A silica photonic crystal elastic gel and its preparation method and application

Abstract

The present invention discloses a silicon dioxide photonic crystal elastic gel and its preparation method and application, belonging to the field of photonic crystal materials. The elastic gel is prepared by the following steps: S1. The silicon dioxide colloidal particles are dispersed in anhydrous ethanol, and then added to a polymer monomer containing a photoinitiator, mixed evenly, heated and evaporated to obtain a concentrated solution; the silicon dioxide colloidal particles can self-assemble in the polymer monomer; the volume fraction of the silicon dioxide colloidal particles in the concentrated solution is 18-28%; S2. The concentrated solution obtained by step S1 is taken, and the concentrated solution is cured into a film by ultraviolet curing; S3. The film prepared in step S2 is immersed in a diol liquid, heated and swollen, and the elastic gel is obtained. The photonic crystal is swollen by the diol liquid, and the refractive index difference between the system composed of the polymer and the diol and the silicon dioxide is increased, so that the silicon dioxide photonic crystal elastic gel with a reflection intensity that is not easy to decay, a large color change range, and high sensitivity is obtained.

Description

Technical Field

[0001] The present invention relates to the field of colloidal photonic crystal materials, and more specifically, to a silica photonic crystal elastic gel and its preparation method and application. Background Art

[0002] Colloidal photonic crystals are two-dimensional or three-dimensional ordered array structures formed by the assembly of monodisperse inorganic or organic particles (also called colloidal particles) with diameters in the micrometer or sub-micrometer range under the action of gravity, electrostatic force, capillary force, etc., similar to a crystal whose repeating unit is an atom or a molecule. Generally, the diffraction peak position of colloidal photonic crystals follows the Bragg diffraction formula, that is, mλ = 2ndsinθ, where m is the diffraction order, λ is the diffraction wavelength, n is the average refractive index of the colloidal photonic crystal, d is the lattice spacing of the colloidal photonic crystal, and θ is the incident light angle. From the above formula, it can be seen that under the action of an external force, the spacing d between the colloidal particles in the colloidal photonic crystal changes, resulting in a change in the wavelength λ of the reflected light, thereby realizing the change of its own structural color. Due to the above-mentioned force-induced color change characteristics of colloidal photonic crystals, weak external force changes can be detected with the naked eye, and they have extensive applications in wearable devices, pressure sensors, anti-counterfeiting, etc.

[0003] Currently, force-induced color change photonic crystals can be classified into several categories such as photonic crystal elastomers, photonic crystal soft particles, and photonic crystal gels according to their different preparation methods. However, photonic crystal elastomers and photonic crystal soft particles are limited by their own close-packed structures, and the spacing between colloidal particles is small, resulting in limited spacing change when subjected to an external force, small color change range, low sensitivity, and serious attenuation of the reflection intensity and rapid decrease of the color brightness during the color change process. Therefore, the application fields of these two types of photonic crystals are greatly limited. Although photonic crystal gels are non-close-packed structures and the spacing between colloidal particles is relatively large, which solves the problems of small color change range and low sensitivity to a certain extent, for the widely studied silica photonic crystal gels at present, they also have the problem of reflection intensity attenuation (see the article Yang D, Ye S, Ge J. From Metastable Colloidal Crystalline Arrays to Fast Responsive Mechanochromic Photonic Gels: An Organic Gel for Deformation-Based Display Panels [J]. Advanced Functional Materials, 2014, 24(21): 3197 - 3205.), and the color brightness of the gel gradually weakens during the color change process, making it difficult for the naked eye to detect the color change. Summary of the Invention

[0004] The present invention aims to solve the problem of serious attenuation of reflection intensity of silica photonic crystal elastic gel in the prior art, and provides a silica photonic crystal elastic gel whose reflection intensity is not easily attenuated, and the elastic gel has a large color change range, high sensitivity and good low-temperature stability.

[0005] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] A silicon dioxide photonic crystal elastic gel, wherein the silicon dioxide photonic crystal elastic gel is prepared by the following preparation method, which specifically comprises the following steps:

[0007] S1. Dispersing silica colloidal particles in anhydrous ethanol, adding to a polymer monomer containing a photoinitiator, mixing evenly, heating and evaporating to obtain a concentrated solution; the silica colloidal particles can self-assemble in the polymer monomer; the volume fraction of the silica colloidal particles in the concentrated solution is 18 to 28%;

[0008] S2. Take the concentrated solution obtained in step S1 and solidify the concentrated solution into a film by UV curing;

[0009] S3. Soak the film prepared in step S2 in a diol liquid, heat and swell it, and obtain a silica photonic crystal elastic gel.

[0010] The colloidal photonic crystal elastic gel of the present invention solves the problems of the prior art by the following principles:

[0011] The silica colloidal particles are dispersed and fixed in the elastic polymer network. Under the action of external force, the elastic polymer is deformed, causing the colloidal particles fixed therein to change in arrangement structure, thereby causing the lattice spacing to change, and finally realizing the mechanochromic function. During the external force, the arrangement order of the colloidal particles will be reduced due to the external force, resulting in a decrease in light reflection intensity, severe attenuation of reflection intensity, and fading. The inventor unexpectedly discovered that after the silica photonic crystal was swollen with a diol liquid, the refractive index of the system composed of the polymer and the diol changed, so that the refractive index difference between the silica colloidal particles and the system increased, thereby increasing the reflection intensity, offsetting the negative impact of the reduced order of the colloidal particles on the reflection intensity, so that the reflection intensity of the silica crystal elastic gel during the color change process is first enhanced and then reduced, that is, the reflection intensity is not attenuated within a certain range, and the wavelength range in which the reflection intensity is not attenuated is defined as the wavelength difference. Within the wavelength difference range, the reflection intensity of the silica photonic crystal elastic gel is not attenuated, and a bright structural color can be maintained.

[0012] In addition, in the preparation method of the present invention, the volume fraction of silica colloidal particles in the concentrated solution is 18-28%. The increase in the volume fraction of silica colloidal particles will cause a blue shift in the reflection spectrum, and a higher volume fraction of photonic crystal colloidal particles will reduce the wavelength difference of the gel. To make the wavelength range where the reflection intensity does not decay larger, the volume fraction of photonic crystal colloidal particles must be controlled within a lower range, that is, below 28%; while if the volume fraction of photonic crystal colloidal particles is too low, it cannot self-assemble in the polymer monomer and cannot exert the force-induced color change function, that is, the volume fraction needs to be above 18%.

[0013] Preferably, the polymer monomer in the preparation method is a mixed monomer composed of ethoxyethoxyethyl acrylate and α-(1-oxo-2-propenyl)-ω-phenoxy-polyethylene oxide. The silica colloidal particles can self-assemble in these two polymer monomers and can maintain a high reflection intensity. After these two polymers are cured, they have good elasticity and will undergo large deformations when subjected to weak external forces, causing the photonic crystal to change color.

[0014] Preferably, the volume ratio of ethoxyethoxyethyl acrylate to α-(1-oxo-2-propenyl)-ω-phenoxy-polyethylene oxide is (5-7):(3-5). The elastic gel prepared at this ratio can maintain the elasticity of the material itself while ensuring that the material has a high reflection intensity, so that bright structural colors can be seen.

[0015] Preferably, the diol liquid in step S3 is polyethylene glycol, diethylene glycol or triethylene glycol. Using polyethylene glycol, diethylene glycol or triethylene glycol for swelling, the refractive index difference between the system composed of it and the polymer monomer and the silica colloidal particles is large, which can better offset the decrease in the reflection intensity of the elastic gel caused by the decrease in the order degree of the colloidal particles, resulting in a large wavelength range where the reflection intensity does not decay and a strong ability to maintain bright colors during the color change process.

[0016] More preferably, the diol liquid in step S3 is polyethylene glycol (PEG). At room temperature, the molecular weight of the liquid polyethylene glycol is 200-600. The refractive index difference between the system composed of it and the polymer monomer and the photonic crystal colloidal particles is larger, and the range where the reflection intensity does not decay is larger. In addition, polyethylene glycol is a solvent with excellent biocompatibility. The products prepared from it can be applied in the fields of biology and medicine, have the potential to be used as biosensors, and do not cause pollution to the environment.

[0017] More preferably, the molecular weight of the polyethylene glycol is 200 to 400. When polyethylene glycol with a molecular weight of 200 to 400 is used, the wavelength difference is larger, that is, the range where the reflection intensity does not decay is larger, and the ability to maintain bright colors during the color change process is stronger. In addition, the polyethylene glycol with a lower molecular weight has a low freezing point, which ensures that the elastic gel will not solidify at low temperatures. Even under the condition of -15°C, it can still be used normally, and can maintain a large color change range and a good ability of reflection intensity not to decay.

[0018] Preferably, in the preparation method, the average particle size of the silica colloidal particles in step S1 is 185 to 300 nm.

[0019] Preferably, in the preparation method, the average particle size of the silica colloidal particles in step S1 is 252 to 275 nm.

[0020] By adjusting the average particle size of the silica colloidal particles, the spacing between the colloidal particles can be changed, thereby adjusting the structural color of the elastic gel. In the range of 185 to 300 nm, the elastic gel has a large color change range, a large range where the reflection intensity does not decay, and high sensitivity; in particular, in the range of 252 to 275 nm, the elastic gel has an even larger color change range, an even larger range where the reflection intensity does not decay, and higher sensitivity.

[0021] Preferably, in the preparation method, after swelling in step S3, the mass fraction of the diol liquid in the silica photonic crystal elastic gel is 22 to 25%. When the mass fraction of the diol liquid is above 22%, the particle spacing of the elastic gel is relatively large, resulting in a large color change range, high sensitivity, and a large range where the reflection intensity does not decay. However, affected by the properties of the polymer, the diol solvent cannot enter the system anymore when the mass fraction reaches 25%.

[0022] Preferably, in the preparation method, the temperature for heating and swelling is 60 to 90°C. At a temperature of 60 to 90°C, the photonic crystal thin film can swell rapidly and reach equilibrium, shortening the preparation time.

[0023] The present invention also provides a preparation method of the above-mentioned silica photonic crystal elastic gel.

[0024] The present invention also provides an application of the above-mentioned silica photonic crystal elastic gel in wearable devices, pressure sensors or anti-counterfeiting fields.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] (1) The present invention swells by using a binary alcohol liquid silica photonic crystal film, changing the refractive index of the system composed of a polymer and a binary alcohol, increasing the refractive index difference between the silica colloidal particles and the system, thereby increasing the reflection intensity, offsetting the negative impact of the decrease in the order degree of the colloidal particles on the reflection intensity, so that the reflection intensity of the gel first increases and then decreases during the color change process, and the reflection intensity does not decay within the wavelength difference range, and can maintain a bright structural color;

[0027] (2) The present invention further increases the particle spacing of the silica colloidal particles through swelling, so that under the action of an external force, the change range of the spacing between the colloidal particles increases, the reflection wavelength range of light becomes larger, the color change range of the gel increases, and at the same time, due to the increase in the particle spacing, the resistance to particle movement becomes smaller, the spacing change is easier, and the reaction to the change in the external force is more sensitive and the sensitivity is higher. Description of the Drawings

[0028] Figure 1 Gel photographs of the silica photonic crystal elastic gel of Example 1 under different pressures.

[0029] Figure 2 Reflection spectra of the silica photonic crystal elastic gel of Example 1 under different pressures.

[0030] Figure 3 Curve of the relationship between the reflection wavelength and the pressure of the silica photonic crystal elastic gel of Example 1.

[0031] Figure 4 Reflection spectra of the silica photonic crystal elastic gel of Example 1 placed for 1 to 3 days. Detailed Embodiments

[0032] The following will clearly and completely describe the technical solution of the present invention in conjunction with specific embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by those of ordinary skill in the art without any creative work belong to the protection scope of the present invention.

[0033] Example 1

[0034] A preparation method of a silica photonic crystal elastic gel specifically includes the following steps:

[0035] S1. Mix 1 L of ethanol, 70 mL of water, and 40 mL of ammonia with stirring at 300 rpm. Then add 5 mL of TEOS to the above solution and stir for 5 h to obtain a white solution. Centrifuge to obtain silica colloidal particles with an average particle size of 213 nm, and wash with excess ethanol and water at least 5 times. Disperse the silica in ethanol, and prepare a 200 mg / mL silica suspension for use by evaporating ethanol or adding ethanol. Mix the polymer monomers ethoxyethoxyethyl acrylate and α-(1-oxo-2-propenyl)-ω-phenoxy-polyethylene oxide in a volume ratio of 7:3. Take 82 μL of the above mixed monomers, add 30 μL of the photoinitiator 2-hydroxy-2-methylpropiophenone and 183.6 μL of the above silica suspension, mix well, and place in an oven at 100 °C for heating and evaporation for 1 h to obtain 100 μL of a concentrated solution, such that the volume fraction of the silica colloidal particles in the concentrated solution is 18%;

[0036] S2. Take 0.05 mL of the concentrated solution in step S1 and place it between two glasses with a spacing of 0.18 mm. Then expose it to ultraviolet light (365 nm, 4.8 mW / cm -2 ) for 3 min. The distance between the ultraviolet light source and the sample is 15 cm to obtain a photo-cured photonic crystal film;

[0037] S3. Immerse the prepared photonic crystal film in polyethylene glycol with a molecular weight of 200 for swelling. Raise the temperature to 80 °C and heat for 60 min to obtain a colloidal photonic crystal elastic gel. The mass fraction of polyethylene glycol in the swollen colloidal photonic crystal elastic gel is 25%.

[0038] Example 2

[0039] The method for preparing the silica photonic crystal elastic gel in this example is the same as that in Example 1, except that: in step S3, the molecular weight of polyethylene glycol is 400.

[0040] Example 3

[0041] The method for preparing the silica photonic crystal elastic gel in this example is the same as that in Example 1, except that: in step S3, the molecular weight of polyethylene glycol is 600.

[0042] Example 4

[0043] The method for preparing the silica photonic crystal elastic gel in this comparative example is the same as that in Example 1, except that: swelling is carried out using a diethylene glycol solvent.

[0044] Example 5

[0045] The method for preparing the silica photonic crystal elastic gel in this comparative example is the same as that in Example 1, except that: triethylene glycol solvent is used for swelling.

[0046] Example 6

[0047] The method for preparing the silica photonic crystal elastic gel in this example is the same as that in Example 1, except that: the addition amount of the silica suspension in step S1 is 285.6 μL, and heating is carried out to make the volume fraction of the silica colloidal particles in the concentrated solution 28%.

[0048] Example 7

[0049] The method for preparing the silica photonic crystal elastic gel in this example is the same as that in Example 1, except that: the average particle size of the silica colloidal particles in the concentrated solution in step S1 is 185 nm.

[0050] Example 8

[0051] The method for preparing the silica photonic crystal elastic gel in this example is the same as that in Example 1, except that: the average particle size of the silica colloidal particles in the concentrated solution in step S1 is 252 nm.

[0052] Example 9

[0053] The method for preparing the silica photonic crystal elastic gel in this example is the same as that in Example 1, except that: the average particle size of the silica colloidal particles in the concentrated solution in step S1 is 275 nm.

[0054] Example 10

[0055] The method for preparing the silica photonic crystal elastic gel in this example is the same as that in Example 1, except that: the average particle size of the silica colloidal particles in the concentrated solution in step S1 is 300 nm.

[0056] Example 11

[0057] The method for preparing the silica photonic crystal elastic gel in this example is the same as that in Example 1, except that: heating is carried out for 40 min to make the mass fraction of polyethylene glycol in the colloidal photonic crystal elastic gel after swelling in step S3 22%.

[0058] Comparative Example 1

[0059] The method for preparing the silica photonic crystal elastic gel in this example is the same as that in Example 1, except that: the addition amount of the silica suspension in step S1 is 387.6 μL, and heating is carried out to make the volume fraction of the silica colloidal particles in the concentrated solution 38%.

[0060] Performance Test 1

[0061] Test the maximum displacement distance of the reflection peak position, that is, the maximum wavelength difference, under the pressure of 0 - 60 kPa for the test examples and comparative examples, and the wavelength range where the reflection intensity is higher than that without external force under the pressure of 0 - 60 kPa, that is, the wavelength difference. The larger the maximum wavelength difference, the larger the color change range of the gel; the larger the wavelength difference, the larger the wavelength range where the reflection intensity does not decay, that is, the more difficult it is for the reflection intensity to decay.

[0062] Performance Test 2

[0063] Test the absolute value k of the slope of the curve of the reflection wavelength vs. pressure for the test examples and comparative examples under the pressure of 0 - 60 kPa. If the absolute value is larger, it indicates that the gel is more sensitive to the change of weak external force and has higher sensitivity.

[0064] Performance Test 3

[0065] Test the reflection light intensity of the gel without external force for the test examples and comparative examples. The larger the reflection light intensity, the brighter the structural color of the gel.

[0066] Performance Test 4

[0067] Test the maximum wavelength difference and the reflection intensity without external force of the gel under the pressure of 0 - 60 kPa at - 15°C for Test Examples 1 - 3.

[0068] Performance Test 5

[0069] Stability test, test the reflection spectrum of the elastic gel for 1 - 3 days.

[0070] Results and Analysis

[0071] Table 1 Test Results of Elastic Gel

[0072]

[0073]

[0074] *k is the absolute value of the slope of the curve of the reflection wavelength vs. pressure of the elastic gel.

[0075] It can be seen from Figure 1 that for the elastic gel prepared in Example 1, under the action of external force, the distance between the colloidal particles gradually decreases, so that the gel shows a color change; it can be seen from Figure 2It can be seen that under the action of a pressure of 0 - 60 kPa, as the pressure increases, the reflection intensity first increases and then decreases. Its wavelength range changes from 650 nm to 370 nm, with a maximum wavelength difference of 280 nm, and the color change range is large. The wavelength range in which the reflection intensity is higher than that without external force is 650 - 450 nm, that is, the wavelength difference is 200 nm, and the reflection intensity of the gel does not decay within this range. From Figure 3 It can be seen that under the action of a pressure of 0 - 60 kPa, the absolute value of the slope of the curve of the reflection wavelength versus pressure is 4.6. A slight change in external force can cause a change in the color of the elastic gel, and the sensitivity is high. From Figure 4 It can be seen that after the elastic gel is placed for three days, the position of its reflection peak and the range intensity basically remain unchanged, indicating that the elastic gel has good thermal stability.

[0076] From Examples 1 - 5, it can be obtained that when the present invention uses polyethylene glycol solvents with different molecular weights, diethylene glycol, and triethylene glycol to swell the silica photonic crystal, the reflection intensity can be maintained without attenuation within a certain range, that is, it has a corresponding wavelength difference range. Compared with swelling using diethylene glycol and triethylene glycol, the maximum wavelength difference, wavelength difference, and the absolute value of the slope of the curve of pressure versus reflection light wavelength are larger when using polyethylene glycol for swelling. And when the molecular weight of polyethylene glycol is 200, the maximum wavelength difference, wavelength difference, and the absolute value of the slope of the curve of pressure versus reflection light wavelength are even larger.

[0077] From Examples 1, 6, and Comparative Example 1, it can be seen that when the volume fraction of silica colloidal particles is 18 - 28%, it has a larger color change range, higher sensitivity, and a larger range where the emission intensity does not decay. In Comparative Example 1, the volume fraction of silica colloidal particles is too large, resulting in a smaller color change range and a smaller range where the emission intensity does not decay. When the volume fraction of silica colloidal particles is less than 18%, they cannot self-assemble in the polymer monomer and cannot exhibit structural color.

[0078] From Examples 1, 7 - 10, it can be seen that when the average particle size of silica colloidal particles is 185 - 300 nm, they all have a larger color change range, higher sensitivity, and a larger range where the emission intensity does not decay. And within the range of 252 - 275 nm, the elastic gel has a larger color change range, a larger range where the emission intensity does not decay, and higher sensitivity.

[0079] From Examples 1, 11, it can be seen that when the mass fraction of polyethylene glycol in the colloidal photonic crystal elastic gel after swelling in step S3 is 22 - 25%, the elastic gel has a large color change range, high sensitivity, and a large range where the emission intensity does not decay.

[0080] Table 2 Maximum wavelength difference and reflection intensity of Examples 1 - 5 at - 15°C

[0081]

[0082] For Examples 1 to 3, the maximum wavelength difference and reflection intensity at -15°C are at the same level or slightly decreased compared with those at room temperature, indicating that the elastic gel swollen with polyethylene glycol can still maintain a large color change range and brighter structural color at low temperature, and has good low-temperature performance. However, for Examples 4 to 5, the structural color cannot be exhibited due to the solidification of the solvent at low temperature, resulting in poor low-temperature performance. When the molecular weight of polyethylene glycol is 200-400, the elastic gel has a larger color change range, higher sensitivity, and a larger range where the reflection intensity does not decay.

[0083] Obviously, the above examples of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill 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 implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A silica photonic crystal elastic gel, characterized in that, The silica photonic crystal elastic gel is prepared by the following preparation method, which specifically includes the following steps: S1. Dispersing silica colloidal particles in absolute ethanol, and then adding them into a polymer monomer containing a photoinitiator. After mixing evenly, heating and evaporating to concentrate to obtain a concentrated solution; the silica colloidal particles can self-assemble in the polymer monomer; the volume fraction of the silica colloidal particles in the concentrated solution is 18-28%; S2. Taking the concentrated solution obtained in step S1 and curing the concentrated solution into a film by ultraviolet curing; S3. Immersing the film prepared in step S2 in a diol liquid and heating and swelling to obtain a silica photonic crystal elastic gel; Wherein, the polymer monomer in step S1 is a mixed monomer composed of ethoxyethoxyethyl acrylate and α-(1-oxo-2-propenyl)-ω-phenoxy-polyethylene oxide; The volume ratio of the ethoxyethoxyethyl acrylate to α-(1-oxo-2-propenyl)-ω-phenoxy-polyethylene oxide is (5-7):(3-5).

2. The silica photonic crystal elastic gel according to claim 1, characterized in that, The diol liquid in step S3 is polyethylene glycol, diethylene glycol or triethylene glycol.

3. The silica photonic crystal elastic gel according to claim 2, wherein The molecular weight of the polyethylene glycol is 200-400.

4. The silica photonic crystal elastic gel according to claim 1, characterized in that, The average particle size of the silica colloidal particles in step S1 is 185-300 nm.

5. The silica photonic crystal elastic gel according to claim 1, wherein The average particle size of the silica colloidal particles in step S1 is 252-275 nm.

6. The silica photonic crystal elastic gel according to claim 1, wherein The mass fraction of the diol liquid in the silica photonic crystal elastic gel in step S3 is 22-25%.

7. The silica photonic crystal elastic gel according to claim 1, wherein The temperature of the heating and swelling in step S3 is 60-90 °C.

8. Application of the silica photonic crystal elastic gel according to any one of claims 1 to 7 in the fields of wearable devices, pressure sensors or anti-counterfeiting.

Images