A mechanochromic photonic crystal and its preparation method and application

Abstract

The invention discloses a mechanochromic photonic crystal and a preparation method and application thereof, and relates to the technical field of luminescent materials. The mechanochromic photonic crystal of the invention realizes low-concentration orderly self-assembly of silicon dioxide by controlling the volume ratio of silicon dioxide to hydroxyethyl acrylate, utilizing the dosage form of a polar solvent and the solvation layer formed by hydroxyethyl acrylate on the surface of silicon dioxide. The mechanochromic photonic crystal prepared by the invention can be used to prepare a photonic crystal film, has the characteristics of a wide adjustable wavelength range, high sensitivity and good stability, and is particularly suitable for use in visual sensors.

Description

Technical Field

[0001] The present invention relates to the technical field of luminescent materials, and more specifically, to a mechanochromic photonic crystal and a preparation method and application thereof. Background Art

[0002] Responsive photonic crystals refer to periodic dielectric structures that can change their reflection wavelength or intensity under external physical and chemical effects. Their optical properties are usually determined by aspects such as lattice spacing, refractive index and crystal orientation. Among them, mechanochromic photonic crystals are a type of mechanically responsive photonic crystals that can convert the strain caused by the force on themselves into changes in lattice constants, thereby changing the optical changes of the photonic crystals. They are widely used in mechanical force sensors, gas pressure sensors, fingerprint recognition, color pattern encryption, etc.

[0003] There are many mechanochromic photonic crystal materials and processes. The composite material obtained by filling the gaps of densely packed colloidal crystals or opal structures with elastomers shows strain-induced reflection peak shift, but since stretching will cause the densely packed colloidal crystals to rearrange, the strain is limited and the adjustable wavelength range is narrow. Although the inverse opal structure composed of densely packed cavities in the elastomer can cover the color changes of visible light, its preparation process is complicated, its mechanical properties are poor, it can only produce very small strains, and the adjustable wavelength range is also narrow, so its application is limited. In addition, the colloid composed of an inelastic core and an elastic shell can form a stable and flexible composite material through melt crystallization technology. The composite material can also show color changes in the full visible light range, but its deformation is not purely elastic, and residual strain will be left, resulting in inability to fully recover after color change, and the colloid only crystallizes near the surface, and the optical performance is limited.

[0004] The prior art discloses a mechanochromic regulation and anti-counterfeiting application of a transparent photonic crystal film. A three-dimensional opal photonic crystal array is constructed using silica colloidal particles, which are embedded in a dimethylsiloxane elastomer to obtain a transparent photonic crystal film. However, the adjustable wavelength range and cyclic stability of the photonic crystal film still need to be improved. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the prior art and provide a mechanochromic photonic crystal. The photonic crystal can achieve full color change and has the characteristics of a wide adjustable wavelength range and high sensitivity. The mechanochromic photonic crystal film prepared by the present invention has good cycle stability and can be preserved for a long time.

[0006] Another object of the present invention is to provide a method for preparing the mechanochromic photonic crystal.

[0007] Another object of the present invention is to provide a mechanochromic photonic crystal film.

[0008] Another object of the present invention is to provide an application of a mechanochromic photonic crystal film in a visualization sensor.

[0009] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0010] A mechanochromic photonic crystal is composed of silicon dioxide particles and hydroxyethyl acrylate, wherein the distribution density of the silicon dioxide particles in the hydroxyethyl acrylate is 184 mg / mL to 918 mg / mL.

[0011] The inventors found that the hydroxyethyl acrylate monomer can form a solvation layer on the surface of the silica particles, which can promote the orderly assembly of the silica particles in hydroxyethyl acrylate at low concentrations, and then control the distribution density of the silica particles in hydroxyethyl acrylate, so that the distance between the centers of adjacent silica particles in hydroxyethyl acrylate is greater than the particle size, forming a non-dense arrangement, with a large particle spacing, the spacing reaches 151nm, can provide a large force, that is, the force-induced deformation range is large, so it has an ultra-wide adjustable wavelength range, can achieve full color change, and because the silica particles are relatively large, the obtained force-induced color photonic crystal can be deformed under a small stress, resulting in a large wavelength shift, high sensitivity, fast response speed, and can achieve rapid response. And because hydroxyethyl acrylate itself is elastic and has adhesion to silica particles, the photonic crystal obtained by the present invention shows a high degree of flexibility, stability and excellent durability, and the prepared photonic crystal film can display a microscopic pattern with a resolution of 30μm.

[0012] In addition, the mechanochromic photonic crystals obtained by the present invention are in a suspended liquid state and do not contain solvent components. Therefore, after long-term storage, the wavelength of the photonic crystals will not change due to the volatilization of the solvent, and the stability is good.

[0013] Preferably, the distribution density of the silicon dioxide particles in hydroxyethyl acrylate is 184 mg / mL to 510 mg / mL, more preferably 306 mg / mL.

[0014] The wavelength of the photonic crystal can be adjusted by adjusting the particle size of the silicon dioxide particles. The mechanochromic photonic crystal of the present invention can be prepared using silicon dioxide particles with an average particle size of 160 to 450 nm.

[0015] At the same silica volume fraction, the larger the silica particle size, the smaller the amount of silica in the photonic crystal, and the worse the mechanical properties of the photonic crystal. In addition, the larger the silica particle size, the farther the initial wavelength of the photonic crystal is from the visible light region. At this time, even if there is a large wavelength difference, when the wavelength changes due to stress, the wavelength change greater than 700nm cannot be observed by the naked eye. Therefore, when the silica particle size is too large, it lacks practical application significance. When the silica particle size is too small, the structural color produced by the final diffraction of the photonic crystal does not change significantly, which is not conducive to the improvement of the adjustable wavelength range.

[0016] Preferably, the average particle size of the silicon dioxide particles is 165 to 320 nm.

[0017] Silica particles within the average particle size range of 165 to 320 nm are more conducive to obtaining a large interparticle distance, and the photonic crystal obtained has a wider tunable wavelength range, more preferably 165 nm to 237 nm, and even more preferably 216 nm.

[0018] Specifically, the PDI of the silica particles is 0.001 to 0.1.

[0019] PDI refers to the uniformity of particle size distribution. The smaller the PDI value of silica particles, the higher the uniformity of the particles. The prepared photonic crystal film has a higher reflectivity and is easier to observe its structural color.

[0020] The present invention also specifically protects a method for preparing a mechanochromic photonic crystal, comprising the following steps:

[0021] S1. The silica particles are dispersed in a polar solvent, and the obtained silica dispersion is mixed with hydroxyethyl acrylate and a photoinitiator to obtain a silica suspension, wherein the volume fraction of silica in the silica suspension is 9 to 45%;

[0022] S2. Dry the silica suspension at 60-100° C. for 1-24 h, and concentrate it to obtain silica / hydroxyethyl acrylate mechanochromic photonic crystals.

[0023] It should be noted that:

[0024] The reason why polar solvents are selected as dispersants for silica in S1 is that the silica particles are mainly affected by electrostatic forces and solvation forces during assembly, and electrostatic repulsion is the main driving force. Dispersing silica particles in polar solvents can give silica particles strong electrostatic repulsion, thereby driving the silica particles to assemble into an ordered structure. In addition, since hydroxyethyl acrylate monomers form a solvation layer on the surface of silica, it can further promote the orderly assembly of silica in hydroxyethyl acrylate at low concentrations, creating conditions for a wide adjustable wavelength range.

[0025] In addition, the volume fraction of silica in S1 will affect the distribution density of silica particles in hydroxyethyl acrylate. If the volume fraction is too small, the distribution concentration will be low, the reflectivity of the obtained photonic crystal will be low, and the structural color change will not be obvious. If the volume fraction is too large, the silica will be densely arranged and the particle spacing will be small. It is easy to rearrange when external force is applied, and the adjustable wavelength range will become narrower. If the volume fraction is too large, after the ethanol evaporates, the viscosity of the precursor will be too high, the photonic crystal will be in a gel state, and the photonic crystal film cannot be prepared.

[0026] The drying temperature in S2 will affect the self-assembly of silica in the hydroxyethyl acrylate monomer. If the temperature is too low, there will be too much residual organic solvent, and the wavelength will change due to the volatilization of the solvent after long-term storage; when the temperature is too high, because hydroxyethyl acrylate is a double-bond monomer, the temperature will cause slight polymerization of hydroxyethyl acrylate, affecting the orderly self-assembly of silica particles, and further affecting the preparation of photonic crystals. The drying temperature is preferably 80-100°C, more preferably 90°C.

[0027] The invention fixes the ordered structure of silicon dioxide in a hydroxyethyl acrylate polymer matrix through polymerization-induced supersaturated crystallization to obtain a photonic crystal film. The structure of the silicon dioxide / hydroxyethyl acrylate mechanochromic photonic crystal is stable after being cured by ultraviolet light irradiation, so the wavelength will not change due to structural collapse after long-term storage. After drying and concentration, no solvent exists in the photonic crystal, and the wavelength will not change due to the volatilization of the solvent. Therefore, the obtained photonic crystal has good cycle stability and storage resistance. After being squeezed from 790nm to 490nm 1000 times, the film can still maintain intact mechanical structure and optical properties.

[0028] Preferably, the drying temperature in S2 is 80-100°C, more preferably 90°C.

[0029] The polar solvent in S1 is any one of anhydrous ethanol, methanol, propanol, isopropanol, acetonitrile and water, and is more preferably anhydrous ethanol.

[0030] Anhydrous ethanol has high polarity, low boiling point and is easy to volatilize, making it more suitable as a dispersant in evaporation and concentration assembly.

[0031] Preferably, the volume fraction of silicon dioxide in the silicon dioxide suspension in S1 is 10 to 25%.

[0032] In the range of 10-25% volume fraction, the prepared photonic crystal has a larger wavelength difference, that is, the air-conditioning wavelength range is wider. More preferably, the volume fraction of silicon dioxide in the silicon dioxide suspension is 10-16%, and more preferably 15%.

[0033] When the volume fraction of silica is 15%, its structural color changes significantly and the adjustable wavelength range is also wide.

[0034] Preferably, the drying time in S2 is 1 to 24 hours.

[0035] The silicon dioxide particles of the present invention can be purchased or prepared conventionally. Preferably, the silicon dioxide particles are prepared in the following manner:

[0036] S1. Tetraethyl orthosilicate (99%), anhydrous ethanol, 25% to 28% ammonia water and deionized water were mixed to obtain a silica suspension;

[0037] S2. performing solid-liquid separation on the silica suspension to obtain a precipitate;

[0038] S3. The precipitated material is purified to obtain silicon dioxide nanoparticles with a particle size of 130 to 450 nm.

[0039] The preparation of silica particles in the above manner can better control the uniformity of the silica particles, and the PDI of the obtained silica particles is less than 0.1.

[0040] The present invention also protects a mechanochromic photonic crystal film, which is composed of the mechanochromic photonic crystal of the present invention.

[0041] Preferably, the method for preparing the mechanochromic photonic crystal comprises the following steps:

[0042] The silicon dioxide / hydroxyethyl acrylate photonic crystal was heated to 4.8-10 mW / cm 2 The film was cured under ultraviolet light for 90 to 180 seconds to obtain a mechanochromic crystal film.

[0043] Wherein, when the volume of the silicon dioxide / hydroxyethyl acrylate photonic crystal is 30-100 μL, the corresponding thickness of the mechanochromic photonic crystal film is 0.09-0.36 mm.

[0044] More preferably, the UV lamp power is 4.8 mW / cm 2 , curing time 180s.

[0045] The photonic crystal film obtained after the mechanochromic photonic crystal of the present invention is cured by ultraviolet light has a stable structure and is durable in preservation.

[0046] The present invention particularly protects the application of a force-induced photonic crystal film in a visualization sensor.

[0047] The visual sensor is a stress-strain sensor, which can judge the magnitude of stress or strain by the change of color, and can also control the change of color by changing the magnitude of stress.

[0048] The mechanochromic photonic crystal film prepared by the invention has high sensitivity and mechanochromic performance with a wide adjustable wavelength and good stability, and is suitable for use in visualization sensors.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The present invention controls the distribution density of silicon dioxide particles in hydroxyethyl acrylate so that the photonic crystal has a large inter-particle spacing, which not only provides a large range of force-induced deformation, but also can produce a large wavelength displacement under a small stress. Therefore, the photonic crystal has a wide adjustable wavelength range, can achieve full-color change and rapid response, and has good stability and durability. The obtained photonic crystal film has a high fracture stress.

[0051] The photonic crystal film remains intact after 1000 cycles of extrusion from 790nm to 490nm, has good cycle stability, can be stored for a long time, and significantly improves its fracture stress due to the cross-linking effect of silicon dioxide, the fracture stress is 50-605kPa, and the strain reaches 70-900%. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a schematic diagram of the structure of the mechanochromic photonic crystal film of the present invention;

[0053] Figure 2 The spectra corresponding to the mechanochromic photonic crystal film of Example 1 under different stresses;

[0054] Figure 3 Spectra corresponding to different stresses of the mechanochromic photonic crystal film of Example 3;

[0055] Figure 4 Spectra corresponding to different stresses of the mechanochromic photonic crystal film of Example 4;

[0056] Figure 5 Spectra corresponding to different stresses of the mechanochromic photonic crystal film of Example 5;

[0057] Figure 6 Spectra corresponding to different stresses of the mechanochromic photonic crystal film of Example 6;

[0058] Figure 7 Spectra corresponding to different stresses of the mechanochromic photonic crystal film of Example 7;

[0059] Figure 8 Spectra corresponding to different stresses of the mechanochromic photonic crystal film of Example 8;

[0060] Fig. 9 Spectra corresponding to different stresses of the mechanochromic photonic crystal film of Example 10;

[0061] Fig.10 Spectra corresponding to different stresses of the mechanochromic photonic crystal film of Example 11;

[0062] Fig.11 Spectra corresponding to different stresses of the mechanochromic photonic crystal film of Example 12;

[0063] Fig.12 This is a wavelength comparison diagram of the mechanochromic photonic crystal film of Example 1 after 60 days of extrusion;

[0064] Fig.13 This is a graph showing the response speed of the mechanochromic photonic crystal film of Example 1;

[0065] Fig.14 This is a graph of wavelength-cycle number of the mechanochromic photonic crystal film of Example 1 after 1000 squeezings;

[0066] Fig.15 This is a dark field microscope image of the mechanochromic photonic crystal film of Example 1;

[0067] Fig.16 Schematic diagram of the spectrum (i.e. wavelength difference) test corresponding to different stresses. DETAILED DESCRIPTION

[0068] The sources of some raw materials used in the present invention are as follows:

[0069] Vinyl propionate: Sigma-Aldrich;

[0070] Photoinitiator: Sigma-Aldrich.

[0071] The PDI of the silica particles was measured using a Malvern nanoparticle size and zeta potential analyzer. The PDI of the silica particles in each embodiment of the present invention was 0.03.

[0072] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0073] Example 1

[0074] A method for preparing a mechanochromic photonic crystal comprises the following steps:

[0075] S1. Dispersing silica particles in anhydrous ethanol, and uniformly mixing the obtained silica dispersion with hydroxyethyl acrylate and photoinitiator 1173 by ultrasonication to obtain a silica suspension, wherein the volume of the anhydrous ethanol is 1.1 mL, the silica particles account for 15% of the total volume of silica and hydroxyethyl acrylate, the average particle size of the silica particles is 216 nm, and the volume proportion of the photoinitiator in every 0.06 mL of hydroxyethyl acrylate is 5%;

[0076] S2. Dry the silica suspension in an oven at 90° C. for 2 h, and concentrate to obtain silica / hydroxyethyl acrylate mechanochromic photonic crystals.

[0077] The mechanochromic photonic crystal film prepared from the above-mentioned photonic crystal comprises the following steps:

[0078] Take a 30 μL volume of silica / hydroxyethyl acrylate photonic crystal, sandwich it between two glass slides with a spacing of 180 μm, let it stand for 10 min, and then place it under a power of 4.8 mW / cm 2 The film was cured under an ultraviolet lamp (365 nm) for 180 s, and the cured film was separated from the glass slide to obtain a mechanochromic crystal film.

[0079] Embodiments 2 to 15

[0080] A method for preparing a mechanochromic photonic crystal, the steps are the same as those in Example 1, and the differences are shown in Table 1.

[0081] Table 1. Mechanochromic photonic crystal parameters

[0082]

[0083] A mechanochromic photonic crystal film, the preparation method is the same as that of Example 1, except that the corresponding photonic crystals are different, see Table 1 for details.

[0084] Comparative Examples 1 to 7

[0085] A method for preparing a mechanochromic photonic crystal. The preparation method is the same as that in Example 1, and the differences are shown in Table 2.

[0086] Table 2. Preparation parameters of mechanochromic photonic crystals

[0087]

[0088]

[0089] A mechanochromic photonic crystal film, the preparation method is the same as that of Example 1, except that the corresponding photonic crystals are different, see Table 2 for details.

[0090] Results

[0091] Wavelength difference test: Fig.16 As shown, a photonic crystal film is sandwiched between a glass sheet and a substrate, a spectrometer (Ocean Optics Maya 2000) probe is fixed on the top of the photonic crystal film, and the reflection spectrum of the photonic crystal film is recorded. The wavelength difference of the photonic crystal film of the present invention under the stress change from 0kPa to 40kPa is calculated to obtain the wavelength difference. The larger the wavelength difference, the wider the adjustable wavelength range. The results are shown in Table 3. Then, objects of the required weight are added on both sides of the glass sheet, and the pressure (P) on the photonic crystal film, that is, the stress change, is calculated by P = mg / S, where m is the weight of the object, g is the acceleration of gravity, and S is the surface area of ​​the photonic crystal film. It should be noted that: (1) When calculating mg, the weight of the glass sheet should also be calculated; (2) When adding weights to squeeze, it is necessary to ensure that the entire film is evenly stressed; (3) Each time a weight is added, the stress area S of the photonic crystal film will increase. Therefore, S needs to be measured after adding weights. The diameter of the photonic crystal film is measured by S = πr 2 Calculated.

[0092] Response speed test: The wavelength change during the extrusion of the photonic crystal film was collected using a time series spectrum (Ocean Optics Maya 2000). The response speed was obtained by calculating the time required for the initial wavelength and the wavelength after extrusion. The results are shown in Table 3.

[0093] Fracture stress and strain test: The fracture stress and strain data of the photonic crystal film were obtained by testing with an electronic universal testing machine (Inspekt Table Blue 5KN), wherein the larger the fracture stress and strain, the better.

[0094] Table 3. Performance parameters of mechanochromic photonic crystal films

[0095]

[0096]

[0097] It can be seen from Table 3 that the distribution concentration and particle size of silicon dioxide have a great influence on the wavelength difference, response speed and stress-strain of the obtained photonic crystal film, while the drying temperature and drying time will affect the preparation of the photonic crystal and ultimately the performance of the photonic crystal film. In Examples 1 to 8, the volume fraction and distribution concentration of silicon dioxide are changed, and the wavelength difference, response speed, fracture stress and strain of the photonic crystal film change accordingly, and do not show a simple linear trend; in Examples 9 to 13, the particle size of silicon dioxide changes, and the performance of the photonic crystal film obtained finally also differs; in addition, from Examples 1 and 14 to 16, it can also be seen that the drying temperature and drying time affect the performance of the wandering crystal film. In Example 1, when the distribution concentration of silicon dioxide is 306 mg / mL, the particle size is 216 nm, and the drying condition is 90 ° C for 2h, the wavelength difference of the photonic crystal film finally obtained is 302 nm, and the response speed is 43ms. At this time, the structural color of the photonic crystal changes clearly, and the range of mechanochromism is wide, the stress and strain of the photonic crystal film is high, and the comprehensive effect is better than that of the photonic crystals in other embodiments. In Comparative Examples 1 to 2, when the volume fraction of silicon dioxide particles is too low, the corresponding structural color cannot be observed, and when its volume fraction is too high, the particles are arranged densely, and the photonic crystal film cannot be prepared.

[0098] Figure 1 Schematic diagram of the structure of the mechanochromic photonic crystal film of the present invention. It can be seen that the photonic crystal film is a positive opal structure, and the silicon dioxide is not tightly arranged, so its mechanochromic deformation range is large and the adjustable wavelength range is wide.

[0099] from Figure 2 It can be seen that the wavelength of the mechanochromic photonic crystal film prepared with silica microspheres with a particle size of 216nm and a volume fraction of 15% in Example 1 is 790nm, and can show a light blue color produced by secondary diffraction. As the stress increases from 0kPa to 40kPa, the wavelength of the photonic crystal film blue-shifts from 790nm to 488nm, with a wavelength difference of 302nm, covering the entire visible light region, and the adjustable wavelength range is wide.

[0100] from Figure 3 It can be seen that the wavelength of the photonic crystal film prepared with silica microspheres with a particle size of 216nm and a volume fraction of 40% in Example 3 is 600nm, which can show yellow. As the stress increases from 0kPa to 40kPa, the wavelength of the photonic crystal film blue shifts from 600nm to 455nm, with a wavelength difference of 145nm, which is lower than that of Example 1.

[0101] Figure 4The spectra corresponding to different stresses of the mechanochromic photonic crystal film of Example 4 show that the wavelength of the photonic crystal film prepared with silica microspheres with a particle size of 216 nm and a volume fraction of 35% in this embodiment is 621 nm. As the stress increases from 0 kPa to 40 kPa, the wavelength of the photonic crystal film blue-shifts from 621 nm to 465 nm, with a wavelength difference of 156 nm, which is an increase compared to Example 3, but still lower than Example 1.

[0102] from Figure 5 It can be seen that the wavelength of the photonic crystal film prepared with silica microspheres with a particle size of 216nm and a volume fraction of 30% in Example 5 is 642nm, which can show red. As the stress increases from 0kPa to 40kPa, the wavelength of the photonic crystal film blue shifts from 642nm to 467nm, with a wavelength difference of 175nm, which is larger than the wavelength difference of Example 4, but smaller than the wavelength difference of Example 1.

[0103] from Figure 6 As can be seen in the figure, the wavelength of the photonic crystal film prepared with silica microspheres with a particle size of 216nm and a volume fraction of 25% in Example 6 is 676nm, which can show a deep red color. As the stress increases from 0kPa to 40kPa, the wavelength of the photonic crystal film blue shifts from 642nm to 467nm, with a wavelength difference of 202nm, indicating that when the silica distribution concentration is 510mg / mL and the drying condition is 90℃ for 2h, the photonic crystal film breaks through the 200nm wavelength difference.

[0104] like Figure 7 As shown, the wavelength of the photonic crystal film prepared with silica microspheres with a particle size of 216nm and a volume fraction of 20% in Example 7 is 722nm. Since the wavelength is in the near infrared, no structural color can be observed. As the stress increases from 0kPa to 40kPa, the wavelength of the photonic crystal film blue shifts from 722nm to 481nm, with a wavelength difference of 241nm. At this time, the distribution concentration is lower than that of Example 6, but higher than that of Example 1, and its wavelength difference is also between that of Example 1 and Example 6.

[0105] from Figure 8 It can be seen that the wavelength of the photonic crystal film prepared with silica microspheres with a particle size of 216nm and a volume fraction of 10% in Example 8 is 875nm. Since the wavelength is in the near infrared, no structural color can be observed. As the stress increases from 0kPa to 40kPa, the wavelength of the photonic crystal film blue-shifts from 875nm to 505nm, and the wavelength difference is 370nm. Although the wavelength difference is greater than that of Example 1, since the wavelength difference of the photonic crystal film is in the near infrared region when no blue shift occurs, the color change cannot be observed for some time during the mechanochromic process, and the overall effect is worse than that of Example 1.

[0106] Fig. 9 The spectra corresponding to different stresses of the mechanochromic photonic crystal film of Example 10 show that the wavelength of the photonic crystal film prepared with silica microspheres with a particle size of 165nm and a volume fraction of 15% in this example is 544nm, which can show green. As the stress increases from 0kPa to 24kPa, the wavelength of the photonic crystal film blue-shifts from 544nm to 391nm, with a wavelength difference of 153nm. At this time, the wavelength difference is smaller than that of Example 1, indicating that even if the silica distribution concentration is the same and the particle size is different, the wavelength difference of the photonic crystal is also different.

[0107] from Fig.10 It can be seen that the wavelength of the photonic crystal film prepared with silica microspheres with a particle size of 192nm and a volume fraction of 15% in Example 11 is 680nm, which can show green. As the stress increases from 0kPa to 40kPa, the wavelength of the photonic crystal film blue shifts from 680nm to 445nm, with a wavelength difference of 235nm, which is larger than the wavelength difference of Example 10, and the wavelength difference is higher than 200nm.

[0108] from Fig.11 It can be seen that the wavelength of the photonic crystal film prepared with silica microspheres with a particle size of 237nm and a volume fraction of 15% in Example 12 is 868nm, but because the wavelength is in the near infrared, no color can be observed. As the stress increases from 0kPa to 40kPa, the wavelength of the photonic crystal film blue-shifts from 868nm to 532nm, with a wavelength difference of 336nm. Although the wavelength difference is large at this time, since the wavelength is in the near infrared when no mechanochromism occurs, the overall effect is worse than that of Example 1.

[0109] Fig.12 This is a wavelength comparison chart of the mechanochromic photonic crystal film of Example 1 after 60 days of extrusion. It can be seen that the mechanochromic photonic crystal prepared by the present invention can still recover to the original wavelength after 60 days of extrusion, that is, no residual strain is generated during the process, and it does not affect subsequent use. Fig.14 It can also be seen that the optical properties of the photonic crystal film can remain intact after 1000 cycles of extrusion from 790nm to 490nm, indicating that the mechanochromic photonic crystal prepared by the present invention has strong cyclic stability and can be preserved for a long time.

[0110] from Fig.13 In the response speed diagram, the color bar on the right is the target value. The closer to red, the higher the reflectivity, that is, the more obvious the structural color. It can be seen that the photonic crystal film prepared by the present invention has high sensitivity and the response speed is only 42ms.

[0111] from Fig.15It can be seen from the dark field microscope image that the photonic crystal film obtained by the present invention has a high resolution and can display a microscopic pattern with a resolution of 30 μm.

[0112] It should be noted that although the remaining embodiments do not provide relevant descriptions of their corresponding characterization results, their relevant properties are equivalent.

[0113] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A mechanochromic photonic crystal, It is characterized in that The mechanochromic photonic crystal is composed of silicon dioxide particles and hydroxyethyl acrylate, wherein the distribution density of the silicon dioxide particles in the hydroxyethyl acrylate is 306 mg / mL to 918 mg / mL, and the particle size of the silicon dioxide particles is 165 to 237 nm; the preparation method of the mechanochromic photonic crystal comprises the following steps: S1. The silica particles are dispersed in a polar solvent, and the obtained silica dispersion is mixed with hydroxyethyl acrylate and a photoinitiator to obtain a silica suspension, wherein the volume fraction of silica in the silica suspension is 10 to 45%; S2. Dry the silica suspension at 60-100° C. and concentrate it to obtain silica / hydroxyethyl acrylate mechanochromic photonic crystals.

2. The mechanochromic photonic crystal according to claim 1, It is characterized in that The PDI of the silicon dioxide particles is 0.001 to 0.

1.

3. The mechanochromic photonic crystal according to claim 1, It is characterized in that The volume fraction of silicon dioxide in the silicon dioxide suspension in S1 is 10-25%.

4. The mechanochromic photonic crystal according to claim 1, It is characterized in that The drying temperature in S2 is 80-100°C.

5. The mechanochromic photonic crystal according to claim 1, It is characterized in that The drying time in S2 is 1 to 24 hours.

6. A mechanochromic photonic crystal film, It is characterized in that The film is composed of the mechanochromic photonic crystal according to any one of claims 1 to 5.

7. Application of the mechanochromic photonic crystal film according to claim 6 in a visual sensor.

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