A PVG liquid crystal material, a PVG waveguide and a preparation method thereof
Patent Information
- Application Number
- CN202611159474.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-01
- Publication Date
- 2026-11-03
AI Technical Summary
The refractive index of existing PVG liquid crystal materials is less than 1.78, which cannot meet the requirements of large field of view, high diffraction efficiency, and ultra-high-definition color display. In addition, they have problems such as poor color uniformity and insufficient optical stability.
Naphthyldiacetylene and tetrafluorobiphenylacetylene are combined as a double rigid conjugated framework, and combined with cyanonaphthalene high refractive index dopant, chiral modifier and photoinitiator, a three-dimensional network is formed by ultraviolet crosslinking, which improves the refractive index of the material and improves color uniformity and long-term optical stability.
It achieves a refractive index breakthrough of 1.8 for liquid crystal materials, solving the problem of insufficient diffraction efficiency in a large field of view. At the same time, it optimizes the uniformity of color across the entire field and long-term optical stability, making it suitable for AR/VR optical waveguides, holographic projection, and high-definition display polarization optical devices.
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Abstract
Description
Technical Field
[0001] This application relates to the field of liquid crystal materials technology, specifically to a PVG liquid crystal material, a PVG waveguide, and a method for preparing the same. Background Technology
[0002] PVG liquid crystal material is a core functional alignment liquid crystal material for holographic waveguides and polarization modulation devices. Its refractive index and birefringence directly determine the diffraction efficiency, viewing angle range, and color reproduction accuracy of optical devices. With the rapid development of high-end optoelectronic display technologies such as AR / VR near-eye displays and holographic projection, increasingly higher requirements are being placed on the refractive index, optical uniformity, and color reproduction accuracy of PVG liquid crystal materials.
[0003] Currently, the refractive index of conventional PVG liquid crystal materials is generally below 1.78, which cannot meet the requirements for large field of view, high diffraction efficiency, and ultra-high-definition color display. To further improve the refractive index of liquid crystal materials, industry professionals have tried various improvement schemes, but significant technical defects still exist: First, by doping the liquid crystal system with highly polar organic molecules or large conjugated molecules to increase the overall molecular polarizability and thus improve the refractive index; however, the refractive index improvement achieved solely through molecular doping modification is very limited, making it difficult to stably break through the 1.8 threshold. Furthermore, the compatibility between high-refractive-index components and the liquid crystal mesocrystalline system is often poor, leading to significant global color deviation in the device, with color uniformity ΔE generally exceeding 2.5, resulting in problems such as localized color shift, uneven brightness, and imbalance in RGB diffraction efficiency. Second, by doping the liquid crystal system with high-refractive-index nanoparticles (such as TiO2, ZrO2, etc.) to improve the overall refractive index of the system using the high refractive index characteristics of the nanoparticles themselves; however, conventional unmodified nanoparticles have insufficient compatibility with the liquid crystal mesocrystalline system, easily leading to defects such as particle aggregation and phase separation. The resulting optical scattering further damages the optical uniformity of the film, reducing the device's transmittance and lifespan.
[0004] Furthermore, existing PVG liquid crystal formulations are formed by mixing small-molecule liquid crystals. However, due to the weak binding force between liquid crystal molecules, they are prone to molecular slippage, orientation disorder, and slow failure of the grating periodic modulation structure after being heated or exposed to ultraviolet light for a long time. This results in a significant decrease in diffraction efficiency, continuous deterioration of the global color difference ΔE, and a greatly shortened device lifespan, making it difficult to meet the requirements for long-term stable use of AR devices.
[0005] Therefore, developing a PVG liquid crystal material with high refractive index, good color uniformity, and optical stability is an urgent problem to be solved in this field. Summary of the Invention
[0006] To overcome the problems of low refractive index, poor color uniformity, and insufficient post-optical stability of existing PVG liquid crystal materials, this application provides a PVG liquid crystal material, a PVG waveguide, and a method for preparing the same.
[0007] In a first aspect, this application provides a PVG liquid crystal material, which adopts the following technical solution: A PVG liquid crystal material comprises the following components in parts by weight: 35-50 parts naphthyldiacetylene, 12-26 parts tetrafluorobiphenylacetylene, 10-22 parts polymerizable liquid crystal monomer, 15-20 parts cyanonaphthalene high refractive index dopant, 1-4 parts KH-550 modified ZrO2 nanoparticles, 1-2 parts chiral modifier, and 0.5-1 part photoinitiator.
[0008] This application provides a PVG liquid crystal material that uses a compound of naphthyldiacetylene and tetrafluorobiphenylacetylene as a double rigid conjugated framework, combined with the synergistic effect of cyanonaphthalene high-refractive-index dopant, chiral modifier and photoinitiator, thereby significantly improving the refractive index of the material while eliminating defects such as film orientation deviation, spectral imbalance and particles, and controlling the color difference ΔE within 1.8. The resulting PVG liquid crystal material is suitable for high-end optoelectronic display scenarios such as AR / VR optical waveguides, holographic projection, high-definition display polarization optical devices, etc., and has broad application prospects.
[0009] In this application, naphthyldiacetylene (1,2-di(naphthyl)acetylene) contains two fused naphthalene rings bridged by rigid acetylene groups, forming a highly conjugated, highly polarizable π-electron system. Under an applied photoelectric field, it can generate strong electron cloud distortion, thereby enabling the refractive index of the liquid crystal material to exceed 1.8. Simultaneously, its extremely high axial stiffness ratio and strong π-π stacking tendency allow it to form a tightly ordered molecular arrangement under the guidance of an orientation layer, providing high birefringence support for the film layer. However, the intermolecular forces of naphthyldiacetylene are too strong, resulting in poor fluidity, low-temperature crystallization, and orientation disorder when used alone, leading to poor color uniformity. To this end, this application introduces tetrafluorobiphenylacetylene as a synergistic component. On the one hand, the high polarizability of its fluorine atoms can synergistically improve the overall refractive index; on the other hand, the steric hindrance effect of fluorine atoms can moderately weaken the excessive aggregation between naphthyl backbone molecules, reduce system viscosity, improve film leveling and processing adaptability, and thus improve color uniformity. Simultaneously, the introduction of the fluorinated structure can also adjust the consistency of molecular orientation in the system, reducing local arrangement disorder and stripe shift caused by differences in molecular structure. Based on this, this application further introduces a polymerizable liquid crystal monomer. Its rigid conjugated backbone can highly match the two mesocrystalline molecular structures mentioned above, exhibiting mutual solubility and no phase separation. The terminal acrylates can undergo ultraviolet crosslinking to form a three-dimensional network, locking the ordered arrangement of the liquid crystal and fundamentally improving the problems of refractive index drift and color difference degradation under long-term use. In summary, this application, through the synergistic combination of naphthyldiacetylene, tetrafluorobiphenylacetylene, and polymerizable liquid crystal monomers, enables liquid crystal materials to stably achieve a refractive index exceeding 1.8, solving the problems of low upper limit of refractive index and insufficient diffraction efficiency in large field of view of traditional products. At the same time, it optimizes the system compatibility and RGB spectrum matching, suppresses the spectral shift of full-color display, and ensures that the final product still has excellent global color uniformity and long-term optical stability under high refractive index conditions.
[0010] Optionally, the PVG liquid crystal material comprises the following components in parts by weight: 40-45 parts naphthyldiacetylene, 15-20 parts tetrafluorobiphenylacetylene, 13-18 parts polymerizable liquid crystal monomer, 15-20 parts cyanonaphthalene high refractive index dopant, 2-3 parts KH-550 modified ZrO2 nanoparticles, 1-2 parts chiral modifier, and 0.5-1 parts photoinitiator.
[0011] Optionally, the cyanonaphthalene high refractive index dopant is selected from one or more of 1-naphthonitrile, 2-naphthonitrile, 6-hydroxy-2-naphthonitrile, 1-bromo-2-cyanonaphthalene, 2,6-naphthodinitrile, 1,4-dicyanonaphthalene, and 1,5-dicyanonaphthalene.
[0012] In this application, the cyanonaphthalene high-refractive-index dopant is uniformly distributed on the core mesocrystalline framework composed of naphthyldiacetylene and tetrafluorobiphenylacetylene. Its strongly polar cyano groups exhibit dipole-dipole interactions with the acetylene groups and fluorine atoms in the main framework molecules. This effectively fills the gaps between molecules without disrupting the regular arrangement of the main framework, further increasing the molecular packing density and improving the refractive index. More importantly, the dipole-dipole interactions between the cyano groups in the dopant and the main framework also help suppress the phase separation tendency of the dopant in the system, ensuring that it remains molecularly uniformly dispersed throughout the film, avoiding optical scattering and color deviation caused by local enrichment or aggregation of the dopant.
[0013] Optionally, the cyanonaphthalene high refractive index dopant is a mixture of 6-hydroxy-2-naphthonitrile and 1-bromo-2-cyanonaphthalene.
[0014] Optionally, the weight ratio of 6-hydroxy-2-naphthonitrile to 1-bromo-2-cyanonphthalein is 1:(0.3-0.6).
[0015] In this application, 6-hydroxy-2-naphthonitrile and 1-bromo-2-cyanonaphthalene are further combined as a high-refractive-index dopant for cyanonaphthalene, which can give full play to their synergistic and complementary effects. Among them, the hydroxyl group of 6-hydroxy-2-naphthonitrile can provide hydrogen bonds, which helps to regulate the molecular arrangement; the bromine atom of 1-bromo-2-cyanonaphthalene can provide a larger molecular volume and polarizability, further improving the refractive index. In addition, the polarity difference between the two can also help to broaden the compatibility range of the system with the host liquid crystal and optimize compatibility, thereby improving color uniformity, molecular orientation order and long-term optical stability while improving the refractive index.
[0016] Optionally, the polymerizable liquid crystal monomer is RM257 and / or RM82.
[0017] Optionally, the tetrafluorobiphenylacetylene is 2,3,2',3'-tetrafluorodiphenylacetylene.
[0018] In this application, the method for preparing the 2,3,2',3'-tetrafluorodiphenylacetylene includes: (1) First, 1,2-difluorobenzene is subjected to low-temperature butyllithium lithiation and iodination to obtain 4-iodo-2,3-difluorobenzene; (2) Then, 4-iodo-2,3-difluorobenzene is coupled with trimethylsilylacetylene and deprotected to obtain 4-acetyleno-2,3-difluorobenzene; (3) 4-ethynyl-2,3-difluorobenzene and 4-iodo-2,3-difluorobenzene were subjected to a cross-coupling reaction of alkynes at 5-25℃ under nitrogen atmosphere via Pd / Cu composite catalysis, triethylamine binding acid, and alkyne.
[0019] Secondly, this application provides a PVG waveguide, which is fabricated using the aforementioned PVG liquid crystal material.
[0020] Thirdly, this application provides a method for fabricating a PVG waveguide, comprising the following steps: substrate plasma activation, linear polarization ultraviolet orientation, isothermal inkjet film formation, and ultraviolet curing; In the ultraviolet curing process: the curing power is 20-30mW / cm². 2 The duration is 25-40 seconds. In summary, this application has the following beneficial effects: 1. This application uses highly conjugated rigid mesocrystalline molecules such as naphthyldiacetylene and tetrafluorobiphenylacetylene to compound with polymerizable liquid crystal monomers. On the one hand, it improves the refractive index of the liquid crystal material at the molecular structure level, breaking through the technical bottleneck of the refractive index of traditional PVG liquid crystal materials being lower than 1.78, and effectively solving the problem of insufficient diffraction efficiency in large field-of-view full-color display scenarios. On the other hand, it can also control the global color difference ΔE within 1.8, completely improving the image quality defects in the existing technology, such as ΔE generally being greater than 2.5, local color shift, uneven brightness and darkness, and imbalance of RGB diffraction efficiency.
[0021] 2. The PVG liquid crystal material of this application further uses KH-550 modified ZrO2 nanoparticles, which can eliminate the hydrophilic agglomeration of powder by grafting amino organic chains through Si-O-Zr covalent bonds, significantly improving the compatibility between nanoparticles and liquid crystal mesocrystalline system, so that they are uniformly dispersed in the system without agglomeration or phase separation, thereby effectively improving the refractive index and improving color uniformity and long-term optical stability without optical defects. Detailed Implementation
[0022] This application provides a PVG liquid crystal material comprising the following components in parts by weight: 35-50 parts naphthyldiacetylene, 12-26 parts tetrafluorobiphenylacetylene, 10-22 parts polymerizable liquid crystal monomer, 15-20 parts cyanonaphthalene high refractive index dopant, 1-4 parts KH-550 modified ZrO2 nanoparticles, 1-2 parts chiral modifier, and 0.5-1 parts photoinitiator.
[0023] This application provides a method for fabricating a PVG waveguide, comprising the following steps: (1) Plasma activation of substrate: The substrate to be coated (such as glass substrate, quartz substrate or flexible polymer substrate) is placed in the plasma treatment chamber, and Ar / O2 mixed gas with a volume ratio of (6-8): (2-4) is used as the working gas. Plasma activation treatment is carried out for 60-90s under the conditions of vacuum degree 8-12Pa and radio frequency power 220-280W. (2) Linearly polarized ultraviolet orientation: A photosensitive orientation agent is coated on the surface of the substrate after plasma activation treatment; after coating, the solvent is removed by pre-baking to form a uniformly thick orientation layer film; then, the orientation layer is exposed and oriented using a 365 nm wavelength linearly polarized ultraviolet light source, with the light intensity controlled at 8-12 mW / cm² and the exposure time being 180-240s. (3) Constant temperature inkjet film formation: Under constant temperature and humidity conditions of 25±0.5℃ and 42-48% RH, PVG liquid crystal prepolymer is uniformly coated onto the oriented substrate by inkjet printing to form a liquid crystal film with a thickness of 400nm-2μm; after coating, the coated substrate is left to stand for 0.5-1.5min to allow the surface of the liquid crystal film to level. (4) Ultraviolet curing: The coated substrate is cured using a 365 nm wavelength ultraviolet light source with a curing power of 20-30 mW / cm². 2 The duration is 25-40 seconds.
[0024] The preparation method of 2,3,2',3'-tetrafluorodiphenylacetylene used in this application is as follows: (1) Under nitrogen protection, 1,2-difluorobenzene (1.0 eq) was dissolved in anhydrous tetrahydrofuran, cooled to -78°C, and n-butyllithium (1.1 eq) was slowly added dropwise to carry out the lithiation reaction. After the reaction was kept at the temperature for 2 h, iodine (1.2 eq) was added and the reaction was continued for 2 h. After extraction, drying and column chromatography purification, 4-iodo-2,3-difluorobenzene was obtained. (2) 4-Iodo-2,3-difluorobenzene (1.0 eq) and trimethylsilylacetylene (1.8 eq) were coupled in a Sonogashira reaction with palladium catalyst (0.03 eq) and cuprous iodide (0.08 eq). After extraction, drying and column chromatography purification, tetrabutylammonium fluoride (1.3 eq) was added to remove the trimethylsilyl protecting group to obtain 4-acetylene-2,3-difluorobenzene. (3) 4-Iodo-2,3-difluorobenzene (1.0 eq) and 4-ethynyl-2,3-difluorobenzene (1.3 eq) were subjected to a cross-coupling reaction of alkynes at 5-25℃ under nitrogen atmosphere via Pd / Cu composite catalysis, triethylamine bound acid, and Sonogashira reaction. The crude product was purified by silica gel column chromatography and low-temperature recrystallization from ethanol to obtain 2,3,2',3'-tetrafluorodiphenylacetylene with a purity ≥99.5%. 1 The 2H NMR spectral data are: δ 7.21 (2H, dd, J=1.9, 0.6 Hz), 7.46 (2H, dd, J=8.1, 0.6 Hz), 7.62 (2H, dd, J=8.1, 1.9 Hz).
[0025] The preparation method of KH-550 modified ZrO2 nanoparticles used in this application is as follows: (1) Add nano ZrO2 to a mixed solvent of ethanol-N,N-dimethylformamide with a volume ratio of 1:1 and a solid-liquid ratio of nano ZrO2 to the mixed solvent of 1:15 (g / mL); stir at 1000 r / min for 30 min, sonicate at 300 W power and 50 kHz frequency for 15 min; then add glacial acetic acid to adjust the pH of the system to 4.5, and stir and activate at 45℃ for 45 min; (2) Dissolve KH-550 in 90% ethanol solution at a mass ratio of 1:15, adjust the pH to 4.5 with glacial acetic acid, and stir for 45 min at room temperature for pre-hydrolysis; (3) The pre-hydrolyzed KH-550 solution was slowly added dropwise to the nano ZrO2 suspension (the mass ratio of nano ZrO2 to KH-550 was 1:0.8); after the addition was completed, the mixture was refluxed and stirred at 90°C for 5 hours. (4) Cool after the reaction is complete; then centrifuge at 10,000 r / min for 20 min using a high-speed centrifuge and collect the precipitate; wash the precipitate 2-3 times with anhydrous ethanol, dry it under vacuum at 45℃ for 12 h, grind it through a 300-mesh sieve to obtain KH-550 modified ZrO2 nanoparticles.
[0026] In the embodiments of this application, the CAS number of 1,2-bis(naphthyl)acetylene is 20199-35-3; the CAS number of 2-naphthoonitrile is 613-46-7; the chiral modifier is R5011, CAS number 44537-61-5; the photoinitiator is irgacure 651, CAS number 24650-42-8; the particle size of ZrO2 nanoparticles is 1-3 nm; the raw materials, reagents, solvents, etc. used in this application are all commercially available.
[0027] The following describes this application in further detail with reference to preparation examples, embodiments, and performance testing. Preparation Examples 1-6
[0028] Preparation Examples 1-6 each provide a PVG liquid crystal prepolymer solution.
[0029] The difference in the above preparation examples lies in the amount of some components added, as shown in Table 1 below.
[0030] The preparation method of the PVG liquid crystal prepolymer provided in Examples 1-6 includes the following steps: First, 1,2-bis(naphthyl)acetylene, 2,3,2',3'-tetrafluorodiphenylacetylene, polymerizable liquid crystal monomer RM82, cyanonaphthalene high refractive index dopant (2-naphthonitrile), chiral modifier 1.5g, and photoinitiator 0.5g are mixed and heated and stirred at 50-65℃ until completely dissolved to form a homogeneous and transparent solution; then, 2g of KH-550 modified ZrO2 nanoparticles are added and ultrasonically dispersed at an ultrasonic power of 300 W and a frequency of 50 kHz for 30 min to obtain a homogeneous and transparent PVG liquid crystal prepolymer.
[0031] Table 1. Amounts of some components added in preparation examples 1-6 Preparation Examples 7-14
[0032] Preparation Examples 7-14 each provide a PVG liquid crystal prepolymer solution.
[0033] The difference between the above preparation example and preparation example 3 is that the type and ratio of the cyanonaphthalene high refractive index dopant are shown in Table 2 below.
[0034] Table 2. Types and proportions of cyanonaphthalene high-refractive-index dopants in Preparation Examples 3 and 7-14 Comparative Preparation Example 1
[0035] Comparative preparation example 1 provides a PVG liquid crystal prepolymer.
[0036] The difference between the above comparative preparation example and preparation example 3 is that the amount of cyanonaphthalene high refractive index dopant added is 0. Comparative Preparation Example 2
[0037] Comparative preparation example 2 provides a PVG liquid crystal prepolymer solution.
[0038] The difference between the above comparative preparation example and preparation example 3 is that 1,2-bis(naphthyl)acetylene was replaced with an equal amount of 2,3,2',3'-tetrafluorodiphenylacetylene. Comparative preparation example 3
[0039] Comparative preparation example 3 provides a PVG liquid crystal prepolymer.
[0040] The difference between the above comparative preparation example and preparation example 3 is that 2,3,2',3'-tetrafluorodiphenylacetylene was replaced with an equal amount of 1,2-bis(naphthyl)acetylene. Comparative preparation example 4
[0041] Comparative preparation example 4 provides a PVG liquid crystal prepolymer.
[0042] The difference between the above comparative preparation example and preparation example 3 is that the amount of polymerizable liquid crystal monomer RM82 added is 0. Comparative preparation example 5
[0043] Comparative preparation example 5 provides a PVG liquid crystal prepolymer solution.
[0044] The difference between the above comparative preparation example and preparation example 3 is that the KH-550 modified ZrO2 nanoparticles were replaced with unmodified ZrO2 nanoparticles. Examples 1-14
[0045] Examples 1-14 each provide a PVG waveguide.
[0046] The difference in the above embodiments is that: (3) the PVG liquid crystal prepolymer used in the isothermal inkjet film formation step is derived from preparation examples 1-14.
[0047] Examples 1-14 each provide a method for fabricating a PVG waveguide, comprising the following steps: (1) Plasma activation of substrate: The substrate to be coated (such as glass substrate, quartz substrate or flexible polymer substrate) is placed in the plasma processing chamber, and Ar / O2 mixed gas with a volume ratio of 7:3 is used as the working gas. Plasma activation is performed for 90s under the conditions of vacuum degree of 10Pa and radio frequency power of 260W. (2) Linear polarized ultraviolet orientation: Photosensitive alignment agent SD1 is coated on the surface of the substrate after plasma activation treatment; after coating, the solvent is removed by pre-baking to form a uniformly thick alignment layer film; then the alignment layer is exposed and aligned using a 365 nm wavelength linear polarized ultraviolet light source, with the light intensity controlled at 10 mW / cm² and the exposure time being 240s. (3) Constant temperature inkjet film formation: Under constant temperature and humidity conditions of 25±0.5℃ and 42-48% RH, PVG liquid crystal prepolymer is uniformly coated onto the oriented substrate by inkjet printing to form a liquid crystal film with a thickness of 1μm; after coating, the coated substrate is left to stand for 1min to allow the surface of the liquid crystal film to level. (4) Ultraviolet curing: The coated substrate was cured using a 365 nm wavelength ultraviolet light source with a curing power of 25 mW / cm². 2 The time is 30 seconds. Comparative Examples 1-5
[0048] Comparative Examples 1-5 each provide a PVG waveguide.
[0049] The difference between the above comparative examples and Example 3 is that the PVG liquid crystal prepolymer used in the isothermal inkjet film formation step (3) of comparative examples 1-5 were respectively derived from comparative preparation examples 1-5. Performance testing
[0050] The PVG waveguides obtained in Examples 1-14 and Comparative Examples 1-5 were subjected to various performance tests, and the results are shown in Table 3 below.
[0051] (1) Refractive index and refractive index fluctuation: The unusual refractive index n of each PVG waveguide was measured at a wavelength of 550 nm using a spectroelometric ellipsometry. e For each sample, measurements were taken at five different locations, and the average value was calculated. Test conditions: incident angle 65°-75°, wavelength scanning range 400-1000 nm, ambient temperature 25±0.5℃. Refractive index fluctuations are expressed as the range of the measurements at the five locations.
[0052] (2) Global color difference: A colorimeter was used to measure the global color of the PVG waveguide. A total of 25 test points (5×5) were set up. Using the standard white field as a reference, the chromaticity coordinates (L, a, b* values) of each point were measured. The color difference ΔE between each point and the center point reference value was calculated according to the CIE 1976 color difference formula. The maximum ΔE value among the 25 points was taken as the global color difference evaluation index. Test conditions: D65 standard light source, ambient temperature 25±0.5℃.
[0053] (3) Film orientation deviation: The molecular orientation uniformity of the PVG waveguide was characterized using an orthogonal polarizing microscope in conjunction with a diffraction spectrometer. The sample was placed under the orthogonal polarizing microscope, and the interference fringe pattern of the film was observed in transmission mode. The fringe direction offset angle of each region of the film surface was measured using image analysis software. At the same time, the diffraction spot distribution of the sample at a wavelength of 550 nm was measured using a diffraction spectrometer. The offset angle of the diffraction spot center relative to the theoretical Bragg diffraction direction was used to characterize the overall orientation deviation of the film. Five different regions of each sample were measured, and the average value was taken.
[0054] (4) Long-term optical stability: The PVG waveguide was placed in an ultraviolet aging chamber for ultraviolet aging test. The wavelength was 340nm, the irradiance was 0.63 W / m², the black panel temperature was 60±2℃, and the aging time was 500h. After aging, the refractive index and global color difference ΔE of the aged sample were tested according to the methods in (1) and (2) above, and the refractive index change rate and color difference degradation value were calculated; refractive index change rate = (n after aging) e -Initial n e ) / initial n e ×100%; Color difference degradation value = ΔE after aging - ΔE initial.
[0055] Table 3 Performance test results of PVG waveguides obtained in Examples 1-14 and Comparative Examples 1-5
[0056] As shown in Table 3, the refractive index n of the PVG waveguides in Examples 1-14 is... e The refractive index ranges from 1.82 to 1.94 (≥1.82), with a fluctuation of 0.0006 to 0.0018 (≤0.002). The global color difference ΔE is 0.9 to 1.7 (≤1.8), and the orientation deviation is 0.18° to 0.38° (≤0.5°). After 500 hours of UV aging, n... e The change rate is 0.7-1.6% (≤1.6%), and the ΔE degradation is 0.1-0.4 (≤0.5), indicating that the PVG waveguide provided in this application has comprehensive performance with high refractive index, excellent film refractive index uniformity, excellent global color uniformity, excellent molecular orientation order, and excellent long-term optical stability, and can be applied to display scenarios such as AR / VR optical waveguides, holographic projection, and high-definition display polarization optical devices.
[0057] Comparative Example 1: The refractive index n of the PVG waveguide obtained without the addition of the cyanonaphthalene high-refractive-index dopant is... e With a value of only 1.75, it fails to meet the requirement of a refractive index ≥1.8, and exhibits a global color difference ΔE as high as 2.6, a refractive index fluctuation as high as 0.0025, and an orientation deviation as high as 0.52°. After 500 hours of UV aging, n e The change rate is as high as 3.2%, and the ΔE degradation is as high as 0.9. This indicates that by adding a cyanonaphthalene high-refractive-index dopant, the strong polar cyano group has a dipole-dipole interaction with the acetylene group and fluorine atom in the main framework molecule. This interaction can effectively fill the gaps between molecules without disrupting the regular arrangement of the main framework, thereby further increasing the molecular packing density of the system. This effectively improves the refractive index of the PVG waveguide and enhances the uniformity of the film's refractive index, color uniformity, molecular orientation order, and long-term optical stability.
[0058] Comparative Example 2 replaced 1,2-bis(naphthyl)acetylene with an equal amount of 2,3,2',3'-tetrafluorodiphenylacetylene (i.e., using only tetrafluorobiphenylacetylene as a single mesocrystalline component), and the refractive index n of the resulting PVG waveguide was... e The refractive index is only 1.79, with a global chromatic aberration ΔE as high as 2.8, a refractive index fluctuation as high as 0.0028, and an orientation deviation as high as 0.55°; Comparative Example 3 replaced 2,3,2',3'-tetrafluorodiphenylacetylene with an equal amount of 1,2-bis(naphthyl)acetylene (i.e., using only naphthylacetylene as a single mesocrystalline component), and the resulting PVG waveguide had a refractive index n eWith a refractive index of only 1.77, a global color difference ΔE as high as 3.0, a refractive index fluctuation as high as 0.0030, and an orientation deviation as high as 0.58°, it is evident that neither naphthyldiacetylene nor tetrafluorobiphenylacetylene can simultaneously achieve high refractive index and excellent color uniformity when used alone. Naphthyldiacetylene, when used alone, exhibits excessively strong intermolecular forces, leading to poor flowability and orientation disorder. Tetrafluorobiphenylacetylene, when used alone, suffers from insufficient conjugation length and polarizability, limiting the improvement in refractive index. Only when the two are combined to produce a synergistic effect can the combined effect of a refractive index ≥1.8 and a global color difference ΔE ≤1.8 be achieved.
[0059] Comparative Example 4: The refractive index n of the PVG waveguide obtained without the addition of polymerizable liquid crystal monomer RM82. e With a value of only 1.75, it fails to meet the requirement of a refractive index ≥1.8, and exhibits a global color difference ΔE as high as 2.8, a refractive index fluctuation as high as 0.0034, and an orientation deviation as high as 0.49°. After 500 hours of UV aging, n e The change rate is as high as 2.4%, and the ΔE degradation is as high as 0.7. This indicates that by adding polymerizable liquid crystal monomers, this application can enable the liquid crystal to align in an orderly manner, fundamentally improving the problems of refractive index drift and color difference degradation under long-term use.
[0060] Comparative Example 5 uses unmodified ZrO2 nanoparticles instead of KH-550 modified ZrO2 nanoparticles, and the resulting PVG waveguide has a refractive index n e The value is 1.82, the global color difference ΔE is as high as 3.2, the refractive index fluctuation is as high as 0.0035, the orientation deviation is as high as 0.60°, and after 500h of UV aging, n e The change rate was as high as 4.0%, and the ΔE degradation was as high as 1.3, both significantly worse than in Example 3. Therefore, it is indicated that the unmodified ZrO2 nanoparticles are not compatible with the liquid crystal mesocrystalline system, and are prone to particle agglomeration and phase separation defects, resulting in increased optical scattering, deterioration of film uniformity, limited refractive index improvement, and decreased optical stability.
[0061] The detection results of Examples 3 and 7-14 show that, in Examples 3 and 7-8, 2-naphthonitrile, 6-hydroxy-2-naphthonitrile, or 1-bromo-2-cyanonaphthalene was used as a single cyanonaphthalene high-refractive-index dopant, and the resulting PVG waveguide had a refractive index n e The refractive index is 1.86-1.87, the global color difference ΔE is 1.3, the refractive index fluctuation is 0.0011-0.0012, and the orientation deviation is 0.25°-0.27°. Examples 9-10 use 2-naphthonitrile and 1-bromo-2-cyanonaphthalene in a weight ratio of 1:0.5 or 6-hydroxy-2-naphthonitrile and 2-naphthonitrile in a weight ratio of 1:0.5 as composite cyanonaphthalene high-refractive-index dopant. The resulting PVG waveguide has a refractive index n... eThe refractive index is 1.87-1.88, the global color difference ΔE is 1.0, the refractive index fluctuation is 0.0010-0.0011, and the orientation deviation is 0.23°-0.24°. Examples 11-14 use 6-hydroxy-2-naphthonitrile and 1-bromo-2-cyanonaphthalene in a weight ratio of 1:(0.3-0.6) as cyanonaphthalene high-refractive-index dopants, resulting in PVG waveguides with a refractive index n... e The value is 1.90-1.94 (≥1.90), the global color difference ΔE is 0.9 (≤0.9), the refractive index fluctuation is 0.0006-0.0008 (≤0.0008), the orientation deviation is 0.18°-0.19° (≤0.19°), and the value after 500h UV aging is n. e The rate of change is 0.7-0.8% (≤0.8%), and the ΔE degradation is 0.1 (≤0.1). This indicates that this application further uses 6-hydroxy-2-naphthonitrile and 1-bromo-2-cyanonaphthalene in a weight ratio of 1:(0.3-0.6) as cyanonaphthalene high-refractive-index dopants, which can maximize the balance between high refractive index enhancement and film optical uniformity optimization, thereby obtaining a PVG waveguide with better overall performance.
[0062] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.
Claims
1. A PVG liquid crystal material, characterized in that, The product comprises the following components in parts by weight: 35-50 parts naphthyldiacetylene, 12-26 parts tetrafluorobiphenylacetylene, 10-22 parts polymerizable liquid crystal monomer, 15-20 parts cyanonaphthalene high refractive index dopant, 1-4 parts KH-550 modified ZrO2 nanoparticles, 1-2 parts chiral modifier, and 0.5-1 part photoinitiator.
2. The PVG liquid crystal material according to claim 1, characterized in that, The PVG liquid crystal material comprises the following components in parts by weight: 40-45 parts naphthyldiacetylene, 15-20 parts tetrafluorobiphenylacetylene, 13-18 parts polymerizable liquid crystal monomer, 15-20 parts cyanonaphthalene high refractive index dopant, 2-3 parts KH-550 modified ZrO2 nanoparticles, 1-2 parts chiral modifier, and 0.5-1 part photoinitiator.
3. The PVG liquid crystal material according to claim 1, characterized in that, The cyanonaphthalene high refractive index dopant is selected from one or more of 1-naphthonitrile, 2-naphthonitrile, 6-hydroxy-2-naphthonitrile, 1-bromo-2-cyanonaphthalene, 2,6-naphthodinitrile, 1,4-dicyanonaphthalene, and 1,5-dicyanonaphthalene.
4. The PVG liquid crystal material according to claim 1, characterized in that, The cyanonaphthalene high refractive index dopant is a mixture of 6-hydroxy-2-naphthoonitrile and 1-bromo-2-cyanonaphthalene.
5. The PVG liquid crystal material according to claim 1, characterized in that, The polymerizable liquid crystal monomer is RM257 and / or RM82.
6. The PVG liquid crystal material according to claim 1, characterized in that, The tetrafluorobiphenylacetylene is 2,3,2',3'-tetrafluorodiphenylacetylene.
7. A PVG waveguide, characterized in that, It is prepared using the PVG liquid crystal material according to any one of claims 1-6.
8. The method for fabricating a PVG waveguide as described in claim 7, characterized in that, Includes the following steps: Plasma activation of substrate, linear polarization ultraviolet orientation, isothermal inkjet film formation, and ultraviolet curing; In the aforementioned UV curing, the curing power is 20-30 mW / cm². 2 The duration is 25-40 seconds.