SiO2 / cnc multi-optical feature composite film and layer stack preparation method

Abstract

The application discloses a SiO2 / CNC multiple optical feature composite film and a layer stack preparation method. A cellulose nanocrystal (CNC) base layer is assembled first, and then a SiO2 / PVP / RhB (Rhodamine B) dispersion liquid is cast. The adhesion and hydrophilicity of PVP are used to tightly combine the CNC photonic layer and the SiO2 photonic crystal layer, and meanwhile, the fluorescence quenching of RhB is overcome, so that the SiO2 / CNC composite film with multiple optical properties is obtained. The composite film presents the structural color of the CNC photonic layer under natural light, presents the birefringent color of the CNC chiral nematic structure under polarized light, presents the dynamic iridescent color of SiO2 under a point light source, and can generate fluorescent color under ultraviolet light excitation. The multiple optical property film has great application potential in the fields of optical anti-counterfeiting and information encryption.

Description

Technical Field

[0001] This invention belongs to the field of composite thin film material technology and optical anti-counterfeiting, specifically involving a SiO2 / CNC multi-optical feature composite thin film and its layer stacking preparation method. Background Technology

[0002] Information anti-counterfeiting plays a crucial role in national defense and daily life. Among these technologies, optical anti-counterfeiting has garnered significant attention due to its ease of identification and controllability. However, single optical anti-counterfeiting technologies suffer from limitations such as low security and vulnerability to attack. Therefore, the combined application of multiple optical anti-counterfeiting technologies is particularly important to meeting the demands for enhanced anti-counterfeiting security.

[0003] SiO2 photonic crystals possess a unique periodic structure, within which light undergoes diffraction and interference, creating structural colors. CNC photonic structures can also produce similar structural colors. By combining these two types of thin films, multi-layered optical anti-counterfeiting can be achieved. However, as inorganic and organic materials respectively, the compatibility differences between SiO2 and CNC can easily lead to the destruction of the self-assembled structure, and the bilayer structure cannot be tightly bonded, ultimately resulting in the loss of their respective optical characteristics. Therefore, the fabrication of composite thin films with multiple optical properties still faces many challenges. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a SiO2 / CNC multi-optical feature composite thin film and a layer stacking preparation method to solve the problems of easy deciphering of single optical anti-counterfeiting and poor bonding of SiO2 / CNC composite thin films in the prior art, so as to prepare an optical composite thin film with multiple anti-counterfeiting properties.

[0005] To achieve the above objectives, the present invention employs the following technical solution: A method for preparing a SiO2 / CNC multi-optical-feature composite thin film by layer stacking includes the following steps: Step 1: Pour the CNC aqueous dispersion onto a glass mold, and after drying and self-assembly, obtain a CNC photonic thin film; Step 2: Disperse SiO2 microspheres in water to obtain a SiO2 aqueous dispersion; Step 3: Disperse RhB in water to obtain an RhB aqueous dispersion; Step 4: Add PVP to SiO2 aqueous dispersion to obtain PVP / SiO2 aqueous dispersion; mix PVP / SiO2 aqueous dispersion and RhB aqueous dispersion to obtain SiO2 / PVP / RhB aqueous dispersion. Step 5: Immerse the CNC photonic film in a water bath, and pour SiO2 / PVP / RhB aqueous dispersion onto the immersed CNC photonic film. After self-assembly, a SiO2 / CNC composite film is obtained.

[0006] A further improvement of the present invention is that: Preferably, in step 1, the mass fraction of the CNC aqueous dispersion is 2%.

[0007] Preferably, in step 1, the temperature of the drying self-assembly process is 20-80℃.

[0008] Preferably, in step 2, the mixing ratio of SiO2 microspheres and water is (0.01-0.03) g: (3-5) mL.

[0009] Preferably, in step 2, the mixing ratio of RhB and water is 0.003g:100mL.

[0010] Preferably, in step 4, the mixing ratio of PVP and SiO2 aqueous dispersion is (0.1-0.3) g: (3-5) mL.

[0011] Preferably, in step 4, the mixing ratio of PVP / SiO2 aqueous dispersion and RhB aqueous dispersion is (3-5) mL: (3-5) g.

[0012] Preferably, in step 5, the soaking temperature is 25-45℃ and the soaking time is 2-4 hours.

[0013] Preferably, in step 5, the drying temperature is 20-80℃.

[0014] A SiO2 / CNC multi-optical-feature composite thin film prepared by any of the above-mentioned layer stacking methods includes a lower CNC photonic thin film and an upper SiO2 photonic crystal layer; wherein the matrix of the upper SiO2 photonic crystal layer is PVP, and SiO2 microspheres and RhB are dispersed in the matrix.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for constructing SiO2 / CNC composite films using a layer-stacking method. First, a CNC substrate layer is prepared; then, a SiO2 / PVP / RhB dispersion is cast, utilizing the adhesive properties of PVP to tightly bond the two layers while overcoming the fluorescence quenching of RhB. This method yields SiO2 / CNC composite films with multiple optical properties. The composite film exhibits a tight bond and displays the structural color of CNC under natural light, the birefringent color of CNC under polarized light, the dynamic iridescent color of SiO2 under a point light source, and fluorescence under ultraviolet light excitation. Therefore, this film possesses multiple optical properties and shows great application potential in fields such as optical anti-counterfeiting, information encryption, and decoration.

[0016] The differences in physical morphology, density, and surface charge between SiO2 and CNC prevent the SiO2 and CNC layers from bonding tightly. This method improves the surface properties of CNC and SiO2 by adding PVP. The pyrrolidone groups in PVP can form hydrogen bonds with the hydroxyl groups on the CNC and SiO2 surfaces, enhancing the interfacial bonding and allowing the SiO2 and CNC layers to bond tightly. Adding RhB achieves photoluminescence, but RhB undergoes solid-state quenching because the dense molecular stacking in solid materials restricts the conformational freedom of Rhodamine molecules. This invention utilizes the ionic groups on the surfaces of PVP and SiO2. These ionic groups form hydrogen bonds or other interactions with dye molecules, thereby blocking the interactions between dye molecules and overcoming solid-state quenching. Simultaneously, under ultraviolet light, RhB is excited and emits fluorescence.

[0017] Furthermore, the addition of PVP ensures uniform dispersion of silica, which is beneficial for ordered assembly, and the adhesive properties of PVP result in a compact film structure. Layered assembly does not disrupt the self-assembly structure of CNC or affect the self-assembly structure of silica.

[0018] Furthermore, under natural light, the periodic crystal structure inside the CNC will interfere and diffract with the light, and the SiO2 structural color will be hidden, so that only the specific structural color of the CNC is displayed.

[0019] Furthermore, under polarized light, the self-assembled CNC exhibits a chiral nematic phase structure. This helical structure leads to anisotropy in the material, causing light with different polarization directions to propagate at different speeds to generate a phase difference, which in turn produces color changes and forms birefringence.

[0020] Furthermore, under a point light source, the color of SiO2 depends on PVP. The addition of PVP increases the transparency of the SiO2 layer (with similar refractive indices). Polydisperse SiO2 and PVP form a uniform dielectric layer. SiO2 microspheres of different sizes are arranged alternately to form different photonic band gaps, which appear as iridescent colors under a point light source. At the same time, due to the strong light from the point light source, the structural color of CNC is hidden. Attached Figure Description

[0021] Figure 1 This is a cross-sectional SEM image of the SiO2 / CNC composite film prepared in Example 1 of this invention.

[0022] Figure 2 This is an optical photograph of the CNC photonic thin film prepared in Example 2 of the present invention.

[0023] Figure 3 This is a POM image of the CNC photonic thin film prepared in Example 3 of the present invention.

[0024] Figure 4 This is a 2D image of the CNC photonic thin film prepared in Example 4 of the present invention using a super depth-of-field microscope.

[0025] Figure 5 These are optical photographs of the SiO2 / CNC composite thin film prepared in Example 5 of this invention under different lighting conditions.

[0026] Figure 6 This is a POM diagram of the SiO2 / CNC composite film prepared in Example 6 of this invention.

[0027] Figure 7 This is a super depth-of-field 2D micrograph of the SiO2 / CNC composite film prepared in Example 7 of the present invention.

[0028] Figure 8 These are optical photographs of the SiO2 / CNC composite thin film prepared in Example 8 of this invention under different lighting conditions. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings: To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0030] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0031] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0032] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0033] This invention discloses a method for constructing SiO2 / CNC composite thin films using a layer stacking method. The preparation method specifically includes the following steps: (1) Pour 3-5g of CNC aqueous dispersion (CNC mass fraction of 2%) onto a glass mold and place it in a drying oven at 20-80 ℃ to induce self-assembly by evaporation to obtain CNC photonic thin film.

[0034] (2) Add 3-5 mL of deionized water and 0.01-0.03 g of SiO2 microspheres to a beaker and stir until homogeneous to obtain a SiO2 aqueous dispersion, wherein the particle size of the SiO2 microspheres is 450-650 nm.

[0035] (3) Add 100 ml of deionized water and 0.003 g of RhB to a beaker, stir well, and obtain an RhB aqueous dispersion.

[0036] (4) Add 0.1-0.3g PVP to 3-5mL of SiO2 aqueous dispersion and add 3-5g RhB aqueous dispersion. After ultrasonic dispersion for 30-40 min, SiO2 / PVP / RhB aqueous dispersion is obtained.

[0037] (5) Place the CNC photonic film in a water bath at 25-45 ℃ and soak it in deionized water for 2-4 h. After taking it out, pour SiO2 / PVP / RhB aqueous dispersion into it and place it in a drying oven at 20-80 ℃ for self-assembly to obtain SiO2 / CNC composite film.

[0038] The method for preparing the SiO2 / CNC composite film of this invention utilizes the adhesiveness and hydrophilicity of PVP to tightly bond the CNC substrate layer and the SiO2 photonic crystal layer. Simultaneously, both SiO2 and PVP can overcome the solid-state quenching of RhB. By leveraging the fluorescence properties of RhB, the fluorescence characteristics of the film are enhanced, resulting in a SiO2 / CNC composite film with multiple optical features. This composite film exhibits the structural color of CNC under natural light, the birefringent color of CNC under polarized light, the dynamic iridescent color of SiO2 under a point light source, and fluorescent colors under ultraviolet light excitation. It possesses multiple optical properties and has great application potential in fields such as optical anti-counterfeiting, information encryption, and decoration.

[0039] The present invention also discloses a SiO2 / CNC multi-optical feature composite film, which includes a lower CNC photonic film and an upper SiO2 photonic crystal layer. After a dispersion liquid is poured into the upper layer of the film, as the solvent evaporates, SiO2 is fixed in the PVP matrix and RhB is uniformly dispersed in the film.

[0040] Example 1 (1) 4g of CNC aqueous dispersion (CNC mass fraction of 2%) was poured onto a glass mold and placed in a drying oven at 30℃ to induce self-assembly by evaporation to obtain CNC photonic thin film.

[0041] (2) Add 4 ml of deionized water and 0.012 g of SiO2 to a beaker and stir until homogeneous to obtain a SiO2 aqueous dispersion.

[0042] (3) Add 100 ml of deionized water and 0.003 g of RhB to a beaker, stir well, and obtain an RhB aqueous dispersion.

[0043] (4) Add 0.12g PVP to 4 ml of SiO2 aqueous dispersion and add 4g RhB aqueous dispersion, and sonicate for 30 min to obtain SiO2 / PVP / RhB aqueous dispersion.

[0044] (5) The CNC photonic film was placed in a 40°C water bath and soaked in deionized water for 2 hours. After taking it out, SiO2 / PVP / RhB aqueous dispersion was poured and placed in a 40°C drying oven for self-assembly to obtain SiO2 / CNC composite film.

[0045] Figure 1 This is a cross-sectional SEM image of the SiO2 / CNC composite film prepared in this embodiment. As can be seen from the figure, the composite film has a distinct layered structure, with the upper layer being a crystalline layer formed by PVP coating SiO2 and the lower layer being a crystalline layer formed by PVP coating CNC.

[0046] Example 2 (1) 3g of CNC aqueous dispersion (CNC mass fraction of 2%) was poured onto a glass mold and placed in a drying oven at 40℃ to induce self-assembly by evaporation to obtain CNC photonic thin film.

[0047] (2) Add 3 ml of deionized water and 0.01 g of SiO2 to a beaker and stir until homogeneous to obtain a SiO2 aqueous dispersion.

[0048] (3) Add 100 ml of deionized water and 0.003 g of RhB to a beaker, stir well, and obtain an RhB aqueous dispersion.

[0049] (4) Add 0.1g PVP to 3 ml of SiO2 aqueous dispersion and add 5g RhB aqueous dispersion, and sonicate for 30 min to obtain SiO2 / PVP / RhB aqueous dispersion.

[0050] (5) The CNC photonic film was placed in a 30 ℃ water bath and soaked in deionized water for 3 h. After taking it out, SiO2 / PVP / RhB aqueous dispersion was poured and placed in a 40 ℃ drying oven for self-assembly to obtain SiO2 / CNC composite film.

[0051] Figure 2 This is an optical photograph of the CNC photonic thin film prepared in this embodiment. As can be seen from the figure, the film has no obvious coffee ring phenomenon and has high gloss and surface smoothness.

[0052] Example 3 (1) 5g of CNC aqueous dispersion (CNC mass fraction of 2%) was poured onto a glass mold and placed in a drying oven at 30℃ to induce self-assembly by evaporation to obtain CNC photonic thin film.

[0053] (2) Add 5 ml of deionized water and 0.015 g of SiO2 to a beaker and stir until homogeneous to obtain a SiO2 aqueous dispersion.

[0054] (3) Add 100 ml of deionized water and 0.003 g of RhB to a beaker, stir well, and obtain an RhB aqueous dispersion.

[0055] (4) Add 0.15g PVP to 4 ml of SiO2 aqueous dispersion and add 3g RhB aqueous dispersion, and sonicate for 30 min to obtain SiO2 / PVP / RhB aqueous dispersion.

[0056] (5) The CNC photonic film was placed in a 30 ℃ water bath and soaked in deionized water for 2 hours. After taking it out, SiO2 / PVP / RhB aqueous dispersion was poured and placed in a 30 ℃ drying oven for self-assembly to obtain SiO2 / CNC composite film.

[0057] Figure 3 The image shows the POM diagram of the CNC photonic thin film prepared in this embodiment. As can be seen from the image, the thin film exhibits obvious birefringence, indicating that the chiral nematic phase structure of the CNC is not destroyed.

[0058] Example 4 (1) 4g of CNC aqueous dispersion (CNC mass fraction of 2%) was poured onto a glass mold and placed in a drying oven at 30 ℃ to induce self-assembly by evaporation to obtain CNC photonic thin film.

[0059] (2) Add 5 ml of deionized water and 0.015 g of SiO2 to a beaker and stir until homogeneous to obtain a SiO2 aqueous dispersion.

[0060] (3) Add 100 ml of deionized water and 0.003 g of RhB to a beaker, stir well, and obtain an RhB aqueous dispersion.

[0061] (4) Add 0.15 g PVP to 5 ml of SiO2 aqueous dispersion and add 3 g RhB aqueous dispersion, and sonicate for 40 min to obtain SiO2 / PVP / RhB aqueous dispersion.

[0062] (5) The CNC photonic film was placed in a 40 ℃ water bath and soaked in deionized water for 1 h. After taking it out, SiO2 / PVP / RhB aqueous dispersion was poured and placed in a 30 ℃ drying oven for self-assembly to obtain SiO2 / CNC composite film.

[0063] Figure 4 This is a 2D image of the CNC photonic thin film prepared in this embodiment using a super depth-of-field microscope. As can be seen from the image, the thin film exhibits obvious birefringence, iridescent colors, and fingerprint-like texture. Example 5 (1) 4g of CNC aqueous dispersion (CNC mass fraction of 2%) was poured onto a glass mold and placed in a drying oven at 60 ℃ to induce self-assembly by evaporation to obtain CNC photonic thin film.

[0064] (2) Add 4 ml of deionized water and 0.012 g of SiO2 to a beaker and stir until homogeneous to obtain a SiO2 aqueous dispersion.

[0065] (3) Add 100 ml of deionized water and 0.003 g of RhB to a beaker, stir well, and obtain an RhB aqueous dispersion.

[0066] (4) Add 0.12g PVP to 4 ml of SiO2 aqueous dispersion and add 4g RhB aqueous dispersion, and sonicate for 30 min to obtain SiO2 / PVP / RhB aqueous dispersion.

[0067] (5) The CNC photonic film was placed in a 30 ℃ water bath and soaked in deionized water for 2 h. After taking it out, SiO2 / PVP / RhB aqueous dispersion was poured and placed in a 30 ℃ drying oven for self-assembly to obtain SiO2 / CNC composite film.

[0068] Figure 5 These are optical photographs of the SiO2 / CNC composite thin film prepared in this embodiment under different lighting conditions. As can be seen from the figures, the composite thin film exhibits the blue color of the CNC photonic layer under natural light and the brilliant iridescent color of the SiO2 photonic crystal layer under point light source.

[0069] Example 6 (1) 4g of CNC aqueous dispersion (CNC mass fraction of 2%) was poured onto a glass mold and placed in a 60℃ drying oven for evaporation-induced self-assembly to obtain a CNC photonic thin film.

[0070] (2) Add 4 ml of deionized water and 0.012 g of SiO2 to a beaker and stir until homogeneous to obtain a SiO2 aqueous dispersion.

[0071] (3) Add 100 ml of deionized water and 0.003 g of RhB to a beaker, stir well, and obtain an RhB aqueous dispersion.

[0072] (4) Add 0.12 g PVP to 4 ml of SiO2 aqueous dispersion and add 3 g RhB aqueous dispersion, and sonicate for 30 min to obtain SiO2 / PVP / RhB aqueous dispersion.

[0073] (5) The CNC photonic film was placed in a 40°C water bath and soaked in deionized water for 2 hours. After taking it out, SiO2 / PVP / RhB aqueous dispersion was poured and placed in a 40°C drying oven for self-assembly to obtain SiO2 / CNC composite film.

[0074] Figure 6 The image shows the POM image of the SiO2 / CNC composite film prepared in this embodiment. As can be seen from the image, the composite film POM image is blue-purple and has a bright birefringence phenomenon, retaining the chiral nematic phase structure of CNC.

[0075] Example 7 (1) 4g of CNC aqueous dispersion (CNC mass fraction of 2%) was poured onto a glass mold and placed in a drying oven at 50℃ to induce self-assembly by evaporation to obtain CNC photonic thin film.

[0076] (2) Add 4 ml of deionized water and 0.012 g of SiO2 to a beaker and stir until homogeneous to obtain a SiO2 aqueous dispersion.

[0077] (3) Add 100 ml of deionized water and 0.003 g of RhB to a beaker, stir well, and obtain an RhB aqueous dispersion.

[0078] (4) Add 0.12g PVP to 4 ml of SiO2 aqueous dispersion and add 3g RhB aqueous dispersion, and sonicate for 30 min to obtain SiO2 / PVP / RhB aqueous dispersion.

[0079] (5) The CNC photonic film was placed in a 40℃ water bath and soaked in deionized water for 2 h. After taking it out, SiO2 / PVP / RhB aqueous dispersion was poured and placed in a 40℃ drying oven for self-assembly to obtain SiO2 / CNC composite film.

[0080] Figure 7 This is a super depth-of-field 3D micrograph of the SiO2 / CNC composite film prepared in this embodiment. As can be seen from the figure, the composite film has high flatness.

[0081] Example 8 (1) 4g of CNC aqueous dispersion (CNC mass fraction of 2%) was poured onto a glass mold and placed in a drying oven at 60℃ to induce self-assembly by evaporation to obtain CNC photonic thin film.

[0082] (2) Add 4 ml of deionized water and 0.012 g of SiO2 to a beaker and stir until homogeneous to obtain a SiO2 aqueous dispersion.

[0083] (3) Add 100ml of deionized water and 0.003g of RhB to a beaker, stir well, and obtain an RhB aqueous dispersion.

[0084] (4) Add 0.12g PVP to 3 ml of SiO2 aqueous dispersion and add 3g RhB aqueous dispersion, and sonicate for 30 min to obtain SiO2 / PVP / RhB aqueous dispersion.

[0085] (5) The CNC photonic film was placed in a 40°C water bath and soaked in deionized water for 2 hours. After taking it out, SiO2 / PVP / RhB aqueous dispersion was poured and placed in a 40°C drying oven for self-assembly to obtain SiO2 / CNC composite film.

[0086] Figure 8 These are optical photographs of the SiO2 / CNC composite film prepared in this embodiment under different lighting conditions. As can be seen from the figures, the film exhibits a uniform and bright blue-violet color under natural light, an iridescent color under a point light source, an orange-red fluorescence under 365nm ultraviolet light excitation, and a yellow fluorescence under 302nm and 254nm ultraviolet light excitation, indicating that the film has different color rendering effects under different lighting conditions.

[0087] Example 9 (1) 4g of CNC aqueous dispersion (CNC mass fraction of 2%) was poured onto a glass mold and placed in a drying oven at 80℃ to induce self-assembly by evaporation, thus obtaining a CNC photonic thin film.

[0088] (2) Add 5 ml of deionized water and 0.03 g of SiO2 to a beaker and stir until homogeneous to obtain a SiO2 aqueous dispersion.

[0089] (3) Add 100ml of deionized water and 0.003g of RhB to a beaker, stir well, and obtain an RhB aqueous dispersion.

[0090] (4) Add 0.1g PVP to 4 ml of SiO2 aqueous dispersion and add 3g RhB aqueous dispersion, and sonicate for 30 min to obtain SiO2 / PVP / RhB aqueous dispersion.

[0091] (5) The CNC photonic film was placed in a water bath at 25°C and soaked in deionized water for 4 hours. After taking it out, SiO2 / PVP / RhB aqueous dispersion was poured and placed in a drying oven at 20°C for self-assembly to obtain SiO2 / CNC composite film.

[0092] Example 10 (1) 4g of CNC aqueous dispersion (CNC mass fraction of 2%) was poured onto a glass mold and placed in a drying oven at 20℃ to induce self-assembly by evaporation to obtain CNC photonic thin film.

[0093] (2) Add 5 ml of deionized water and 0.03 g of SiO2 to a beaker and stir until homogeneous to obtain a SiO2 aqueous dispersion.

[0094] (3) Add 100ml of deionized water and 0.003g of RhB to a beaker, stir well, and obtain an RhB aqueous dispersion.

[0095] (4) Add 0.3g PVP to 5 ml of SiO2 aqueous dispersion and add 3g RhB aqueous dispersion, and sonicate for 30 min to obtain SiO2 / PVP / RhB aqueous dispersion.

[0096] (5) The CNC photonic film was placed in a 40°C water bath and soaked in deionized water for 3 hours. After taking it out, SiO2 / PVP / RhB aqueous dispersion was poured and placed in an 80°C drying oven for self-assembly to obtain SiO2 / CNC composite film.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a SiO2 / CNC multi-optical feature composite thin film by layer stacking, characterized in that, Includes the following steps: Step 1: The CNC aqueous dispersion is poured onto a glass mold, dried, and self-assembled to obtain a CNC photonic thin film; the CNC photonic thin film exhibits a chiral nematic phase structure; Step 2: Disperse SiO2 microspheres in water to obtain a SiO2 aqueous dispersion; wherein the particle size of the SiO2 microspheres is in the range of 450-650 nm. Step 3: Disperse RhB in water to obtain an RhB aqueous dispersion; Step 4: Add PVP to SiO2 aqueous dispersion to obtain PVP / SiO2 aqueous dispersion; mix PVP / SiO2 aqueous dispersion and RhB aqueous dispersion to obtain SiO2 / PVP / RhB aqueous dispersion. Step 5: Immerse the CNC photonic film in a water bath, and pour SiO2 / PVP / RhB aqueous dispersion onto the immersed CNC photonic film. After self-assembly, a SiO2 / CNC composite film is obtained.

2. The method for preparing a SiO2 / CNC multi-optical feature composite thin film by layer stacking according to claim 1, characterized in that, In step 1, the mass fraction of the CNC aqueous dispersion is 2%.

3. The method for preparing a SiO2 / CNC multi-optical feature composite thin film by layer stacking according to claim 1, characterized in that, In step 1, the temperature for the drying self-assembly process is 20-80℃.

4. The method for preparing a SiO2 / CNC multi-optical feature composite thin film by layer stacking according to claim 1, characterized in that, In step 2, the mixing ratio of SiO2 microspheres and water is (0.01-0.03) g: (3-5) mL.

5. The method for preparing a SiO2 / CNC multi-optical feature composite thin film by layer stacking according to claim 1, characterized in that, In step 3, the mixing ratio of RhB and water is 0.003g:100mL.

6. The method for preparing a SiO2 / CNC multi-optical feature composite thin film by layer stacking according to claim 1, characterized in that, In step 4, the mixing ratio of PVP and SiO2 aqueous dispersion is (0.1-0.3) g : (3-5) mL.

7. The method for preparing a SiO2 / CNC multi-optical feature composite thin film by layer stacking according to claim 1, characterized in that, In step 4, the mixing ratio of PVP / SiO2 aqueous dispersion and RhB aqueous dispersion is (3-5) mL: (3-5) g.

8. The method for preparing a SiO2 / CNC multi-optical feature composite thin film by layer stacking according to claim 1, characterized in that, In step 5, the soaking temperature is 25-45℃ and the soaking time is 2-4 hours.

9. The method for preparing a SiO2 / CNC multi-optical feature composite thin film by layer stacking according to claim 1, characterized in that, In step 5, the drying temperature is 20-80℃.

10. A SiO2 / CNC multi-optical-feature composite thin film prepared by the layer stacking method according to any one of claims 1-9, characterized in that, It includes a lower CNC photonic thin film and an upper SiO2 photonic crystal layer; the matrix of the upper SiO2 photonic crystal layer is PVP, and SiO2 microspheres and RhB are dispersed in the matrix.

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