Liquid crystal functionalized nanoparticles and methods of making and materials

Abstract

This invention relates to the field of holographic polymer-dispersed liquid crystal materials technology, providing liquid crystal functionalized nanoparticles, their preparation method, and materials. The liquid crystal functionalized nanoparticles include a nanoparticle core, a surface-modified layer bonded to the nanoparticle core, and a liquid crystal functionalized layer bonded to the surface-modified layer. Advantages: Liquid crystal transformation is achieved by chemically bonding small-molecule liquid crystal building blocks to the nanoparticles. By limiting the types of liquid crystal building blocks, the compatibility between the nanoparticles and the HPDLC system is improved, effectively solving the aggregation problem of traditional nanoparticle-doped HPDLC. Furthermore, this invention utilizes the inductive effect of the liquid crystal building blocks bonded to the nanoparticles and the high diffusion coefficient of the small-molecule liquid crystal building blocks, combined with the chemical potential gradient driving the holographic photopolymerization process and the excellent compatibility between the nanoparticles and the liquid crystal, to achieve directional enrichment of nanoparticles into liquid crystal microregions, further improving phase separation regularity.

Description

Technical Field

[0001] This invention relates to the field of holographic polymer-dispersed liquid crystal materials technology, and more specifically, to a liquid crystal functionalized nanoparticle, its preparation method, and materials. Background Technology

[0002] The core performance of holographic polymer-dispersed liquid crystals (HPDLCs) is determined by the refractive index modulation (Δn), which is essentially the difference in refractive index between the liquid crystal-rich region and the polymer-rich region after phase separation. According to coupled-wave theory, diffraction efficiency is directly related to the refractive index modulation, and improving Δn is key to overcoming the performance bottleneck of HPDLC devices.

[0003] In existing technologies, the solutions for improving the refractive index modulation of HPDLC mainly fall into two categories: one is to optimize the composition ratio of liquid crystal and polymer by selecting high birefringence liquid crystal and low refractive index polymer materials. However, due to the inherent refractive index difference of the materials, Δn is difficult to exceed 0.15. At the same time, simply changing the refractive index of a single component will cause significant changes in the surface energy, viscosity, film-forming properties, etc. between the components, which will destroy the compatibility between the polymer and the liquid crystal, resulting in poor phase separation effect and reducing the optimization efficiency of the refractive index modulation. The second is to directly dope nanoparticles, using the high refractive index characteristics of nanoparticles to increase the effective refractive index of the liquid crystal-rich region. However, in this type of solution, the nanoparticles are inert dopants, which have poor compatibility with liquid crystal molecules and are prone to aggregation, resulting in disordered phase separation structure, which leads to a decrease in the optical uniformity of HPDLC and limits its practical application.

[0004] Chinese patent CN114456415A discloses a method for preparing nanoparticle-doped liquid crystal / polymer thin films, but the nanoparticles are not modified with liquid crystals and are only used as infrared shielding or mechanical enhancement additives, without involving the optimization of refractive index modulation. Summary of the Invention

[0005] The present invention aims to overcome at least one defect (deficiency) of the prior art and provides a liquid crystal functionalized nanoparticle, preparation method and material, which can effectively improve the refractive index modulation of holographic polymer dispersed liquid crystal materials and improve diffraction efficiency.

[0006] One objective of this invention is to provide a liquid crystal functionalized nanoparticle, comprising a nanoparticle core, a surface modification layer bonded to the nanoparticle core, and a liquid crystal functionalized layer bonded to the surface modification layer.

[0007] In one or more embodiments of the present invention, the surface modification layer is formed by bonding a surface modifier to the surface of the nanoparticle core. The liquid crystal functionalized layer is a functional layer comprising at least liquid crystal units, which modify the nanoparticle core, thereby liquidizing it. It can be understood that the liquid crystal functionalized nanoparticles are formed by sequentially modifying the nanoparticle core with a surface modifier and then with a liquid crystal functionalized layer.

[0008] Liquid crystal functionalization is an effective way to improve the compatibility of nanoparticles with HPDLC systems. This invention grafts a liquid crystal functionalization layer onto the surface of nanoparticles, enabling the nanoparticles to possess both the high refractive index characteristics of nanomaterials and the orientation characteristics of liquid crystal molecules. This not only avoids nanoparticle aggregation but also synergistically enhances the phase separation effect between liquid crystal and polymer, thereby significantly improving the refractive index modulation of HPDLC and increasing diffraction efficiency.

[0009] Furthermore, the nanoparticle core is a high-refractive-index nanoparticle with a refractive index greater than or equal to 1.8; and / or The surface modifier is a silane coupling agent.

[0010] Preferably, the silane coupling agent is selected from amino, hydroxyl, or epoxy groups. The refractive index is 1.8-3. The nanoparticle core is a metal oxide, metal sulfide, or metal. The metal oxide includes, but is not limited to, titanium dioxide (TiO2), zirconium oxide (ZrO2), zinc oxide (ZnO), and barium titanate (BaTiO3) nanoparticles; the metal sulfide includes, but is not limited to, zinc sulfide (ZnS); and the metal includes, but is not limited to, gold (Au) and silver (Ag). The introduction of high-refractive-index nanoparticles can further expand the refractive index difference between the liquid crystal-rich region and the polymer-rich region in the HPDLC system. Simultaneously, the surface plasmon effect of some metal nanoparticles, such as gold (Au) and silver (Ag), can help improve optical performance.

[0011] Preferably, the silane coupling agent is selected from one or more of 3-aminopropyltriethoxysilane (APTES), γ-mercaptopropyltrimethoxysilane (MPTMS), mercaptoundecanoic acid, γ-methacryloyloxypropyltrimethoxysilane (KH-570), vinyltriethoxysilane (A-151), γ-isocyanate propyltriethoxysilane, γ-ureopropyltriethoxysilane (A-1160), and bis-[3-(triethoxysilyl)propyl]tetrasulfide (Si-69). The silane coupling agent is bonded to the nanoparticle core to form a surface modification layer. Its function is to introduce active functional groups onto the surface of the nanoparticle core, providing binding sites for the grafting of the liquid crystal functionalized layer, while simultaneously improving the dispersibility of the nanoparticles.

[0012] Furthermore, the liquid crystal functionalized layer includes liquid crystal units and connecting arms, wherein the liquid crystal units are grafted onto the surface modified layer via the connecting arms, and the connecting arms have at least one active functional group selected from carboxyl, isocyanate, mercapto, alkenyl, and azide groups.

[0013] In one or more embodiments of the present invention, when the liquid crystal module does not contain carboxyl (-COOH), isocyanate (-NCO), mercapto (-SH), alkenyl (-CH=CH2), or azide (-N3), it is connected to the surface modification layer via a connecting arm. One end of the connecting arm is covalently connected to the active functional group of the surface modification layer, and the other end is covalently connected to the liquid crystal module. That is, the liquid crystal functionalized layer in this embodiment consists of the liquid crystal module bonded to the connecting arm and the connecting arm bonded to the surface modification layer.

[0014] In one or more embodiments of the present invention, the connecting arm has a first active functional group for reacting with the surface modification layer and a second active functional group for reacting with the liquid crystal module, wherein the first active functional group is a thiol or a carboxyl group, and the second active functional group is a carboxyl group or a hydroxyl group.

[0015] Furthermore, the connecting arm is selected from one or more of the following: bisaccharide, sebacic acid, mercaptopropionic acid, mercaptoundecanoic acid, isocyanate propyltriethoxysilane, 4-pentenoic acid, and propynic acid.

[0016] Another object of the present invention is to provide a method for preparing liquid crystal functionalized nanoparticles, which includes the following steps: S1. Nanoparticle core pretreatment: The nanoparticle cores are dispersed in an organic solvent, and then treated with acid to remove impurities and hydroxyl contaminants from the surface of the nanoparticle cores. After centrifugation, the precipitate is collected, washed, and dried to obtain the pretreated nanoparticle cores. S2. Surface modification: The pretreated nanoparticle cores are dispersed in a solvent, a surface modifier is added to react, after the reaction is completed, the precipitate is collected by centrifugation, washed, and dried to obtain surface-modified nanoparticles. S3. Liquid crystal functional grafting, including the following steps: S31. The connecting arm is subjected to an amidation reaction or a mercapto-alkene click reaction with the surface-modified nanoparticles, so that the connecting arm is grafted onto the surface-modified layer to obtain an intermediate. S32. The liquid crystal motif is subjected to an esterification reaction with the intermediate to graft the liquid crystal motif onto the connecting arm, thereby obtaining liquid crystal functionalized nanoparticles. For example, the surface modifier has an amino group, forming a surface-active layer with an amino group, the first active functional group of the linker arm is a carboxyl group, the second functional group is a carboxyl group, and the liquid crystal unit has a hydroxyl group; thus, the linker arm is grafted onto the surface modified layer through an amidation reaction between its carboxyl group and the amino group of the surface modified layer; the liquid crystal unit is grafted onto the linker arm through an esterification reaction between its hydroxyl group and the free carboxyl group at the end of the linker arm.

[0017] For example, the surface modifier has an alkenyl group, forming a surface-active layer with an alkenyl group. The first active functional group of the linker arm is a thiol group, and the second functional group is a carboxyl group. The liquid crystal unit has a hydroxyl group. In this way, the linker arm is grafted onto the surface-modified layer through a thiol-alkene click reaction between its thiol group and the alkenyl group of the surface-modified layer, and the end of the linker arm exposes a carboxyl group. The liquid crystal unit is grafted onto the linker arm through an esterification reaction between its hydroxyl group and the carboxyl group at the end of the linker arm.

[0018] The amount of the nanoparticle core is 95-110 parts, the amount of the surface modifier is 5-20 parts, and the total amount of the liquid crystal unit and the connecting arm is 10-40 parts. The mass ratio of the liquid crystal unit to the connecting arm is (2-3):1.

[0019] Preferably, the nanoparticle core comprises 98-105 parts, the surface modifier comprises 8-15 parts, and the total amount of the liquid crystal module and connecting arm comprises 15-25 parts. Appropriate proportions ensure that the liquid crystal functionalized layer uniformly covers the surface of the nanoparticle core, while avoiding nanoparticle aggregation caused by excessive modification.

[0020] In one or more embodiments of the present invention, the following steps are specifically included: S1. Pretreatment of nanoparticle cores: Add nanoparticle cores to anhydrous ethanol and disperse in an ultrasonic disperser for 30-60 min at a dispersion power of 80-120 W to obtain a uniform nanoparticle dispersion. Then add 1-3% (w / w) dilute hydrochloric acid to the dispersion to adjust the pH to 3.5-4 and stir for 10-20 min to remove impurities and hydroxyl contaminants from the nanoparticle surface. Then centrifuge at 3000-5000 r / min for 10-15 min, collect the precipitate, wash with anhydrous ethanol 3-5 times, and vacuum dry at 60-80℃ for 2-4 h to obtain the pretreated nanoparticle cores.

[0021] S2. Preparation of surface-modified layer: The pretreated nanoparticle cores are added to a mixed solvent of anhydrous ethanol and deionized water in a volume ratio of 3:1-5:1. After stirring evenly, the surface modifier is added, and the mixture is stirred at a constant temperature of 60-80℃ for 2-4 hours at a stirring speed of 200-300 r / min. After the reaction is completed, the mixture is centrifuged at a speed of 4000-6000 r / min for 15-20 minutes. The precipitate is collected, washed 3-5 times with anhydrous ethanol, and vacuum dried at a temperature of 70-90℃ for 3-5 hours to obtain surface-modified nanoparticles.

[0022] S3. Liquid crystal functional grafting, including the following steps: S31. Linker Arm Grafting (Amide Reaction): The above-mentioned surface-aminated ZnS nanoparticles were dispersed in anhydrous DMF and ultrasonically dispersed for 20-40 min at an ultrasonic power of 75-105 W. A linker arm, 10-25 parts of N,N'-dicyclohexylcarbodiimide (DCC), and 1-3 parts of 4-dimethylaminopyridine (DMAP) were added. Under nitrogen protection, the mixture was stirred at a constant temperature of 45-70℃ for 6-9 h at a stirring speed of 200-400 r / min. This reaction utilizes DCC / DMAP to catalyze the amidation reaction between a carboxyl group of adipic acid and an amino group on the nanoparticle surface, forming an amide bond, thereby grafting the linker arm onto the nanoparticle surface and retaining a free carboxyl group at the end of the linker arm. After the reaction was completed, the mixture was centrifuged at a speed of 5000~7000 r / min for 15~30 min. The precipitate was collected and washed 2~6 times each with DMF and anhydrous ethanol, and then dried under vacuum to obtain the ZnS nanoparticle intermediate with grafted arms.

[0023] S32. Liquid Crystal Unit Grafting (Steglich Esterification): The ZnS nanoparticle intermediate grafted with the above-mentioned connecting arms was dispersed in anhydrous DMF and ultrasonically dispersed for 25 min (90 W). 20 parts of 4-cyano-4'-hydroxybiphenyl (liquid crystal unit), 10-25 parts of DCC, and 1-3 parts of DMAP were added. Under nitrogen protection, the mixture was stirred at a constant temperature of 45-70℃ for 6-9 h at a stirring speed of 200-400 r / min. This reaction utilizes the Steglich esterification reaction between the free carboxyl groups at the adipic acid terminus on the surface of the DCC / DMAP catalyzed by the intermediate and the hydroxyl groups of the liquid crystal unit, forming ester bonds and grafting the liquid crystal unit onto the connecting arms. After the reaction was completed, the mixture was filtered, and the filtrate was centrifuged at 5000~7000 r / min for 15~25 min. The precipitate was collected and washed 2~8 times with a mixed solvent of DMF and anhydrous ethanol at a volume ratio of 1:1 to remove unreacted liquid crystal building blocks and catalyst. The precipitate was then vacuum dried at 70~100℃ for 4~7 h to obtain liquid crystal functionalized ZnS nanoparticles.

[0024] In the above scheme, the surface modifier has an amino group and the connecting arm has a carboxyl group; The connecting wall, after being attached to the surface-modified nanoparticles, exposes a carboxyl group at its end, and the liquid crystal unit has a hydroxyl group; or, the connecting wall, after being attached to the surface-modified nanoparticles, exposes a hydroxyl group at its end, and the liquid crystal unit has a carboxyl group.

[0025] In step S2, if the water bath temperature is too low, the silane coupling agent will not be hydrolyzed sufficiently, and the surface modification will not be thorough; if the temperature is too high, the silane coupling agent will self-polymerize, affecting the modification effect.

[0026] In one or more embodiments of the present invention, the following steps are specifically included: S1. Pretreatment of nanoparticle cores: Add nanoparticle cores to anhydrous ethanol and disperse in an ultrasonic disperser for 30-60 min at a dispersion power of 80-120 W to obtain a uniform nanoparticle dispersion. Then add 1-3% (w / w) dilute hydrochloric acid to the dispersion to adjust the pH to 3.5-4 and stir for 10-20 min to remove impurities and hydroxyl contaminants from the nanoparticle surface. Then centrifuge at 3000-5000 r / min for 10-15 min, collect the precipitate, wash with anhydrous ethanol 3-5 times, and vacuum dry at 60-80℃ for 2-4 h to obtain the pretreated nanoparticle cores.

[0027] S2. Preparation of surface-modified layer: The pretreated nanoparticle cores are added to a mixed solvent of anhydrous ethanol and deionized water in a volume ratio of 3:1-5:1. After stirring evenly, the surface modifier is added, and the mixture is stirred at a constant temperature of 60-80℃ for 2-4 hours at a stirring speed of 200-300 r / min. After the reaction is completed, the mixture is centrifuged at a speed of 4000-6000 r / min for 15-20 minutes. The precipitate is collected, washed 3-5 times with anhydrous ethanol, and vacuum dried at a temperature of 70-90℃ for 3-5 hours to obtain surface-modified nanoparticles.

[0028] S3. Liquid crystal functional grafting, including the following steps: (1) Linker grafting (thiol-ene click reaction): The surface-modified ZnS nanoparticles were added to anhydrous DMF and ultrasonically dispersed for 20-40 min at an ultrasonic power of 75-105 W. Initiator and linker were added, and the mixture was stirred at a constant temperature of 50-85℃ for 5-8 h under nitrogen protection at a stirring speed of 150-300 r / min. After the reaction was completed, the mixture was centrifuged at a speed of 5000-7000 r / min for 10-25 min. The precipitate was collected, washed 2-5 times with anhydrous ethanol, and vacuum dried to obtain ZnS nanoparticles (intermediate) with carboxyl groups attached to the surface.

[0029] (2) Grafting of liquid crystal building blocks (esterification reaction): The above intermediates were dispersed in anhydrous DMF, and liquid crystal building blocks, 10-25 parts DCC and 1-3 parts DMAP were added. Under nitrogen protection, the mixture was stirred at a constant temperature of 45-70℃ for 6-9 h at a stirring speed of 200-400 r / min. After the reaction was completed, the mixture was centrifuged at a speed of 5000-7000 r / min for 15-30 min. The precipitate was collected and washed 2-8 times with a mixed solvent of DMF and anhydrous ethanol at a volume ratio of 1:1. The precipitate was then dried under vacuum at 70-100℃ for 4-7 h to obtain liquid crystal functionalized ZnS nanoparticles.

[0030] In the above scheme, the surface modifier has an alkenyl group and the linker arm has a thiol group; The connecting wall, after being attached to the surface-modified nanoparticles, exposes a carboxyl group at its end, and the liquid crystal unit has a hydroxyl group; or, the connecting wall, after being attached to the surface-modified nanoparticles, exposes a hydroxyl group at its end, and the liquid crystal unit has a carboxyl group.

[0031] Furthermore, the liquid crystal functionalized layer is composed of liquid crystal units, which are directly grafted onto the surface modified layer, and the liquid crystal units have at least one active functional group selected from hydroxyl, amino, carboxyl, alkenyl and thiol groups.

[0032] In one or more embodiments of the present invention, when the liquid crystal unit itself contains at least one active functional group selected from hydroxyl, amino, carboxyl, alkenyl, or thiol groups, it can directly undergo a covalent reaction with the active functional groups of the surface-modified layer without the need for connecting arms. That is, in this embodiment, the liquid crystal functionalized layer is composed of liquid crystal units bonded to the surface-modified layer.

[0033] Another object of the present invention is to provide a method for preparing liquid crystal functionalized nanoparticles, for use with the above-mentioned liquid crystal functionalized nanoparticles, comprising the following steps: S1. Nanoparticle core pretreatment: The nanoparticle cores are dispersed in an organic solvent, and then treated with acid to remove impurities and hydroxyl contaminants from the surface of the nanoparticle cores. After centrifugation, the precipitate is collected, washed, and dried to obtain the pretreated nanoparticle cores. S2. Surface modification: The pretreated nanoparticle cores are dispersed in a solvent, a surface modifier is added to react, after the reaction is completed, the precipitate is collected by centrifugation, washed, and dried to obtain surface-modified nanoparticles. S3. Liquid crystal functionalization grafting: Liquid crystal units are grafted onto the surface modification layer using a direct grafting method, wherein the direct grafting method is one of the following: amidation direct reaction, esterification direct reaction, mercapto-alkene click reaction, hydrosilylation reaction, and direct coordination reaction.

[0034] The nanoparticle core is used in an amount of 95-110 parts, the surface modifier in an amount of 5-20 parts, and the liquid crystal module in an amount of 10-40 parts. Preferably, the nanoparticle core is used in an amount of 95-105 parts, the surface modifier in an amount of 8-15 parts, and the liquid crystal module in an amount of 15-25 parts. Appropriate proportions ensure that the liquid crystal functionalized layer uniformly covers the surface of the nanoparticle core, while avoiding nanoparticle aggregation caused by excessive modification.

[0035] In one or more embodiments of the present invention, the applicability of different direct grafting methods is as follows: Amide-direct reaction: The surface modification layer contains amino groups (-NH2), and the liquid crystal unit contains carboxyl groups (-COOH); or the surface modification layer contains carboxyl groups, and the liquid crystal unit contains amino groups, and the reaction is carried out under EDC / NHS activation.

[0036] Esterification direct reaction: The surface modification layer contains hydroxyl groups and the liquid crystal unit contains carboxyl groups; or the surface modification layer contains carboxyl groups and the liquid crystal unit contains hydroxyl groups, and the reaction is carried out under DCC / DMAP catalysis.

[0037] Thiol-alkene click reaction: The surface modification layer contains thiol groups (-SH), and the liquid crystal unit contains alkenyl groups (-CH=CH2), and the reaction is initiated by ultraviolet light or heat.

[0038] Hydrosilylation reaction: The surface modification layer contains Si-H, the liquid crystal unit contains alkenyl groups, and the reaction is carried out in the presence of a platinum catalyst.

[0039] Direct coordination reaction: For gold and silver nanoparticles, the liquid crystal building blocks contain thiol groups (-SH), which directly form Au-S or Ag-S coordination bonds under stirring at room temperature.

[0040] Furthermore, the liquid crystal unit is a nematic liquid crystal molecule.

[0041] Preferably, the nematic liquid crystal molecules are selected from one or more of biphenyl, phenylcyclohexane, fluorinated biphenyl, azobenzene, Schiff base, diphenylacetylene, and alkene liquid crystal molecules.

[0042] The compatibility of the chemical structure of the liquid crystal building blocks with the liquid crystals used in HPDLC systems (such as E7 liquid crystals, mainly composed of cyanobiphenyls) is crucial in determining whether nanoparticles can be uniformly dispersed and migrate with the liquid crystals. When liquid crystal building blocks with significantly different chemical structures from the system's liquid crystals are selected, the interaction between the liquid crystal layer on the nanoparticle surface and the system's liquid crystal molecules is weak, failing to form an effective compatible interface. Consequently, the nanoparticles struggle to migrate and accumulate in the dark region along with the liquid crystal molecules during photopolymerization. Furthermore, the grafting rate is also affected by the varying reactivity of the liquid crystal building blocks, resulting in limited functionalization of the nanoparticles into liquid crystals.

[0043] Another object of the present invention is to provide a holographic polymer-dispersed liquid crystal material, comprising, by weight, 40-60 parts of photopolymerizable monomer, 30-50 parts of liquid crystal, 0.5-2 parts of photoinitiator, 1-5 parts of other additives, and 1-10 parts of liquid crystal functionalized nanoparticles of any one of the above.

[0044] In one or more embodiments of the present invention, preferably, the photopolymerizable monomer comprises 50-55 parts, the liquid crystal comprises 35-45 parts, the photoinitiator comprises 1-1.5 parts, and other additives comprises 2-4 parts, and the liquid crystal functionalized nanoparticles comprise 3-7 parts of any of the above. The photopolymerizable monomer is selected from acrylate monomers such as trimethylolpropane triacrylate or dipropylene glycol diacrylate; the liquid crystal is selected from nematic liquid crystals, such as E7 liquid crystal; the photoinitiator is selected from titanoceramic, dye / co-initiator systems, benzophenone, and benzoin ether photoinitiators; and the other additives are selected from crosslinking agents, surfactants, and leveling agents. The liquid crystal unit of the liquid crystal functionalized nanoparticles has the same or substantially the same core and / or end groups as the liquid crystal.

[0045] In one or more embodiments of the present invention, the holographic polymer-dispersed liquid crystal material further includes, by weight, 0.5 to 10 parts of co-initiator and 5 to 15 parts of solvent.

[0046] Another object of the present invention is to provide a method for fabricating an HPDLC device, comprising the following steps: S1. Mix and disperse all components of the above-mentioned holographic polymer-dispersed liquid crystal to form a mixed system; S2. Coat the mixture onto a glass substrate; S3. Expose the glass substrate in a holographic interference light field and cool it to obtain an HPDLC device.

[0047] In one or more embodiments of the present invention, the following steps are specifically included: S1. Mixing and stirring: Add the photopolymerizable monomer, liquid crystal, liquid crystal functionalized nanoparticles, photoinitiator, and other additives to a beaker and stir at room temperature for 30-60 minutes at a stirring speed of 200-300 r / min to obtain a uniform mixture. Then, add the mixture to an ultrasonic disperser and disperse for 20-30 minutes at a power of 100-120W to further eliminate agglomeration.

[0048] S2. Coating: The uniformly dispersed mixture is coated onto a clean glass substrate with a coating thickness of 0.5~10µm, preferably 1~5µm.

[0049] S3. Photopolymerization and phase separation: The coated glass substrate is placed in a holographic interference light field and the polymerization reaction is initiated by visible light irradiation with a wavelength of 400-780nm, a light intensity of 1-50mW / cm², and an irradiation time of 0.5-10min. After photopolymerization, the substrate is naturally cooled to room temperature to obtain a holographic polymer-dispersed liquid crystal material.

[0050] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention achieves liquid crystallization transformation by chemically bonding small molecule liquid crystal building blocks to nanoparticles. By limiting the types of liquid crystal building blocks, the compatibility between nanoparticles and HPDLC systems is improved, allowing nanoparticles to be uniformly dispersed. This effectively solves the aggregation problem of traditional nanoparticles doped with HPDLC, improves phase separation regularity, and thus effectively improves refractive index modulation and diffraction efficiency. In addition, this invention utilizes the inductive effect of liquid crystal building blocks bonded to nanoparticles and the high diffusion coefficient of small molecule liquid crystal building blocks. Combined with the chemical potential gradient driving process in holographic photopolymerization and the excellent compatibility between nanoparticles and liquid crystals, it achieves directional enrichment of nanoparticles into liquid crystal microregions, further improving phase separation regularity. This is beneficial for improving refractive index modulation and diffraction efficiency, and avoids the waste of some nanoparticles remaining in the polymer-rich region, thereby improving the utilization rate of nanoparticles.

[0051] (2) The nanoparticle liquid crystal functionalization method provided by the present invention is simple and highly controllable. It achieves stable connection between liquid crystal moieties and nanoparticles through connecting arm grafting or direct grafting, without the need for complex equipment, and is suitable for large-scale production.

[0052] (3) The raw materials selected in this invention are widely available and have low cost, avoiding the use of expensive special materials and reducing the preparation cost of HPDLC. At the same time, the process is green and environmentally friendly, with no harmful gases generated, which is in line with the development trend of green preparation.

[0053] (4) The HPDLC preparation process of the present invention is simple and the composition ratio is reasonable. The addition of liquid crystal functionalized nanoparticles not only improves the refractive index modulation, but also improves the optical uniformity and mechanical stability of HPDLC in some embodiments of the present invention, reduces the driving threshold voltage, shortens the response time, and improves the diffraction efficiency. It can meet the application requirements of high-end optoelectronic devices such as AR / VR display, optical communication, and holographic storage, and has broad application prospects. Detailed Implementation

[0054] 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.

[0055] Table 1

[0056] Example 1 The liquid crystal functionalized ZnS nanoparticles of this embodiment include a nanoparticle core, a surface modification layer bonded to the nanoparticle core, and a liquid crystal functionalized layer bonded to the surface modification layer. The liquid crystal functionalized layer includes connecting arms and liquid crystal units. The liquid crystal functionalized ZnS nanoparticles are prepared by the following method: Nanoparticle core pretreatment: 100 ZnS nanoparticles with a particle size of 20-30 nm were added to anhydrous ethanol and dispersed for 40 min using an ultrasonic disperser with a dispersion power of 100 W to obtain a uniform dispersion. 2% dilute hydrochloric acid was added to the dispersion to adjust the pH to 4, and the mixture was stirred for 15 min. The mixture was then centrifuged at 4000 r / min for 12 min, and the precipitate was collected. The precipitate was washed four times with anhydrous ethanol and then vacuum dried at 70 °C for 3 h to obtain the pretreated ZnS nanoparticles.

[0057] Surface modification: The pretreated ZnS nanoparticles were added to a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 4:1. After stirring evenly, 10 parts of 3-aminopropyltriethoxysilane (APTES) were added, and the pH was adjusted to 4-5 with acetic acid. In this example, the pH was preferably 4. The mixture was stirred at a constant temperature of 70°C for 3 hours at a stirring speed of 250 r / min. After the reaction was completed, the mixture was centrifuged at a speed of 5000 r / min for 18 minutes. The precipitate was collected, washed 4 times with anhydrous ethanol, and vacuum dried at 80°C for 4 hours to obtain surface-modified ZnS nanoparticles.

[0058] S3, LCD functional grafting: (1) Linker grafting (amidation reaction): The above-mentioned surface-aminated ZnS nanoparticles were dispersed in anhydrous DMF and ultrasonically dispersed for 25 min (power 90W). 10 parts adipic acid, 15 parts N,N'-dicyclohexylcarbodiimide (DCC) and 2 parts 4-dimethylaminopyridine (DMAP) were added, and the mixture was stirred at a constant temperature of 60℃ for 6 h under nitrogen protection at a stirring speed of 300 r / min. This reaction utilizes DCC / DMAP to catalyze the amidation reaction between one carboxyl group of adipic acid and the amino group on the surface of the nanoparticles to form an amide bond, thereby grafting the adipic acid linker to the surface of the nanoparticles and keeping the end of the linker free carboxyl group. After the reaction, the mixture was centrifuged (6000 r / min, 20 min), the precipitate was collected, washed three times each with DMF and anhydrous ethanol, and dried under vacuum to obtain the adipic acid-grafted ZnS nanoparticle intermediate.

[0059] (2) Liquid crystal module grafting (Steglich esterification reaction): The adipic acid-grafted ZnS nanoparticle intermediate was dispersed in anhydrous DMF and ultrasonically dispersed for 25 min (90 W). 20 parts of 4-cyano-4'-hydroxybiphenyl (liquid crystal module), 15 parts of DCC, and 2 parts of DMAP were added, and the mixture was stirred at a constant temperature of 60 °C for 8 h under nitrogen protection at a stirring speed of 300 r / min. This reaction utilizes the free carboxyl groups at the adipic acid end of the intermediate surface catalyzed by DCC / DMAP to undergo a Steglich esterification reaction with the hydroxyl groups of the liquid crystal module, forming ester bonds, and grafting the liquid crystal module onto the linker arm. After the reaction was completed, the precipitated dicyclohexylurea (DCU) was removed by filtration. The filtrate was centrifuged (6000 r / min, 20 min), the precipitate was collected, and washed five times with a mixed solvent of DMF and anhydrous ethanol at a volume ratio of 1:1 to remove unreacted liquid crystal building blocks and catalyst. The precipitate was then dried under vacuum at 90 °C for 5 h to obtain liquid crystal functionalized ZnS nanoparticles.

[0060] Example 2 The liquid crystal functionalized ZnS nanoparticles of this embodiment include a nanoparticle core, a surface modification layer bonded to the nanoparticle core, and a liquid crystal functionalized layer bonded to the surface modification layer. The liquid crystal functionalized layer includes connecting arms and liquid crystal units.

[0061] The difference from Example 1 is that the silane coupling agent is KH-570, and the surface modification steps are also different.

[0062] The liquid crystal functionalized ZnS nanoparticles were prepared by the following method: Nanoparticle core pretreatment: 100 ZnS nanoparticles with a particle size of 20-30 nm were added to anhydrous ethanol and dispersed for 40 min using an ultrasonic disperser with a dispersion power of 100 W to obtain a uniform dispersion. 2% dilute hydrochloric acid was added to the dispersion to adjust the pH to 4, and the mixture was stirred for 15 min. The mixture was then centrifuged at 4000 r / min for 12 min, and the precipitate was collected. The precipitate was washed four times with anhydrous ethanol and then vacuum dried at 70 °C for 3 h to obtain the pretreated ZnS nanoparticles.

[0063] Surface modification: 100 parts of pretreated ZnS nanoparticles were added to a 4:1 volume ratio ethanol / water mixed solvent; 10 parts of γ-methacryloyloxypropyltrimethoxysilane (KH-570) were added, the pH was adjusted to 4-5 with acetic acid, and the mixture was stirred at a constant temperature of 70℃ for 4 hours; after centrifugation and washing, and vacuum drying, KH-570 surface-modified ZnS nanoparticles were obtained. S3, LCD functional grafting: (1) Linker grafting (thiol-ene click reaction): The surface-modified ZnS nanoparticles were added to anhydrous DMF and ultrasonically dispersed for 25 min (90 W). 12 parts of mercaptopropionic acid (linker arm) and 0.5 parts of azobisisobutyronitrile (AIBN, thermal initiator) were added. Under nitrogen protection, the mixture was stirred at a constant temperature of 70 °C for 6 h at a stirring speed of 200 r / min. After the reaction was completed, the mixture was centrifuged (6000 r / min, 15 min), the precipitate was collected, washed three times with anhydrous ethanol, and vacuum dried to obtain ZnS nanoparticles (intermediate) with carboxyl groups attached to their surface.

[0064] (2) Grafting of liquid crystal building blocks (esterification reaction): The above intermediate was dispersed in anhydrous DMF, and 24 parts of 4-cyano-4′-hydroxybiphenyl (liquid crystal building blocks), 15 parts of DCC and 2 parts of DMAP were added. Under nitrogen protection, the mixture was stirred at a constant temperature of 60℃ for 8 h at a stirring speed of 300 r / min. After the reaction was completed, the mixture was centrifuged (6000 r / min, 20 min), the precipitate was collected, washed 5 times with a mixed solvent of DMF and anhydrous ethanol at a volume ratio of 1:1, and dried under vacuum at 90℃ for 5 h to obtain liquid crystal functionalized ZnS nanoparticles.

[0065] Example 3 The liquid crystal functionalized ZnS nanoparticles of this embodiment include a nanoparticle core, a surface modification layer bonded to the nanoparticle core, and a liquid crystal functionalized layer bonded to the surface modification layer. The liquid crystal functionalized layer includes connecting arms and liquid crystal units.

[0066] The difference from Example 1 is that the connecting arm is sebacic acid, and the liquid crystal functionalization grafting is also different.

[0067] The liquid crystal functionalized ZnS nanoparticles were prepared by the following method: Nanoparticle core pretreatment: 100 ZnS nanoparticles with a particle size of 20-30 nm were added to anhydrous ethanol and dispersed for 40 min using an ultrasonic disperser with a dispersion power of 100 W to obtain a uniform dispersion. 2% dilute hydrochloric acid was added to the dispersion to adjust the pH to 4, and the mixture was stirred for 15 min. The mixture was then centrifuged at 4000 r / min for 12 min, and the precipitate was collected. The precipitate was washed four times with anhydrous ethanol and then vacuum dried at 70 °C for 3 h to obtain the pretreated ZnS nanoparticles.

[0068] Surface modification: The pretreated ZnS nanoparticles were added to a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 4:1. After stirring evenly, 10 parts of 3-aminopropyltriethoxysilane (APTES) were added, and the mixture was stirred at a constant temperature of 70℃ for 3 hours at a stirring speed of 250 r / min. After the reaction was completed, the mixture was centrifuged at a speed of 5000 r / min for 18 minutes. The precipitate was collected, washed 4 times with anhydrous ethanol, and dried under vacuum at 80℃ for 4 hours to obtain surface-modified ZnS nanoparticles.

[0069] S3, LCD functional grafting: (1) Linker grafting (amidation reaction): The above-mentioned surface-aminated ZnS nanoparticles were dispersed in anhydrous DMF and ultrasonically dispersed for 25 min (power 90W). 8 parts sebacic acid, 15 parts N,N'-dicyclohexylcarbodiimide (DCC), and 2 parts 4-dimethylaminopyridine (DMAP) were added. Under nitrogen protection, the mixture was stirred at a constant temperature of 60℃ for 6 h at a stirring speed of 300 r / min. This reaction utilizes DCC / DMAP to catalyze the amidation reaction between a carboxyl group of sebacic acid and an amino group on the surface of the nanoparticles, forming an amide bond, thereby grafting sebacic acid linker arms onto the surface of the nanoparticles and retaining free carboxyl groups at the ends of the linker arms. After the reaction, the mixture was centrifuged (6000 r / min, 20 min), the precipitate was collected, washed three times each with DMF and anhydrous ethanol, and vacuum dried to obtain the sebacic acid-grafted ZnS nanoparticle intermediate.

[0070] (2) Liquid crystal module grafting (Steglich esterification reaction): The above-mentioned sebacic acid-grafted ZnS nanoparticle intermediate was dispersed in anhydrous DMF and ultrasonically dispersed for 25 min (power 90W). 20 parts of 4-cyano-4'-hydroxybiphenyl (liquid crystal module), 15 parts of DCC and 2 parts of DMAP were added, and the mixture was stirred at a constant temperature of 60℃ for 8 h under nitrogen protection at a stirring speed of 300 r / min. This reaction utilizes the free carboxyl groups at the sebacic acid end of the intermediate surface catalyzed by DCC / DMAP to undergo a Steglich esterification reaction with the hydroxyl groups of the liquid crystal module, forming ester bonds, and grafting the liquid crystal module onto the linker arm. After the reaction was completed, the precipitated dicyclohexylurea (DCU) was removed by filtration. The filtrate was centrifuged (6000 r / min, 20 min), the precipitate was collected, and washed five times with a mixed solvent of DMF and anhydrous ethanol at a volume ratio of 1:1 to remove unreacted liquid crystal building blocks and catalyst. The precipitate was then dried under vacuum at 90 °C for 5 h to obtain liquid crystal functionalized ZnS nanoparticles.

[0071] Example 4 The liquid crystal functionalized ZnS nanoparticles of this embodiment include a nanoparticle core, a surface modification layer bonded to the nanoparticle core, and a liquid crystal functionalized layer bonded to the surface modification layer, wherein the liquid crystal functionalized layer is a liquid crystal unit.

[0072] The difference from Example 1 is that there is no connecting arm, the liquid crystal unit is 4-methoxybiphenyl-4'-carboxylic acid, and the liquid crystal functionalization grafting steps are different accordingly, using the amidation reaction direct grafting method.

[0073] The liquid crystal functionalized ZnS nanoparticles were prepared by the following method: Nanoparticle core pretreatment: 100 ZnS nanoparticles with a particle size of 20-30 nm were added to anhydrous ethanol and dispersed for 40 min using an ultrasonic disperser with a dispersion power of 100 W to obtain a uniform dispersion. 2% dilute hydrochloric acid was added to the dispersion to adjust the pH to 4, and the mixture was stirred for 15 min. The mixture was then centrifuged at 4000 r / min for 12 min, and the precipitate was collected. The precipitate was washed four times with anhydrous ethanol and then vacuum dried at 70 °C for 3 h to obtain the pretreated ZnS nanoparticles.

[0074] Surface modification: The pretreated ZnS nanoparticles were added to a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 4:1. After stirring evenly, 10 parts of 3-aminopropyltriethoxysilane (APTES) were added, and the mixture was stirred at a constant temperature of 70℃ for 3 hours at a stirring speed of 250 r / min. After the reaction was completed, the mixture was centrifuged at a speed of 5000 r / min for 18 minutes. The precipitate was collected, washed 4 times with anhydrous ethanol, and dried under vacuum at 80℃ for 4 hours to obtain surface-modified ZnS nanoparticles.

[0075] Liquid crystal functionalization grafting: Surface-modified ZnS nanoparticles were added to DMF and ultrasonically dispersed for 25 min. EDC (12 parts) and NHS (8 parts) were added and activated at room temperature for 30 min. 4-Methoxybiphenyl-4'-carboxylic acid (20 parts) were added and reacted at room temperature for 24 h with a stirring speed of 250 r / min. After the reaction, the mixture was centrifuged (6000 r / min, 20 min), washed 5 times with a DMF / ethanol mixed solvent, and vacuum dried at 90 °C for 5 h to obtain liquid crystal functionalized ZnS nanoparticles.

[0076] Example 5 The liquid crystal functionalized ZnS nanoparticles of this embodiment include a nanoparticle core, a surface modification layer bonded to the nanoparticle core, and a liquid crystal functionalized layer bonded to the surface modification layer, wherein the liquid crystal functionalized layer is a liquid crystal unit.

[0077] The difference from Example 1 is that there is no connecting arm, the silane coupling agent is γ-mercaptopropyltrimethoxysilane (MPTMS), the liquid crystal unit is 4-allylbiphenyl, and the surface modification step and liquid crystal functionalization grafting step are also different. The liquid crystal functionalization grafting adopts the mercapto-olefin click reaction direct grafting method.

[0078] The liquid crystal functionalized ZnS nanoparticles were prepared by the following method: Nanoparticle core pretreatment: 100 ZnS nanoparticles with a particle size of 20-30 nm were added to anhydrous ethanol and dispersed for 40 min using an ultrasonic disperser with a dispersion power of 100 W to obtain a uniform dispersion. 2% dilute hydrochloric acid was added to the dispersion to adjust the pH to 4, and the mixture was stirred for 15 min. The mixture was then centrifuged at 4000 r / min for 12 min, and the precipitate was collected. The precipitate was washed four times with anhydrous ethanol and then vacuum dried at 70 °C for 3 h to obtain the pretreated ZnS nanoparticles.

[0079] Surface modification: The pretreated ZnS nanoparticles were added to a mixed solvent of anhydrous ethanol and deionized water at a volume ratio of 5:1 and stirred until homogeneous. Then, 15 parts of γ-mercaptopropyltrimethoxysilane (MPTMS) were added and stirred at a constant temperature of 70℃ for 3 hours at a stirring speed of 250 r / min. After the reaction was completed, the mixture was centrifuged at a speed of 5000 r / min for 18 minutes. The precipitate was collected, washed four times with anhydrous ethanol, and dried under vacuum at 80℃ for 4 hours to obtain surface-thiolized ZnS nanoparticles.

[0080] Liquid crystal functionalization grafting: Surface-thiolized ZnS nanoparticles were added to DMF solvent and ultrasonically dispersed for 25 min at 90 W. 20 parts of 4-allylbiphenyl (liquid crystal building blocks) and 0.5 parts of dimethylbenzoyl ketal (DMPA, as a photoinitiator) were added, and the mixture was reacted under 365 nm UV irradiation for 30 min with a stirring speed of 200 r / min. After the reaction, the mixture was centrifuged at 6000 r / min for 22 min, and the precipitate was collected and washed five times with a 1:1 (v / v) mixture of DMF and anhydrous ethanol to remove unreacted liquid crystal building blocks and photoinitiator residues. Finally, the mixture was vacuum dried at 90 °C for 5 h to obtain liquid crystal functionalized ZnS nanoparticles.

[0081] Example 6 The liquid crystal functionalized Au nanoparticles of this embodiment include a nanoparticle core, a surface modification layer bonded to the nanoparticle core, and a liquid crystal functionalized layer bonded to the surface modification layer. The liquid crystal functionalized layer is a liquid crystal unit. The liquid crystal functionalized Au nanoparticles are prepared by the following method (using the direct grafting method of amidation reaction): Nanoparticle core pretreatment: 100 portions of Au nanoparticles with a particle size of 30-40 nm were added to anhydrous ethanol and dispersed for 30 min using an ultrasonic disperser with a power of 120 W to obtain a uniform dispersion. 3% (w / w) dilute hydrochloric acid was added to the dispersion to adjust the pH to 3.5. The mixture was stirred for 12 min, centrifuged at 3500 r / min for 10 min, and the precipitate was collected. The precipitate was washed three times with anhydrous ethanol and dried under vacuum at 65 °C for 2.5 h to obtain the pretreated Au nanoparticles.

[0082] Surface modification: The pretreated Au nanoparticles were added to anhydrous ethanol, and 15 parts of mercaptoundecanoic acid were added. The mixture was stirred at room temperature for 24 h, centrifuged at 4500 r / min for 15 min, the precipitate was collected, washed three times with anhydrous ethanol, and dried under vacuum at 85 °C for 3.5 h to obtain surface-modified Au nanoparticles (carboxyl groups were introduced on the surface).

[0083] Liquid crystal functionalization grafting: Surface-modified Au nanoparticles were added to DMF and ultrasonically dispersed for 25 min at 90 W. 12 parts EDC and 8 parts NHS were added and activated at room temperature for 30 min. Then, 20 parts 4-aminobiphenyl (liquid crystal building blocks) were added and reacted at room temperature for 12 h with a stirring speed of 250 r / min. After the reaction, the mixture was centrifuged at 6000 r / min for 22 min. The precipitate was collected and washed 5 times with a 1:1 mixture of DMF and anhydrous ethanol to remove unreacted liquid crystal building blocks, EDC, and NHS. Finally, the mixture was vacuum dried at 90 °C for 5 h to obtain liquid crystal functionalized Au nanoparticles.

[0084] Example 7 The holographic polymer-dispersed liquid crystal material of this embodiment comprises, by weight: 52 parts of trimethylolpropane triacrylate, 40 parts of E7 liquid crystal, 5 parts of liquid crystal functionalized ZnS nanoparticles provided in Example 1, 1.5 parts of visible light initiator RB, 4 parts of N-phenylglycine (NPG, as a co-initiator), and 3 parts of ethylene glycol dimethacrylate.

[0085] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: The mixture was stirred for 45 minutes at a stirring speed of 250 r / min, ultrasonically dispersed for 25 minutes at a dispersion power of 110 W, and coated with a thickness of 10 μm. It was then irradiated in a holographic field with a wavelength of 532 nm and a light intensity of 20 mW / cm² for 2 minutes and allowed to cool naturally to obtain the HPDLC device.

[0086] The refractive index modulation of the HPDLC device obtained in this embodiment is 0.152.

[0087] Example 8 The holographic polymer-dispersed liquid crystal material of this embodiment, by weight, includes: 48 parts of triethylene glycol diacrylate (TEGDA), 45 parts of E7 liquid crystal, 2 parts of liquid crystal functionalized ZnS nanoparticles provided in Example 2, 1.5 parts of visible light initiator RB, 4 parts of N-phenylglycine (NPG, as a co-initiator), 6 parts of N-ethylpyrrolidone (NVP, as a solvent), and 3 parts of trimethylolpropane triacrylate (TMPTA, crosslinking agent).

[0088] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: Add the above components to a beaker and stir at room temperature for 50 min (stirring speed 280 r / min); ultrasonic dispersion: 20 min (power 100 W); coating: coating thickness 12 μm; photopolymerization: holographic field irradiation at wavelength 532 nm and light intensity 15 mW / cm² for 2 min, followed by natural cooling to obtain HPDLC device.

[0089] The refractive index modulation of the HPDLC device obtained in this embodiment is 0.156.

[0090] Example 9 The holographic polymer-dispersed liquid crystal material of this embodiment comprises, by weight: 48 parts of triethylene glycol diacrylate (TEGDA), 45 parts of E7 liquid crystal, 2 parts of liquid crystal functionalized ZnS nanoparticles provided in Example 3, 1.5 parts of visible light initiator RB, 4 parts of N-phenylglycine (NPG, as a co-initiator), 6 parts of N-ethylpyrrolidone (NVP, as a solvent), and 3 parts of trimethylolpropane triacrylate (TMPTA, crosslinking agent).

[0091] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: Add the above components to a beaker and stir at room temperature for 50 min (stirring speed 280 r / min); ultrasonic dispersion: 20 min (power 100 W); coating: coating thickness 12 μm; photopolymerization: holographic field irradiation at wavelength 532 nm and light intensity 15 mW / cm² for 2 min, followed by natural cooling to obtain HPDLC device.

[0092] The refractive index modulation of the HPDLC device obtained in this embodiment is 0.158.

[0093] Example 10 The holographic polymer-dispersed liquid crystal material of this embodiment comprises, by weight, 48 parts of triethylene glycol diacrylate (TEGDA), 45 parts of E7 liquid crystal, 2 parts of liquid crystal functionalized ZnS nanoparticles provided in Example 4, 1.5 parts of visible light initiator RB, 4 parts of N-phenylglycine (NPG, as a co-initiator), 6 parts of N-ethylpyrrolidone (NVP, as a solvent), and 3 parts of trimethylolpropane triacrylate (TMPTA, crosslinking agent).

[0094] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: Add the above components to a beaker and stir at room temperature for 50 min (stirring speed 280 r / min); ultrasonic dispersion: 20 min (power 100 W); coating: coating thickness 12 μm; photopolymerization: holographic field irradiation at wavelength 532 nm and light intensity 15 mW / cm² for 2 min, followed by natural cooling to obtain HPDLC device.

[0095] The refractive index modulation of the HPDLC device obtained in this embodiment is 0.153.

[0096] Example 11 The holographic polymer-dispersed liquid crystal material of this embodiment, by weight, includes: 48 parts of triethylene glycol diacrylate (TEGDA), 45 parts of E7 liquid crystal, 2 parts of liquid crystal functionalized ZnS nanoparticles provided in Example 5, 1.5 parts of visible light initiator RB, 4 parts of N-phenylglycine (NPG, as a co-initiator), 6 parts of N-ethylpyrrolidone (NVP, as a solvent), and 3 parts of trimethylolpropane triacrylate (TMPTA, crosslinking agent).

[0097] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: Add the above components to a beaker and stir at room temperature for 50 min (stirring speed 280 r / min); ultrasonic dispersion: 20 min (power 100 W); coating: coating thickness 12 μm; photopolymerization: holographic field irradiation at wavelength 532 nm and light intensity 15 mW / cm² for 2 min, followed by natural cooling to obtain HPDLC device.

[0098] The refractive index modulation of the HPDLC device obtained in this embodiment is 0.150.

[0099] Example 12 The holographic polymer-dispersed liquid crystal material of this embodiment, by weight, includes: 48 parts of triethylene glycol diacrylate (TEGDA), 45 parts of E7 liquid crystal, 2 parts of liquid crystal functionalized Au nanoparticles provided in Example 6, 1.5 parts of visible light initiator RB, 4 parts of N-phenylglycine (NPG, as a co-initiator), 6 parts of N-ethylpyrrolidone (NVP, as a solvent), and 3 parts of trimethylolpropane triacrylate (TMPTA, crosslinking agent).

[0100] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: Add the above components to a beaker and stir at room temperature for 50 min (stirring speed 280 r / min); ultrasonic dispersion: 20 min (power 100 W); coating: coating thickness 12 μm; photopolymerization: holographic field irradiation at wavelength 532 nm and light intensity 15 mW / cm² for 2 min, followed by natural cooling to obtain HPDLC device.

[0101] The refractive index modulation of the HPDLC device obtained in this embodiment is 0.151.

[0102] Comparative Example 1 The holographic polymer-dispersed liquid crystal material of this comparative example, by mass parts, includes: 52 parts of trimethylolpropane triacrylate, 40 parts of E7 liquid crystal, 5 parts of ZnS nanoparticles, 1.5 parts of visible light initiator RB, 4 parts of N-phenylglycine (NPG, as a co-initiator), and 3 parts of ethylene glycol dimethacrylate.

[0103] The ZnS nanoparticles underwent the nanoparticle core pretreatment described in Example 1, but did not undergo surface modification or liquid crystal functionalization grafting.

[0104] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: All components of the above-mentioned holographic polymer-dispersed liquid crystal material were mixed and stirred for 45 minutes at a stirring speed of 250 r / min, ultrasonically dispersed for 25 minutes at a dispersion power of 110 W, and coated with a thickness of 10 μm. The material was then irradiated in a holographic field with a wavelength of 532 nm and a light intensity of 20 mW / cm² for 2 minutes and allowed to cool naturally to obtain an HPDLC device.

[0105] The refractive index modulation of the HPDLC device obtained in this comparative example is 0.105.

[0106] Comparative Example 2 The holographic polymer-dispersed liquid crystal material of this comparative example, by mass parts, includes: 52 parts of trimethylolpropane triacrylate, 40 parts of E7 liquid crystal, 5 parts of ZnS nanoparticles, 1.2 parts of benzophenone, and 3 parts of ethylene glycol dimethacrylate.

[0107] The ZnS nanoparticles underwent the nanoparticle core pretreatment and surface modification treatment as described in Example 1, but did not undergo liquid crystal functionalization grafting treatment.

[0108] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: The mixture was stirred for 45 minutes at a stirring speed of 250 r / min, ultrasonically dispersed for 25 minutes at a dispersion power of 110 W, and coated with a thickness of 10 μm. It was then irradiated in a holographic field with a wavelength of 532 nm and a light intensity of 20 mW / cm² for 2 minutes and allowed to cool naturally to obtain the HPDLC device.

[0109] The refractive index modulation of the HPDLC device obtained in this comparative example is 0.118.

[0110] Comparative Example 3 The holographic polymer-dispersed liquid crystal material of this comparative example, by mass parts, includes: 52 parts of trimethylolpropane triacrylate, 40 parts of E7 liquid crystal, 5 parts of liquid crystal functionalized ZnS nanoparticles, 1.2 parts of benzophenone, and 3 parts of ethylene glycol dimethacrylate.

[0111] The preparation method of liquid crystal functionalized ZnS nanoparticles is basically the same as that in Example 1, except that: in this comparative example, 3-aminopropyltriethoxysilane is 2 parts, 4-cyano-4'-hydroxybiphenyl is 4 parts, and adipic acid is 1 part.

[0112] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: The mixture was stirred for 45 minutes at a stirring speed of 250 r / min, ultrasonically dispersed for 25 minutes at a dispersion power of 110 W, and coated with a thickness of 10 μm. It was then irradiated in a holographic field with a wavelength of 532 nm and a light intensity of 20 mW / cm² for 2 minutes and allowed to cool naturally to obtain the HPDLC device.

[0113] The refractive index modulation of the HPDLC device obtained in this comparative example is 0.110.

[0114] Comparative Example 4 The holographic polymer-dispersed liquid crystal material of this comparative example, by mass parts, includes: 52 parts of trimethylolpropane triacrylate, 40 parts of E7 liquid crystal, 5 parts of liquid crystal functionalized ZnS nanoparticles, 1.2 parts of benzophenone, and 3 parts of ethylene glycol dimethacrylate.

[0115] The preparation method of liquid crystal functionalized ZnS nanoparticles is basically the same as that in Example 1, except that: the amount of 3-aminopropyltriethoxysilane, 4-cyano-4'-hydroxybiphenyl, and adipic acid in this comparative example is 30 parts.

[0116] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: The mixture was stirred for 45 minutes at a stirring speed of 250 r / min, ultrasonically dispersed for 25 minutes at a dispersion power of 110 W, and coated with a thickness of 10 μm. It was then irradiated in a holographic field with a wavelength of 532 nm and a light intensity of 20 mW / cm² for 2 minutes and allowed to cool naturally to obtain HPDLC material.

[0117] The refractive index modulation of the HPDLC device obtained in this comparative example is 0.101.

[0118] Comparative Example 5 The holographic polymer-dispersed liquid crystal material of this comparative example, by mass parts, includes: 52 parts of trimethylolpropane triacrylate, 40 parts of E7 liquid crystal, 0.5 parts of liquid crystal functionalized ZnS nanoparticles, 1.2 parts of benzophenone, and 3 parts of ethylene glycol dimethacrylate.

[0119] The preparation method of liquid crystal functionalized ZnS nanoparticles is exactly the same as that in Example 1.

[0120] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: The mixture was stirred for 45 minutes at a stirring speed of 250 r / min, ultrasonically dispersed for 25 minutes at a dispersion power of 110 W, and coated with a thickness of 10 μm. It was then irradiated in a holographic field with a wavelength of 532 nm and a light intensity of 20 mW / cm² for 2 minutes and allowed to cool naturally to obtain HPDLC material.

[0121] The refractive index modulation of the HPDLC device obtained in this comparative example is 0.122.

[0122] Comparative Example 6 The holographic polymer-dispersed liquid crystal material of this comparative example, by mass parts, includes: 52 parts of trimethylolpropane triacrylate, 40 parts of E7 liquid crystal, 15 parts of liquid crystal functionalized ZnS nanoparticles, 1.2 parts of benzophenone, and 3 parts of ethylene glycol dimethacrylate.

[0123] The preparation method of liquid crystal functionalized ZnS nanoparticles is exactly the same as that in Example 1.

[0124] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: The mixture was stirred for 45 minutes at a stirring speed of 250 r / min, ultrasonically dispersed for 25 minutes at a dispersion power of 110 W, and coated with a thickness of 10 μm. It was then irradiated in a holographic field with a wavelength of 532 nm and a light intensity of 20 mW / cm² for 2 minutes and allowed to cool naturally to obtain the HPDLC device.

[0125] The refractive index modulation of the HPDLC device obtained in this comparative example is 0.106.

[0126] Comparative Example 7 The holographic polymer-dispersed liquid crystal material of this comparative example, by mass parts, includes: 52 parts of trimethylolpropane triacrylate, 40 parts of E7 liquid crystal, 15 parts of liquid crystal functionalized ZnS nanoparticles, 1.2 parts of benzophenone, and 3 parts of ethylene glycol dimethacrylate.

[0127] The preparation method of liquid crystal functionalized ZnS nanoparticles is basically the same as that in Example 1, except that the liquid crystal unit is cholesterol succinate monoester.

[0128] HPDLC devices were fabricated using the above-mentioned holographic polymer-dispersed liquid crystal material: The mixture was stirred for 45 minutes at a stirring speed of 250 r / min, ultrasonically dispersed for 25 minutes at a dispersion power of 110 W, and coated with a thickness of 10 μm. It was then irradiated in a holographic field with a wavelength of 532 nm and a light intensity of 20 mW / cm² for 2 minutes and allowed to cool naturally to obtain the HPDLC device.

[0129] The refractive index modulation of the HPDLC device obtained in this comparative example is 0.105.

[0130] The diffraction efficiency of the HPDLC devices in Examples 7-12 and Comparative Examples 1-7 was tested using a grating diffraction efficiency tester.

[0131] The test results are shown in Table 2: Table 2. Diffraction efficiency test results of HPDLC devices in Examples 7-12 and Comparative Examples 1-7

[0132] Example 2 used KH-570 as a silane coupling agent. KH-570 contains polymerizable acrylate double bonds, which can not only be grafted onto the surface of nanoparticles through siloxane bonds, but also copolymerize with acrylate monomers in the HPDLC system through double bonds, further enhancing the binding force between nanoparticles and the polymer matrix. The chemically bonded copolymerization significantly enhances the anchoring effect of nanoparticles in the polymer matrix, effectively inhibiting the migration and aggregation of nanoparticles in the system and ensuring long-term dispersion stability. Secondly, nanoparticles, as physical crosslinking points, can improve the crosslinking density and mechanical strength of the polymer network, improving the structural stability of the HPDLC grating. In addition, stronger interfacial bonding helps maintain a regular phase separation structure during holographic photopolymerization, reducing light scattering loss caused by interfacial debonding, thereby further improving diffraction efficiency and optical uniformity.

[0133] Example 3 used sebacic acid as a linker arm. Sebacic acid has a carbon chain length of 10 carbons, and a sufficiently long linker arm can provide more free movement space for the liquid crystal building blocks, which is conducive to the formation of a more ordered arrangement of the liquid crystal building blocks on the surface of nanoparticles, and is expected to further improve the compatibility and synergistic effect with the liquid crystal molecules in the system.

[0134] Example 4 uses 4-methoxybiphenyl-4'-carboxylic acid as the liquid crystal unit. 4-methoxybiphenyl-4'-carboxylic acid contains a biphenyl structure and a methoxy end group, which has a similar structure to the components in the E7 liquid crystal. It exhibits good compatibility with the system's liquid crystal, and using this liquid crystal unit eliminates the need for connecting arms, further simplifying the process.

[0135] Example 12 uses TEGDA as a polymer monomer, and with a high liquid crystal content and light conditions, Au functionalized nanoparticles can still achieve good diffraction efficiency in this system, indicating that the present invention has wide formulation adaptability.

[0136] In Comparative Example 1, the ZnS nanoparticles underwent only pretreatment without modification or liquid crystal functionalization grafting. Lacking organic functional groups on their surface, they exhibit poor interfacial compatibility with acrylate monomers and liquid crystal molecules, making them prone to aggregation. This hinders the migration of liquid crystals within the system and also makes it difficult for the nanoparticles to migrate with the liquid crystal molecules to the dark region for enrichment. The phase separation structure is disrupted, affecting the improvement of the refractive index in the liquid crystal-rich region and reducing optical uniformity. The ZnS nanoparticles in Comparative Example 2 underwent pretreatment and surface modification but were not grafted with liquid crystal functionalization. The nanoparticles modified only with silane coupling agents (such as APTES) after pretreatment possessed polar functional groups such as amino groups on their surface. This modification can improve the compatibility between the nanoparticles and the polymer matrix to some extent and reduce aggregation; however, their surface lacks liquid crystal building blocks similar in structure to liquid crystal molecules, making it difficult for them to migrate to the dark region along with the liquid crystal molecules during photopolymerization, thus limiting their effect on improving the refractive index of the liquid crystal-rich region.

[0137] In Comparative Example 3, the amounts of silane coupling agent and liquid crystal functionalized layer in the ZnS nanoparticles were too small. The silane coupling agent had insufficient coverage on the nanoparticle surface, resulting in uneven liquid crystal grafting, with some nanoparticles showing excessively low or no liquid crystal grafting. Simultaneously, the insufficient liquid crystal functionalized layer led to inadequate liquid crystal cell density on the nanoparticle surface, limiting the improvement in compatibility with the system's liquid crystal molecules.

[0138] In Comparative Example 4, the ZnS nanoparticles contained excessive amounts of silane coupling agent and liquid crystal functionalized layer. Excessive silane coupling agent can cause self-polymerization on the surface of nanoparticles, forming a multi-layer cross-linked structure, leading to cross-linking and aggregation between nanoparticles through siloxane bridging; excessive grafting of liquid crystal units results in an excessively thick organic layer, and the long liquid crystal chains on the surface of each nanoparticle become entangled with each other, also leading to aggregation.

[0139] In Comparative Example 5, the amount of liquid crystal functionalized ZnS nanoparticles added was too low, resulting in insufficient number of functionalized liquid crystal nanoparticles in the system and limited effect on improving the refractive index of the liquid crystal-rich region.

[0140] In Comparative Example 6, the amount of liquid crystal functionalized ZnS nanoparticles added was too high. Excessive nanoparticles would interfere with the normal phase separation process of HPDLC, hinder the diffusion of monomers to the bright area and the migration of liquid crystals to the dark area, resulting in abnormal crosslinking density of the polymer network and affecting the integrity of the grating structure.

[0141] In Comparative Example 7, the ZnS nanoparticles used cholesterol-based liquid crystal building blocks, which differ significantly from the liquid crystal chemical structure in the HPDLC system. The interaction between the liquid crystal layer on the surface of the nanoparticles and the liquid crystal molecules in the system is weak, making it impossible to form an effective compatible interface. Consequently, the nanoparticles are difficult to migrate to the dark region for enrichment along with the liquid crystal molecules during photopolymerization.

[0142] 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 liquid crystal functionalized nanoparticle, characterized in that, It includes a nanoparticle core, a surface modification layer bonded to the nanoparticle core, and a liquid crystal functionalized layer bonded to the surface modification layer.

2. The liquid crystal functionalized nanoparticles according to claim 1, characterized in that, The nanoparticle core is a high-refractive-index nanoparticle with a refractive index value greater than or equal to 1.8; and / or The surface-modified layer is formed by attaching a surface modifier to the nanocore, and the surface modifier is a silane coupling agent.

3. The liquid crystal functionalized nanoparticles according to claim 1, characterized in that, The liquid crystal functionalized layer includes liquid crystal units and connecting arms. The liquid crystal units are grafted onto the surface modified layer via the connecting arms, and the connecting arms have at least one active functional group selected from carboxyl, isocyanate, mercapto, alkenyl, and azide groups.

4. The liquid crystal functionalized nanoparticles according to claim 3, characterized in that, The connecting arm is selected from one or more of the following: bisaccharide, sebacic acid, mercaptopropionic acid, mercaptoundecanoic acid, isocyanate propyltriethoxysilane, 4-pentenoic acid, and propynic acid.

5. The liquid crystal functionalized nanoparticles according to claim 1, characterized in that, The liquid crystal functionalized layer is composed of liquid crystal units, which are directly grafted onto the surface modified layer. The liquid crystal units have at least one active functional group selected from hydroxyl, amino, carboxyl, alkenyl and thiol groups.

6. A method for preparing liquid crystal functionalized nanoparticles, used to prepare the liquid crystal functionalized nanoparticles according to any one of claims 3 or 4, characterized in that, Includes the following steps: S1. Nanoparticle core pretreatment: The nanoparticle cores are dispersed in an organic solvent, and then treated with acid to remove impurities and hydroxyl contaminants from the surface of the nanoparticle cores. After centrifugation, the precipitate is collected, washed, and dried to obtain the pretreated nanoparticle cores. S2. Surface modification: The pretreated nanoparticle cores are dispersed in a solvent, a surface modifier is added to react, after the reaction is completed, the precipitate is collected by centrifugation, washed, and dried to obtain surface-modified nanoparticles. S3. Liquid crystal functional grafting, including the following steps: S31. React the connecting arm with the surface-modified nanoparticles to graft the connecting arm onto the surface-modified layer to obtain an intermediate. S32. React the liquid crystal unit with the intermediate to graft the liquid crystal unit onto the connecting arm to obtain liquid crystal functionalized nanoparticles. The amount of the nanoparticle core is 95-110 parts, the amount of the surface modifier is 5-20 parts, and the total amount of the liquid crystal unit and the connecting arm is 10-40 parts.

7. The method for preparing liquid crystal functionalized nanoparticles according to claim 6, characterized in that, The mass ratio of the liquid crystal element to the connecting arm is (2~3):

1.

8. A method for preparing liquid crystal functionalized nanoparticles, used to prepare the liquid crystal functionalized nanoparticles of claim 5, characterized in that, Includes the following steps: S1. Nanoparticle core pretreatment: The nanoparticle cores are dispersed in an organic solvent, and then treated with acid to remove impurities and hydroxyl contaminants from the surface of the nanoparticle cores. After centrifugation, the precipitate is collected, washed, and dried to obtain the pretreated nanoparticle cores. S2. Surface modification: The pretreated nanoparticle cores are dispersed in a solvent, a surface modifier is added to react, after the reaction is completed, the precipitate is collected by centrifugation, washed, and dried to obtain surface-modified nanoparticles. S3. Liquid crystal functionalization grafting: Liquid crystal units are grafted onto the surface modification layer using a direct grafting method, wherein the direct grafting method is one of the following: direct amidation reaction, direct esterification reaction, mercapto-alkene click reaction, hydrosilylation reaction, and direct coordination reaction. The amount of the nanoparticle core is 95-110 parts, the amount of the surface modifier is 5-20 parts, and the amount of the liquid crystal unit is 10-40 parts.

9. A holographic polymer-dispersed liquid crystal material, characterized in that, By weight, it comprises 40-60 parts of photopolymerizable monomer, 30-50 parts of liquid crystal, 0.5-2 parts of photoinitiator, 1-5 parts of other additives, and 1-10 parts of liquid crystal functionalized nanoparticles as described in any one of claims 1-5.

10. A method for fabricating an HPDLC device, characterized in that, Includes the following steps: S1. Mix and disperse all components of the holographic polymer-dispersed liquid crystal material according to claim 9 to form a mixed system; S2. Coat the mixture onto a glass substrate; S3. Expose the glass substrate in a holographic interference light field and then cool it.

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