Composite film with multiple optical characteristics and blending pouring preparation method

Abstract

The invention discloses a multi-optical characteristic composite film and a blending pouring preparation method, and belongs to the technical field of optical encryption and anti-counterfeiting. According to the method, polyvinylpyrrolidone (PVP), sorbitol and polyethylene glycol (PEG) are introduced to serve as dispersing agents to play a coating role on SiO2 and CNC, so that the compatibility of SiO2 and CNC is improved, the SiO2 can form a homogeneous film after coating due to the fact that the refractive index of the dispersing agents is similar to that of SiO2, and therefore the transparency of the film is improved; good dispersibility and high transparency enable SiO2 in the composite film to present gorgeous iridescent color. The obtained composite film shows the structural color of a CNC photon layer under natural light, shows the bright structural color of CNC under natural light, shows the SiO2 structural color with a dynamic change effect under a point light source, shows the structural color and fingerprint texture texture of CNC under a super depth-of-field microscope, and shows the birefringence color of CNC under a polarizing microscope. The film with multiple optical characteristics has great application potential in the fields of optical anti-counterfeiting, information encryption and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical encryption and anti-counterfeiting, and particularly relates to a composite thin film with multiple optical characteristics and a preparation method by co-blending casting method. Background Art

[0002] Structural color refers to the color generated by the interaction between the ordered micro-structure of an object and incident light. Compared with traditional pigment colors, it has the characteristics of environmental protection, bright color, and strong durability. As inorganic and organic photonic crystal materials, silica and cellulose nanocrystals can self-assemble to form structural colors. Both of these two structural colors have the limitation of a single color effect. To obtain a photonic crystal material with multiple optical characteristics, existing research often composes the two with other materials with optical characteristics, such as lanthanide polymers, gold nanorods, or rhodamine B and other materials with luminescent characteristics. The resulting composite thin film has both the optical characteristics of CNC and photoluminescence characteristics. However, the cost of fluorescent substances is relatively high and the authentication method is complex. Some research shows that in the preparation process of most composite thin films with multiple optical characteristics, there are problems such as complex preparation processes and single color display, which greatly limit the application of such composite thin films in the fields of optical encryption, anti-counterfeiting, etc. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above-mentioned disadvantages of the prior art and provide a composite thin film with multiple optical characteristics and a preparation method by co-blending casting method, so as to solve the practical application problems of the composite thin film with multiple optical characteristics limited by poor material compatibility and single color in the prior art.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions: A preparation method by co-blending casting method for a composite thin film with multiple optical characteristics, comprising the following steps: Step 1, mix silica microspheres with water to form a silica aqueous dispersion, and mix cellulose nanocrystals with water to form a cellulose nanocrystal aqueous dispersion; Step 2, mix the silica aqueous dispersion with a dispersant to obtain a mixed solution. After mixing the mixed solution with the cellulose nanocrystal aqueous dispersion, pour it into a container, and obtain a SiO 2 / CNC composite thin film after evaporation-induced self-assembly and drying.

[0005] A further improvement of the present invention lies in: Preferably, in Step 1, the mass fraction of the silica aqueous dispersion is 0.3%.

[0006] Preferably, in Step 1, the mass fraction of the cellulose nanocrystal aqueous dispersion is 2%.

[0007] Preferably, in step 2, the mixing volume ratio of the silica aqueous dispersion and the cellulose nanocrystal aqueous dispersion is 1:4.

[0008] Preferably, the dispersant is one or more of polyvinylpyrrolidone, sorbitol, polyethylene glycol, and trimethylsiloxysilicate.

[0009] Preferably, when the dispersant is polyvinylpyrrolidone, the addition amount of the dispersant is 0.24%-4.8% of the total mass of the silica aqueous dispersion and the cellulose nanocrystal aqueous dispersion.

[0010] Preferably, when the dispersant is polyvinylpyrrolidone, a film-forming agent is added.

[0011] Preferably, the film-forming agent is one or more of polyvinyl alcohol and polyurethane.

[0012] Preferably, when the dispersant is sorbitol, polyethylene glycol or trimethylsiloxysilicate, the addition amount of the dispersant is 0.5%-3.0% of the total mass of the silica aqueous dispersion and the cellulose nanocrystal aqueous dispersion.

[0013] A multiple optical feature composite film prepared by the co-blending casting method described in any one of the above, comprising a stacked upper layer and a lower layer, the lower layer being a SiO 2 photonic crystal layer, the upper layer being a CNC photonic crystal layer, and SiO being embedded in the CNC photonic crystal layer 2 particles.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a preparation method of a multiple optical feature composite film. By introducing a dispersant, a multiple optical feature composite film of silica and cellulose nanocrystals is obtained; in the present invention, the introduction of the dispersant weakens the self-assembled structure damage caused by the compatibility difference between SiO 2 and CNC. The co-blending method blends the aqueous dispersions of SiO 2 , CNC and the dispersant, and then pours them into a mold for evaporation-induced self-assembly. During the self-assembly process, SiO 2 tends to aggregate in the lower layer, with large and small microspheres arranged alternately, and a small amount of SiO 2 embedded in the CNC layer. CNC aggregates in the upper layer. As the aqueous solution evaporates, CNC is assembled from dispersed nanoparticles into nematic-like liquid crystal aggregates and cholesteric-like liquid crystal aggregates in sequence, and finally forms a CNC film with a chiral nematic phase. Due to the good dispersibility of the dispersant for SiO 2 and good compatibility with CNC, the dispersant will coat CNC and SiO during the film-forming process 2 to promote SiO2 While being uniformly dispersed, the destruction of the self-assembled structure caused by the difference in compatibility between the two is reduced; and the dispersant and SiO 2 have a similar refractive index to CNC (the similar refractive index makes the film a homogeneous film with high transparency, and the structural color of SiO 2 can appear because of the structural color of SiO 2 The structural color can only be presented by backlighting), based on these characteristics of the dispersant, SiO 2 and CNC can retain their respective structural characteristics and exhibit multiple optical properties.

[0015] Furthermore, adding a proper proportion of the dispersant during the preparation process can, while retaining the characteristic structures of silica and cellulose nanocrystals, make up for the brittleness problem of the composite film caused by PVP, and solve the practical application problem of the composite film with multiple optical characteristics limited by poor material compatibility and single color in the prior art.

[0016] Furthermore, when the dispersant is PVP, a film-forming agent is introduced to make up for the brittleness problem of the composite film caused by PVP.

[0017] The present invention also discloses a composite film with multiple optical characteristics. The composite film is a composite film with multiple optical characteristics of silica and cellulose nanocrystals; the composite film exhibits different optical properties under the excitation of a point light source, natural light, and polarized light, realizing the superposition of optical characteristics; it has the advantages of low cost, simple preparation process, rich optical characteristics, convenient and fast expression, etc., and has great application potential in the fields of optical anti-counterfeiting, optical encryption, and decoration. Description of the Drawings

[0018] Figure 1 is the film-forming effect diagram of the silica and cellulose nanocrystal dispersion solution with a mass ratio of 1:4 prepared in Example 1; Figure 2 is the SEM and optical effect comparison diagram of the silica photonic crystal film before and after adding polyvinylpyrrolidone prepared in Examples 2-3; Among them, Figure (a) is for Example 2, and Figure (b) is for Example 3; Figure 3 is the optical effect of the silica / cellulose nanocrystal / polyvinylpyrrolidone composite film with a polyvinylpyrrolidone dosage of 2.4% prepared in Example 4; Figure 4 is the optical effect of the silica / cellulose nanocrystal / polyvinylpyrrolidone composite film with a polyvinylpyrrolidone dosage of 1.2% prepared in Example 5; Figure 5Optical effect diagram of the silica / cellulose nanocrystal / polyvinylpyrrolidone / polyvinyl alcohol (silica:cellulose nanocrystal = 1:4, polyvinylpyrrolidone = 0.6%) composite film prepared in Example 6 with 15% polyvinyl alcohol content; Figure 6 Optical effect diagram of the composite film prepared in Example 7 with 1.5% sorbitol content; Figure 7 Optical effect diagram of the composite film prepared in Example 8 with 2.5% sorbitol content; Figure 8 Optical effect diagram of the composite film prepared in Example 9 with 1.0% polyethylene glycol content; Figure 9 Optical effect diagram of the composite film prepared in Example 10 with 1.5% polyethylene glycol content; Figure 10 Optical effect diagram of the composite film prepared in Example 11 with 2.5% polyethylene glycol content. Detailed implementation manners

[0019] The present invention will be further described in detail below with reference to the accompanying drawings: To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art with respect to the present invention. In case of conflict, the definition in this specification shall prevail.

[0020] In this article, unless otherwise specified, "comprising", "including", "containing", "having" or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0021] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0022] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0023] The present invention discloses a method for preparing a composite film with multiple optical characteristics, and the preparation method specifically comprises the following steps: (1) Add 150-170 ml of anhydrous ethanol, 30-40 ml of deionized water, and 3.8-4.8 ml of 28% ammonia water into a beaker, mix well, add 4.0-4.8 ml of tetraethyl orthosilicate, and react at 60°C at a low speed for 10 h to obtain seed solution A.

[0024] (2) Add 150-170 ml of anhydrous ethanol, 30-35 ml of deionized water, and 20-40 ml of 28% ammonia water into a beaker, and add the seed solution A obtained in (1) to obtain a reaction solution B.

[0025] (3) In a beaker, water, anhydrous ethanol and 28% aqueous ammonia were mixed in a volume ratio of 3:10:7 and stirred to obtain reaction solution C. 10-30 ml of TEOS and 10-30 ml of reaction solution C were added dropwise to reaction solution B and stirred at a low speed to obtain solution D. The reaction temperature was 28-38°C and the reaction time was 4-5 h.

[0026] (4) After centrifuging solution D, the solution is dried with anhydrous ethanol, and the process is repeated three times and then dried. After sufficient grinding, silica microspheres with a particle size of 450-650 nm and a specific polydisperse distribution can be obtained; the specific drying temperature is 40-45°C, and the drying time is 6-10 hours.

[0027] (5) Silica microspheres are dispersed in water to form a silica dispersion with a concentration of 0.3%. A certain amount of 0.3% SiO 2 The aqueous dispersion was mixed with the dispersant and ultrasonically treated for 30 min. Then a certain amount of 2% cellulose nanocrystal aqueous dispersion, 0.3% SiO 2 The volume ratio of the aqueous dispersion to the 2% CNC aqueous dispersion was 1:4, ultrasonically blended for 10 min, poured into a round polystyrene petri dish with a diameter of 35 mm, evaporated at 40-45 °C to induce self-assembly, and dried to obtain SiO 2 / CNC composite film.

[0028] In the above process, a dispersant is first added to the silica dispersion to make the SiO 2 particles disperse evenly, and then cellulose nanocrystals are added to reduce the influence of SiO 2 particles on the dispersibility of cellulose nanocrystals.

[0029] Preferably, the dispersant is one or more of polyvinylpyrrolidone (PVP), sorbitol, polyethylene glycol, and trimethylsiloxysilicate. The mass percentage of the added polyvinylpyrrolidone (PVP) in the whole system is 0.24% - 4.8%, and the mass percentage of one or more of sorbitol, polyethylene glycol, and trimethylsiloxysilicate in the whole system is 0.5% - 3.0%. It should be noted that the above-mentioned whole system is a mixed system of SiO 2 aqueous dispersion and CNC aqueous dispersion.

[0030] Furthermore, when PVP is used as the dispersant, to make up for the brittleness problem of the composite film caused by the dispersant PVP, a film-forming agent solution is added to the PVP system, and the other steps are the same as above.

[0031] Preferably, the film-forming agent is one or more of polyvinyl alcohol (PVA) and polyurethane. The concentration of the added PVA solution is 8%, the mass percentage of the PVA solution in the whole system is 0 - 30%, and the ultrasonic treatment time is 10 - 20 min.

[0032] A multiple optical characteristic composite film prepared by the above method, due to the action of gravity, the lower layer of the composite film is mainly SiO 2 photonic crystal layer, and the upper layer is CNC photonic crystal layer (with a small amount of silica particles embedded in this layer).

[0033] The main materials of the multiple optical characteristic composite film are nano-silica (SiO 2 ), and cellulose nanocrystals (CNC). Among them, CNC has birefringence characteristics under natural light due to its characteristic chiral nematic phase structure. In the multiple optical characteristic composite film, the chiral nematic phase and anisotropic crystal structure of CNC can be retained in the solid film, so the film also has birefringence characteristics and iridescence characteristics under a point light source. Birefringence refers to the phenomenon that when a light beam is incident on an anisotropic crystal, it is decomposed into two beams of light and refracted along different directions. When light propagates in an anisotropic medium, its propagation speed and refractive index value change with the vibration direction, and its refractive index value is more than one; when a light wave is incident on an anisotropic medium, except in special directions, double refraction will occur, and it is decomposed into two polarized lights with perpendicular vibration directions, different propagation speeds, and unequal refractive indices. This phenomenon is double refraction.

[0034] The following is further illustrated with specific examples.

[0035] Example 1 (1)Add 155 ml of absolute ethanol, 32 ml of deionized water, and 4 ml of 28% ammonia water into a beaker. After mixing, add 4.4 ml of tetraethyl orthosilicate and react at a low speed to obtain seed solution A; (2)Add 155 ml of absolute ethanol, 30 ml of deionized water, and 21 ml of 28% ammonia water into a beaker. Add the seed solution A obtained in (1) to obtain reaction solution B; (3)Mix water, absolute ethanol, and 28% ammonia water in a volume ratio of 3:10:7 in a beaker and stir to obtain reaction solution C; (4)Drop 12 ml of TEOS and 15 ml of reaction solution C into reaction solution B and stir at a low speed to obtain solution D; (5)After centrifuging solution D, dry it with absolute ethanol, repeat three times and then dry it in an oven. After fully grinding, silica microspheres with a particle size of 450 - 650 nm and a specific polydisperse distribution can be obtained; (6)Add 0.3% silica aqueous dispersion and 2% cellulose nanocrystal aqueous dispersion into a beaker and blend and cast a film in a volume ratio of 1:4.

[0036] Figure 1 It is the effect diagram of casting a film with a mass ratio of 1:4 of the silica and cellulose nanocrystal dispersion prepared in Example 1. It can be seen from the figure that the film-forming property of the film is poor, the transparency is low and it is whitish, with a faint blue luster.

[0037] Example 2 (1)Add 165 ml of absolute ethanol, 37 ml of deionized water, and 3.8 ml of 28% ammonia water into a beaker. After mixing, add 4.2 ml of tetraethyl orthosilicate and react at a low speed to obtain seed solution A; (2)Add 165 ml of absolute ethanol, 34 ml of deionized water, and 25 ml of 28% ammonia water into a beaker. Add the seed solution A obtained in (1) to obtain reaction solution B; (3)Mix water, absolute ethanol, and 28% ammonia water in a volume ratio of 3:10:7 in a beaker and stir to obtain reaction solution C; (4)Drop 15 ml of TEOS and 12 ml of reaction solution C into reaction solution B and stir at a low speed to obtain solution D; (5)After centrifuging solution D, dry it with absolute ethanol, repeat three times and then dry it in an oven. After fully grinding, silica microspheres with a particle size of 450 - 650 nm and a specific polydisperse distribution can be obtained; (6)Add 0.3% SiO 2The aqueous dispersion was ultrasonically treated for 30 min, poured into a round polystyrene Petri dish with a diameter of 35 mm, and subjected to evaporation-induced self-assembly at 40 °C.

[0038] Example 3 (1) 165 ml of absolute ethanol, 32 ml of deionized water, and 4.2 ml of 28% ammonia water were added to a beaker. After mixing, 4.6 ml of tetraethyl orthosilicate was added, and the reaction was carried out at a low speed to obtain seed solution A; (2) 165 ml of absolute ethanol, 32 ml of deionized water, and 24 ml of 28% ammonia water were added to a beaker, and the seed solution A obtained in (1) was added to obtain reaction solution B; (3) Water, absolute ethanol, and 28% ammonia water were mixed in a volume ratio of 3:10:7 in a beaker, and stirred to obtain reaction solution C; (4) 13 ml of TEOS and 10 ml of reaction solution C were added dropwise to reaction solution B, and stirred at a low speed to obtain solution D; (5) After centrifuging solution D, it was washed with absolute ethanol, repeated three times, and then dried. After thorough grinding, silica microspheres with a particle size in the range of 465 - 650 nm and a specific polydisperse distribution could be obtained; (6) 6% of polyvinylpyrrolidone was added to a 0.3% SiO 2 aqueous dispersion, ultrasonically treated for 30 min, poured into a round polystyrene Petri dish with a diameter of 35 mm, and subjected to evaporation-induced self-assembly at 40 - 45 °C; (7) The apparent structure of the silica film before and after the addition of polyvinylpyrrolidone was characterized by scanning electron microscopy; (8) After adding polyvinylpyrrolidone, the silica was coated with polyvinylpyrrolidone, and the orderliness of the microsphere arrangement was improved.

[0039] Figure 2 It is a comparison diagram of the SEM optical effects of silica before and after the addition of polyvinylpyrrolidone prepared in Example 2 and Example 3. As can be seen from the figure, when polyvinylpyrrolidone was not added, the silica microspheres showed agglomeration and were arranged randomly, and the film had no structural color; the addition of polyvinylpyrrolidone improved the dispersion of silica in water, making the self-assembly of silica more orderly, thus increasing the light transmittance of the film.

[0040] Example 4 (1) 165 ml of absolute ethanol, 35 ml of deionized water, and 4.6 ml of 28% ammonia water were added to a beaker. After mixing, 4.6 ml of tetraethyl orthosilicate was added, and the reaction was carried out at a low speed to obtain seed solution A; (2) Add 165 ml of absolute ethanol, 35 ml of deionized water, and 24 ml of 28% ammonia water to a beaker, and add the seed solution A obtained in (1) to obtain reaction solution B; (3) Mix water, absolute ethanol, and 28% ammonia water in a volume ratio of 3:10:7 in a beaker, and stir to obtain reaction solution C; (4) Add 13 ml of TEOS and 15 ml of reaction solution C dropwise to reaction solution B, and stir at a low speed to obtain solution D; (5) After centrifuging solution D, dry it with absolute ethanol, repeat three times and then dry it in an oven. After fully grinding, silica microspheres with a particle size of 450 - 650 nm and a specific polydisperse distribution can be obtained; (6) Add a certain amount of polyvinylpyrrolidone to a 0.3% SiO 2 aqueous dispersion, ultrasonically treat for 30 min, then add a certain amount of 2% CNC aqueous dispersion, and ultrasonically blend for 10 min. The volume ratio of the 0.3% SiO 2 aqueous dispersion to the 2% CNC aqueous dispersion is 1:4, and the polyvinylpyrrolidone accounts for 2.4% of the mass percentage of the SiO 2 / CNC solution system. Pour it into a circular polystyrene culture dish with a diameter of 35 mm, and perform evaporation-induced self-assembly at 40 °C.

[0041] Figure 3 It is the optical effect of the silica / cellulose nanocrystal / polyvinylpyrrolidone (silica:cellulose nanocrystal = 1:4) composite film prepared in this example with a polyvinylpyrrolidone dosage of 2.4%. As can be seen from the figure, under natural light, the film has no structural color, the surface is uniform and has a high transparency. Under a point light source, the film shows iridescence, and when the polyvinylpyrrolidone dosage is 2.4%, the iridescence is greatly improved.

[0042] Example 5 (1) Add 155 ml of absolute ethanol, 33 ml of deionized water, and 4.0 ml of 28% ammonia water to a beaker, mix them, and then add 4.4 ml of tetraethyl orthosilicate, and react at a low speed to obtain seed solution A; (2) Add 155 ml of absolute ethanol, 33 ml of deionized water, and 24 ml of 28% ammonia water to a beaker, and add the seed solution A obtained in (1) to obtain reaction solution B; (3) Mix water, absolute ethanol, and 28% ammonia water in a volume ratio of 3:10:7 in a beaker, and stir to obtain reaction solution C; (4) Add 12 ml of TEOS and 15 ml of reaction solution C15 dropwise to reaction solution B, and stir at a low speed to obtain solution D; (5) After centrifuging solution D, it is dried with absolute ethanol. After repeating this three times and then drying in an oven, and fully grinding, silica microspheres with a particle size of 450 - 650 nm and a specific polydisperse distribution can be obtained; (6) A certain amount of polyvinylpyrrolidone is added to a 0.3% SiO 2 aqueous dispersion, and it is ultrasonically treated for 30 min. Then a certain amount of 2% CNC aqueous dispersion is added, and ultrasonic blending is carried out for 10 min. The volume ratio of the 0.3% SiO 2 aqueous dispersion to the 2% CNC aqueous dispersion is 1:4, and the mass percentage of polyvinylpyrrolidone in the SiO 2 / CNC solution system is 1.2%. It is poured into a circular polystyrene culture dish with a diameter of 35 mm, and evaporation-induced self-assembly is carried out at 40 °C.

[0043] Figure 4 It is the optical effect of the silica / cellulose nanocrystal / polyvinylpyrrolidone (silica: cellulose nanocrystal = 1:4) composite film prepared in this example with a polyvinylpyrrolidone dosage of 1.2%. It can be seen from the figure that polyvinylpyrrolidone can not only act as a dispersant for silica, but also adsorb on the surface of cellulose nanocrystals, resulting in an increase in the pitch of cellulose nanocrystals, thereby causing a red shift in the structural color.

[0044] Example 6 (1) Add 160 ml of absolute ethanol, 34 ml of deionized water, and 4.0 ml of 28% ammonia water to a beaker, mix them, and then add 4.4 ml of tetraethyl orthosilicate, and react at a low speed to obtain seed solution A; (2) Add 160 ml of absolute ethanol, 35 ml of deionized water, and 25 ml of 28% ammonia water to a beaker, and add the seed solution A obtained in (1) to get reaction solution B; (3) Mix water, absolute ethanol, and 28% ammonia water in a volume ratio of 3:10:7 in a beaker, and stir to obtain reaction solution C; (4) Add 12 ml of TEOS and 15 ml of reaction solution C dropwise to reaction solution B, and stir at a low speed to obtain solution D; (5) After centrifuging solution D, it is dried with absolute ethanol. After repeating this three times and then drying in an oven, and fully grinding, silica microspheres with a particle size of 450 - 645 nm and a specific polydisperse distribution can be obtained; (6) Take 4 ml of 0.3% silica aqueous dispersion and mix it with PVP and PVA solutions, ultrasonically treat it for 30 min, and then add 1 ml of 2% CNC aqueous dispersion, where the concentration of PVA solution is 8%, the mass percentage of PVA solution in the system is 15%, the amount of PVP is 0.6%, and the mass ratio of silica to cellulose nanocrystal solution is 1:4. Ultrasonic blending is carried out for 10 min, and after casting, evaporation is carried out at 40 °C to induce self-assembly, and SiO is obtained after drying. 2 / CNC composite film.

[0045] Figure 5 This is an optical effect diagram of the composite film of silicon dioxide / cellulose nanocrystal / polyvinyl pyrrolidone / polyvinyl alcohol (silicon dioxide: cellulose nanocrystal = 1:4, polyvinyl pyrrolidone = 0.6%) prepared in this example with a polyvinyl alcohol dosage of 15%. It can be seen from the figure that under natural light, with the increase of polyvinyl alcohol dosage, the structural color of cellulose nanocrystal gradually red-shifts, and under point light source, with the increase of polyvinyl alcohol dosage, the iridescent color of silicon dioxide becomes more brilliant.

[0046] Example 7 (1) Add 155 ml of anhydrous ethanol, 34 ml of deionized water, and 4.2 ml of 28% ammonia water into a beaker, mix, add 4.6 ml of ethyl orthosilicate, and react at a low speed to obtain seed solution A; (2) Add 165 ml of anhydrous ethanol, 32 ml of deionized water and 23 ml of 28% ammonia water into a beaker, and add the seed solution A obtained in (1) to obtain a reaction solution B; (3) In a beaker, water, anhydrous ethanol and 28% aqueous ammonia were mixed in a volume ratio of 3:10:7 and stirred to obtain a reaction solution C; (4) Add 15 ml of TEOS and 14 ml of reaction solution C dropwise to reaction solution B, and stir at a low speed to obtain solution D; (5) After centrifuging solution D, the solution was dried with anhydrous ethanol, and the process was repeated three times and then dried. After sufficient grinding, silica microspheres with a particle size of 450-650 nm and a specific polydisperse distribution were obtained; (6) At 0.3% SiO 2 A certain amount of sorbitol was added to the aqueous dispersion and ultrasonically treated for 30 min. Then a certain amount of 2% CNC aqueous dispersion was added and ultrasonically blended for 10 min. 2 The volume ratio of water dispersion to 2% CNC water dispersion is 1:4, and sorbitol accounts for 1% of SiO 2 The mass percentage of the / CNC solution system was 1.5%. It was poured into a round polystyrene petri dish with a diameter of 35 mm and evaporated at 40 °C to induce self-assembly.

[0047] Figure 6 This is an optical effect diagram of the composite film prepared in this example with a sorbitol dosage of 1.5%. As can be seen from the figure, the film appears iridescent, but the color is uneven, and there is a large area of ​​white area with low light transmittance.

[0048] Example 8 (1) Add 155 ml of anhydrous ethanol, 34 ml of deionized water, and 4.0 ml of 28% ammonia water into a beaker, mix, add 4.4 ml of ethyl orthosilicate, and react at a low speed to obtain seed solution A; (2) Add 155 ml of anhydrous ethanol, 34 ml of deionized water and 24 ml of 28% ammonia water into a beaker, and add the seed solution A obtained in (1) to obtain a reaction solution B; (3) In a beaker, water, anhydrous ethanol and 28% aqueous ammonia were mixed in a volume ratio of 3:10:7 and stirred to obtain a reaction solution C; (4) Add 15 ml of TEOS and 13 ml of reaction solution C dropwise to reaction solution B, and stir at a low speed to obtain solution D; (5) After centrifuging solution D, the solution was dried with anhydrous ethanol, and the process was repeated three times and then dried. After sufficient grinding, silica microspheres with a particle size of 450-650 nm and a specific polydisperse distribution were obtained; (6) At 0.3% SiO 2 A certain amount of sorbitol was added to the aqueous dispersion and ultrasonically treated for 30 min. Then a certain amount of 2% CNC aqueous dispersion was added and ultrasonically blended for 10 min. 2 The volume ratio of water dispersion to 2% CNC water dispersion is 1:4, and sorbitol accounts for 1% of SiO 2 The mass percentage of the / CNC solution system was 2.5%. It was poured into a round polystyrene petri dish with a diameter of 35 mm and evaporated at 40 °C to induce self-assembly.

[0049] Figure 7 This is an optical effect diagram of the composite film prepared in this example with a sorbitol dosage of 2.5%. As can be seen from the figure, the composite film presents a uniform and bright iridescence, the transparency of the film is increased, and sorbitol promotes the orderly self-assembly of silica, so that the film presents a uniform and gorgeous dynamic iridescence under the illumination of a point light source.

[0050] Example 9 (1) Add 154 ml of anhydrous ethanol, 35 ml of deionized water, and 4.2 ml of 28% ammonia water into a beaker, mix, add 4.4 ml of ethyl orthosilicate, and react at a low speed to obtain seed solution A; (2) Add 154 ml of anhydrous ethanol, 35 ml of deionized water and 25 ml of 28% ammonia water into a beaker, and add the seed solution A obtained in (1) to obtain a reaction solution B; (3) In (1), water, absolute ethanol, and 28% ammonia water were mixed in a beaker in a volume ratio of 3:10:7, and stirred to obtain reaction solution C; (4) 15 ml of TEOS and 20 ml of reaction solution C were added dropwise to reaction solution B, and stirred at a low speed to obtain solution D; (5) After centrifuging solution D, it was dried with absolute ethanol, repeated three times and then dried in an oven. After sufficient grinding, silica microspheres with a particle size of 455 - 650 nm and a specific polydisperse distribution could be obtained; (6) A certain amount of polyethylene glycol was added to the 0.3% SiO 2 aqueous dispersion, ultrasonically treated for 30 min, and then a certain amount of 2% CNC aqueous dispersion was added, and ultrasonically blended for 10 min. The volume ratio of the 0.3% SiO 2 aqueous dispersion to the 2% CNC aqueous dispersion was 1:4, and the polyethylene glycol accounted for 1.0% of the mass percentage of the SiO 2 / CNC solution system. It was poured into a round polystyrene petri dish with a diameter of 35 mm, and evaporation-induced self-assembly was carried out at 40°C.

[0051] Figure 8 It is the optical effect diagram of the composite film prepared in this example with a polyethylene glycol dosage of 1.0%. It can be seen from the figure that the composite film is white under the irradiation of a point light source and has no iridescence effect, indicating that too low a dosage of polyethylene glycol is likely to lead to insufficient dispersibility.

[0052] Example 10 (1) In a beaker, 155 ml of absolute ethanol, 36 ml of deionized water, and 4.6 ml of 28% ammonia water were mixed, and then 4.8 ml of tetraethyl orthosilicate was added, and the reaction was carried out at a low speed to obtain seed solution A; (2) In a beaker, 155 ml of absolute ethanol, 36 ml of deionized water, and 24 ml of ammonia water were added, and the seed solution A obtained in (1) was added to obtain reaction solution B; (3) In a beaker, water, absolute ethanol, and 28% ammonia water were mixed in a volume ratio of 3:10:7, and stirred to obtain reaction solution C; (4) 14 ml of TEOS and 20 ml of reaction solution C were added dropwise to reaction solution B, and stirred at a low speed to obtain solution D; (5) After centrifuging solution D, it was dried with absolute ethanol, repeated three times and then dried in an oven. After sufficient grinding, silica microspheres with a particle size of 450 - 650 nm and a specific polydisperse distribution could be obtained; (6) In the 0.3% SiO 2A certain amount of polyethylene glycol was added to the aqueous dispersion, ultrasonicated for 30 min, and then a certain amount of 2% CNC aqueous dispersion was added, followed by ultrasonic blending for 10 min. 0.3% SiO 2 The volume ratio of the aqueous dispersion to the 2% CNC aqueous dispersion was 1:4, and polyethylene glycol accounted for 1.5% of the mass percentage of the SiO 2 / CNC solution system. It was poured into a circular polystyrene Petri dish with a diameter of 35 mm and subjected to evaporation-induced self-assembly at 40 °C.

[0053] Figure 9 This is the optical effect diagram of the composite film prepared in this example with 1.5% polyethylene glycol. It can be seen from the figure that the film begins to show iridescence, but the color is uneven, and there are still large areas of white regions with low light transmittance.

[0054] Example 11 (1) In a beaker, 155 ml of absolute ethanol, 32 ml of deionized water, and 4.0 ml of 28% ammonia water were mixed, and then 4.4 ml of tetraethyl orthosilicate was added, and the reaction was carried out at low speed to obtain seed solution A; (2) In a beaker, 155 ml of absolute ethanol, 32 ml of deionized water, and 25 ml of ammonia water were added, and the seed solution A obtained in (1) was added to obtain reaction solution B; (3) In a beaker, water, absolute ethanol, and 28% ammonia water were mixed in a volume ratio of 3:10:7, and stirred to obtain reaction solution C; (4) 13 ml of TEOS and 15 ml of reaction solution C were added dropwise to reaction solution B, and stirred at low speed to obtain solution D; (5) After centrifuging solution D, it was dried with absolute ethanol, repeated three times and then dried in an oven, and after sufficient grinding, silica microspheres with a particle size of 450 - 650 nm showing a specific polydisperse distribution could be obtained; (6) In 0.3% SiO 2 A certain amount of polyethylene glycol was added to the aqueous dispersion, ultrasonicated for 30 min, and then a certain amount of 2% CNC aqueous dispersion was added, followed by ultrasonic blending for 10 min. 0.3% SiO 2 The volume ratio of the aqueous dispersion to the 2% CNC aqueous dispersion was 1:4, and polyethylene glycol accounted for 2.5% of the mass percentage of the SiO 2 / CNC solution system. It was poured into a circular polystyrene Petri dish with a diameter of 35 mm and subjected to evaporation-induced self-assembly at 40 °C.

[0055] Figure 10 This is the optical effect diagram of the composite film prepared in this example with 2.5% polyethylene glycol. It can be seen from the figure that the brightness of the iridescence decreases, indicating that excessive polyethylene glycol will interfere with the assembly of silica, thus affecting its structural color.

[0056] Example 12 (1)Add 156 ml of absolute ethanol, 34 ml of deionized water, and 4.2 ml of 28% ammonia water into a beaker. After mixing, add 4.6 ml of tetraethyl orthosilicate and react at a low speed to obtain seed solution A; (2)Add 156 ml of absolute ethanol, 35 ml of deionized water, and 25 ml of 28% ammonia water into a beaker. Add the seed solution A obtained in (1) to obtain reaction solution B; (3)Mix water, absolute ethanol, and 28% ammonia water in a volume ratio of 3:10:7 in a beaker and stir to obtain reaction solution C; (4)Drop 12 ml of TEOS and 15 ml of reaction solution C into reaction solution B and stir at a low speed to obtain solution D; (5)After centrifuging solution D, dry it with absolute ethanol, repeat three times and then dry it in an oven. After sufficient grinding, silica microspheres with a particle size of 450 - 645 nm and a specific polydisperse distribution can be obtained; (6)Take 4 ml of the aqueous dispersion of silica and mix it with PVP and PVA solutions, and perform ultrasonic treatment for 30 min. Among them, the concentration of the PVA solution is 8%, the mass percentage of the PVA solution in the system is 15%, the mass percentage of PVP in the system is 0.24%. Then add 1 ml of 2% CNC aqueous dispersion, and the mass ratio of silica to cellulose nanocrystal solution is 1:4. Ultrasonically blend for 10 min, pour it, and perform evaporation-induced self-assembly at 45 °C. After drying, obtain SiO 2 / CNC composite film.

[0057] Example 13 (1)Add 156 ml of absolute ethanol, 34 ml of deionized water, and 4.4 ml of 28% ammonia water into a beaker. After mixing, add 4.6 ml of tetraethyl orthosilicate and react at a low speed to obtain seed solution A; (2)Add 156 ml of absolute ethanol, 35 ml of deionized water, and 25 ml of 28% ammonia water into a beaker. Add the seed solution A obtained in (1) to obtain reaction solution B; (3)Mix water, absolute ethanol, and 28% ammonia water in a volume ratio of 3:10:7 in a beaker and stir to obtain reaction solution C; (4)Drop 12 ml of TEOS and 15 ml of reaction solution C into reaction solution B and stir at a low speed to obtain solution D; (5)After centrifuging solution D, dry it with absolute ethanol, repeat three times and then dry it in an oven. After sufficient grinding, silica microspheres with a particle size of 450 - 645 nm and a specific polydisperse distribution can be obtained; (6) Take 4 ml of silica aqueous dispersion and mix it with PVP and PVA solutions, and ultrasonically treat it for 30 min. Among them, the concentration of PVA solution is 8%, the mass percentage of PVA solution in the system is 15%, and the mass percentage of PVP in the system is 4.8%. Then add 1 ml of 2% CNC aqueous dispersion, the mass ratio of silica to cellulose nanocrystal solution is 1:4, and ultrasonically mix it for 10 min. After casting, evaporate at 45°C to induce self-assembly, and obtain SiO after drying. 2 / CNC composite film.

[0058] Embodiment 14 (1) Add 156 ml of anhydrous ethanol, 34 ml of deionized water, and 4.2 ml of 28% ammonia water into a beaker, mix, add 4.4 ml of ethyl orthosilicate, and react at a low speed to obtain seed solution A; (2) Add 156 ml of anhydrous ethanol, 35 ml of deionized water and 25 ml of 28% ammonia water into a beaker, and add the seed solution A obtained in (1) to obtain a reaction solution B; (3) In a beaker, water, anhydrous ethanol and 28% aqueous ammonia were mixed in a volume ratio of 3:10:7 and stirred to obtain a reaction solution C; (4) Add 12 ml of TEOS and 15 ml of reaction solution C dropwise to reaction solution B, and stir at a low speed to obtain solution D; (5) After centrifuging solution D, the solution was dried with anhydrous ethanol, and the process was repeated three times and then dried. After sufficient grinding, silica microspheres with a particle size of 450-645 nm and a specific polydisperse distribution were obtained; (6) 4 ml of silica aqueous dispersion was mixed with sorbitol and ultrasonicated for 30 min. Then 1 ml of 2% CNC aqueous dispersion was added, wherein the mass ratio of silica to cellulose nanocrystal solution was 1:4 and the amount of sorbitol added was SiO 2 / CNC solution system, ultrasonically blended for 10 min, and then cast at 45 °C for evaporation to induce self-assembly. After drying, SiO 2 / CNC composite film.

[0059] Embodiment 15 (1) Add 156 ml of anhydrous ethanol, 34 ml of deionized water, and 4.4 ml of 28% ammonia water into a beaker, mix, add 4.6 ml of ethyl orthosilicate, and react at a low speed to obtain seed solution A; (2) Add 156 ml of anhydrous ethanol, 35 ml of deionized water and 25 ml of 28% ammonia water into a beaker, and add the seed solution A obtained in (1) to obtain a reaction solution B; (3) In a beaker, water, anhydrous ethanol and 28% aqueous ammonia were mixed in a volume ratio of 3:10:7 and stirred to obtain a reaction solution C; (4) Add 12 ml of TEOS and 15 ml of reaction solution C dropwise to reaction solution B, and stir at a low speed to obtain solution D; (5) After centrifuging solution D, the solution was dried with anhydrous ethanol, and the process was repeated three times and then dried. After sufficient grinding, silica microspheres with a particle size of 450-645 nm and a specific polydisperse distribution were obtained; (6) Take 4 ml of silica aqueous dispersion and mix it with PVP and PVA solutions, and ultrasonically treat it for 30 min. Among them, the concentration of PVA solution is 8%, the mass percentage of PVA solution in the system is 15%, and the mass percentage of PVP in the system is 4.8%. Then add 1 ml of 2% CNC aqueous dispersion, the mass ratio of silica to cellulose nanocrystal solution is 1:4, and ultrasonically mix it for 10 min. After casting, evaporate at 45°C to induce self-assembly, and obtain SiO after drying. 2 / CNC composite film.

[0060] Example 16 (1) Add 156 ml of anhydrous ethanol, 34 ml of deionized water, and 4.4 ml of 28% ammonia water into a beaker, mix, add 4.6 ml of ethyl orthosilicate, and react at a low speed to obtain seed solution A; (2) Add 156 ml of anhydrous ethanol, 35 ml of deionized water and 25 ml of 28% ammonia water into a beaker, and add the seed solution A obtained in (1) to obtain a reaction solution B; (3) In a beaker, water, anhydrous ethanol and 28% aqueous ammonia were mixed in a volume ratio of 3:10:7 and stirred to obtain a reaction solution C; (4) Add 12 ml of TEOS and 15 ml of reaction solution C dropwise to reaction solution B, and stir at a low speed to obtain solution D; (5) After centrifuging solution D, the solution was dried with anhydrous ethanol, and the process was repeated three times and then dried. After sufficient grinding, silica microspheres with a particle size of 450-645 nm and a specific polydisperse distribution were obtained; (6) 4 ml of silica aqueous dispersion was mixed with sorbitol and ultrasonicated for 30 min. Then 1 ml of 2% CNC aqueous dispersion was added, wherein the mass ratio of silica to cellulose nanocrystal solution was 1:4 and the amount of sorbitol added was SiO 2 / CNC solution system, ultrasonically blended for 10 min, and then cast at 45 °C to induce self-assembly. After drying, SiO 2 / CNC composite film.

[0061] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a composite film with multiple optical characteristics by a co-casting method, characterized in that: The following steps are involved: Step 1, mixing silica microspheres with water to form a silica aqueous dispersion, and mixing cellulose nanocrystals with water to form a cellulose nanocrystal aqueous dispersion; Step 2: Mix the silicon dioxide aqueous dispersion and the dispersant to obtain a mixed solution, mix the mixed solution with the cellulose nanocrystal aqueous dispersion, pour the mixture into a container, evaporate to induce self-assembly and dry to obtain a SiO2 / CNC composite film.

2. The method for preparing a composite film with multiple optical characteristics by a co-casting method according to claim 1, characterized in that: In step 1, the mass fraction of the silica aqueous dispersion is 0.3%.

3. The method for preparing a composite film with multiple optical characteristics by a co-casting method according to claim 1, characterized in that: In step 1, the mass fraction of the cellulose nanocrystal aqueous dispersion is 2%.

4. The method for preparing a composite film with multiple optical characteristics by a co-casting method according to claim 1, characterized in that: In step 2, the mixing volume ratio of the silica aqueous dispersion and the cellulose nanocrystal aqueous dispersion is 1:

4.

5. The method for preparing a composite film with multiple optical characteristics by a co-casting method according to claim 1, characterized in that: The dispersant is one or more of polyvinyl pyrrolidone, sorbitol, polyethylene glycol and trimethylsiloxysilicate.

6. The method for preparing a composite film with multiple optical characteristics by a co-casting method according to claim 5, characterized in that: When the dispersant is polyvinyl pyrrolidone, the amount of the dispersant added is 0.24%-4.8% of the total mass of the silicon dioxide aqueous dispersion and the cellulose nanocrystal aqueous dispersion.

7. The method for preparing a composite film with multiple optical characteristics by a blending casting method according to claim 6, characterized in that: When the dispersant is polyvinyl pyrrolidone, a film-forming agent is added.

8. The method for preparing a composite film with multiple optical characteristics by a blending casting method according to claim 7, characterized in that: The film-forming agent is one or more of polyvinyl alcohol and polyurethane.

9. The method for preparing a composite film with multiple optical characteristics by a co-casting method according to claim 1, characterized in that: When the dispersant is sorbitol, polyethylene glycol or trimethylsiloxysilicate, the amount of the dispersant added is 0.5%-3.0% of the total mass of the silicon dioxide aqueous dispersion and the cellulose nanocrystal aqueous dispersion.

10. A composite film with multiple optical characteristics prepared by the blending casting method according to any one of claims 1 to 9, characterized in that: The invention comprises a stacked upper layer and a lower layer, wherein the lower layer is a SiO2 photonic crystal layer, and the upper layer is a CNC photonic crystal layer, wherein SiO2 particles are embedded in the CNC photonic crystal layer.

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