A lignin nanoparticle-based photonic crystal thin film and a preparation method thereof

Abstract

The application discloses a kind of photonic crystal film based on lignin nanoparticles and preparation method, in the dispersion liquid of lignin nanoparticles, 2-dihydroxymethyl propionic acid and p-toluene sulfonic acid are added in protective atmosphere and hyperbranched reaction is carried out, and reaction liquid is obtained;The reaction liquid is dialyzed in deionized water, and small molecules and homopolymerization 2-dihydroxymethyl propionic acid generated by side reaction can be removed, and the water dispersion of modified lignin nanoparticles is obtained;The water dispersion of modified lignin nanoparticles is added dropwise to hard transparent material, and drying is carried out by the way of electric heating and air circulation, and the photonic crystal film based on lignin nanoparticles is obtained.The application obtains H-LNP with polyhydroxy through hyperbranched reaction, and this polyhydroxy structure gives H-LNPs good self-assembly tendency, so that it can form thin film with clear structural color under the condition of evaporation-induced self-assembly.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photonic crystals, and particularly relates to a photonic crystal film based on lignin nanoparticles and a preparation method thereof. BACKGROUND

[0002] A photonic crystal is a material with a periodic structure, the periodic structure of which has a scale comparable to or smaller than the wavelength of light. Its basic principle is to use the periodic arrangement of media or the refractive index difference between media to realize the diffraction and interference of light. When light passes through a photonic crystal, it will be limited and scattered by the lattice structure, causing the wavelength of light to be limited or diffracted in the material, forming a specific photonic band gap. These photonic band gaps make light unable to propagate in a specific frequency range, thereby producing a photonic band gap, so that the photonic crystal has specific optical properties, such as optical isolation, optical waveguide, photonic modulation, etc. The design and preparation of photonic crystals can realize precise control of optical properties by adjusting the lattice structure and material refractive index, so it has wide application prospects.

[0003] The preparation of traditional photonic crystals usually uses a combination of high-refractive-index and low-refractive-index materials to construct a lattice with a periodic structure. Common high-refractive-index materials include silicon dioxide, titanium dioxide, etc., while low-refractive-index materials include polymers, air, etc. The preparation methods mainly include self-assembly, solvent evaporation method, photolithography technology, etc. In the self-assembly method, the material is usually self-assembled into a periodic structure by template self-assembly method using physical or chemical means. Although the traditional photonic crystal preparation method has achieved certain success, there are still some challenges and limitations. First, the preparation cost of traditional materials is high, the preparation process is complex, and special equipment and conditions are needed, which limits its application in large-scale production. Second, the traditional preparation method has certain limitations on the selection and processing of materials, in addition, the traditional photonic crystal preparation method often requires a long preparation period and high-precision processing technology, which limits its flexibility and operability in some practical applications. Chinese patent CN114507016 discloses a preparation method of a photonic crystal, which uses nanoparticles and polymers to prepare by co-assembly method. The photonic crystal prepared by this method still needs a large amount of polymer as a component, involves a large amount of synthetic polymer, and the nanoparticles used are all inorganic nanoparticles, which requires high precision and requirements of processing technology.

[0004] With the needs of sustainable development and environmental protection, natural biomass as the preparation material of photonic crystal has attracted much attention. Lignin is an important compound in natural biomass, mainly existing in plant cell walls, and has good mechanical properties and chemical stability. Due to the particularity of its molecular structure, lignin can be used to prepare nanoparticles with stable structure and dispersion, which has unique advantages in the preparation of photonic crystals. Using lignin as the raw material of photonic crystal not only can realize the regulation of optical properties, but also can effectively utilize the waste lignin resources, realize the regeneration and recycling of resources. At present, the method for preparing photonic crystal based on lignin is mainly centrifugal assembly method. The centrifugal assembly method is to disperse monodisperse lignin nanoparticles in a solvent, and to realize the self-assembly of lignin by controlling the concentration of the dispersion liquid and the centrifugal force. However, at present, the preparation of monodisperse lignin nanoparticles is difficult, and the energy consumption of regulating lignin nanoparticles by centrifugation is too large, and the cost is high. SUMMARY

[0005] In view of the problems in the prior art, the present application provides a photonic crystal film based on lignin nanoparticles and a preparation method. The photonic crystal film with rainbow color is prepared by a non-centrifugal regulation method, which is easy to operate, low in cost and low in energy consumption. The H-LNP with multiple hydroxyl groups is obtained by hyperbranched reaction. The multiple hydroxyl structure endows the H-LNP with good self-assembly tendency, so that the H-LNP can form a thin film with clear structural color under the condition of evaporation-induced self-assembly.

[0006] The present application is realized by the following technical solutions:

[0007] A preparation method of a photonic crystal film based on lignin nanoparticles, comprising the following steps:

[0008] S1, under a protective atmosphere, 2-dimethylol propionic acid and p-toluenesulfonic acid are added to a dispersion liquid of lignin nanoparticles for hyperbranched reaction, the mass of 2-dimethylol propionic acid and p-toluenesulfonic acid is 5%-20% and 0.1%-10% of the mass of lignin nanoparticles respectively, to obtain a reaction liquid;

[0009] S2, the reaction liquid is dialyzed in deionized water to remove small molecules and homopolymerized 2-dimethylol propionic acid generated by side reactions, to obtain a water dispersion liquid of modified lignin nanoparticles;

[0010] S3, the water dispersion liquid of modified lignin nanoparticles is added dropwise to a hard transparent material, and dried by electric heating and air circulation, to obtain a photonic crystal film based on lignin nanoparticles.

[0011] Preferably, the dispersion liquid of lignin nanoparticles in S1 is obtained by the following process:

[0012] Sodium lignosulfonate, alkali lignin, groundwood lignin or enzymatic hydrolysis lignin is dissolved in ethylene glycol in a mass percentage of 0.1%-2%, then stirred at room temperature, and hydrochloric acid with a concentration of 0.01M-0.1M is added to form lignin nanoparticles, the obtained mixture is dialyzed in deionized water, and the lignin nanoparticles in the mixture are replaced into an organic reagent to obtain a dispersion of lignin nanoparticles.

[0013] Further, the addition rate of the hydrochloric acid is 0.01ml / min-0.2ml / min, and the volume is 1%-30% of the ethylene glycol.

[0014] Further, the organic reagent is N,N dimethylformamide.

[0015] Preferably, the hyperbranched reaction in S1 is carried out at 80℃-180℃ for 1h-10h.

[0016] Further, when the time of the hyperbranched reaction is within 2h, the 2-dimethylol propionic acid and p-toluenesulfonic acid in S1 are added at one time.

[0017] When the time t of the hyperbranched reaction exceeds 2h, the 2-dimethylol propionic acid and p-toluenesulfonic acid in S1 are divided into (n1+1) / 2 or n2 / 2 portions in equal amounts, n1 is the time number of t only retaining an odd integer, and n2 is the time number of t only retaining an even integer, and then 1 portion of 2-dimethylol propionic acid and 1 portion of p-toluenesulfonic acid are added every 1h.

[0018] Preferably, the hard transparent material in S3 is a glass slide.

[0019] Preferably, S3 adjusts the mass percentage of the modified lignin nanoparticles in the water dispersion of the modified lignin nanoparticles to 0.01%-2%, and then drops the modified lignin nanoparticles onto the hard transparent material, so that a photonic crystal film based on lignin nanoparticles is formed on the hard transparent material.

[0020] Preferably, the drying method in S3 is air drying in a drying oven at 30℃-150℃ for 30min-12h.

[0021] A photonic crystal film based on lignin nanoparticles obtained by the preparation method of the photonic crystal film based on lignin nanoparticles according to any one of the above.

[0022] Compared with the prior art, the present application has the following beneficial technical effects:

[0023] The present application discloses a preparation method of a photonic crystal film based on lignin nanoparticles, which comprises the following steps: controlling the amount of 2-dimethylol propionic acid and p-toluenesulfonic acid to facilitate the hyperbranched reaction of the lignin nanoparticles, removing small molecules and homopolymerized 2-dimethylol propionic acid generated in the side reaction through dialysis in deionized water, and preparing well-dispersed polyhydroxyl lignin nanoparticles, and then, through the method of dropwise adding and subsequent electric heating and air circulation drying, the drying speed can be reasonably controlled, which is beneficial to the regular movement of the polyhydroxyl lignin nanoparticles under the condition of evaporation-induced self-assembly, and the formation of a dendritic morphology, and finally, a thin film with clear structural color is obtained.

[0024] Further, the present application utilizes sodium lignosulfonate, alkali lignin, groundwood lignin or enzymatic hydrolysis lignin to obtain lignin nanoparticles, effectively utilizes the waste lignin resources, and converts the waste lignin resources into high-value photonic crystal materials, which is helpful for resource regeneration and recycling.

[0025] The present application discloses a preparation method of a photonic crystal film based on lignin nanoparticles, which comprises the following steps: controlling the amount of 2-dimethylol propionic acid and p-toluenesulfonic acid to facilitate the hyperbranched reaction of the lignin nanoparticles, removing small molecules and homopolymerized 2-dimethylol propionic acid generated in the side reaction through dialysis in deionized water, and preparing well-dispersed polyhydroxyl lignin nanoparticles, and then, through the method of dropwise adding and subsequent electric heating and air circulation drying, the drying speed can be reasonably controlled, which is beneficial to the regular movement of the polyhydroxyl lignin nanoparticles under the condition of evaporation-induced self-assembly, and the formation of a dendritic morphology, and finally, a thin film with clear structural color is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1a The X-ray photoelectron spectrum of pure sodium lignosulfonate.

[0027] Figure 1b The X-ray photoelectron spectrum of the lignin nanoparticles after the reaction in Example 1.

[0028] Figure 2A photograph of the photonic crystal based on lignin nanoparticles produced in Example 4.

[0029] Figure 3a A reflectance spectrum in the visible wavelength range of the photonic crystal based on lignin nanoparticles produced in Example 3.

[0030] Figure 3b A plot of the distribution of the color produced by the photonic crystal based on lignin nanoparticles produced in Example 3 in the CIE 1931 standard color space.

[0031] Figure 4a A surface microtopography plot of the red-orange region of the photonic crystal based on lignin nanoparticles produced in Example 4.

[0032] Figure 4b A surface microtopography plot of the yellow-green region of the photonic crystal based on lignin nanoparticles produced in Example 4.

[0033] Figure 4c A surface microtopography plot of the cyan-blue region of the photonic crystal based on lignin nanoparticles produced in Example 4.

[0034] Figure 5a A photograph of the photonic crystal obtained in Comparative Example 1.

[0035] Figure 5b A SEM image of the photonic crystal obtained in Comparative Example 1.

[0036] Figure 6a A photograph of the photonic crystal obtained in Comparative Example 2.

[0037] Figure 6b A SEM image of the photonic crystal obtained in Comparative Example 2.

[0038] Figure 7a A scanning electron microscope image of the directional aggregation of lignin nanoparticles in the photonic crystal thin film obtained in Example 1.

[0039] Figure 7b A scanning electron microscope image of the directional aggregation of lignin nanoparticles in the photonic crystal thin film obtained in Example 2.

[0040] Figure 7c A scanning electron microscope image of the directional aggregation of lignin nanoparticles in the photonic crystal thin film obtained in Example 3.

[0041] Figure 7d A scanning electron microscope image of the directional aggregation of lignin nanoparticles in the photonic crystal thin film obtained in Example 4.

[0042] Figure 8a A photograph of the photonic crystal based on lignin nanoparticles produced in Example 4. Figure 7aEnlarged view in a medium rectangular frame.

[0043] Figure 8b For Figure 7b Enlarged view in a medium rectangular frame.

[0044] Figure 8c For Figure 7c Enlarged view in a medium rectangular frame.

[0045] Figure 8d For Figure 7d Enlarged view in a medium rectangular frame.

[0046] Figure 9a For the surface electrostatic potential result diagram of the lignin nanoparticles with multiple hydroxyl groups grafted by the embodiment of the application.

[0047] Figure 9b For the adsorption model diagram of the lignin nanoparticles with multiple hydroxyl groups grafted by the embodiment of the application.

[0048] Figure 10 For the micro mechanism diagram of the photonic crystal characteristics generated by the H-LNPs film obtained by the application. DETAILED DESCRIPTION

[0049] The technical solutions of the application will be described below in detail with the drawings, process steps, specific implementation conditions and materials in the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0050] The application is a preparation method of a photonic crystal film based on lignin nanoparticles, comprising the following steps:

[0051] Step 1, a certain amount of sodium lignosulfonate, alkali lignin, groundwood lignin or enzymatic hydrolysis lignin is dissolved in ethylene glycol, the mass percentage is 0.1%-2%, after stirring at room temperature, 0.01M-0.1M hydrochloric acid is added, the volume is 1%-30% of ethylene glycol, the adding speed is controlled at 0.01ml / min-0.2ml / min, the LNPs with good dispersity are prepared by adjusting the pH value, and the obtained mixed solution is dialyzed in deionized water.

[0052] Step 2, the lignin nanoparticles in the lignin nanoparticle (LNPs) aqueous dispersion obtained in step 1) are replaced into N, N dimethylformamide, with a three-necked flask as a reaction container, argon gas is introduced as a protective gas, 2-dimethylol propionic acid and p-toluenesulfonic acid are added into the three-necked flask, the addition amount of 2-dimethylol propionic acid and p-toluenesulfonic acid is 5%-20% and 0.1%-10% of the mass of the lignin nanoparticles respectively, hyperbranched reaction is carried out at 80-180 ℃ for 1-10 h, when the time of hyperbranched reaction is within 2 h, 2-dimethylol propionic acid and p-toluenesulfonic acid are added at one time; when the time t of hyperbranched reaction is more than 2 h, 2-dimethylol propionic acid and p-toluenesulfonic acid are first divided into (n1+1) / 2 or n2 / 2 parts according to the amount, n1 is the time number of t only retaining an integer and being an odd number, n2 is the time number of t only retaining an integer and being an even number, then 1 part of 2-dimethylol propionic acid and 1 part of p-toluenesulfonic acid are added every 1 h, the reaction is completed after the addition is completed, and the obtained reaction solution is dialyzed in deionized water to remove small molecules and homopolymerized 2-dimethylol propionic acid generated in a side reaction.

[0053] Step 3, the mass percentage of the modified lignin nanoparticle (hydroxyl group-containing lignin nanoparticle, H-LNPs) dispersion obtained by dialysis is adjusted to 0.01%-2%, and then the lignin nanoparticle dispersion is added dropwise on a hard transparent material and dried at 30-150 ℃ for 30 min-12 h, the drying mode is a blast drying oven drying, evaporation-induced self-assembly occurs, and a lignin nanoparticle-based photonic crystal material is obtained.

[0054] The following examples are used to illustrate the present application with sodium lignosulfonate as a raw material.

[0055] Example 1

[0056] Sodium lignosulfonate is first dissolved in ethylene glycol to have a mass percentage of 0.56%, stirred at room temperature for 2 hours, then 0.025 M hydrochloric acid is added, the volume is 15% of the volume of ethylene glycol, the drop speed is controlled to be 0.04 ml / min, and the obtained mixed solution is dialyzed in deionized water.

[0057] The lignin nanoparticles in the lignin nanoparticle aqueous dispersion are replaced into N, N dimethylformamide, with a three-necked flask as a reaction container, argon gas is introduced as a protective gas, 2-dimethylol propionic acid and p-toluenesulfonic acid are added into the three-necked flask, the addition amount of 2-dimethylol propionic acid and p-toluenesulfonic acid is 14.2% and 4.1% of the mass of the lignin nanoparticles respectively, reaction is carried out at 140 ℃ for 1 h, and then the reaction solution is dialyzed in deionized water.

[0058] The mass percentage of the obtained dispersion (the lignin nanoparticles after reaction are denoted as H1-LNPs) obtained by dialysis is adjusted to 0.8%, and then the lignin nanoparticle dispersion is added dropwise on a glass slide and dried, a photonic crystal is obtained after drying in a blast oven at 60 ℃ for 30 min.

[0059] Example 2

[0060] The sodium lignosulfonate was first dissolved in ethylene glycol to a mass percentage of 0.56%, stirred for 2 hours at room temperature, then 0.025M hydrochloric acid was added, the volume was 15% of the volume of ethylene glycol, the drop rate was controlled at 0.04ml / min, and the resulting solution was dialyzed in deionized water.

[0061] The lignin nanoparticles in the lignin nanoparticle aqueous dispersion were replaced into N,N dimethylformamide, argon was introduced as a protective gas, 2-dimethylol propionic acid and p-toluenesulfonic acid were added to the three-necked flask, which were equivalent to 14.2% and 4.1% of the mass of the lignin nanoparticles, respectively, and the reaction was carried out at 140°C for 2h, wherein 1 portion of 2-dimethylol propionic acid and p-toluenesulfonic acid was added every 1h, and the reaction solution was dialyzed in deionized water.

[0062] The mass percentage of the dialyzed dispersion (the lignin nanoparticles after reaction are denoted as H2-LNPs) was adjusted to 0.8%, dropped on a glass slide and dried, and a photonic crystal was obtained after drying in a 60°C air oven for 30min.

[0063] Example 3

[0064] The sodium lignosulfonate was first dissolved in ethylene glycol to a mass percentage of 0.56%, stirred for 2 hours at room temperature, then 0.025M hydrochloric acid was added, the volume was 15% of the volume of ethylene glycol, the drop rate was controlled at 0.04ml / min, and the resulting solution was dialyzed in deionized water.

[0065] The lignin nanoparticles in the lignin nanoparticle aqueous dispersion were replaced into N,N dimethylformamide, argon was introduced as a protective gas, 2-dimethylol propionic acid and p-toluenesulfonic acid were added to the three-necked flask, which were equivalent to 14.2% and 4.1% of the mass of the lignin nanoparticles, respectively, and the reaction was carried out at 140°C for 3h, wherein 1 portion of 2-dimethylol propionic acid and p-toluenesulfonic acid was added every 1h, and the reaction solution was dialyzed in deionized water.

[0066] The mass percentage of the dialyzed dispersion (the lignin nanoparticles after reaction are denoted as H3-LNPs) was adjusted to 0.8%, dropped on a glass slide and dried, and a photonic crystal was obtained after drying in a 60°C air oven for 30min.

[0067] Example 4

[0068] Sodium lignin sulfonate was first dissolved in ethylene glycol to a mass percentage of 0.56%, stirred at room temperature for 2 hours, and then 0.025M hydrochloric acid was added at a volume of 15% of the volume of ethylene glycol at a drip rate of 0.04 ml / min. The resulting solution was dialyzed in deionized water.

[0069] The lignin nanoparticles in the lignin nanoparticle aqueous dispersion were replaced with N,N-dimethylformamide, and a three-necked flask was used as a reaction vessel. Argon was introduced as a protective gas, and 2-dihydroxymethylpropionic acid and 4.1% p-toluenesulfonic acid equivalent to 14.2% of the mass of the lignin nanoparticles were added. The reaction was carried out at 140°C for 4 hours, with 1 part of 2-dihydroxymethylpropionic acid and p-toluenesulfonic acid added every 1 hour. The reaction solution was dialyzed in deionized water.

[0070] The mass percentage of the dialyzed dispersion (lignin nanoparticles after the reaction were recorded as H4-LNPs) was adjusted to 0.8%, dropped on a glass slide to dry, and dried in a forced air oven at 60° C. for 30 minutes to obtain a photonic crystal.

[0071] from Figure 7a and Figure 8a It can be clearly seen that H1-LNPs have a tendency to self-assemble close to each other. Figure 7b and Figure 8b It can be clearly seen that the assembly trend of H2-LNPs is further obvious, and the spherical particles are assembled in a fixed direction, showing a radial arrangement trend. Figure 7c and Figure 8c The morphology of H3-LNPs can be clearly seen in the figure. With the increase of the degree of hyperbranching, the assembly between the spheres appears a tree-like morphology. Figure 7d and Figure 8d The morphology of H4-LNPs can be clearly seen in the figure. After four hyperbranching reactions, the self-assembly behavior between the spheres is more obvious, and obvious tree-like morphology accumulation appears. The diameter of the assembled tree-like structure can reach 30μm.

[0072] Comparative Example 1

[0073] Sodium lignin sulfonate was first dissolved in ethylene glycol to a mass percentage of 0.56%, stirred at room temperature for 2 hours, and then 0.025M hydrochloric acid was added at a volume of 15% of the volume of ethylene glycol at a drip rate of 0.04 ml / min. The resulting solution was dialyzed in deionized water.

[0074] The lignin nanoparticles in the lignin nanoparticle aqueous dispersion were replaced into N,N dimethylformamide, with a three-necked flask as the reaction container, argon gas was bubbled as the protective gas, 14.2% of 2-dimethylol propionic acid and 4.1% of p-toluenesulfonic acid equivalent to the mass of the lignin nanoparticles were added, the reaction was carried out at 140°C for 4h, wherein 1 part of 2-dimethylol propionic acid and p-toluenesulfonic acid was added every 1h, and the reaction liquid was dialyzed in deionized water.

[0075] The mass percentage of the dialyzed dispersion was adjusted to 0.8%, and was dropped on a glass slide and dried, and a photonic crystal was obtained after drying in a vacuum oven at 60°C for 30min.

[0076] Comparative Example 2

[0077] The sodium lignosulfonate was first dissolved in ethylene glycol to have a mass percentage of 0.56%, stirred at room temperature for 2h, then 0.025M hydrochloric acid was added, the volume was 15% of the volume of ethylene glycol, the drop rate was controlled at 0.04ml / min, and the obtained solution was dialyzed in deionized water.

[0078] The lignin nanoparticles in the lignin nanoparticle aqueous dispersion were replaced into N,N dimethylformamide, with a three-necked flask as the reaction container, argon gas was bubbled as the protective gas, 14.2% of 2-dimethylol propionic acid and 4.1% of p-toluenesulfonic acid equivalent to the mass of the lignin nanoparticles were added, the reaction was carried out at 140°C for 4h, wherein 1 part of 2-dimethylol propionic acid and p-toluenesulfonic acid was added every 1h, and the reaction liquid was dialyzed in deionized water.

[0079] The mass percentage of the dialyzed dispersion was adjusted to 0.8%, and was dropped on a glass slide and dried, and a photonic crystal was obtained after drying in a vacuum oven at 60°C for 30min.

[0080] From Figure 5a It can be seen that, at the speed of vacuum drying at 60°C, the H-LNPs film did not produce any color due to the too fast drying speed.

[0081] From Figure 5b It can be seen that, the too fast drying speed will cause the H-LNPs to quickly assemble and then wrinkle and crack, and cannot form a micro-morphology with the characteristics of photonic crystal.

[0082] From Figure 6a It can be seen that, the natural drying at room temperature indeed produces the characteristics of photonic crystal Figure 6b It can also be seen microscopically that, the H-LNPs naturally dried at room temperature can form a concave structure that meets the characteristics of photonic crystal), but due to the too slow drying speed, the drying interface advances too slowly, causing the movement of H-LNPs to be irregular, and finally causing the arrangement of color to be chaotic.

[0083] Example 5

[0084] Sodium lignin sulfonate was first dissolved in ethylene glycol to a mass percentage of 0.56%, stirred at room temperature for 2 hours, and then 0.025M hydrochloric acid was added at a volume of 15% of the volume of ethylene glycol at a drip rate of 0.04 ml / min. The resulting solution was dialyzed in deionized water.

[0085] The lignin nanoparticles in the lignin nanoparticle aqueous dispersion were replaced with N,N-dimethylformamide. A three-necked flask was used as a reaction vessel, argon was introduced as a protective gas, and 2-dihydroxymethylpropionic acid and 4.1% p-toluenesulfonic acid equivalent to 14.2% of the mass of the lignin nanoparticles were added. The reaction was carried out at 140°C for 5 hours, with 1 part of 2-dihydroxymethylpropionic acid and p-toluenesulfonic acid added every 1 hour. The reaction solution was dialyzed in deionized water.

[0086] The mass percentage of the dialyzed dispersion was adjusted to 0.8%, dropped onto a glass slide and air-dried, and then dried in a forced air oven at 60° C. for 30 min to obtain a photonic crystal.

[0087] Example 6

[0088] Sodium lignin sulfonate was first dissolved in ethylene glycol to a mass percentage of 0.56%, stirred at room temperature for 2 hours, and then 0.025M hydrochloric acid was added at a volume of 15% of the volume of ethylene glycol at a drip rate of 0.04 ml / min. The resulting solution was dialyzed in deionized water.

[0089] The lignin nanoparticles in the lignin nanoparticle aqueous dispersion were replaced with N,N-dimethylformamide, and a three-necked flask was used as a reaction vessel. Argon was introduced as a protective gas, and 2-dihydroxymethylpropionic acid and 4.1% p-toluenesulfonic acid equivalent to 14.2% of the mass of the lignin nanoparticles were added. The reaction was carried out at 140°C for 4 hours, with 1 part of 2-dihydroxymethylpropionic acid and p-toluenesulfonic acid added every 1 hour. The reaction solution was dialyzed in deionized water.

[0090] The mass percentage of the dialyzed dispersion was adjusted to 0.01%, dropped onto a glass slide and air-dried, and then dried in a forced air oven at 60° C. for 30 min to obtain a photonic crystal.

[0091] Example 7

[0092] Sodium lignin sulfonate was first dissolved in ethylene glycol to a mass percentage of 0.56%, stirred at room temperature for 2 hours, and then 0.025M hydrochloric acid was added at a volume of 15% of the volume of ethylene glycol at a drip rate of 0.04 ml / min. The resulting solution was dialyzed in deionized water.

[0093] The lignin nanoparticles in the lignin nanoparticle aqueous dispersion were replaced with N,N-dimethylformamide, and a three-necked flask was used as a reaction vessel. Argon was introduced as a protective gas, and 2-dihydroxymethylpropionic acid and 4.1% p-toluenesulfonic acid equivalent to 14.2% of the mass of the lignin nanoparticles were added. The reaction was carried out at 140°C for 4 hours, with 1 part of 2-dihydroxymethylpropionic acid and p-toluenesulfonic acid added every 1 hour. The reaction solution was dialyzed in deionized water.

[0094] The mass percentage of the dialyzed dispersion was adjusted to 0.1%, dropped onto a glass slide and air-dried, and then dried in a forced air oven at 60° C. for 30 min to obtain a photonic crystal.

[0095] Example 8

[0096] Sodium lignin sulfonate was first dissolved in ethylene glycol to a mass percentage of 0.56%, stirred at room temperature for 2 hours, and then 0.025M hydrochloric acid was added at a volume of 15% of the volume of ethylene glycol at a drip rate of 0.04 ml / min. The resulting solution was dialyzed in deionized water.

[0097] The lignin nanoparticles in the lignin nanoparticle aqueous dispersion were replaced with N,N-dimethylformamide, and a three-necked flask was used as a reaction vessel. Argon was introduced as a protective gas, and 2-dihydroxymethylpropionic acid and 4.1% p-toluenesulfonic acid equivalent to 14.2% of the mass of the lignin nanoparticles were added. The reaction was carried out at 140°C for 4 hours, with 1 part of 2-dihydroxymethylpropionic acid and p-toluenesulfonic acid added every 1 hour. The reaction solution was dialyzed in deionized water.

[0098] The mass percentage of the dialyzed dispersion was adjusted to 1%, dropped onto a glass slide and air-dried, and then dried in a forced air oven at 60° C. for 30 min to obtain a photonic crystal.

[0099] Example 9

[0100] Sodium lignin sulfonate was first dissolved in ethylene glycol to a mass percentage of 0.56%, stirred at room temperature for 2 hours, and then 0.025M hydrochloric acid was added at a volume of 15% of the volume of ethylene glycol at a drip rate of 0.04 ml / min. The resulting solution was dialyzed in deionized water.

[0101] The lignin nanoparticles in the lignin nanoparticle aqueous dispersion were replaced with N,N-dimethylformamide, and a three-necked flask was used as a reaction vessel. Argon was introduced as a protective gas, and 2-dihydroxymethylpropionic acid and 4.1% p-toluenesulfonic acid equivalent to 14.2% of the mass of the lignin nanoparticles were added. The reaction was carried out at 140°C for 4 hours, with 1 part of 2-dihydroxymethylpropionic acid and p-toluenesulfonic acid added every 1 hour. The reaction solution was dialyzed in deionized water.

[0102] The dialyzed dispersion liquid with a mass percentage of 1.5% is dropped on a glass slide and dried to obtain a photonic crystal after drying in a blast oven at 60°C for 30 min.

[0103] Figure 1a Figure 4 is an X-ray photoelectron spectrogram of pure sodium lignosulfonate LS, Figure 1b Figure 5 is an X-ray photoelectron spectrogram of lignin nanoparticles H1-LNPs after reaction, and it can be seen from comparison that a C=O peak at 288.33 eV appears after reaction, indicating that H1-LNPs are successfully prepared by reaction.

[0104] Figure 2 Figure 6 is a digital photo of a lignin nanoparticle-based photonic crystal prepared in Example 4, and the prepared material has a typical photonic crystal structural color, and it is to be noted that the red circle part on the outside is lignin particles that do not form a photonic crystal arrangement, which is caused by disordered arrangement during drying, and is caused by too low concentration or insufficient surface tension of the outer circle.

[0105] Figure 3a Figure 7 is a reflection spectrum of a lignin nanoparticle-based photonic crystal prepared in Example 3 in a visible light wavelength range, and it can be seen from the figure that obvious reflection peaks appear at 428 nm to 628 nm, indicating that the rainbow color spots generated by the photonic crystal are caused by reflection of visible light, and the picture above the curve represents standard colors under different visible light bands as a comparison. Figure 3b Figure 8 is a distribution of colors generated by a photonic crystal in a CIE1931 standard color space, and the generated color distribution is relatively wide and covers most standard colors.

[0106] Figure 4a Figure 9 is a micro-morphology of a red-orange region of a lignin nanoparticle-based photonic crystal prepared in Example 4, Figure 4b Figure 10 is a micro-morphology of a yellow-green region, Figure 4c Figure 11 is a micro-morphology of a cyan-blue region, which is observed and photographed by an environmental scanning electron microscope at a voltage of 10 kV after gold spraying of the sample. It can be seen from Figure 4a 、 Figure 4b and Figure 4c that the prepared photonic crystal surface appears uniform distribution of concave structures, and the inverse opal structure self-assembled forms a periodic symmetric photonic band gap, so that the H-LNPs film has typical photonic crystal characteristics.

[0107] The present application uses a method of molecular surface electrostatic potential to reveal the mechanism of self-assembly of H-LNPs. As shown in Figure 9a , the maximum electrostatic potential energy (ESP Max) of L-LNPS after grafting is obviously reduced, but as Figure 9aThe arrow marks the maximum value of the hydrogen atom at the four hydroxyl end of the grafted small molecules (the picture is symmetrical structure, where one arrow is blocked). The grafted lignin sulfonate sodium is more likely to form the adsorption model of Figure 9b , where the electrostatic potential energy is 2.151 eV, representing the grafting reaction will occur here.

[0108] As shown in Figure 10 , due to the mutual attraction of H-LNPs assembly and the surface tension of different components during evaporation, the surface of the H-LNPs film will have holes of different diameters at the end of self-assembly. This inverse opal structure formed by self-assembly forms a periodic symmetric photonic band gap, so that the H-LNPs film has typical photonic crystal characteristics. When the incident light shines on the large pore area formed by the aggregation of small size H-LNPs, the pore diameter is close to the wavelength corresponding to red and orange, so the reflected light presents orange and red; when the incident light shines on the small pore area formed by the aggregation of large size H-LNPs, the pore diameter is close to the wavelength corresponding to blue and purple, and the reflected light presents blue and purple.

Claims

1. A method for preparing a photonic crystal film based on lignin nanoparticles, characterized in that: The steps include: S1, under a protective atmosphere, adding 2-dimethylolpropionic acid and p-toluenesulfonic acid to a dispersion of lignin nanoparticles, and performing a hyperbranching reaction at 80° C.-180° C. for 1 h-10 h. When the hyperbranching reaction time is less than 2 h, 2-dimethylolpropionic acid and p-toluenesulfonic acid are added at one time. When the hyperbranching reaction time t exceeds 2 h, 2-dimethylolpropionic acid and p-toluenesulfonic acid are first divided into (n1+1) / 2 or n2 / 2 parts according to the amount, n1 is the number of times when t is an odd number after retaining only integers, and n2 is the number of times when t is an even number after retaining only integers, and then 1 part of 2-dimethylolpropionic acid and 1 part of p-toluenesulfonic acid are added every 1 h, and the masses of 2-dimethylolpropionic acid and p-toluenesulfonic acid are 5%-20% and 0.1%-10% of the mass of the lignin nanoparticles, respectively, to obtain a reaction solution. S2, dialyzing the reaction solution in deionized water to obtain an aqueous dispersion of modified lignin nanoparticles; S3. After adjusting the mass percentage of the modified lignin nanoparticles in the aqueous dispersion of the modified lignin nanoparticles to 0.01%-2%, the modified lignin nanoparticles are added dropwise to a hard transparent material. The modified lignin nanoparticles are dried in a forced air drying oven at 30°C-150°C for 30 min-12 h to form a photonic crystal film based on the lignin nanoparticles on the hard transparent material, thereby obtaining a photonic crystal film based on the lignin nanoparticles.

2. The method for preparing a photonic crystal film based on lignin nanoparticles according to claim 1, characterized in that: The dispersion of lignin nanoparticles described in S1 was obtained by the following process: Sodium lignin sulfonate, alkali lignin, groundwood lignin or enzymatically hydrolyzed lignin is dissolved in ethylene glycol at a mass percentage of 0.1%-2%, and then stirred at room temperature. Hydrochloric acid with a concentration of 0.01M-0.1M is added to form lignin nanoparticles. The resulting mixture is dialyzed in deionized water, and the lignin nanoparticles therein are then replaced with an organic reagent to obtain a dispersion of lignin nanoparticles.

3. The method for preparing a photonic crystal film based on lignin nanoparticles according to claim 2, characterized in that: The hydrochloric acid is added at a rate of 0.01 mL / min-0.2 mL / min, and its volume is 1%-30% of the ethylene glycol.

4. The method for preparing a photonic crystal film based on lignin nanoparticles according to claim 2, characterized in that: The organic reagent is N,N-dimethylformamide.

5. The method for preparing a photonic crystal film based on lignin nanoparticles according to claim 1, characterized in that: The hard transparent material described in S3 is a glass slide. 6 . A photonic crystal film based on lignin nanoparticles obtained by the preparation method of the photonic crystal film based on lignin nanoparticles according to any one of claims 1 to 5 .

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