A self-healing cellulose nanocrystal photonic film and its preparation method

Abstract

The present invention belongs to the field of new materials, and in particular relates to a self-healing cellulose nanocrystal photonic film and a preparation method thereof. Specifically, cellulose nanocrystals are self-assembled to obtain a cellulose nanocrystal iridescent film, which is then soaked and swollen in a dimethyl sulfoxide solution to organically combine a self-healing component with the cellulose nanocrystal iridescent film. The film is endowed with self-healing ability through self-healing repair capabilities such as dynamic covalent borate bonds, dynamic covalent disulfide bonds, dynamic covalent imine bonds, and non-covalent hydrogen bonds. A soft and elastic polymer material is formed by polymerizing monomers to prepare a soft and elastic self-healing cellulose nanocrystal photonic film, the bright structural color of which can be changed by stretching or compressing, and the film can achieve self-healing by controlling environmental conditions.

Description

Technical Field

[0001] The present invention belongs to the field of new materials, and in particular relates to a self-healing cellulose nanocrystal photonic film and a preparation method thereof. Background Art

[0002] In nature, organisms consistently display a variety of colors, crucial for their reproduction and evolution. Their vibrant colors are not limited to traditional pigments like dyes and pigments, but also include structural colors generated by regular structures. Structural color results from the interaction of light with nanostructures, such as interference, diffraction, and scattering. Due to the diffuse scattering of irregularly arranged materials, structural colors are often brighter and more stable than pigments. In nature, the kondensata and margarita fruits produce structural colors from a cholesteric phase structure. Inspired by this, scientists have fabricated photonic films with a cholesteric liquid crystal structure using cellulose nanocrystals as building blocks. These films are composed of an ordered array of spatially periodic layers. Due to the Bragg diffraction effect, photons are bandgapped within this array. Light waves with frequencies falling within the photonic bandgap are selectively blocked from the cholesteric structure, while incident left-handed circularly polarized light is selectively partially reflected, resulting in vibrant structural colors. The more ordered the layered structure, the brighter the color. The relationship between the reflected light wavelength, the pitch, the average refractive index of the sample, and the incident light angle is shown in the following formula: max =nPsinθ, where λ max is the reflected wavelength of light, P is the pitch, n is the average refractive index of the sample, and θ is the angle between the incident light and the crystal plane.

[0003] With the increasing emphasis on reusability and sustainable development, self-healing materials are becoming an increasingly popular research topic. Self-healing materials have attracted widespread interest among researchers due to their ability to spontaneously repair damage and restore mechanical properties. The self-healing function of self-healing materials is achieved through the destruction and reformation of internal bonds within the material. This ability to automatically repair damage can help extend the material's service life and enable its recyclability. Self-healing materials can be divided into non-covalent bonds and dynamic covalent bonds based on the characteristics of the bond formation. Interactions based on non-covalent bonds include hydrogen bonds, ionic bonds, host-guest interactions, and hydrophobic interactions, and are characterized by weak mechanical properties. Interactions based on dynamic covalent bonds include the formation of new chemical bonds, such as imine bonds, disulfide bonds, borate bonds, and Diels-Alder reactions.

[0004] In the past five years, cellulose nanocrystal cholesteric liquid crystal structure materials have developed rapidly, but the following challenges still remain: Cholesteric liquid crystal structure is an ordered layered structure prepared by self-assembly of cellulose nanocrystals. Because the interaction between cellulose nanocrystals is mainly weak interaction forces such as hydrogen bonds, without other strong physical or chemical forces, it is brittle and easily broken. Secondly, there is the problem of organically combining cellulose nanocrystals with other components. Combining components with cellulose nanocrystals usually uses a co-assembly method, but co-assembly can easily lead to the loss or impact of the self-assembly ability of cellulose nanocrystals, causing the ordered array of spatially periodic layered arrangements to disappear or have defects, which in turn affects the structural color of the cellulose nanocrystals.

[0005] At present, researchers have almost no research on the self-healing field of cellulose nanocrystals. This material can well fill the gap in the field of self-healing of cellulose nanocrystals. Summary of the Invention

[0006] In response to the many shortcomings of the existing technology, the present invention provides a self-healing cellulose nanocrystal photonic film and a preparation method thereof. Specifically, after cellulose nanocrystals are self-assembled to obtain a cellulose nanocrystal iridescent film, the film is soaked and swollen in a dimethyl sulfoxide solution, and the self-healing component is organically combined with the cellulose nanocrystal iridescent film. The film is endowed with self-healing ability through dynamic covalent borate bonds, dynamic covalent disulfide bonds, dynamic covalent imine bonds, non-covalent hydrogen bonds, etc.; a soft and elastic polymer material is formed by polymerizing monomers to prepare a soft and elastic self-healing cellulose nanocrystal photonic film; after natural light is reflected by the cellulose nanocrystal photonic film, the wavelength of the reflected light is related to the pitch, the average refractive index of the sample, and the angle of the incident light. The pitch can be changed after stretching or compression, thereby giving it a bright structural color. At the same time, it can achieve self-healing by controlling environmental conditions.

[0007] The specific technical solutions of this application are as follows:

[0008] A self-healing cellulose nanocrystal photonic film comprises, by weight, 40-50 parts of cholesteric cellulose nanocrystal iridescent film, 3-20 parts of a self-healing component, and 30-50 parts of a soft and elastic polymer monomer formed by polymerization.

[0009] The cholesteric cellulose nanocrystal iridescent film is prepared by mixing cellulose nanocrystals with hydrophilic small molecules and evaporating the water solvent through self-assembly, wherein the amount of the hydrophilic small molecules added is 20wt%-30wt% of the net content of the cellulose nanocrystals;

[0010] Furthermore, the cellulose nanocrystals are prepared by hydrolyzing commercial conifer pulp in sulfuric acid, and have a length of 150 nm to 180 nm and a width of 5 nm to 10 nm. The concentration of the cellulose nanocrystals in the aqueous solution of the cellulose nanocrystals obtained after hydrolysis is 4 wt %. The hydrophilic small molecules include, but are not limited to, one or more of glucose, ribose, sucrose, and glycerol.

[0011] The hydrophilic small molecules are selected because they have the ability to form hydrogen bonds and other interactive forces with cellulose nanocrystals, forming an ordered array of periodic layers. The hydrophilic small molecules bind to the cellulose nanocrystals through hydrogen bonds between the layers, and they can exist stably, so that the cellulose nanocrystals have sufficient gaps to accommodate the prepolymer solution.

[0012] The substrate in the self-assembly strategy for preparing the above-mentioned cholesteric cellulose nanocrystal iridescent film is glass, plastic culture dishes, such as polystyrene culture dishes, etc.; the self-assembly strategy is a conventional evaporation-induced self-assembly method (EISA), vacuum-assisted self-assembly method (VASA), etc., and the inventors will not elaborate on it.

[0013] The self-healing components include but are not limited to 3-acrylamidophenylboronic acid (3-ABA) and polyvinyl alcohol (PVA) forming dynamic covalent borate ester bonds, waterborne polyurethane (WPU) with dynamic covalent disulfide bonds, polyacrylamide (PAM) and hyaluronic acid (HA) with dynamic covalent imine bonds, and polyacrylamide (PAM) cross-linked with non-covalent hydrogen bonds, etc., which have cross-linking self-healing capabilities.

[0014] The monomers polymerized to form a soft elastic polymer include but are not limited to one of a mixture of ethyl acrylate (EA) / hydroxyethyl acrylate (2-HEA), a mixture of methyl acrylate (MA) / methyl methacrylate (MMA), a mixture of allyl acrylate (ALA) / hydroxypropyl acrylate (2-HPA), and polydimethylsiloxane (PDMS). When the above two monomers are mixed, the molar ratio of the two monomers is 1:0.1.

[0015] The cholesteric cellulose nanocrystal iridescent film possesses a cholesteric liquid crystal structure, forming an ordered array of spatially periodic layers. Its interaction with light produces vibrant structural colors, endowing the cellulose nanocrystal photonic film with a vibrant structural color. The self-healing component breaks and reforms internal bonds, automatically repairing damage and imparting self-healing capabilities to the cellulose nanocrystal photonic film. The polymerized soft and elastic polymer monomers, through thermal polymerization, form an elastomer, imparting the cellulose nanocrystal photonic film with softness and stretchability. The self-healing component and the polymerized soft and elastic polymer monomers are hydrogen-bonded and cross-distributed within the voids of the cellulose nanocrystal iridescent film. After thermal polymerization, the cholesteric liquid crystal structure of the cellulose nanocrystal iridescent film is retained within the elastomer.

[0016] The inventors also provide a method for preparing the self-healing cellulose nanocrystal photonic film, the specific steps of which are as follows:

[0017] (1) Preparation of cholesteric cellulose nanocrystal iridescent film: Cellulose nanocrystals and hydrophilic small molecules are evenly mixed as the precursor solution, and the mixture is prepared by self-assembly strategy. After the solvent water evaporates, the cholesteric cellulose nanocrystal iridescent film is obtained;

[0018] The cholesteric cellulose nanocrystal iridescent film prepared at this time has bright structural colors, but it is highly brittle, cannot be folded or stretched, and has limited elongation, so subsequent processing steps are required.

[0019] (2) Swelling of cholesteric cellulose nanocrystal iridescent film: The cholesteric cellulose nanocrystal iridescent film was immersed in a mixed solution of dimethyl sulfoxide and polymerization initiator 2,2-azobisisobutyronitrile under nitrogen atmosphere. The concentration of 2,2-azobisisobutyronitrile in the mixed solution was 15-30 mg / ml, so that it swelled to obtain a cellulose nanocrystal film with a loose internal structure and a certain thickness on the surface. The thickness varied with the swelling time, and the swelling time was 30 min - 90 min, and the thickness was 0.4 mm - 0.6 mm.

[0020] The main purpose of adding the initiator in advance in this step is to allow it to fully enter the interior of the cellulose nanocrystal iridescent film, so that the subsequent polymerization reaction can proceed fully. After this step, the pitch of the cellulose nanocrystal film increases, the color red shifts to the infrared region, and it becomes transparent and extremely easy to break, similar to the jelly state.

[0021] (3) Preparation of self-healing cellulose nanocrystal photonic film: The self-healing components in the formula are mixed with the monomers that form soft elastic polymers and the initiator as a prepolymer solution, and the molar ratio of the monomer to the initiator is 1:0.001. The swollen cholesteric cellulose nanocrystal iridescent film is immersed in the prepolymer solution for 4-10 hours, and then heated to 50℃-80℃ under a nitrogen atmosphere and polymerized for 12-24 hours to obtain a self-healing cellulose nanocrystal photonic film.

[0022] The immersion time in this step is different, and the amount of self-healing components entering the interior of the cellulose nanocrystal iridescent film is different, which affects the self-healing ability of the final photonic film. Among them, the self-healing component is the key to the self-healing ability of the cellulose nanocrystal photonic film. It has the characteristics of non-covalent bond or dynamic covalent bond-based interaction, internal bond destruction and reformation, and restoration of its own performance. Therefore, the above-mentioned immersion time is selected.

[0023] The cellulose nanocrystal photonic membrane obtained at this time undergoes swelling and monomer polymerization, and the pitch increases, the color red-shifts to the infrared region, and becomes transparent. It has excellent softness, low modulus and high rebound properties. It can be folded, bent, and twisted at will, showing good toughness. It can be stretched more than 5 times its own length without breaking and can restore to its original state. It can be stretched and compressed like a low-strength spring, and presents bright structural colors after stretching or compression. After the photonic membrane is damaged or broken, it can spontaneously repair the damage and restore mechanical properties under certain environmental conditions.

[0024] At present, most cellulose nanocrystal hydrogel self-healing materials are co-assembled by mixing self-healing components with cellulose nanocrystal aqueous solutions. The existing co-assembly method tends to affect its self-assembly ability to a greater or lesser extent, thereby affecting the ordered array of periodic layered arrangements, and ultimately affecting its structural color. This invention adopts a self-assembly method to first prepare a cholesteric cellulose nanocrystal iridescent film, and then through swelling, prepolymer liquid infiltration, and polymerization, this problem can be well avoided. Secondly, most existing cellulose nanocrystal photonic films lack elasticity, have low mechanical properties, and are not stretchable. In this invention, due to the introduction of a soft elastomer, the photonic film is given good elasticity and stretchability. At the same time, the introduction of a self-healing component makes the cellulose nanocrystal photonic film have self-healing ability.

[0025] In summary, the soft, elastic, self-healing cellulose nanocrystal photonic film provided by the present invention can change its bright structural color by stretching or compressing, and can also achieve self-healing by controlling environmental conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure and self-healing repair of the self-healing cellulose nanocrystal photonic membrane obtained by the present invention;

[0027] (a) The original cholesteric cellulose nanocrystal iridescent film is brittle, easily broken, cannot be folded or stretched, has limited elongation, and has no self-healing ability.

[0028] (b) The cellulose nanocrystal iridescent film is soaked and swelled in a dimethyl sulfoxide solution, and the internal voids become larger. The self-healing component is mixed with the polymerized soft elastic polymer monomer to soak the cellulose nanocrystal iridescent film and then thermally polymerized, making the cellulose nanocrystal photonic film have self-healing ability;

[0029] (c) The cellulose nanocrystal photonic membrane self-heals under certain environmental conditions. The internal dynamic covalent bonds or non-covalent bonds can be destroyed and then formed again, restoring their own properties, thereby self-healing and repairing damage or breakage.

[0030] Figure 2 A physical picture of the self-healing cellulose nanocrystal photonic film obtained in Example 1 of the present invention and a physical picture of the film after self-healing;

[0031] (a) is a photo of the self-healing cellulose nanocrystal photonic film obtained in Example 1;

[0032] (b) is a photo of the self-healing cellulose nanocrystal photonic film obtained in Example 1 after self-healing, and the box in the figure is a partial enlarged view of the self-healing part;

[0033] (c) is a photograph of the self-healing cellulose nanocrystal photonic film obtained in Example 1 after self-healing, showing a heavy object being lifted. The square in the figure is a partial magnified view of the self-healing part. DETAILED DESCRIPTION

[0034] The present invention will be further explained below in conjunction with specific implementation examples. The following implementation examples are only intended to further fully and clearly explain the present invention. The described examples are only part of the implementation examples of the present invention and do not constitute all implementation examples. All other implementation examples created based on this invention fall within the scope of protection of this invention. Unless otherwise specified, the following examples are all completed using conventional technical operations.

[0035] The cellulose nanocrystals used in the following examples were prepared by hydrolyzing commercial coniferous pulp in sulfuric acid. They had a length of 150 nm to 180 nm and a width of 5 nm to 10 nm. The concentration of the cellulose nanocrystals in the aqueous solution of the cellulose nanocrystals obtained after hydrolysis was 4 wt%.

[0036] The hydrophilic small molecules include but are not limited to one or more of glucose, ribose, sucrose, and glycerol.

[0037] The self-healing components include but are not limited to 3-acrylamidophenylboronic acid (3-ABA) and polyvinyl alcohol (PVA) forming dynamic covalent borate ester bonds, waterborne polyurethane (WPU) with dynamic covalent disulfide bonds, polyacrylamide (PAM) and hyaluronic acid (HA) with dynamic covalent imine bonds, and polyacrylamide (PAM) cross-linked with non-covalent hydrogen bonds, etc., which have cross-linking self-healing capabilities.

[0038] The monomers polymerized to form a soft elastic polymer include but are not limited to one of a mixture of ethyl acrylate (EA) / hydroxyethyl acrylate (2-HEA), a mixture of methyl acrylate (MA) / methyl methacrylate (MMA), a mixture of allyl acrylate (ALA) / hydroxypropyl acrylate (2-HPA), and polydimethylsiloxane (PDMS). When the above two monomers are mixed, the molar ratio of the two monomers is 1:0.1.

[0039] Example 1

[0040] A self-healing cellulose nanocrystal photonic film, comprising components by weight: 50 parts of cholesteric cellulose nanocrystal iridescent film, 10 parts of a self-healing component, and 40 parts of a soft and elastic polymer monomer formed by polymerization;

[0041] The self-healing components are: 3-acrylamidophenylboronic acid and polyvinyl alcohol, which form a dynamic covalent borate ester bond, with a mass ratio of 4:15;

[0042] The monomers for forming the soft elastic polymer by polymerization are: ethyl acrylate / hydroxyethyl acrylate, and the molar ratio of the two monomers is 1:0.1.

[0043] Its specific preparation method is as follows:

[0044] (1) Preparation of cholesteric cellulose nanocrystal iridescent film: A cellulose nanocrystal aqueous solution hydrolyzed with sulfuric acid was mixed evenly with glucose small molecules to form a cellulose nanocrystal / glucose dispersion as the precursor solution. The amount of glucose added was 25 wt% of the net content of the cellulose nanocrystals. The film was prepared by evaporation-induced self-assembly strategy. The substrate was a polystyrene culture dish with a diameter of 9 cm. After the water evaporated, a cholesteric cellulose nanocrystal iridescent film was obtained.

[0045] The cholesteric cellulose nanocrystal iridescent film prepared at this time has bright structural colors, but it is highly brittle, cannot be folded or stretched, and has limited elongation.

[0046] (2) Swelling of cholesteric cellulose nanocrystal iridescent film: The cholesteric cellulose nanocrystal iridescent film was immersed in a mixture of dimethyl sulfoxide and 2,2-azobisisobutyronitrile under a nitrogen atmosphere. The concentration of 2,2-azobisisobutyronitrile was 24.6 mg / ml, and the film was allowed to swell for 60 min, thereby obtaining a cellulose nanocrystal film with a loose internal structure.

[0047] At this time, a cellulose nanocrystal film with a thickness of 0.5 mm was obtained. After swelling, the pitch increased, the color shifted to the infrared region, and it became transparent and extremely easy to break, similar to a jelly state.

[0048] (3) Preparation of self-healing cellulose nanocrystal photonic film: The formulated amounts of 3-acrylamidophenylboronic acid and polyvinyl alcohol capable of forming dynamic covalent borate ester bonds were mixed with ethyl acrylate / hydroxyethyl acrylate and 2,2-azobisisobutyronitrile as a prepolymer solution, and the molar ratio of the monomer to the initiator 2,2-azobisisobutyronitrile was 1:0.001. The swollen cholesteric cellulose nanocrystal iridescent film was soaked in the prepolymer solution for 8 h, and then heated to 60 °C in a nitrogen atmosphere for polymerization for 20 h to obtain a self-healing cellulose nanocrystal photonic film.

[0049] The 3-acrylamidophenylboronic acid and polyvinyl alcohol that form dynamic covalent borate bonds are key to the self-healing ability of the cellulose nanocrystal photonic membrane. This self-healing membrane exhibits the properties of borate bond-based interactions, destruction and reformation of borate bonds, and restoration of its own properties. After swelling and monomer polymerization, the cellulose nanocrystal photonic membrane exhibits increased pitch, a red-shifted color to the infrared region, and a transparent state. The membrane exhibits excellent flexibility, low modulus, and high resilience. It can be folded, bent, and twisted arbitrarily, exhibiting excellent toughness and stretching to more than five times its own length without breaking and returning to its original state. It can be stretched and compressed like a low-strength spring, exhibiting bright structural colors after stretching or compression. After damage or breakage, the membrane can spontaneously repair damage and restore its mechanical properties under certain environmental conditions.

[0050] The resulting soft, elastic photonic membrane can self-heal in a Tris-HCl buffer solution at 25°C within 30 minutes. Tris-HCl buffer is a 100M aqueous solution of tris (hydroxymethylaminomethane) with a pH adjusted to 8.5 using HCl.

[0051] Two of the soft and elastic photonic membranes obtained above were stacked, and a few drops of Tris-HCl buffer solution were dripped on the stacking part to soak the stacked fragments. The self-healing process was completed at room temperature of 25°C. After 30 minutes, the part where the solution was dripped became dry, and the two photonic membranes were self-healed and connected. After self-healing, the photonic membrane spontaneously repaired the damage and restored its mechanical properties, and could lift and stretch objects 6000 times its own weight. Figure 2 shown.

[0052] In addition to the Tris-HCl buffer solution added dropwise, ammonia water with a pH greater than 8.05 can also be used as a self-healing condition.

[0053] Example 2

[0054] A self-healing cellulose nanocrystal photonic film, comprising, by weight, 45 parts of a cholesteric cellulose nanocrystal iridescent film, 20 parts of a self-healing component, and 35 parts of a monomer that is polymerized to form a soft and elastic polymer;

[0055] The self-healing component is a water-based polyurethane that forms dynamic covalent disulfide bonds.

[0056] The monomers for polymerizing to form the soft elastic polymer are: methyl acrylate / methyl methacrylate, and the molar ratio of the two monomers is 1:0.1.

[0057] Its specific preparation method is as follows:

[0058] (1) Preparation of cholesteric cellulose nanocrystal iridescent film: The above-mentioned sulfuric acid-hydrolyzed cellulose nanocrystal aqueous solution was evenly mixed with glycerol small molecules to form a cellulose nanocrystal / glycerol dispersion as the precursor solution, wherein the amount of glycerol added was 20 wt% of the net content of cellulose nanocrystals. The film was prepared by evaporation-induced self-assembly strategy, and the substrate was a borosilicate culture dish with a diameter of 3.5 cm. After the water evaporated, the cholesteric cellulose nanocrystal iridescent film was obtained.

[0059] The cholesteric cellulose nanocrystal iridescent film prepared at this time has bright structural colors, but it is highly brittle, cannot be folded or stretched, and has limited elongation.

[0060] (2) Swelling of cholesteric cellulose nanocrystal iridescent film: The cholesteric cellulose nanocrystal iridescent film was immersed in a mixture of dimethyl sulfoxide and 2,2-azobisisobutyronitrile under a nitrogen atmosphere. The concentration of 2,2-azobisisobutyronitrile in the mixture was 30 mg / ml, and the film was allowed to swell for 30 min, thereby obtaining a cellulose nanocrystal film with a loose internal structure.

[0061] At this time, a cellulose nanocrystal film with a thickness of 0.4 mm was obtained. After swelling, the pitch increased, the color shifted to the infrared region, and it became transparent. It was very easy to break, similar to the jelly state.

[0062] (3) Preparation of self-healing cellulose nanocrystal photonic membrane: The formulated amount of aqueous polyurethane capable of forming dynamic covalent disulfide bonds was mixed with methyl acrylate / methyl methacrylate and 2,2-azobisisobutyronitrile as a prepolymer solution, and the molar ratio of the monomer to the initiator 2,2-azobisisobutyronitrile was 1:0.001. The swollen cholesteric cellulose nanocrystal iridescent membrane was soaked in the prepolymer solution for 4 h, and then heated to 70 °C in a nitrogen atmosphere for 18 h to obtain a self-healing cellulose nanocrystal photonic membrane.

[0063] The waterborne polyurethane that forms dynamic covalent disulfide bonds is the key to the self-healing ability of the cellulose nanocrystal photonic membrane. This self-healing membrane exhibits the properties of disulfide bond-based interactions, the destruction and reformation of disulfide bonds, and the restoration of its own properties, resulting in a self-healing cellulose nanocrystal photonic membrane. After swelling and monomer polymerization, the cellulose nanocrystal photonic membrane increases its pitch and red-shifts its color to the infrared region, becoming transparent. It exhibits excellent flexibility, low modulus, and high resilience. It can be folded, bent, and twisted arbitrarily, exhibiting excellent toughness and being able to stretch to more than five times its own length without breaking and returning to its original state. It can be stretched and compressed like a low-strength spring, exhibiting bright structural colors after stretching or compression. After damage or breakage, the membrane can spontaneously repair the damage and restore its mechanical properties under certain environmental conditions.

[0064] The soft and elastic photonic membrane can achieve self-healing in the presence of deionized water at 25°C within 2 h.

[0065] Two sheets of the aforementioned soft, elastic photonic membranes were stacked, and a few drops of deionized water were dripped onto the stack to wet the sections. The self-healing process was then completed at room temperature (25°C). After two hours, the section containing the deionized water dried, and the two photonic membranes were joined. After self-healing, the membranes spontaneously repaired the damage and restored their mechanical properties, capable of lifting objects up to 7,000 times their own weight.

[0066] Example 3

[0067] A self-healing cellulose nanocrystal photonic film, comprising, by weight, 40 parts of a cholesteric cellulose nanocrystal iridescent film, 15 parts of a self-healing component, and 45 parts of a monomer that is polymerized to form a soft and elastic polymer;

[0068] The self-healing components are polyacrylamide and hyaluronic acid that form dynamic covalent imine bonds, with a molar ratio of 1:1.

[0069] The monomers polymerized to form the soft elastic polymer are: allyl acrylate / hydroxypropyl acrylate, and the molar ratio of the two monomers is 1:0.1.

[0070] Its specific preparation method is as follows:

[0071] (1) Preparation of cholesteric cellulose nanocrystal iridescent film: The aqueous solution of cellulose nanocrystals hydrolyzed with sulfuric acid was mixed evenly with sucrose small molecules to form a cellulose nanocrystal / sucrose dispersion as the precursor solution, wherein the amount of sucrose added was 30 wt% of the net content of the cellulose nanocrystals. The film was prepared by evaporation-induced self-assembly strategy. The substrate was a polystyrene culture dish with a diameter of 9 cm. After the water evaporated, the cholesteric cellulose nanocrystal iridescent film was obtained.

[0072] The cholesteric cellulose nanocrystal iridescent film prepared at this time has bright structural colors, but it is highly brittle, cannot be folded or stretched, and has limited elongation.

[0073] (2) Swelling of cholesteric cellulose nanocrystal iridescent film: The cholesteric cellulose nanocrystal iridescent film was immersed in a mixture of dimethyl sulfoxide and 2,2-azobisisobutyronitrile under a nitrogen atmosphere. The concentration of 2,2-azobisisobutyronitrile in the mixture was 15 mg / ml, and the film was allowed to swell for 90 min, thereby obtaining a cellulose nanocrystal film with a loose internal structure.

[0074] At this time, a cellulose nanocrystal film with a thickness of 0.6 mm was obtained. After swelling, the pitch increased, the color shifted to the infrared region, and it became transparent and extremely easy to break, similar to a jelly state.

[0075] (3) Preparation of self-healing cellulose nanocrystal photonic membrane: The components of polyacrylamide and hyaluronic acid capable of forming dynamic covalent imine bonds were mixed with allyl acrylate / hydroxypropyl acrylate and 2,2-azobisisobutyronitrile as a prepolymer solution, and the molar ratio of the monomer to the initiator 2,2-azobisisobutyronitrile was 1:0.001. The swollen cholesteric cellulose nanocrystal iridescent membrane was soaked in the prepolymer solution for 10 h, and then heated to 65 ° C in a nitrogen atmosphere for 24 h to obtain a self-healing cellulose nanocrystal photonic membrane.

[0076] The polyacrylamide and hyaluronic acid that form dynamic covalent imine bonds are key to the self-healing ability of the cellulose nanocrystal photonic membrane. This self-healing membrane exhibits the properties of imine bond-based interactions, imine bond destruction and reformation, and restoration of its own properties, resulting in a self-healing cellulose nanocrystal photonic membrane. After swelling and monomer polymerization, the cellulose nanocrystal photonic membrane increases its pitch and red-shifts its color to the infrared region, becoming transparent. It exhibits excellent flexibility, low modulus, and high resilience. It can be folded, bent, and twisted arbitrarily, exhibiting excellent toughness and being able to stretch to more than five times its own length without breaking and returning to its original state. It can be stretched and compressed like a low-strength spring, exhibiting bright structural colors after stretching or compression. After damage or breakage, the membrane can spontaneously repair the damage and restore its mechanical properties under certain environmental conditions.

[0077] The soft and elastic photonic membrane can achieve self-healing in the presence of deionized water at room temperature of 25°C within 1 h.

[0078] Two of the aforementioned soft, elastic photonic membranes were stacked, and a few drops of deionized water were dripped onto the stack to soak the sections. The self-healing process was then completed at room temperature (25°C). After one hour, the section with the deionized water dried, and the two photonic membranes were joined. After self-healing, the membranes spontaneously repaired the damage and restored their mechanical properties, capable of lifting objects up to 6,500 times their own weight.

[0079] The various technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the various technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should all be considered to be within the scope of this specification. The description of the above implementation cases can be used to help understand the principles and methods of the present invention. However, the above implementation cases are not exclusive and should not be construed as limiting the present invention. At the same time, for those skilled in the art, according to the principles and methods of the present invention, flexible changes can be made in the specific implementation methods and application scopes.

Claims

1. A self-healing cellulose nanocrystal photonic film, characterized in that: The components thereof include, by weight: 40-50 parts of cholesteric cellulose nanocrystal iridescent film, 3-20 parts of self-healing component, and 30-50 parts of soft elastic polymer monomer formed by polymerization; The preparation method thereof comprises the following specific steps: (1) Preparation of cholesteric cellulose nanocrystal iridescent film: Cellulose nanocrystals and hydrophilic small molecules are evenly mixed as the precursor solution, and the mixture is prepared by self-assembly strategy. After the solvent water evaporates, the cholesteric cellulose nanocrystal iridescent film is obtained; (2) Swelling of cholesteric cellulose nanocrystal iridescent film: The cholesteric cellulose nanocrystal iridescent film was immersed in a mixed solution of dimethyl sulfoxide and 2,2-azobisisobutyronitrile, an initiator of the polymerization reaction, under a nitrogen atmosphere to allow it to swell, thereby obtaining a cellulose nanocrystal film with a loose internal structure and a certain thickness on the surface. The swelling time was 30 min-90 min, and the thickness was 0.4 mm-0.6 mm. (3) Preparation of self-healing cellulose nanocrystal photonic film: The self-healing components in the formula are mixed with the monomers that form a soft elastic polymer and the initiator as a prepolymer solution, and the swollen cholesteric cellulose nanocrystal iridescent film is immersed in the prepolymer solution for 4-10 hours, and then heated to 50℃-80℃ under a nitrogen atmosphere and polymerized for 12-24 hours to obtain a self-healing cellulose nanocrystal photonic film.

2. The self-healing cellulose nanocrystal photonic film according to claim 1, characterized in that: The cholesteric cellulose nanocrystal iridescent film is prepared by mixing cellulose nanocrystals with hydrophilic small molecules and evaporating the water solvent through self-assembly, wherein the addition amount of the hydrophilic small molecules is 20wt%-30wt% of the net content of the cellulose nanocrystals.

3. The self-healing cellulose nanocrystal photonic film according to claim 2, characterized in that: The cellulose nanocrystals are prepared by hydrolyzing commercial coniferous pulp in sulfuric acid, and have a length of 150nm-180nm and a width of 5nm-10nm; the concentration of the cellulose nanocrystals in the cellulose nanocrystal aqueous solution obtained after hydrolysis is 4 wt%; the hydrophilic small molecules are selected from one or more of glucose, ribose, sucrose, and glycerol.

4. The self-healing cellulose nanocrystal photonic film according to claim 1, characterized in that: The self-healing component is selected from one or more of 3-acrylamidophenylboronic acid and polyvinyl alcohol forming dynamic covalent borate ester bonds, aqueous polyurethane forming dynamic covalent disulfide bonds, polyacrylamide and hyaluronic acid forming dynamic covalent imine bonds, and polyacrylamide cross-linked by non-covalent hydrogen bonds.

5. The self-healing cellulose nanocrystal photonic film according to claim 1, characterized in that: The monomers polymerized to form the soft elastic polymer are selected from a mixture of ethyl acrylate / hydroxyethyl acrylate, a mixture of methyl acrylate / methyl methacrylate, and a mixture of allyl acrylate / hydroxypropyl acrylate.

6. The self-healing cellulose nanocrystal photonic film according to claim 5, characterized in that: When two monomers are mixed, the molar ratio of the two monomers is 1:0.

1.

7. The method for preparing the self-healing cellulose nanocrystal photonic film according to claim 1, characterized in that: The specific steps are as follows: (1) Preparation of cholesteric cellulose nanocrystal iridescent film: Cellulose nanocrystals and hydrophilic small molecules are evenly mixed as the precursor solution, and the mixture is prepared by self-assembly strategy. After the solvent water evaporates, the cholesteric cellulose nanocrystal iridescent film is obtained; (2) Swelling of cholesteric cellulose nanocrystal iridescent film: The cholesteric cellulose nanocrystal iridescent film was immersed in a mixed solution of dimethyl sulfoxide and 2,2-azobisisobutyronitrile, an initiator of the polymerization reaction, under a nitrogen atmosphere to allow it to swell, thereby obtaining a cellulose nanocrystal film with a loose internal structure and a certain thickness on the surface. The swelling time was 30 min-90 min, and the thickness was 0.4 mm-0.6 mm. (3) Preparation of self-healing cellulose nanocrystal photonic film: The self-healing components in the formula are mixed with the monomers that form a soft elastic polymer and the initiator as a prepolymer solution, and the swollen cholesteric cellulose nanocrystal iridescent film is immersed in the prepolymer solution for 4-10 hours, and then heated to 50℃-80℃ under a nitrogen atmosphere and polymerized for 12-24 hours to obtain a self-healing cellulose nanocrystal photonic film.

8. The method for preparing the self-healing cellulose nanocrystal photonic film according to claim 7, characterized in that: In step (2), the concentration of 2,2-azobisisobutyronitrile in the mixed solution is 15-30 mg / ml.

9. The method for preparing the self-healing cellulose nanocrystal photonic film according to claim 7, characterized in that: The molar ratio of monomer to initiator in step (3) is 1:0.001.

Images