Holographic polymer liquid crystal composite material and preparation method thereof

Abstract

The invention belongs to the technical field of holographic optics, and particularly relates to a holographic polymer liquid crystal composite material which comprises monomers, a photosensitizer, a photo-initiation system and liquid crystals, the photosensitizer is BDEA, the photo-initiation system is HABI and MBO, the photosensitizer and the photo-initiation system form a three-component system BDEA / HABI / MBO, the monomers comprise POEA and TMPEOTA, and the TMPEOTA has Mn-692. The liquid crystal is a nematic P0616A type liquid crystal, the P0616A liquid crystal and a BDEA / HABI / MBO three-component photo-initiation system are combined and applied to a holographic polymeric material for the first time, a breakthrough is made in the aspects of improving holographic recording sensitivity and pattern resolution to form a clear polymer-liquid crystal interphase structure, and the diffraction efficiency of holographic patterns is improved. The holographic recording system with high efficiency and low energy consumption is realized, and the application range of holographic recording materials is expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of holographic optics, and in particular relates to a holographic polymer liquid crystal composite material and a preparation method thereof. Background Art

[0002] Holography through laser interferometry is a technique that precisely processes ultrafine structures down to the nanometer level. Because all information from the laser light can be reconstructed in these ultrafine structures through periodic refractive index modulation, the resulting holographic gratings are considered indispensable components for industries such as 3D displays, augmented / virtual reality, high-density data storage, and advanced anti-counterfeiting. In particular, the combination of liquid crystals and holographic materials not only facilitates convenient holographic processing but also allows for the imposition of diverse stimulus-responsive functionalities.

[0003] Generally, photopolymers consist of three main components: a photoinitiator system, monomers, and film-forming agents. In certain circumstances, other components such as chain transfer agents, leveling agents, plasticizers, and crosslinkers may also be required. In photopolymers, the photoinitiator system absorbs light energy to generate free radicals, which in turn initiate polymerization of the monomers. The most important performance indicators for evaluating photopolymers include maximum diffraction efficiency and refractive index modulation.

[0004] Holographic polymer / liquid crystal composites are a type of structurally ordered composite material with holographic properties, consisting of a periodic arrangement of a polymer-rich phase and a liquid crystal-rich phase. Formed through polymerization-induced phase separation under coherent laser light, these composites can store the entire information of an object and have important applications in the storage and display of color three-dimensional (3D) images visible to the naked eye. Furthermore, due to their excellent electro-optical response and high refractive index modulation, they also show great potential for application in augmented reality.

[0005] However, the main problem currently is that the refractive index modulation degree of photopolymers is relatively small, which has become a major bottleneck affecting practical applications. The current main solution is to improve this problem by introducing liquid crystals (LCs). Liquid crystals are a type of fluid soft matter that can maintain crystal order and exhibit unique characteristics of low viscosity, high refractive index and fast stimulus response. However, the interaction mechanism between liquid crystal materials and photoinitiator systems is relatively complex, and the various components have a synergistic effect during the holographic polymerization process, which has a complex impact on properties such as diffraction efficiency and refractive index modulation degree. Therefore, selecting suitable holographic polymer / liquid crystal composite components and optimizing their content and structure to improve diffraction efficiency and refractive index modulation degree is an urgent problem to be solved. Summary of the Invention

[0006] In view of the above problems, the present invention provides a holographic polymer liquid crystal composite material and a preparation method thereof.

[0007] The complete technical solution of the present invention includes:

[0008] A holographic polymer liquid crystal composite material comprises monomers, photosensitizers, photoinitiator systems and liquid crystals.

[0009] Furthermore, the photosensitizer is BDEA, the photoinitiator system is HABI and MBO, and the photosensitizer and the photoinitiator system form a three-component system BDEA / HABI / MBO.

[0010] Further, the monomers include POEA and TMPEOTA, wherein the M of the TMPEOTA is n ~692.

[0011] Furthermore, the liquid crystal is a nematic P0616A liquid crystal.

[0012] Furthermore, in the holographic polymer liquid crystal, the mass ratio of POEA to TMPEOTA is 1:1, and the mass ratio of the monomer to the liquid crystal is 70:30.

[0013] Furthermore, based on the total mass of the monomers and the liquid crystal, BDEA accounts for 0.125% of the total mass of the monomers and the liquid crystal, MBO accounts for 0.125% of the total mass of the monomers and the liquid crystal, and HABI accounts for 1.25% of the total mass of the monomers and the liquid crystal.

[0014] Furthermore, the diffraction efficiency of the holographic polymer liquid crystal composite material is not less than 85%.

[0015] Furthermore, when the film thickness is 10 μm, the refractive index modulation degree Δn of the holographic polymer liquid crystal composite material is not less than 1.7×10-2.

[0016] Furthermore, the preparation method of the holographic polymer liquid crystal composite material comprises adding BDEA, MBO, HABI, mixed monomers POEA / TMPEOTA, and P0616A in a light-proof container in order according to a ratio, mixing them uniformly to obtain a holographic recording mixed solution, adding the holographic recording mixed solution to a liquid crystal cell with an inner surface coated with indium tin oxide in a dark room, and allowing it to stand for a certain period of time, then using a beam splitter prism to split a 532nm laser into two coherent beams of the same frequency, constant phase difference, and consistent vibration direction, and simultaneously irradiating the liquid crystal cell containing the holographic mixed solution, with the angle bisectors of the two coherent beams perpendicular to the surface of the liquid crystal cell, and the light intensity of each beam being 5.0mW·cm -2 , the illumination time is 2 minutes, the angle between the two coherent light beams is 30°, and a holographic polymer liquid crystal composite material with a grating structure is obtained.

[0017] Furthermore, the relative error between the measured grating period and the theoretical grating period is no more than 2.2%, and the grating depth is 62.1±2.3 nm.

[0018] Furthermore, the holographic polymer liquid crystal composite material is used as an anti-counterfeiting material.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The first application of P0616A liquid crystals in conjunction with a BDEA / HABI / MBO three-component photoinitiator system for holographic polymeric materials. This combination, leveraging the high birefringence of P0616A and the excellent performance of the BDEA / HABI / MBO visible light initiator system in holographic recording, has resulted in a breakthrough in improving holographic recording sensitivity and pattern resolution.

[0021] 2. Optimized microscopic phase separation was achieved. During the polymerization process, the P0616A liquid crystal and the polymer matrix formed a distinct phase separation structure, which is conducive to the formation of high-quality holographic gratings. The high initiation efficiency of the BDEA / HABI / MBO system rapidly triggered the polymerization reaction, further promoting the phase separation of the liquid crystal, forming a clear polymer-liquid crystal interphase structure and improving the diffraction efficiency of the holographic pattern.

[0022] 3. The ability to initiate polymerization in the visible light band (e.g., 532 nm) opens new possibilities for the application of holographic recording materials. Combined with the high birefringence of P0616A liquid crystal, it is expected to realize high-efficiency, low-energy holographic recording systems, thus expanding the application range of holographic recording materials.

[0023] 4. The content of each component is optimized, which significantly improves the diffraction efficiency of the holographic material and achieves precise control of the holographic pattern performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diffraction efficiency diagram of the holographic polymer liquid crystal composite material of the present invention.

[0025] Figure 2 This is a holographic leaf pattern of the material of the present invention in anti-counterfeiting applications.

[0026] Figure 3 This is a grid structure diagram of the material of the present invention.

[0027] Figure 4 A comparison chart of the diffraction efficiency of different ratios of monomers and liquid crystals.

[0028] Figure 5 A comparison chart of the diffraction efficiency of monomers with different mixing ratios.

[0029] Figure 6 A comparison chart of the diffraction efficiency of photoinitiator systems with different proportions. DETAILED DESCRIPTION

[0030] The following is a clear and complete description of the technical solutions in the embodiments of the present invention, in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0031] A holographic polymer / liquid crystal composite material, specifically comprising:

[0032] 1. Two monomers

[0033] (1) Acrylates, specifically POEA

[0034]

[0035] (2) 2. Photosensitizer: Choose a bichalcone organic dye that responds to green laser:

[0036]

[0037] 3. Photoinitiator system: (1)

[0039] (2)

[0041]

[0042] The two photoinitiator systems and photosensitizer form a three-component system BDEA / HABI / MBO. 4. Liquid crystal: choose nematic P0616A liquid crystal

[0043]

[0044] The proportions of the above components are shown in Table 1.

[0045] Table 1 Group distribution ratio

[0046]

[0047] In the above ratio, the mass ratio of POEA to TMPEOTA is 1:1, and the mass ratio of monomer to liquid crystal is 70:30;

[0048] Based on the total mass of the monomers and the liquid crystal, BDEA accounts for 0.125% of the total mass of the monomers and the liquid crystal, MBO accounts for 0.125% of the total mass of the monomers and the liquid crystal, and HABI accounts for 1.25% of the total mass of the monomers and the liquid crystal.

[0049] The holographic grating preparation process of the present invention is as follows: BDEA, MBO, HABI, the mixed monomers POEA / TMPEOTA, and P0616A are added sequentially to a brown reagent bottle according to the proportions listed in the table above. Ultrasonication is then applied for 30 minutes to obtain a uniformly mixed holographic recording mixture. In a darkroom, the holographic recording mixture is added to a liquid crystal cell (cavity thickness: 10 μm) coated with indium tin oxide (ITO) on the inner surface. The cell is then mounted on a dry plate holder and allowed to stand for 60 seconds.

[0050] A 532nm laser beam is split by a beam splitter into two coherent beams with the same frequency, constant phase difference, and consistent vibration direction. The beams are then simultaneously irradiated onto a liquid crystal cell containing a holographic mixture. The angle bisectors of the two coherent beams are perpendicular to the surface of the liquid crystal cell, and the intensity of each beam is 5.0mW·cm -2 The illumination time is 2 minutes. The angle between the two coherent beams is 30°. A clear grating structure is obtained, such as Figure 3 As shown, Figure 3 (a) is a plan view, Figure 3 (b) is a three-dimensional diagram. As can be seen from the figure, in the grating structure of the material of the present invention, the grating period and depth are as follows.

[0051]

[0052] Where: writing The wavelength of the writing laser is 532nm.

[0053] According to the angle between the two coherent light beams (θ set =30°) and the Bragg equation (1), the theoretical period (Λ) of the holographic grating is 1028 nm.

[0054] The grating periods measured by SEM and AFM are 1040±10nm and 1023±10nm, respectively, close to the theoretical grating period, with a relative error of no more than 2.2%. This ensures that optical performance indicators such as diffraction efficiency and spectral resolution meet design expectations, with precise spectral resolution or wavelength selectivity, stable diffraction efficiency, and more reliable performance. The grating depth measured by AFM is 62.1±2.3nm.

[0055] like Figure 1 As shown, the holographic polymer / liquid crystal composite material obtained in the present invention reaches a maximum diffraction efficiency of 86% after irradiation for 100 seconds.

[0056] The diffraction efficiency is defined as the diffraction intensity at the Bragg angle (I D ) and transmitted light intensity (I T ) and the ratio of the total diffracted light intensity:

[0057]

[0058] The holographic polymer / liquid crystal composite material with the grating structure prepared by the present invention can realize the recording of leaf patterns, and thus be applied to the field of advanced anti-counterfeiting, such as Figure 2 shown.

[0059] The relatively low refractive index modulation of existing photopolymers has become a major bottleneck in their practical applications. Table 2 compares the diffraction efficiency and refractive index modulation of the three-component system BDEA / HABI / MBO before and after the addition of liquid crystals. As can be seen, with the addition of liquid crystals, the composite material of the present invention achieves a diffraction efficiency of 86% and a refractive index modulation of Δn = 1.74 × 10⁻², even at a film thickness of 10 μm. At these thicknesses, the diffraction efficiency and refractive index modulation are zero without liquid crystals.

[0060] Table 2 Comparison of diffraction efficiency and refractive modulation of the three-component system by adding liquid crystal (film thickness is 10 μm)

[0061] Diffraction efficiency (%) Refractive index modulation BDEA / HABI / MBO 0 0 BDEA / HABI / MBO (added with liquid crystal) 86％ <![CDATA[1.74×10 -2 ]]>

[0062] As mentioned previously, the refractive index modulation of current photopolymers is relatively small, a major bottleneck hindering their practical applications. This refractive index modulation occurs because, after exposure, monomers polymerize in the bright stripe regions, resulting in a concentration of monomers in the bright stripe regions and a concentration of inert substances that do not participate in the polymerization reaction in the dark stripe regions. Consequently, the difference in refractive index between these two regions creates refractive index modulation. The greater the refractive index modulation, the more holographic data can be stored per unit volume of the recording medium.

[0063] To increase the refractive index difference between these two regions, this paper combines P0616A liquid crystal with a BDEA / HABI / MBO three-component photoinitiator system for the first time in holographic polymer materials. P0616A is a high-birefringence liquid crystal material (Δn = 0.20), while the BDEA / HABI / MBO system is a highly efficient visible light initiator system that exhibits excellent performance in holographic recording. This combination of the two achieves a breakthrough in improving holographic recording sensitivity and pattern resolution.

[0064] The present invention also achieves an optimized microscopic phase separation structure. The poor compatibility of the P0616A liquid crystal with the polymer matrix facilitates the formation of a distinct phase separation structure during polymerization, facilitating the formation of high-quality holographic gratings. The BDEA / HABI / MBO system exhibits high initiation efficiency, enabling rapid polymerization, further promoting phase separation of the liquid crystal, and forming a clear polymer-liquid crystal interphase structure, thereby improving the diffraction efficiency of the holographic pattern.

[0065] In addition, traditional holographic polymer materials mostly use ultraviolet light initiation systems, while the BDEA / HABI / MBO system can initiate polymerization in the visible light band (such as 532nm), which provides new possibilities for the application expansion of holographic recording materials. Combined with the high birefringence characteristics of P0616A liquid crystal, it is expected to realize a high-efficiency, low-energy holographic recording system. This expands the application range of holographic recording materials.

[0066] Finally, based on the in-depth understanding of the interaction mechanism between liquid crystal materials and photoinitiator systems, the present invention systematically studied the synergistic effect of P0616A liquid crystal and BDEA / HABI / MBO photoinitiator system in the holographic polymerization process. The optimization adjustment of the content of each component was achieved, and the liquid crystal concentration (such as Figure 4 As shown), photoinitiator ratio (as shown Figure 6 As shown), monomer concentration (as Figure 5 It can be seen from the before and after diagram (shown) that the diffraction efficiency of the holographic material is significantly improved by optimizing the proportion of each component, achieving precise control of the holographic pattern performance.

[0067] The above applications are only some embodiments of the present application. For those skilled in the art, without departing from the inventive concept of the present application, several modifications and improvements can be made, which all fall within the scope of protection of the present application.

Claims

1. A holographic polymer liquid crystal composite material, characterized in that: It includes monomers, photosensitizers, photoinitiator systems and liquid crystals.

2. The holographic polymer liquid crystal composite material according to claim 1, characterized in that: The photosensitizer is BDEA, the photoinitiator system is HABI and MBO, and the photosensitizer and the photoinitiator system form a three-component system BDEA / HABI / MBO.

3. The holographic polymer liquid crystal composite material according to claim 2, characterized in that: The monomers include POEA and TMPEOTA, wherein the M n ~692.

4. The holographic polymer liquid crystal composite material according to claim 3, characterized in that: The liquid crystal is a nematic P0616A liquid crystal.

5. The holographic polymer liquid crystal composite material according to claim 4, characterized in that: In the holographic polymer liquid crystal, the mass ratio of POEA to TMPEOTA is 1:1, and the mass ratio of the monomer to the liquid crystal is 70:

30.

6. The holographic polymer liquid crystal composite material according to claim 5, characterized in that: Based on the total mass of the monomers and the liquid crystal, BDEA accounts for 0.125% of the total mass of the monomers and the liquid crystal, MBO accounts for 0.125% of the total mass of the monomers and the liquid crystal, and HABI accounts for 1.25% of the total mass of the monomers and the liquid crystal.

7. The holographic polymer liquid crystal composite material according to claim 6, characterized in that: The diffraction efficiency of the holographic polymer liquid crystal composite material is not less than 85%.

8. The holographic polymer liquid crystal composite material according to claim 6, characterized in that: When the film thickness is 10 μm, the refractive index modulation degree Δn of the holographic polymer liquid crystal composite material is not less than 1.7×10-2.

9. The method for preparing the holographic polymer liquid crystal composite material according to any one of claims 1 to 8, characterized in that: BDEA, MBO, HABI, mixed monomers POEA / TMPEOTA, and P0616A were added to an opaque container in order according to the ratio and mixed evenly to obtain a holographic recording mixture. The holographic recording mixture was added to a liquid crystal cell with an inner surface coated with indium tin oxide in a dark room and allowed to stand for a certain period of time. A 532nm laser was then split by a beam splitter prism into two coherent beams with the same frequency, constant phase difference, and consistent vibration direction. The two beams simultaneously illuminated the liquid crystal cell containing the holographic mixture, with the angle bisectors of the two coherent beams perpendicular to the liquid crystal cell surface. The intensity of each beam was 5.0mW·cm -2 , the illumination time is 2 minutes, the angle between the two coherent light beams is 30°, and a holographic polymer liquid crystal composite material with a grating structure is obtained.

10. Use of the holographic polymer liquid crystal composite material according to any one of claims 1 to 8 as an anti-counterfeiting material.

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