Holographic polymer dispersed liquid crystal composition, device and method

Abstract

The invention relates to the technical field of holographic projection display, and provides a holographic polymer dispersed liquid crystal composition, device and method, the composition comprises the following components by mass: 0.5-2 parts of a photoinitiator, 2-5 parts of a co-initiator, 0-15 parts of a first monomer, 5-12 parts of a second monomer, 1-5 parts of a third monomer, 10-15 parts of mercaptan, 10-15 parts of olefin, 5-10 parts of a solvent, and 30-40 parts of liquid crystal; wherein the first monomer is a monofunctional acrylate monomer, the second monomer is a bifunctional acrylate monomer, and the third monomer is a polyfunctional acrylate monomer. The method has the advantages that on the premise of reducing the influence on the diffraction efficiency of the P-polarized light, the refractive index modulation of the S-polarized light is selectively enhanced, and the specificity improvement of the diffraction efficiency of the S-polarized light is realized.

Description

Technical Field

[0001] This invention relates to the field of holographic projection display technology, and more specifically, to a holographic polymer-dispersed liquid crystal composition, device, and method. Background Technology

[0002] Holographic polymer-dispersed liquid crystal (HPDLC) is an advanced photonic material prepared using holographic optical interference-induced phase separation technology. The basic process involves placing a mixture containing photopolymerizable monomers, nematic liquid crystals, photoinitiators, and other functional additives in the interference field of two or more coherent laser beams. Within the alternating bright and dark interference fringe regions, the monomers undergo differentiated polymerization reactions, thereby displacing and enriching the liquid crystals in the polymer-depleted phase regions. This ultimately leads to the spontaneous formation of a bulk phase grating structure with alternating periodic polymer-enriched regions and liquid crystal droplet-enriched regions. Due to its outstanding advantages such as high diffraction efficiency, fast electro-optic response, and the ability to dynamically switch diffracted states using an electric field, HPDLC gratings show great application potential in next-generation display technologies, optical storage, tunable filters, and optical switches.

[0003] In existing technologies, the preparation of HPDLCs generally relies on free radical chain polymerization based on acrylate monomers. This reaction mechanism is characterized by rapid initiation and high degree of polymerization, but it also leads to significant curing shrinkage and stress accumulation within the polymer network. These factors interfere with the regular formation of liquid crystal droplets, resulting in excessively wide size distribution and irregular morphology, and reducing the interfacial order between the polymer network and liquid crystal molecules, thus affecting the anchoring strength. The direct consequence is that the refractive index modulation (Δn) of the final grating often falls short of the theoretical optimal value, thereby limiting further improvements in diffraction efficiency, especially under specific polarization directions.

[0004] In recent years, to overcome the shortcomings of traditional free radical polymerization, researchers have begun to explore alternative polymerization systems based on thiol-ene click chemistry. The thiol-ene reaction is a step-growth polymerization, and its reaction process is more gentle and uniform, which can significantly reduce shrinkage stress and network defects.

[0005] However, current technologies are limited to extensive microstructure manipulation, without actively designing polarization characteristics. Whether using traditional free radical polymerization or thiol-olefin polymerization, the process goal of existing technologies is to achieve higher overall diffraction efficiency or better overall electro-optic performance. The reaction process and the final polymer network / liquid crystal droplet composite structure respond equally to P- and S-beams, making it impossible to pre-set or guide the grating's ability to modulate different polarized light at the fabrication stage. This results in significant randomness in the polarization-related characteristics of the fabricated grating, such as the ratio of P- to S-beam diffraction efficiency, failing to meet the precise polarization performance design requirements of high-end optical devices. Currently, no publicly disclosed technology demonstrates how to specifically and significantly adjust the S-beam diffraction efficiency through materials chemistry. This technological gap severely limits the application of HPDLC technology in cutting-edge optical systems requiring complex polarization management functions. Summary of the Invention

[0006] The present invention aims to overcome at least one defect (deficiency) of the prior art and provide a holographic polymer-dispersed liquid crystal composition, device and method that specifically improves the diffraction efficiency of S-rays.

[0007] One object of the present invention is to provide a holographic polymer-dispersed liquid crystal composition, wherein, by weight, the holographic polymer-dispersed liquid crystal composition comprises: Photoinitiator 0.5-2 parts, co-initiator 2-5 parts, first monomer 0-15 parts, second monomer 5-12 parts, third monomer 1-5 parts, thiol 10-15 parts, olefin 10-15 parts, solvent 5-10 parts, liquid crystal 30-40 parts. The first monomer is a monofunctional acrylate monomer, the second monomer is a difunctional acrylate monomer, and the third monomer is a polyfunctional acrylate monomer.

[0008] In this technical solution, by precisely controlling the competitive dynamics between the thiol-ene click chemistry reaction (R_thiol-ene) and the free radical polymerization reaction (R_radical) in the HPDLC holographic recording process, a polymer network with anisotropic microstructure is shaped. This selectively enhances the refractive index modulation of S-polarized light while reducing the impact on the diffraction efficiency of P-polarized light, ultimately achieving a specific improvement in the S-polarized light diffraction efficiency (DE).

[0009] Specifically, this scheme achieves precise control over the reaction rates of click chemistry and free radical polymerization by carefully selecting the chemical structures of various monomers, along with the selection of thiols and olefins, and the relative proportions of each component. The goal is to make the two reactions proceed asynchronously but with partial overlap. In the bright region of the holographic interference fringes, illumination initiates polymerization. Due to the differences in the kinetics of the two reactions, a heterogeneous polymer network growth front is formed. This competitive growth ultimately results in a polymer network that is not completely isotropic at the microscopic level. Its crosslinking density or segment arrangement may have a different physical constraint on the direction perpendicular to the substrate plane than on the direction parallel to the substrate. The former is usually more closely related to the electric field vector direction of S-light, while the latter is usually related to P-light. The aforementioned polymer network with microscopic anisotropy produces different anchoring strengths for liquid crystal droplets in different directions. Specifically, it exerts a stronger or more "rigid" constraint on the orientation of liquid crystal molecules in the direction perpendicular to the substrate. According to coupled-wave theory, the diffraction efficiency η is proportional to the square of the refractive index modulation Δn (η ∝ Δn²). Therefore, increasing the selectivity of Δn_s will directly lead to a significant increase in the S-ray diffraction efficiency (DE_s), while the stability of Δn_p ensures that the P-ray diffraction efficiency (DE_p) remains basically unchanged.

[0010] It can be understood that the core principle of this invention is to transform the macroscopic control of reaction kinetics, namely the competition between thiol-olefin and free radical reactions, into the structural design of the microscopic anisotropy of polymer networks, and further into the differentiation of interface anchoring energy, ultimately achieving selective enhancement of diffraction performance of specific polarized light.

[0011] Further, the first monomer is selected from one or more of cyclohexyl methacrylate, methyl laurate, isodecyl methacrylate, isooctyl acrylate, butyl acrylate, methyl acrylate, benzyl methacrylate, 2-phenoxyethyl methacrylate, dicyclopentyl methacrylate, and isobornyl methacrylate.

[0012] Further, the second monomer is selected from one or more of 4-(ethoxy)bisphenol A dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, and ethylene glycol dimethacrylate.

[0013] Furthermore, the third monomer is selected from one or two of pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, and hyperbranched acrylate.

[0014] Further, the photoinitiator is selected from one of the following: Bengal rose red, diiodofluorescein, methylene blue, TPO, rhodamine 6G, 3,3'-carbonylbis(7-diethylaminocoumarin), and initiator 184; and / or, The co-initiator is selected from benzoyl peroxide or N-phenylglycine.

[0015] Furthermore, the solvent is selected from one or more of N-vinylpyrrolidone, chloroform, tetrahydrofuran, and toluene.

[0016] Furthermore, the liquid crystal is selected from one or more of BL038, GXP-6003, BL087, and TL213.

[0017] Another object of the present invention is to provide a holographic grating device, said holographic grating device being prepared from any of the above-described holographic polymer-dispersed liquid crystal compositions.

[0018] Another object of the present invention is to provide a method for fabricating the above-mentioned holographic grating device, comprising the following steps: S1. Mix the components of the composition evenly to obtain a mixture; S2. Pour the mixture into the liquid crystal cell; S3. Place the LCD box in a dark room and let it stand still; S4. Expose the settled liquid crystal cell in the interference light field of the dual-beam light source.

[0019] Furthermore, All components were mixed uniformly using an ultrasonic dispersion device; and / or The thickness of the liquid crystal cell is controlled within 4~7μm; and / or The liquid crystal cell is left to stand in the dark room for 1-2 hours; and / or The exposure time of the liquid crystal cell in the interference light field is 1-5 minutes; and / or The included angle of the dual-beam light source is 35~60°; and / or The illumination power of the dual-beam light source is 5±1 mW / cm². 2 Preferably, the thickness of the liquid crystal cell is controlled at 5 μm.

[0020] In this technical solution, the specific improvement of the P-light diffraction efficiency of the grating device is achieved by adjusting the exposure time, power, and preparation steps during holographic recording in conjunction with the composition of the composition.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention shapes a polymer network with anisotropic microstructure by precisely controlling the competitive dynamics of the thiol-ene click chemistry reaction and the free radical polymerization reaction in the HPDLC holographic recording process. This selectively enhances the refractive index modulation of S-polarized light while reducing the impact on the diffraction efficiency of P-polarized light, and ultimately achieves a specific improvement in the diffraction efficiency of S-light. Detailed Implementation

[0022] To enable those skilled in the art to better understand this solution, the present invention will be further described in detail below with reference to specific embodiments. Unless otherwise specified, the process methods used in the embodiments are conventional methods; and unless otherwise specified, the materials used are commercially available.

[0023]

[0024] Example 1 The holographic polymer-dispersed liquid crystal composition of this embodiment comprises, by mass fraction: 0.5 parts 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts N-phenylglycine, 15 parts cyclohexyl methacrylate, 11.5 parts 4-(ethoxy)bisphenol A dimethacrylate, 1 part trimethylolpropane triacrylate, 15 parts 1,4-butanedithiol, 15 parts divinyl ether, 5 parts N-vinylpyrrolidone, and 35 parts BL038.

[0025] The weighed raw materials were ultrasonically mixed for 30 minutes in an ultrasonic instrument at 60°C to obtain a homogeneous photopolymer system. Under vacuum conditions, the photopolymer system was filled into a liquid crystal cell with a thickness of 5 μm. After filling, the liquid crystal cell and the system were moved to a dark room and left to stand for 1 hour. Then, the system was moved to an irradiation chamber at a 60° angle with an irradiation power of 5 mW / cm². 2 The grating device was obtained by interferometric exposure for 5 minutes in the interference light field of a dual-beam light source.

[0026] The P-ray diffraction efficiency and S-ray diffraction efficiency of the holographic grating device samples were tested using a grating diffraction efficiency tester. The haze of the holographic grating device samples was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0027] Example 2 The holographic polymer-dispersed liquid crystal composition of this embodiment comprises, by mass fraction: 2 parts photoinitiator 184, 5 parts benzoyl peroxide, 8 parts isobornyl acrylate, 5 parts ethylene glycol dimethacrylate, 3 parts pentaerythritol tetraacrylate, 20 parts 1,4-butanedithiol, 20 parts divinyl ether, 7 parts chloroform, and 30 parts GXP-6003.

[0028] The weighed raw materials were ultrasonically mixed for 30 minutes in an ultrasonic instrument at 60°C to obtain a homogeneous photopolymer system. Under vacuum conditions, the photopolymer system was filled into a liquid crystal cell with a thickness of 5 μm. After filling, the liquid crystal cell and the system were moved to a dark room and left to stand for 1 hour. Then, the system was moved to an irradiation chamber at a 60° angle with an irradiation power of 5 mW / cm². 2 The grating device was obtained by interferometric exposure for 5 minutes in the interference light field of a dual-beam light source.

[0029] The P-ray diffraction efficiency and S-ray diffraction efficiency of the holographic grating device samples were tested using a grating diffraction efficiency tester. The haze of the holographic grating device samples was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0030] Comparative Example 1 The holographic polymer-dispersed liquid crystal composition of this comparative example comprises, by mass fraction, the following raw materials weighed from a brown sample vial: 0.5 parts 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts N-phenylglycine, 31 parts cyclohexyl methacrylate, 24.5 parts 4-(ethoxy)bisphenol A dimethacrylate, 2 parts trimethylolpropane triacrylate, 5 parts N-vinylpyrrolidone, and 35 parts BL038; The weighed raw materials were ultrasonically mixed for 30 minutes in an ultrasonic instrument at 60°C to obtain a homogeneous photopolymer system. Under vacuum conditions, the photopolymer system was filled into a liquid crystal cell with a thickness of 5 μm. After filling, the liquid crystal cell and the system were moved to a dark room and left to stand for 1 hour. Then, the system was moved to an irradiation chamber at a 60° angle with an irradiation power of 5 mW / cm². 2 The grating device was obtained by interferometric exposure for 5 minutes in the interference light field of a dual-beam light source.

[0031] The P-ray diffraction efficiency and S-ray diffraction efficiency of the holographic grating device samples were tested using a grating diffraction efficiency tester. The haze of the holographic grating device samples was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0032] Comparative Example 2 The holographic polymer-dispersed liquid crystal composition of this comparative example comprises, by mass fraction: 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 28.75 parts of 1,4-butanedithiol, 28.75 parts of divinyl ether, 5 parts of N-vinylpyrrolidone, and 35 parts of BL038. The weighed raw materials were ultrasonically mixed for 30 minutes in an ultrasonic instrument at 60°C to obtain a homogeneous photopolymer system. Under vacuum conditions, the photopolymer system was filled into a liquid crystal cell with a thickness of 5 μm. After filling, the liquid crystal cell and the system were moved to a dark room and left to stand for 1 hour. Then, the system was moved to an irradiation chamber at a 60° angle with an irradiation power of 5 mW / cm². 2 The grating device was obtained by interferometric exposure for 5 minutes in the interference light field of a dual-beam light source.

[0033] The P-ray diffraction efficiency and S-ray diffraction efficiency of the holographic grating device samples were tested using a grating diffraction efficiency tester. The haze of the holographic grating device samples was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0034] Comparative Example 3 The holographic polymer-dispersed liquid crystal composition of this comparative example comprises, by mass fraction: 0.5 parts 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts N-phenylglycine, 15 parts cyclohexyl methacrylate, 11.5 parts 4-(ethoxy)bisphenol A dimethacrylate, 1 part trimethylolpropane triacrylate, 5 parts 1,4-butanedithiol, 25 parts divinyl ether, 5 parts N-vinylpyrrolidone, and 35 parts BL038; The weighed raw materials were ultrasonically mixed for 30 minutes in an ultrasonic instrument at 60°C to obtain a homogeneous photopolymer system. Under vacuum conditions, the photopolymer system was filled into a liquid crystal cell with a thickness of 5 μm. After filling, the liquid crystal cell and the system were moved to a dark room and left to stand for 1 hour. Then, the system was moved to an irradiation chamber at a 60° angle with an irradiation power of 5 mW / cm². 2 The grating device was obtained by interferometric exposure for 5 minutes in the interference light field of a dual-beam light source.

[0035] The P-ray diffraction efficiency and S-ray diffraction efficiency of the holographic grating device samples were tested using a grating diffraction efficiency tester. The haze of the holographic grating device samples was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0036] Comparative Example 4 The holographic polymer-dispersed liquid crystal composition of this comparative example comprises, by mass fraction: 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 15 parts of cyclohexyl methacrylate, 11.5 parts of 4-(ethoxy)bisphenol A dimethacrylate, 1 part of trimethylolpropane triacrylate, 30 parts of 1,4-butanedithiol, 5 parts of N-vinylpyrrolidone, and 35 parts of BL038; The weighed raw materials were ultrasonically mixed for 30 minutes in an ultrasonic instrument at 60°C to obtain a homogeneous photopolymer system. Under vacuum conditions, the photopolymer system was filled into a liquid crystal cell with a thickness of 5 μm. After filling, the liquid crystal cell and the system were moved to a dark room and left to stand for 1 hour. Then, the system was moved to an irradiation chamber at a 60° angle with an irradiation power of 5 mW / cm². 2 The grating device was obtained by interferometric exposure for 5 minutes in the interference light field of a dual-beam light source.

[0037] The P-ray diffraction efficiency and S-ray diffraction efficiency of the holographic grating device samples were tested using a grating diffraction efficiency tester. The haze of the holographic grating device samples was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0038] Comparative Example 5 The holographic polymer-dispersed liquid crystal composition of this comparative example comprises, by mass fraction: 0.5 parts of 3,3'-carbonylbis(7-diethylaminocoumarin), 2 parts of N-phenylglycine, 1.5 parts of cyclohexyl methacrylate, 16 parts of 4-(ethoxy)bisphenol A dimethacrylate, 10 parts of trimethylolpropane triacrylate, 15 parts of 1,4-butanedithiol, 15 parts of divinyl ether, 5 parts of N-vinylpyrrolidone, and 35 parts of BL038; The weighed raw materials were ultrasonically mixed for 30 minutes in an ultrasonic instrument at 60°C to obtain a homogeneous photopolymer system. Under vacuum conditions, the photopolymer system was filled into a liquid crystal cell with a thickness of 5 μm. After filling, the liquid crystal cell and the system were moved to a dark room and left to stand for 1 hour. Then, the system was moved to an irradiation chamber at a 60° angle with an irradiation power of 5 mW / cm². 2 The grating device was obtained by interferometric exposure for 5 minutes in the interference light field of a dual-beam light source.

[0039] The P-ray diffraction efficiency and S-ray diffraction efficiency of the holographic grating device samples were tested using a grating diffraction efficiency tester. The haze of the holographic grating device samples was tested using a haze meter at 23±2℃ according to GB 2410-2008 "Test Methods for Transmittance and Haze of Transparent Plastics". The results are shown in Table 1.

[0040] Table 1. Test results of Examples 1-2 and Comparative Examples 1-5

[0041] As can be seen from Comparative Example 1 and Examples 1-2, the composition of this scheme, by adding thiols and olefins as limited components, significantly improves the diffraction efficiency of S light while reducing the impact on P light diffraction efficiency.

[0042] In Comparative Example 2, the monomer specified in this scheme was not added. Although the S-ray diffraction efficiency was improved, the P-ray diffraction efficiency was significantly reduced. This indicates that the thiols and olefins in the composition need to be combined with the monomer specified in this scheme to achieve asymmetric control of polarized light diffraction efficiency.

[0043] In Comparative Example 3, the proportions of olefins and thiols added to the composition were outside the range specified in this scheme; in Comparative Example 4, no olefins were added; in Comparative Example 5, the proportions of the three monomers were outside the range specified in this scheme. The S-ray diffraction efficiency of Comparative Examples 3 to 5 did not show a significant improvement, and the P-ray diffraction efficiency was significantly reduced. This indicates that the proportions of olefins and thiols specified in the composition of this scheme need to be combined with other components specified in other proportions to achieve a weak effect on the P-ray diffraction efficiency and a significant improvement in the S-ray diffraction efficiency.

[0044] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A holographic polymer-dispersed liquid crystal composition, characterized in that, The holographic polymer-dispersed liquid crystal composition comprises, by weight,: Photoinitiator 0.5-2 parts, 2-5 parts of co-initiator First monomer, 0-15 parts, The second monomer is 5-12 parts. The third monomer is 1-5 parts. Thiols 10-15 parts, 10-15 parts of olefins Solvent 5-10 parts, 30-40 LCD screens; The first monomer is a monofunctional acrylate monomer, the second monomer is a difunctional acrylate monomer, and the third monomer is a polyfunctional acrylate monomer. The first monomer is selected from one or more of cyclohexyl methacrylate, methyl laurate, isodecyl methacrylate, isooctyl acrylate, butyl acrylate, methyl acrylate, benzyl methacrylate, 2-phenoxyethyl methacrylate, dicyclopentyl methacrylate, and isobornyl methacrylate. The second monomer is selected from one or more of 4-(ethoxy)bisphenol A dimethacrylate, triethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, and ethylene glycol dimethacrylate; The third monomer is selected from one or two of pentaerythritol triacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, and hyperbranched acrylate.

2. The holographic polymer-dispersed liquid crystal composition according to claim 1, characterized in that, The photoinitiator is selected from one of the following: Bengal rose red, diiodofluorescein, methylene blue, TPO, rhodamine 6G, 3,3'-carbonylbis(7-diethylaminocoumarin), and initiator 184; and / or, The co-initiator is selected from benzoyl peroxide or N-phenylglycine.

3. The holographic polymer-dispersed liquid crystal composition according to claim 1, characterized in that, The solvent is selected from one or more of N-vinylpyrrolidone, chloroform, tetrahydrofuran, and toluene.

4. The holographic polymer-dispersed liquid crystal composition according to claim 1, characterized in that, The liquid crystal is selected from one or more of BL038, GXP-6003, BL087, and TL213.

5. A holographic grating device, characterized in that, The holographic grating device is prepared from the holographic polymer dispersed liquid crystal composition according to any one of claims 1 to 4.

6. A method for fabricating the holographic grating device according to claim 5, characterized in that, Includes the following steps: S1. Mix the components of the composition evenly to obtain a mixture; S2. Pour the mixture into the liquid crystal cell; S3. Place the LCD box in a dark room and let it stand still; S4. Expose the settled liquid crystal cell in the interference light field of the dual-beam light source.

7. The preparation method according to claim 6, characterized in that, All components were mixed uniformly using an ultrasonic dispersion device; and / or The thickness of the liquid crystal cell is controlled within 4~7μm; and / or The liquid crystal cell is left to stand in the dark room for 1-2 hours; and / or The exposure time of the liquid crystal cell in the interference light field is 1-5 minutes; and / or The included angle of the dual-beam light source is 35~60°; and / or The illumination power of the dual-beam light source is 5±1 mW / cm². 2 .

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