Holographic polymer dispersed liquid crystal material based on chain transfer reaction

Abstract

The invention discloses a holographic polymer dispersed liquid crystal material based on chain transfer reaction, and belongs to the technical field of holographic optics. The acrylic monomer, the photoinitiator, the photosensitizer, the liquid crystal and the chain transfer agent are mixed according to the optimal mass ratio to prepare the holographic polymer grating material, the holographic grating performance of the material is remarkably improved by introducing the reversible addition-fragmentation chain transfer polymerization component, and compared with a material without using the reversible addition-fragmentation chain transfer agent, the holographic grating performance of the material is remarkably improved. And the refractive index modulation degree is improved by 58%. The material has a relatively high refractive index modulation degree, is simple to prepare and low in cost, obviously improves the optical performance, and has a very high application value in the fields of holographic optical storage and AR intelligent display equipment.

Description

Technical Field

[0001] The invention relates to a holographic polymer dispersed liquid crystal material based on reversible addition-fragmentation chain transfer polymerization, belonging to the technical field of holographic optics. Background Art

[0002] With the development of science and technology, especially the rapid development of information science and technology in recent years, virtual reality (VR) and augmented reality (AR) technology have become one of the hot areas of high-tech development in the world. Virtual images are displayed on devices with perspective capabilities through optical systems. These virtual information can be in the form of text, graphics, videos, etc., aiming to provide additional auxiliary information to enhance users' understanding and interaction with the real world. VR / AR devices come in various forms, and the specific form is highly dependent on the optical components that transmit light signals. Compared with traditional optical components, optical components based on holographic polymer materials are the key to miniaturization and lightweight of VR / AR optical components. The performance of holographic polymer materials directly affects the VR / AR display effect. Optimizing the performance of holographic polymer materials is of great significance to promoting the advancement of advanced VR / AR technology.

[0003] Holographic photopolymer is a new type of polymer material that initiates monomer polymerization based on holographic interference technology. It is an important component of holographic optical elements. It is widely used in many fields such as augmented reality, data storage, holographic waveguides, and sensors due to its low price, rich variety, and simple preparation process. Among them, the refractive index modulation of the volume holographic grating produced by holographic interference exposure is a key performance indicator that determines the application potential of the material in holographic optical elements. In order to further improve the refractive index modulation of photopolymers, many studies are devoted to preparing new composite materials by incorporating additional functional components into photopolymer materials, such as nanoparticles, liquid crystals, and matrices.

[0004] The combination of liquid crystal and photopolymer adds a new property, which makes it have the easy processability of polymer, the unique electro-optical properties of liquid crystal and controllable optical diffraction. Holographic polymer dispersed liquid crystals (HPDLCs) composite materials are prepared by the principle of photopolymerization-induced phase separation and have a periodic ordered structure. Figure 1As shown in the figure, before exposure, the monomer and liquid crystal are evenly distributed in the material. During exposure, photopolymerization is initiated in the bright area of ​​the interference pattern generated by the coherent laser beam, prompting the monomer to diffuse from the dark area to the bright area to participate in the polymerization reaction. At the same time, due to the effect of chemical potential, the liquid crystal diffuses to the dark area, and finally forms a periodic distribution of polymer and liquid crystal, causing refractive index modulation and generating a grating. Therefore, the refractive index difference of the grating and the degree of separation between the liquid crystal and the polymer determine the refractive index modulation of the grating. However, the mismatch between the photopolymerization reaction rate and the liquid crystal diffusion rate limits the high performance and multifunctionality of HPDLC.

[0005] From the current research status at home and abroad, it can be seen that in order to improve the properties of HPDLC, on the one hand, new components such as nanoparticles, quantum dots, nanotubes, etc. can be introduced into the polymer composite system, and on the other hand, the components of HPDLC can be optimized, such as adding chain transfer agents or free radical scavengers, changing photoinitiators, designing new monomers, and introducing chemical cross-linking agents, etc. At present, there is still a gap in the research of HPDLC composite materials based on chain transfer agent doping.

[0006] The polymerization mechanism of photopolymer is light-initiated free radical polymerization. First, the photoinitiator absorbs photons to generate initial free radicals, which polymerize with monomers to form monomer free radicals. The monomer free radicals and a large number of monomers are added to form a chain growth reaction. When two long chains meet, chain termination will occur. Therefore, chain transfer agents are introduced into the polymer system to improve the holographic performance by reducing the molecular weight and polymerization rate of the growing polymer chain during the polymerization process. Summary of the invention

[0007] The object of the present invention is to provide a preparation and application of a holographic polymer dispersed liquid crystal material based on reversible addition-fragmentation chain transfer polymerization based on the above considerations.

[0008] A holographic polymer dispersed liquid crystal material based on reversible addition-fragmentation chain transfer polymerization, characterized in that the raw material composition includes the following as shown in Table 1:

[0009] Table 1: Material composition and its function

[0010]

[0011] The acrylate monomer is selected from tricyclodecane dimethanol diacrylate (A-DCP); the liquid crystal is selected from GXP-6037; the photoinitiator is selected from N-phenylglycine (NPG); the photosensitizer is selected from Rose Bengal; and the reversible addition-fragmentation chain transfer agent is selected from 4-cyano-4-[[(dodecylthiocarbonyl)-thio]pentanoic acid (CDTPA).

[0012] Preparation of holographic polymer dispersed liquid crystal material based on reversible addition-fragmentation chain transfer polymerization:

[0013] (1) Prepare a holographic polymer dispersed liquid crystal polymer solution. In a clean brown bottle, mix the acrylic monomer, liquid crystal, photosensitizer, photoinitiator and chain transfer agent in proportion and stir until they are uniform and transparent; prepare a clean quartz substrate, use a pipette to drop the prepared material on the surface of the quartz substrate, then place another quartz substrate on the material and fix it with a binder clip.

[0014] (2) The wavelength is 532nm and the exposure intensity is 40mW / cm 2 Double interference lithography was performed with coherent light, and the photochemical reaction under exposure generated a polymer grating film. By comparing the films doped with and without chain transfer agents, it was proved that the chain transfer agent played a role in improving the holographic performance of the material. At the same time, the refractive index modulation degree of the HPDLC film doped with 0.5wt.% chain transfer agent can be as high as 0.07.

[0015] The material of the invention is applied to holographic optical storage and holographic waveguide display materials.

[0016] The application of the high-performance holographic polymer dispersed liquid crystal composite film material based on chain transfer agent doping obtained by the present invention has great potential for application in AR intelligent display devices.

[0017] Advantages of the present invention

[0018] 1. By adding a reversible addition-fragmentation chain transfer polymerization component to the holographic polymer dispersed liquid crystal composite system, the holographic grating performance of the material is significantly improved. Compared with the material without the reversible addition-fragmentation chain transfer agent, its refractive index modulation is increased by 58%.

[0019] 2. The preparation process is simple, the cost is low, and the optical performance is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of HPDLC formation;

[0021] Figure 2 Reagent molecular structure (a) tricyclodecane dimethanol diacrylate (A-DCP) (b) Rose Bengal (Rose Bengal) (c) N-phenylglycine (NPG) (d) 4-cyano-4-[[(dodecylsulfanylthiocarbonyl)thio]pentanoic acid (CDTPA);

[0022] Figure 3 Holographic grating recording optical path;

[0023] Figure 4 (a) The grating period is 700 nm and the exposure intensity is 40 mW / cm 2(a) The refractive index modulation curve with time at different CDTPA doping concentrations; (b) The refractive index modulation curve with CDTPA concentration;

[0024] Figure 5 Transmission grating photograph recorded at a CDTPA doping concentration of 0.5 wt.%. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with examples, but the present invention is not limited to the following examples.

[0026] A high-performance holographic polymer dispersed liquid crystal composite film material based on chain transfer agent doping, characterized in that the raw material composition includes the following as shown in Table 1:

[0027] Table 1: Material composition and its function

[0028]

[0029] The acrylate monomer is selected from tricyclodecane dimethanol diacrylate (A-DCP); the liquid crystal is selected from GXP-6037; the photoinitiator is selected from N-phenylglycine (NPG); the photosensitizer is selected from Rose Bengal; and the chain transfer agent is selected from 4-cyano-4-[[(dodecylthiocarbonyl)-thio]pentanoic acid (CDTPA).

[0030] (1) Prepare a holographic polymer dispersed liquid crystal polymer solution. Add a clean magnet to the clean small brown bottle, add tricyclodecane dimethanol diacrylate and GXP-6037 to the small brown bottle in a ratio of 6:4, and add 0.7wt.% of photosensitizer Rose Bengal and 1.4wt.% of photoinitiator NPG, and then add chain transfer agents of different mass fractions (0wt.%-0.6wt.%). Note that the above operations need to be completed under light-proof conditions. Finally, place the reagent bottle on a magnetic stirrer and stir for about 120 minutes until the solution becomes transparent and uniform. Prepare a clean glass substrate, use a pipette to drop the prepared material on the glass surface, then place another layer of glass on the material to control the thickness of the material, and fix it with a binder clip to make a "sandwich" structure.

[0031] (2) Holographic recording experiment. The experimental optical path is as follows Figure 3 As shown in the figure, a 532nm continuous laser is used as the recording light source, the attenuation plate controls the light intensity, the recording beam uses s-polarization, and the beam is expanded and collimated by a spatial light filter and a lens. A beam splitter is used to split the laser beam into two beams, namely the object light and the reference light, and the intensity ratio between the two beams is 1:1. The written grating period is 700nm, and the exposure intensity is 40mW / cm 2The recording of holographic grating is achieved through appropriate interference between them. The polymer grating film (thickness of about 3 to 5 μm) is obtained by double-beam interference recording. The formation and quality of the grating are detected by using a He-Ne laser beam with a wavelength of 633 nm as the detection light and p-polarization.

[0032] The experimental results are as follows Figure 4 As shown, the doping of CDTPA will affect the refractive index modulation degree of HPDLC materials. Figure 4 (a)-(b) It can be seen that with the increase of chain transfer agent concentration, the refractive index modulation degree continues to increase. When the CDTPA doping concentration is 0.5wt.%, the refractive index modulation degree reaches a maximum value of 0.07. After that, the refractive index modulation degree decreases with the increase of doping concentration. Figure 5 The photo of the transmission grating with a period of 700nm recorded based on HPDLC is shown. It can be seen that the film sample has a high degree of transparency, and bright diffraction light is generated at a certain angle under white light illumination, showing good grating quality and high diffraction performance. The experimental results show that the prepared holographic grating has great potential in the application of holographic optical storage and AR smart display devices.

Claims

1. A holographic polymer dispersed liquid crystal material based on chain transfer reaction, characterized in that: The raw material composition includes the following: The acrylate monomer is selected from tricyclodecane dimethanol diacrylate (A-DCP); the liquid crystal is selected from GXP-6037; the photoinitiator is selected from N-phenylglycine (NPG); the photosensitizer is selected from Rose Bengal; and the chain transfer agent is selected from 4-cyano-4-[[(dodecylsulfanylthiocarbonyl)thio]pentanoic acid (CDTPA).

2. The method for preparing a holographic polymer dispersed liquid crystal material based on a chain transfer reaction according to claim 1, characterized in that: (1) Prepare a holographic polymer dispersed liquid crystal polymer solution. In a clean brown bottle, mix the acrylic monomer, liquid crystal, photosensitizer, photoinitiator and chain transfer agent in proportion and stir until they are uniform and transparent; Prepare a clean quartz substrate, use a pipette to drop the prepared material on the surface of the quartz substrate, then place another quartz substrate on the material and fix it with a binder clip; (2) Double interference lithography is performed using coherent light with a wavelength of 532 nm, and the photochemical reaction that occurs under exposure generates a polymer grating film.

3. The preparation method according to claim 2, characterized in that: The exposure intensity is 40mW / cm 2 , the period of the interference light is 700nm.

4. The preparation method according to claim 2, characterized in that: The refractive index modulation degree of HPDLC film doped with 0.5wt.% chain transfer agent can be as high as 0.

07.

5. Application of the holographic polymer dispersed liquid crystal material based on chain transfer reaction as claimed in claim 1 in holographic optical storage and holographic waveguide display materials.

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