerizable liquid crystal forms a closer bond with the polymer matrix during the photopolymerization reaction, the liquid crystal polymer after the polymerizable liquid crystal is polymerized is no longer in a liquid state, and even if the device packaging is not sealed enough, it will not cause liquid crystal polymerization. The liquid crystal polymer will not deteriorate when it flows out of the device; secondly, since the orientation of the polymerizable liquid crystal is fixed after polymerization and it is evenly distributed in the polymer matrix, a more sophisticated refractive index modulation structure is formed. This structure enables the H-PDLC to have a higher refractive index modulation capability, thereby enabling more complex and precise optical functions; thirdly, the holographic polymer dispersed liquid crystal mixed material also makes its preparation method simple and easy to operate, and the reaction conditions are easy to control. By optimizing the reaction conditions and parameters, H-PDLC gratings with different performance requirements can be prepared, and the harshness of the packaging conditions is greatly reduced, which can meet the needs of different application occasions; fourthly, since the H-PDLC prepared in the application embodiment has excellent properties such as high stability and high refractive index modulation capability, it can be widely used in display, diffraction grating, optical waveguide devices and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic flow chart of an embodiment of a method for preparing a holographic polymer dispersed liquid crystal hybrid material of the present application;

[0017] Figure 2 It is a schematic flow chart of an embodiment of a method for preparing a volume holographic grating of the present application;

[0018] Figure 3 It is a schematic flow chart of another embodiment of the method for preparing a volume holographic grating of the present application;

[0019] Figure 4 It is a schematic diagram of the molecular structures of acrylate monomers A1, A2 and photoinitiator TPO used in an embodiment of the holographic polymer dispersed liquid crystal hybrid material of the present application;

[0020] Figure 5 It is a molecular structure diagram of the polymerizable nematic liquid crystal RM1 and the photosensitizer used in an embodiment of the holographic polymer dispersed liquid crystal hybrid material of the present application;

[0021] Figure 6 It is a schematic diagram of the reaction principle in the method for preparing the volume holographic grating of the present application;

[0022] Figure 7 It is a schematic diagram of the molecular structure of polymerizable nematic liquid crystals RM2 and RM3 used in an embodiment of the holographic polymer dispersed liquid crystal hybrid material of the present application. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0024] The flowcharts shown in the accompanying drawings are only examples and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps may also be decomposed, combined or partially merged, so the actual execution order may change according to actual conditions.

[0025] In the subsequent description, the suffixes such as "module", "component" or "unit" used to represent elements are only used to facilitate the description of the present application, and have no special meanings. Therefore, "module", "component" or "unit" can be used in a mixed manner.

[0026] Holographic Polymer Dispersed Liquid Crystal (H-PDLC) is a new optoelectronic material that combines holographic technology with polymer dispersed liquid crystal (PDLC). Its unique structure and working mechanism make H-PDLC have broad application prospects in the optoelectronic field. H-PDLC is prepared by uniformly dispersing liquid crystal droplets in a polymer matrix and periodically modulating the arrangement of liquid crystal droplets using holographic technology to produce a grating structure with specific optical properties, achieve specific optical functions, and is used for holographic display.

[0027] Although H-PDLC technology has many advantages, it still faces some challenges in practical applications. The key issues can be summarized as follows: First, small molecule liquid crystals are used in traditional H-PDLC material systems to increase refractive index modulation. Usually, this type of small molecule liquid crystal has the defect of a narrow operating temperature, that is, the solid phase-nematic phase transition temperature (TCN) and the nematic phase-isotropic liquid phase transition temperature (TNI) are close; even within the operating temperature range, the refractive index of small molecule liquid crystals will fluctuate significantly with temperature changes, which limits the uniformity and stability of device operation. Second, in addition to low temperature tolerance, traditional H-PDLC devices require good packaging. Insufficient sealing of the packaging will cause the small molecule liquid crystal in solution to flow out of the closed system, resulting in loss of device performance. Insufficient sealing of the packaging will also cause the liquid crystal molecules to deteriorate under water / oxygen erosion. The above defects are also the main limitations for H-PDLC devices to be introduced to the market on a large scale.

[0028] In order to solve the above problems, the embodiments of the present application provide a holographic polymer dispersed liquid crystal hybrid material, a preparation method of the holographic polymer dispersed liquid crystal hybrid material, a preparation method of a volume holographic grating, a volume holographic grating, a volume holographic optical waveguide and a holographic device. The holographic polymer dispersed liquid crystal hybrid material includes a polymerizable liquid crystal, a polymerizable monomer, a photoinitiator and a cross-linking agent. First, since the polymerizable liquid crystal can be polymerized, it can form a closer bond with the polymer matrix during the photopolymerization reaction, so its anti-aging, heat resistance, chemical corrosion resistance and other properties are significantly improved, thereby being able to extend the service life of the H-PDLC and significantly improve the stability and durability of the H-PDLC. Moreover, since the polymerizable liquid crystal forms a closer bond with the polymer matrix during the photopolymerization reaction, the liquid crystal polymer after the polymerizable liquid crystal is polymerized is no longer in a liquid state. Even if the sealing of the device package is insufficient, the liquid crystal polymer will not flow out of the device, and the liquid crystal polymer will not deteriorate. Second 2. Since the orientation of the polymerizable liquid crystal is fixed after polymerization and its distribution in the polymer matrix is ​​uniform, a more sophisticated refractive index modulation structure is formed. This structure enables the H-PDLC to have a higher refractive index modulation capability, thereby enabling more complex and precise optical functions to be achieved; therefore, the holographic polymer dispersed liquid crystal hybrid material can provide material support for the preparation of a volume holographic grating with high stability and high refractive index modulation capability; thirdly, the holographic polymer dispersed liquid crystal hybrid material also makes its preparation method simple and easy to operate, and the reaction conditions are easy to control. By optimizing the reaction conditions and parameters, H-PDLC gratings with different performance requirements can be prepared, and the harshness of the packaging conditions is greatly reduced, which can meet the needs of different application scenarios; fourthly, since the H-PDLC prepared in the application embodiment has excellent properties such as high stability and high refractive index modulation capability, it can be widely used in display, diffraction grating, optical waveguide devices and other fields.

[0029] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0030] The embodiment of the present application provides a holographic polymer dispersed liquid crystal hybrid material, wherein the holographic polymer dispersed liquid crystal hybrid material includes a polymerizable liquid crystal, a polymerizable monomer, a photoinitiator, and a cross-linking agent.

[0031] Polymerizable liquid crystal is a molecule with a special structure, which has liquid crystal and polymerization properties. It can be polymerized to form liquid crystal polymers under external stimulation. Liquid crystal polymers are a type of polymer material with a liquid crystal phase.

[0032] The polymerizable monomer may refer to a monomer that can undergo a polymerization reaction, including but not limited to: an acrylate monomer, a styrene monomer, a urethane monomer, and the like.

[0033] Photoinitiators can be compounds that can absorb energy of a certain wavelength in the ultraviolet region (250-420 nm) or visible region (400-800 nm) to generate free radicals, cations, etc., thereby initiating polymerization, cross-linking and curing of monomers. Photoinitiators include, but are not limited to: photoinitiator 1173 (2-hydroxy-2-methyl-1-phenylpropanone), photoinitiator 184 (1-hydroxycyclohexylphenyl ketone), photoinitiator 907 (2-methyl-2-(4-morpholinyl)-1-[4-(methylthio)phenyl]-1-propanone), photoinitiator TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide), photoinitiator TPO-L (2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester), etc.

[0034] Cross-linking agents are mainly used in polymer materials. The molecular structure of polymer materials is like long lines. When not cross-linked, they have low strength, are easy to break, and have no elasticity. The role of cross-linking agents is to generate chemical bonds between linear molecules, so that the linear molecules are connected to each other to form a network structure, which can improve the strength and elasticity of polymer materials. Cross-linking agents include but are not limited to: DCP (diisopropylbenzene peroxide), BPO (benzoyl peroxide), DTBP (di-tert-butyl peroxide), DBHP (diisopropylbenzene hydroperoxide), etc.

[0035] In the embodiment of the present application, since the polymerizable liquid crystal can be polymerized and can form a closer bond with the polymer matrix during the photopolymerization reaction, its anti-aging, heat resistance, chemical corrosion resistance and other properties are significantly improved, thereby extending the service life of the H-PDLC and significantly improving the stability and durability of the H-PDLC. Moreover, since the polymerizable liquid crystal forms a closer bond with the polymer matrix during the photopolymerization reaction, the liquid crystal polymer after the polymerizable liquid crystal is polymerized is no longer in a liquid state. Even if the device packaging is not sealed enough, the liquid crystal polymer will not flow out of the device and will not deteriorate. Since the orientation of the polymerizable liquid crystal is fixed after polymerization and its distribution in the polymer matrix is ​​uniform, a more refined refractive index modulation structure is formed. This structure enables the H-PDLC to have a higher refractive index modulation capability, thereby enabling more complex and precise optical functions. Therefore, the holographic polymer dispersed liquid crystal hybrid material can provide material support for the preparation of a volume holographic grating with high stability and high refractive index modulation capability.

[0036] In some embodiments, the photoinitiator includes a first photoinitiator and a second photoinitiator, and the absorption spectrum of the first photoinitiator is different from the absorption spectrum of the second photoinitiator.

[0037] The absorption spectrum of the first photoinitiator is different from the absorption spectrum of the second photoinitiator, that is, the wavelength range of the light source to which the first photoinitiator is sensitive is different from the wavelength range of the light source to which the second photoinitiator is sensitive. For example, the first photoinitiator is sensitive to a first light source in a first wavelength range (e.g., a blue light source in a wavelength range of 400nm-500nm), and the second photoinitiator is sensitive to a second light source in a second wavelength range (e.g., an ultraviolet light source in a wavelength range of 10nm-400nm).

[0038] In some embodiments, the mass ratio of the polymerizable liquid crystal to the polymerizable monomer is 0.3:0.7-0.7:0.3. For example, the mass ratio of the polymerizable liquid crystal monomer to the polymerizable monomer is 0.3:0.7, 1:2, 1:1, 2:1, 0.7:0.3, etc. Within this mass ratio range, on the one hand, the polymerizable monomer can be polymerized to form a polymer matrix that meets the requirements, and on the other hand, the polymerizable liquid crystal can be evenly distributed in the polymer matrix after polymerization, forming a more refined refractive index modulation structure.

[0039] In some embodiments, the polymerizable liquid crystal includes at least one of (2-methyl-1,4-phenylenebis(4-(3-((3-methylbutylene-3-ol)methoxy)propoxy)benzoate)), (4-((4-hydroxybenzoyl)oxy)-3-methylphenyl 4-(3-((3-methylbutylene-3-ol)methoxy)propoxy)benzoate), and (2-cyano-1,4-phenylenebis(4-(3-((3-methylbutylene-3-ol)methoxy)propoxy)benzoate).

[0040] Among them, the full English name of (2-methyl-1,4-phenylene bis(4-(3-((3-methyloxetan-3-yl)methoxy)propoxy)benzoate)) is (2-methyl-1,4-phenylene bis(4-(3-((3-methyloxetan-3-yl)methoxy)propoxy)benzoate)), and (2-methyl-1,4-phenylene bis(4-(3-((3-methyloxetan-3-yl)methoxy)propoxy)benzoate)) is abbreviated as RM1 in the embodiments of the present application. Its molecular structure is as follows Figure 5 shown.

[0041] Among them, the full English name of (4-((4-hydroxybenzoyl)oxy)-3-methylphenyl 4-(3-((3-methyloxetan-3-yl)methoxy)propoxy)benzoate) is: (4-((4-hydroxybenzoyl)oxy)-3-methylphenyl4-(3-((3-methyloxetan-3-yl)methoxy)propoxy)benzoate), (4-((4-hydroxybenzoyl)oxy)-3-methylphenyl 4-(3-((3-methyloxetan-3-yl)methoxy)propoxy)benzoate) is abbreviated as RM2 in the embodiment of the application, and its molecular structure is as follows Figure 7 shown.

[0042] Among them, the full English name of (2-cyano-1,4-phenylene bis(4-(3-((3-methyloxetan-3-yl)methoxy)propoxy)benzoate)) is: (2-cyano-1,4-phenylene bis(4-(3-((3-methyloxetan-3-yl)methoxy)propoxy)benzoate)), (2-cyano-1,4-phenylene bis(4-(3-((3-methyloxetan-3-yl)methoxy)propoxy)benzoate)) is abbreviated as RM3 in the embodiments of the present application, and its molecular structure is as follows Figure 7 shown.

[0043] In some embodiments, the polymerizable monomer includes an acrylate monomer. Acrylate monomers are also called acrylic ester monomers, which are common and easy to obtain. Acrylate monomers include, but are not limited to, phenoxyethyl acrylate (PHEA), ethoxylated bisphenol A diacrylate (such as EM2261), isobornyl acrylate (IBOA), acrylic acid, methyl acrylate, ethyl acrylate, isobutyl acrylate, n-octyl acrylate, and the like.

[0044] See also Figure 1 , Figure 1 It is a flow chart of an embodiment of a method for preparing a holographic polymer dispersed liquid crystal hybrid material of the present application, and the method comprises: step S101 and step S102.

[0045] Step S101: providing a polymerizable liquid crystal, a polymerizable monomer, a photoinitiator and a cross-linking agent.

[0046] Step S102: uniformly mixing the polymerizable liquid crystal, polymerizable monomer, photoinitiator and cross-linking agent to obtain the holographic polymer dispersed liquid crystal mixed material.

[0047] In some embodiments, the photoinitiator includes a first photoinitiator and a second photoinitiator, and the absorption spectrum of the first photoinitiator is different from the absorption spectrum of the second photoinitiator.

[0048] In some embodiments, the mass ratio of the polymerizable liquid crystal to the polymerizable monomer is 0.3:0.7-0.7:0.3.

[0049] In some embodiments, the polymerizable liquid crystal includes at least one of (2-methyl-1,4-phenylenebis(4-(3-((3-methylbutylene-3-ol)methoxy)propoxy)benzoate)), (4-((4-hydroxybenzoyl)oxy)-3-methylphenyl 4-(3-((3-methylbutylene-3-ol)methoxy)propoxy)benzoate), and (2-cyano-1,4-phenylenebis(4-(3-((3-methylbutylene-3-ol)methoxy)propoxy)benzoate).

[0050] In some embodiments, the polymerizable monomer includes an acrylate monomer.

[0051] An embodiment of the present application further provides an application of any of the above-mentioned holographic polymer dispersed liquid crystal hybrid materials, wherein the holographic polymer dispersed liquid crystal hybrid material is used to prepare a volume holographic grating.

[0052] See also Figure 2 , Figure 2 1 is a flow chart of an embodiment of a method for preparing a volume holographic grating of the present application, the method comprising: step S201 to step S203.

[0053] Step S201: providing a holographic polymer dispersed liquid crystal mixed material, wherein the holographic polymer dispersed liquid crystal mixed material is any one of the holographic polymer dispersed liquid crystal mixed materials described above.

[0054] Step S202: uniformly distributing the holographic polymer dispersed liquid crystal mixed material on the surface of the substrate.

[0055] The substrate of the embodiment of the present application can be a transparent substrate, and the substrate can be an optical glass or resin substrate with specific functions. Before the holographic polymer dispersed liquid crystal mixed material is evenly distributed on the surface of the substrate, the adhesion between the holographic polymer dispersed liquid crystal mixed material and the substrate can be cleaned and enhanced by UVO (ultraviolet light irradiation) or Plasma, and then the holographic polymer dispersed liquid crystal mixed material is evenly coated on the substrate to form a coating layer on the surface of the substrate. The coating method used can be spin coating, scraping, slit coating, inkjet printing and other methods.

[0056] Step S203: Use a light beam to irradiate the surface of a substrate on which the holographic polymer-dispersed liquid crystal hybrid material is uniformly distributed, so that the polymerizable monomers in the first area of ​​the holographic polymer-dispersed liquid crystal hybrid material irradiated by the light undergo a first polymerization reaction, and the polymerizable liquid crystals in the second area of ​​the holographic polymer-dispersed liquid crystal hybrid material irradiated by the light undergo a second polymerization reaction, thereby obtaining the volume holographic grating.

[0057] The surface of the substrate includes a plurality of first regions and second regions arranged adjacent to each other, that is, the first region, the second region, the first region, the second region, ..., which are arranged adjacent to each other. The holographic polymer dispersed liquid crystal mixed material of the embodiment of the present application includes a polymerizable liquid crystal, a polymerizable monomer, a photoinitiator, and a crosslinking agent. After the holographic polymer dispersed liquid crystal mixed material is uniformly distributed on the surface of the substrate, the surface of the substrate is irradiated with a light beam, and the polymerizable monomer in the first region irradiated by the light undergoes a first polymerization reaction, and the polymerizable liquid crystal in the second region irradiated by the light undergoes a second polymerization reaction, thereby obtaining a volume holographic grating. The preparation method is simple and easy to operate, and the reaction conditions are easy to control. By optimizing the reaction conditions and parameters, H-PDLC volume holographic gratings with different performance requirements can be prepared. Since the polymerizable liquid crystal becomes a polymer liquid crystal after the polymerization reaction, the polymer liquid crystal is non-liquid, fixed, and does not flow, so the harshness of the packaging conditions is greatly reduced, which can meet the needs of different application occasions.

[0058] In some embodiments, the substrate has no grating structure, and step S203, irradiating the surface of the substrate on which the holographic polymer dispersed liquid crystal mixed material is uniformly distributed with a light beam, may include: sub-steps S2031 and S2032, such as Figure 3 shown.

[0059] Sub-step S2031: controlling the first light beam to form interference fringes on the surface of the substrate, so that the polymerizable monomers in the bright area of ​​the holographic polymer dispersed liquid crystal hybrid material irradiated by the light undergo a first polymerization reaction under the action of the first photoinitiator.

[0060] Sub-step S2032: Control the second light beam to irradiate the surface of the substrate, so that the polymerizable liquid crystal in the dark area of ​​the holographic polymer dispersed liquid crystal material that is not irradiated by the first light beam undergoes a second polymerization reaction under the irradiation of the second light beam and the action of the second photoinitiator, thereby obtaining the volume holographic grating, and the absorption spectrum of the second photoinitiator is different from the absorption spectrum of the first photoinitiator.

[0061] The purpose of the substrate in the embodiment of the present application is to support the HPDLC grating or as an optical waveguide material. The substrate morphology is mainly a planar structure, and can also be other periodic ordered structures. The substrate in the embodiment of the present application has no grating structure and is illuminated by a two-step method: the first step of illumination is to generate interference fringes when the first light beam is illuminated. When the interference fringes illuminate the surface of the substrate, not all areas of the surface of the substrate are illuminated by light. One of the two adjacent areas of the surface of the substrate is illuminated by light, and the other second area is not illuminated by light. The absorption spectrum of the first photoinitiator matches the emission spectrum of the first light beam. The first photoinitiator can absorb a large amount of light energy from the first light beam. The polymerizable monomers in the bright area (i.e., the first area) illuminated by light undergo a first polymerization reaction under the action of the first photoinitiator. The polymerizable monomers in the bright area undergo a first polymerization reaction, resulting in a decrease in the concentration of the polymerizable monomers in the bright area. The concentration of the polymerizable monomers in the dark area (i.e., the second area) is higher than the concentration of the polymerizable monomers in the bright area. High, so the polymerizable monomers in the dark area will migrate to the bright area, the dark area is not irradiated, and the polymerizable liquid crystal in the dark area will not undergo a second polymerization reaction; the second step of illumination mainly requires the polymerizable liquid crystal in the dark area that was not irradiated in the previous step to undergo a second polymerization reaction. During the first step of illumination, the polymerizable monomer in the bright area that was irradiated has undergone a first polymerization reaction. Therefore, the second step of illumination can be an indiscriminate irradiation of the second light beam, that is, the surface of the substrate is irradiated indiscriminately, and all areas of the surface of the substrate are irradiated by the light of the second light beam. The absorption spectrum of the second initiator matches the emission spectrum of the second light beam, and the second photoinitiator can absorb a large amount of light energy from the second light beam. At this time, the polymerizable liquid crystal in the dark area that was not irradiated in the previous step undergoes a second polymerization reaction under the irradiation of the second light beam and the action of the second photoinitiator. At the same time, the absorption spectrum of the second photoinitiator is different from the absorption spectrum of the first photoinitiator, and the absorption spectrum of the first photoinitiator does not match the emission spectrum of the second light beam. It is difficult for the first photoinitiator to absorb a large amount of light energy from the second light beam, so it can avoid further overpolymerization of the first polymerization reaction that has occurred in the polymerizable monomer.

[0062] Of course, the second step of illumination can also be differential illumination, that is, only the dark area that was not illuminated in the previous step is illuminated. The specific method can be to control the second light beam to form interference fringes on the surface of the substrate. The interference fringes generated by the second light beam can be opposite to the interference fringes generated by the first light beam.

[0063] When preparing volume holographic gratings in related technologies, a substrate with a grating structure is also used. The embodiment of the present application may also use a substrate with a grating structure. When using a substrate with a grating structure, a first light beam may be used to irradiate in a first direction, so that the polymerizable monomer in the bright area (i.e., the first area) irradiated by the light undergoes a first polymerization reaction, and a second light beam may be used to irradiate in a second direction. The area irradiated by the light this time is a dark area not irradiated by the first light beam, so that the polymerizable liquid crystal in the dark area not irradiated by the first light beam undergoes a second polymerization reaction under the irradiation of the second light beam.

[0064] Compared with the related art that uses a substrate with a grating structure, it is necessary to perform fine processing on the substrate in advance to obtain a substrate with a grating structure, which increases the preparation steps and complexity. The embodiment of the present application uses a substrate without a grating structure, which can simplify the preparation steps and complexity; the second step of illumination in the embodiment of the present application uses indiscriminate illumination, which is simpler to operate.

[0065] In some embodiments, the light source of the first light beam includes a blue light source, and the exposure dose of the blue light source is 10-100 mW / cm 2 , for example: 30mW / cm 2 The continuous irradiation time of the blue light source is 1-30 minutes, for example: 1 minute; the light source of the second light beam includes a UV-LED lamp, and the exposure dose of the UV-LED lamp is 10-100mW / cm 2 , for example: 50mW / cm 2 The continuous irradiation time of the UV-LED lamp is 1-30 minutes, for example: 10 minutes.

[0066] Specifically, by controlling the irradiation time and intensity of the light source, the coating layer is subjected to a step-by-step photopolymerization reaction. First, a low-intensity light source is used for the first step of polymerization. In the embodiment of the present application, a blue light with a wavelength of 400-450nm can be selected as the reaction light source. Interference exposure at a specific angle is performed according to the required grating period to form a light field with alternating bright and dark areas. The first step of polymerization occurs in the bright area to form the skeleton of the volume holographic grating. The exposure dose and time of this process are optimized according to the polymerization components. The commonly used exposure dose is 30mW / cm 2, and continue irradiation for 1 minute. The main reaction in the first step of polymerization is the polymerization of polymerizable monomers (such as acrylate compounds). The components of the reaction also include other functional compounds such as the first photoinitiator (sensitive to blue light) and the cross-linking agent. Then the second step of polymerization is carried out, and a UV-LED lamp is used for flood exposure. In this process, the liquid crystal molecules in the dark area of ​​the first step of polymerization are polymerized under the action of the second photoinitiator (sensitive to ultraviolet light) to form a polymer network structure. The director of the liquid crystal in the polymer network can be along a fixed direction or distributed amorphously, and finally a more compact polymer dispersed liquid crystal grating (50mW / cm 2 , continuous irradiation for 10 minutes).

[0067] In one embodiment, see Figures 4 to 6 , Figure 4 The first step of the polymerization reaction uses acrylate monomers A1 and A2, and the first photoinitiator TPO; Figure 5 The polymerizable nematic liquid crystal RM1 used in the second step polymerization reaction and the photosensitizer (i.e., the second photoinitiator); Figure 6 It is a schematic diagram of the reaction principle in the method for preparing the volume holographic grating in the embodiment of the present application.

[0068] The present application also provides a volume holographic grating, which is prepared by any of the above-mentioned methods for preparing the volume holographic grating.

[0069] The present application also provides a volume holographic optical waveguide, wherein the volume holographic optical waveguide comprises the volume holographic grating as described above.

[0070] The present application also provides a holographic device, which includes the volume holographic optical waveguide as described above. The holographic device includes but is not limited to: head-mounted holographic devices and non-head-mounted holographic devices; head-mounted holographic devices include AR glasses, extended reality (XR) devices, etc.; non-head-mounted holographic devices include vehicle-mounted / airborne head-up display (HUD) devices, holographic projection devices, etc.

[0071] The embodiments of the present application are described below with reference to a number of specific examples.

[0072] Preparation of polymerizable liquid crystals:

[0073] Preparation method of polymerizable liquid crystal RM1: Using a round-bottom bottle as a container, first weigh 2.1 g of N,N'-dicyclohexylcarbodiimide (10.17 mmol), then add 0.62 g (5 mmol) of methylhydroquinone and 2.8 g (10 mmol) of 4-(3-((3-methyloxetane)methoxypropoxy)benzoic acid, use 40 mL of dichloromethane as solvent, stir under an ice bath, and finally add 0.12 g (1 mmol) of 4-dimethylaminopyridine as a base. After stirring for 0.5 hour, transfer to room temperature to react for 16 hours, and separate by column chromatography to obtain white solid RM1 with a yield of 78%.

[0074] Preparation method of polymerizable liquid crystal RM2: using a round-bottom bottle as a container, first weigh 2.1 g of N,N'-dicyclohexylcarbodiimide (10.17 mmol), then add 0.62 g (5 mmol) of methylhydroquinone, use 40 mL of dichloromethane as solvent, place it in an ice bath and stir, 0.69 g (5 mmol) of 4-hydroxybenzoic acid is added dropwise for 12 hours, 0.12 g (1 mmol) of 4-dimethylaminopyridine is added as a base, and after stirring for 0.5 hours, the mixture is transferred to room temperature and reacted for 16 hours; then the mixture is placed in an ice bath again, 1.4 g (5 mmol) of a mixed solution of 4-(3-((3-methyloxetanyl)methoxypropoxy)benzoic acid and dichloromethane (10 mL) is added dropwise, the room temperature is restored and the reaction is continued for 16 hours, and white solid RM2 is obtained by column chromatography separation with a yield of 59%.

[0075] Preparation method of polymerizable liquid crystal RM3: Using a round-bottom bottle as a container, first weigh 2.1 g of N,N'-dicyclohexylcarbodiimide (10.17 mmol), then add 0.67 g (5 mmol) of 2,5-dihydroxybenzonitrile and 2.8 g (10 mmol) of 4-(3-((3-methyloxetane)methoxypropoxy)benzoic acid, use 40 mL of dichloromethane as solvent, stir in an ice bath, and finally add 0.12 g (1 mmol) of 4-dimethylaminopyridine as a base, keep stirring in the ice bath for 0.5 hour, then transfer to room temperature for reaction for 16 hours, and separate by column chromatography to obtain white solid RM3 with a yield of 83%.

[0076] Embodiment 1-embodiment 4:

[0077] (1) Material selection: Select polymerizable liquid crystal as the main raw material, and prepare auxiliary materials such as photoinitiator, polymerizable monomer, cross-linking agent, etc.

[0078] (2) Preparation of holographic polymer dispersed liquid crystal material: polymerizable liquid crystal, photoinitiator, polymerizable monomer, cross-linking agent, etc. are uniformly mixed in a certain proportion to form a holographic polymer dispersed liquid crystal material.

[0079] (3) Coating of holographic polymer dispersed liquid crystal material: A transparent substrate is used, which may be a transparent optical glass or a transparent resin substrate. The substrate is cleaned by UVO or Plasma before spin coating. The holographic polymer dispersed liquid crystal material prepared in step (2) is then uniformly coated on the surface of the substrate to form a coating layer. The coating method used may be spin coating, scraper coating, slit coating, inkjet printing, or the like.

[0080] (4) By controlling the irradiation time and intensity of the light source, the coating layer is subjected to a step-by-step photopolymerization reaction. First, a blue light with a wavelength of 400-450nm is selected as the reaction light source, and interference exposure at a specific angle is performed according to the required grating period to form a light field with alternating bright and dark areas. The first step of polymerization occurs in the bright area, and the exposure dose is 30mW / cm 2 , and continued irradiation for 1 minute. The main reaction in the first step of polymerization is the free radical polymerization of the reaction monomer (acrylate compound). The reaction components are photoinitiator, monomer (acrylate), cross-linking agent and other functional compounds. Then the second step of polymerization is carried out, using UV-LED lamp for flood exposure. In this process, the dark area in the first step of polymerization is mainly polymerized by the liquid crystal molecules under the action of the photoinitiator (ultraviolet), forming a polymer network structure. The director of the liquid crystal in the network can be along a fixed direction or amorphous distribution, and finally a more compact polymer dispersed liquid crystal grating is formed (50mW / cm 2 , continuous irradiation for 10 minutes).

[0081] In Examples 1 to 4, the specific components and contents of the holographic polymer dispersed liquid crystal mixed material are shown in Table 1.

[0082] Table 1

[0083]

[0084]

[0085] Comparative Example:

[0086] (1) Material selection: The traditional non-polymeric liquid crystal Merck's E7 series was selected as the main raw material, and auxiliary materials such as photoinitiators, polymerizable monomers, and cross-linking agents were prepared.

[0087] (2) Preparation of holographic polymer dispersed liquid crystal material: Liquid crystal, photoinitiator, polymerizable monomer, cross-linking agent, etc. are uniformly mixed in a certain proportion to form a holographic polymer dispersed liquid crystal material.

[0088] (3) Coating of holographic polymer dispersed liquid crystal material: A transparent substrate is used, which may be a transparent optical glass or a transparent resin substrate. The substrate is cleaned by UVO or Plasma before spin coating. The holographic polymer dispersed liquid crystal material prepared in step (2) is then uniformly coated on the surface of the substrate to form a coating layer. The coating method used may be spin coating, scraper coating, slit coating, inkjet printing, or the like.

[0089] (4) By controlling the irradiation time and intensity of the light source, the coating layer is subjected to a step-by-step photopolymerization reaction. Specific process: First, a blue light with a wavelength of 400-450nm is selected as the reaction light source, and interference exposure at a specific angle is performed according to the required grating period to form a light field with alternating bright and dark areas. The first step of polymerization occurs in the bright area, and the exposure dose is 30mW / cm 2 , and irradiation was continued for 1 minute. The first step of polymerization mainly involved free radical polymerization of the reaction monomer (acrylate compound), and the reaction components included photoinitiator, monomer (acrylate), crosslinking agent and other functional compounds. Then the second step of thermal polymerization and diffusion was carried out, using an oven for high temperature heating (comparative example 80°C for 10 minutes). In this process, the liquid crystal molecules were mainly diffused into the dark area, and finally a more compact polymer dispersed liquid crystal grating was formed.

[0090] In the comparative example, the specific components and contents of the holographic polymer dispersed liquid crystal material are shown in Table 2.

[0091] Table 2

[0092]

[0093] The volume holographic gratings obtained in the above-mentioned Examples 1 to 4 and the comparative examples were subjected to refractive index modulation test, aging resistance test, heat resistance test, and chemical corrosion resistance test.

[0094] Refractive index modulation degree detection method: detection is carried out according to ISO 17901-2: Methods for measurement of hologram recording characteristics.

[0095] Anti-aging testing method: test the initial diffraction efficiency of the volume holographic grating, then place the volume holographic grating naturally at room temperature and humidity for 7 days, and test the diffraction efficiency of the volume holographic grating after 7 days. If the diffraction efficiency of the volume holographic grating after 7 days can maintain 90% of the initial diffraction efficiency, the anti-aging property of the volume holographic grating is considered qualified (abbreviated as OK), otherwise it is unqualified (abbreviated as NG).

[0096] Heat resistance testing method: test the initial diffraction efficiency of the volume holographic grating, then store the volume holographic grating at 80°C for 7 days, and test the diffraction efficiency of the volume holographic grating after 7 days of storage. If the diffraction efficiency of the volume holographic grating after 7 days of storage can maintain 90% of the initial diffraction efficiency, the heat resistance of the volume holographic grating is considered to be qualified (abbreviated as OK), otherwise it is unqualified (abbreviated as NG).

[0097] The detection method of chemical corrosion resistance is as follows: the initial diffraction efficiency of the volume holographic grating is detected, and then the volume holographic grating is stored in ethanol vapor for 7 days, and the diffraction efficiency of the volume holographic grating after 7 days of storage is detected. If the diffraction efficiency of the volume holographic grating after 7 days of storage can maintain 90% of the initial diffraction efficiency, the chemical corrosion resistance of the volume holographic grating is considered to be qualified (abbreviated as OK), otherwise it is unqualified (abbreviated as NG).

[0098] The test results of the volume holographic gratings prepared in the above-mentioned Examples 1 to 4 and the comparative example are shown in Table 3:

[0099] Table 3

[0100]

[0101] The holographic polymer dispersed liquid crystal mixed material comprises a polymerizable liquid crystal, a polymerizable monomer, a photoinitiator and a cross-linking agent. First, since the polymerizable liquid crystal can be polymerized, it can form a closer bond with the polymer matrix during the photopolymerization reaction, so its anti-aging, heat resistance, chemical corrosion resistance and other properties are significantly improved, thereby extending the service life of the H-PDLC and significantly improving the stability and durability of the H-PDLC. Moreover, since the polymerizable liquid crystal forms a closer bond with the polymer matrix during the photopolymerization reaction, the liquid crystal polymer after the polymerizable liquid crystal is polymerized is no longer in a liquid state, and even if the device packaging is not sealed enough, the liquid crystal polymer will not flow out of the device and will not deteriorate. Second, since the orientation of the polymerizable liquid crystal is fixed after polymerization and its distribution in the polymer matrix is ​​uniform, the formation The holographic polymer dispersed liquid crystal hybrid material can provide material support for preparing a volume holographic grating with high stability and high refractive index modulation capability. Thirdly, the holographic polymer dispersed liquid crystal hybrid material also makes its preparation method simple and easy to operate, and the reaction conditions are easy to control. By optimizing the reaction conditions and parameters, H-PDLC gratings with different performance requirements can be prepared, and the harshness of the packaging conditions is greatly reduced, which can meet the needs of different application scenarios. Fourthly, since the H-PDLC prepared in the application embodiment has excellent properties such as high stability and high refractive index modulation capability, it can be widely used in display and other fields.

[0102] It should be understood that the terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0103] It should also be understood that the term “and / or” used in the specification and appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0104] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A holographic polymer dispersed liquid crystal hybrid material, characterized in that: The holographic polymer dispersed liquid crystal mixed material comprises polymerizable liquid crystal, polymerizable monomer, photoinitiator and cross-linking agent.

2. The material according to claim 1, characterized in that The mass ratio of the polymerizable liquid crystal to the polymerizable monomer is 0.3:0.7-0.7:0.

3.

3. The material according to claim 1, characterized in that The polymerizable liquid crystal includes at least one of (2-methyl-1,4-phenylenebis(4-(3-((3-methylbutylene-3-yl)methoxy)propoxy)benzoate)), (4-((4-hydroxybenzoyl)oxy)-3-methylphenyl 4-(3-((3-methylbutylene-3-yl)methoxy)propoxy)benzoate), and (2-cyano-1,4-phenylenebis(4-(3-((3-methylbutylene-3-yl)methoxy)propoxy)benzoate).

4. The material according to claim 1, characterized in that The polymerizable monomer includes an acrylate monomer.

5. A method for preparing a holographic polymer dispersed liquid crystal hybrid material, characterized in that: The method comprises: Providing polymerizable liquid crystal, polymerizable monomer, photoinitiator and cross-linking agent; The polymerizable liquid crystal, polymerizable monomer, photoinitiator and cross-linking agent are mixed evenly to obtain the holographic polymer dispersed liquid crystal mixed material.

6. A method for preparing a volume holographic grating, characterized in that: The method comprises: Providing a holographic polymer dispersed liquid crystal hybrid material, wherein the holographic polymer dispersed liquid crystal hybrid material is the holographic polymer dispersed liquid crystal hybrid material according to any one of claims 1 to 4; uniformly distributing the holographic polymer dispersed liquid crystal mixed material on the surface of the substrate; A light beam is used to irradiate the surface of a substrate on which the holographic polymer dispersed liquid crystal hybrid material is uniformly distributed, so that the polymerizable monomers in the first area of ​​the holographic polymer dispersed liquid crystal hybrid material irradiated by the light undergo a first polymerization reaction, and the polymerizable liquid crystals in the second area of ​​the holographic polymer dispersed liquid crystal hybrid material irradiated by the light undergo a second polymerization reaction, thereby obtaining the volume holographic grating.

7. The method according to claim 6, characterized in that The substrate has no grating structure, and the light beam is used to irradiate the surface of the substrate on which the holographic polymer dispersed liquid crystal material is evenly distributed, comprising: Controlling the first light beam to form interference fringes on the surface of the substrate, so that the polymerizable monomers in the bright area of ​​the holographic polymer dispersed liquid crystal hybrid material irradiated by the light undergo a first polymerization reaction under the action of the first photoinitiator; A second light beam is controlled to irradiate the surface of the substrate, so that the polymerizable liquid crystal in the dark area of ​​the holographic polymer dispersed liquid crystal mixed material not irradiated by the first light beam undergoes a second polymerization reaction under the irradiation of the second light beam and the action of a second photoinitiator, thereby obtaining the volume holographic grating, and the absorption spectrum of the second photoinitiator is different from the absorption spectrum of the first photoinitiator.

8. A volume holographic grating, characterized in that: The volume holographic grating is prepared by the method for preparing a volume holographic grating according to any one of claims 6 to 7.

9. A volume holographic optical waveguide, characterized in that: The volume holographic optical waveguide comprises the volume holographic grating as claimed in claim 8.

10. A holographic device, characterized in that: The holographic device comprises the volume holographic optical waveguide of claim 9.

Images