A solvent-responsive hydrogel with structural color characteristics and preparation method thereof

Abstract

The present invention relates to a solvent-responsive hydrogel with structural color characteristics and a preparation method thereof, comprising: 1) preparing cellulose nanocrystals with negative surface charges; 2) dispersing hydrogel monomers and cellulose nanocrystals in a solvent to obtain a dispersion; 3) adding a crosslinker, a photoinitiator, and a black fiber material to the dispersion to obtain a precursor solution; 4) heating and evaporating the precursor solution, polymerizing it with LED ultraviolet light, and immersing it in deionized water to obtain a hydrogel; and 5) immersing the hydrogel in an organic solvent for stimulation to obtain a solvent-responsive hydrogel with structural color characteristics. The present invention regulates the elastic modulus and structural color of the hydrogel by changing the type of organic solvent. Under organic solvent stimulation, the hydrogel has an ultra-wide range of variable stiffness and structural color characteristics, possesses the strongest mechanical property enhancement effect, and can increase the elastic modulus of the hydrogel by more than 7,000 times, thus having high application value and prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogel materials, and in particular relates to a solvent-responsive hydrogel with structural color characteristics and a preparation method thereof. Background Art

[0002] Stimuli-responsive hydrogels are "smart" hydrogels that undergo reversible changes in volume, shape, and mechanical properties when exposed to external environmental stimuli, such as temperature, pH, mechanical force, solvent, and ionic strength. These hydrogels have broad application prospects in smart materials, including environmental monitoring, drug delivery, and flexible sensors. Solvent-responsive hydrogels, a commonly studied type of hydrogel, can transform their mechanical properties in response to different solvents, enhancing the material's stiffness and strength.

[0003] Although most reported solvent-responsive hydrogels have achieved improved mechanical properties through solvent exchange, the hydrogels have changed from a soft state to a rigid state, and the elastic modulus before and after stimulation has increased by hundreds of times, greatly expanding their application range. However, this stiffness increase has not reached the order of thousands of times, and the stiffness transition range is limited, which restricts the application of solvent-responsive hydrogels themselves.

[0004] On the other hand, hydrogels with only mechanical properties have a very limited response, which limits their application range. If structural color assembly units are introduced into hydrogels to prepare stimulus-responsive hydrogels with structural color characteristics, they can achieve dual responses of color and mechanical properties in response to solvent stimuli, which can greatly broaden their applications in solvent detection, information encryption and other fields. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a solvent-responsive hydrogel with structural color characteristics and a preparation method thereof.

[0006] The present invention solves the technical problem by the following technical solutions:

[0007] A method for preparing a solvent-responsive hydrogel having structural color characteristics, the method comprising the following steps:

[0008] S1, using absorbent cotton as raw material, and preparing cellulose nanocrystals with negative surface charge through chemical treatment;

[0009] S2, dispersing 3 wt% to 5 wt% of a hydrogel monomer having solvent stimulus responsive properties and 6 wt% to 10 wt% of the cellulose nanocrystals in 80 wt% to 90 wt% of a solvent to obtain a dispersion;

[0010] S3, adding 0.01wt% to 0.03wt% of a crosslinking agent, 0.5wt% to 1.2wt% of a photoinitiator, and 0.005wt% to 0.009wt% of a black fiber material to the dispersion obtained in S2, and mixing thoroughly to obtain a precursor solution;

[0011] S4, heating and evaporating the precursor solution obtained in S3 to a certain solid content, and then polymerizing it under LED ultraviolet light conditions to prepare a hydrogel with structural color characteristics, and then soaking the hydrogel in deionized water to obtain a soft hydrogel;

[0012] S5. The soft hydrogel in the above state is taken out from the deionized water and immersed in an organic solvent for stimulation to obtain a solvent-responsive hydrogel with structural color characteristics.

[0013] Moreover, the S1 chemical treatment is one or more of acid hydrolysis, enzyme hydrolysis, TEMPO oxidation, and ionic liquid method.

[0014] Moreover, the negatively charged zeta potential of the S1 cellulose nanocrystals is -70 to -40 mV.

[0015] Moreover, the S1 cellulose nanocrystals are one or more of sulfonic cellulose nanocrystals, carboxy cellulose nanocrystals, and carboxymethyl cellulose nanocrystals; the S2 hydrogel monomers are one or more of acrylamide, N,N-dimethylacrylamide, N-tert-butylacrylamide, and methacrylamide; the S2 solvent is deionized water; the S3 cross-linking agent is one or more of N,N-methylenebisacrylamide and polyethylene glycol dimethacrylate; the S3 photoinitiator is one or more of HMPP1173, HMPP2959, HMPP4265, HMPP500, and HMPP819DW; and the S3 black fiber material is one or more of carbon nanotubes, black cellulose nanofibers, and carbon fibers.

[0016] Moreover, the S3 mixing method is one or more of magnetic stirring, shaking, and ultrasound.

[0017] Furthermore, the S4 is heated and evaporated to a solid content of 50% to 70%.

[0018] Moreover, the wavelength of the S4LED ultraviolet light is one of 365nm, 395nm, and 405nm.

[0019] Moreover, the S5 organic solvent is one or more of ethylene glycol, methanol, ethanol, n-propanol, and acetone, and the stimulation time of the organic solvent is 5 minutes to 12 hours.

[0020] A solvent-responsive hydrogel with structural color characteristics is characterized by being prepared by the method described above.

[0021] The advantages and beneficial effects of the present invention are:

[0022] 1. The preparation method of the present invention is simple, efficient, and environmentally friendly. The hydrogel prepared by the present invention is uniformly distributed, and the stiffness and strength increase with the increase of stimulation time under the same solvent stimulation, and then remain unchanged after reaching a certain level. The elastic modulus of the hydrogel of the present invention after solvent response is 1403-1556 MPa, and the tensile strength is 19.56-21.69 MPa.

[0023] 2. The present invention controls the range of change of the hydrogel structural color under the stimulation of the same solvent by adjusting the content of cellulose nanocrystals, and the color wavelength change generated by the controllable solvent response is 410nm to 675nm.

[0024] 3. The present invention can also control the maximum mechanical properties and color wavelength range of the hydrogel by adopting different solvent stimuli, so that the hydrogel has both structural color and super mechanical properties within a specific range, greatly improving the application ability of the solvent-responsive hydrogel, and making the hydrogel have a wider application prospect in functional materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a preparation flow chart of the present invention;

[0026] Figure 2 This is a comparison diagram of the soft hydrogel of the present invention before and after stimulation with an organic solvent;

[0027] Figure 3 The CIE chromaticity diagram of the soft hydrogel in the present invention before and after stimulation with an organic solvent;

[0028] Figure 4 This is a comparison diagram of the elastic modulus of the soft hydrogel of the present invention before and after stimulation with an organic solvent;

[0029] Figure 5 The color images and polarization images of the solvent-responsive hydrogels prepared by stimulating different organic solvents in the present invention are shown;

[0030] Figure 6 This is a comparison chart of the mechanical properties of solvent-responsive hydrogels prepared by stimulating different organic solvents in the present invention. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0032] Example 1

[0033] A solvent-responsive hydrogel with structural color characteristics and a preparation method thereof, wherein the innovation lies in the steps of the preparation method:

[0034] 1) Using absorbent cotton as raw material, cellulose nanocrystals with a negatively charged surface zeta potential of -50 mV were prepared by acid hydrolysis.

[0035] 2) dispersing 4 wt% acrylamide monomer and 8% cellulose nanocrystals in 87 wt% solvent to obtain a dispersion; adding 0.02 wt% N,N-methylenebispropylamide, 1 wt% photoinitiator HMPP1173, and 0.005 wt% carbon nanotubes to the dispersion, and mixing by shaking to obtain a precursor solution;

[0036] 3) The precursor solution obtained in 2) is heated and evaporated to 50 wt% of the original solution mass, and then polymerized under 365 nm LED ultraviolet light conditions to prepare a hydrogel with structural color characteristics, and then the hydrogel is immersed in deionized water to obtain a soft hydrogel.

[0037] 4) The soft hydrogel immersed in deionized water was taken out and immersed in propanol for stimulation for 30 minutes to obtain the solvent-responsive hydrogel having structural color characteristics.

[0038] Example 2

[0039] A solvent-responsive hydrogel with structural color characteristics and a preparation method thereof, wherein the innovation lies in the steps of the preparation method:

[0040] 1) Using absorbent cotton as raw material, cellulose nanocrystals with a negatively charged surface zeta potential of -60 mV were prepared by acid hydrolysis.

[0041] 2) dispersing 4 wt% acrylamide monomer and 8% cellulose nanocrystals in 87 wt% solvent to obtain a dispersion; adding 0.02 wt% N,N-methylenebispropylamide, 1 wt% photoinitiator HMPP1173, and 0.005 wt% carbon nanotubes to the dispersion, and mixing by shaking to obtain a precursor solution;

[0042] 3) The precursor solution obtained in 2) is heated and evaporated to 60 wt% of the original solution mass, and then polymerized under 395 nm LED ultraviolet light conditions to prepare a hydrogel with structural color characteristics, and then the hydrogel is immersed in deionized water to obtain a soft hydrogel.

[0043] 4) The soft hydrogel immersed in deionized water was taken out, and immersed in ethanol for stimulation for 60 minutes to obtain the solvent-responsive hydrogel with structural color characteristics.

[0044] Example 3

[0045] A solvent-responsive hydrogel with structural color characteristics and a preparation method thereof, wherein the innovation lies in the steps of the preparation method:

[0046] 1) Using absorbent cotton as raw material, cellulose nanocrystals with a negatively charged surface zeta potential of -70 mV were prepared by acid hydrolysis.

[0047] 2) dispersing 4 wt% acrylamide monomer and 8% cellulose nanocrystals in 87 wt% solvent to obtain a dispersion; adding 0.02 wt% N,N-methylenebispropylamide, 1 wt% photoinitiator HMPP1173, and 0.005 wt% carbon nanotubes to the dispersion, and mixing by shaking to obtain a precursor solution;

[0048] 3) The precursor solution obtained in 2) is heated and evaporated to 50 wt% of the original solution mass, and then polymerized under 405 nm LED ultraviolet light conditions to prepare a hydrogel with structural color characteristics, and then the hydrogel is immersed in deionized water to obtain a soft hydrogel.

[0049] 4) The soft hydrogel immersed in deionized water was taken out, and immersed in methanol for stimulation for 120 minutes to obtain the solvent-responsive hydrogel having structural color characteristics.

[0050] The following is an analysis of the prepared solvent-responsive hydrogel with structural color characteristics using Example 1 as an example.

[0051] like Figure 2 The following figure shows a comparison of the soft hydrogel of the present invention before and after organic solvent stimulation. (a) shows the different shapes of the soft hydrogel, and (b) shows the corresponding shape after organic solvent stimulation. The figure shows that the composite hydrogel can respond to organic solvent stimulation. When immersed in deionized water, its internal structure is filled with water molecules, appearing soft and expanded, with a large pitch. The wavelength of the structural color is in the infrared region and cannot be observed with the naked eye. When the hydrogel is immersed in propanol for solvent stimulation, the changes in its internal nanostructure cause the appearance to become hard, accompanied by the appearance of visible structural color characteristics.

[0052] like Figure 3 As shown in the figure, it is a CIE chromaticity diagram of the soft hydrogel before and after stimulation with organic solvents. As can be seen from the figure, after stimulation with propanol, the color of the hydrogel shifts from black to blue.

[0053] like Figure 4The figure shows a comparison of the elastic modulus of the state-soft hydrogel of the present invention before and after organic solvent stimulation. As can be seen from the figure, the elastic modulus of the hydrogel obtained after propanol stimulation increased from 0.19 MPa before stimulation to 1331 MPa, an increase of more than 7,000 times in stiffness, achieving a significant improvement in mechanical properties.

[0054] like Figure 5 Figure 2 shows the color and polarization images of solvent-responsive hydrogels produced using different organic solvents. As shown, different solvents have varying degrees of blue-shifting effects on the structural color of the superhydrogel. Propanol stimulation results in the largest blue-shift, resulting in the smallest wavelength of the hydrogel, a bluish-purple color. Propanol stimulation results in a moderate blue-shift, resulting in a green hydrogel. Methanol stimulation results in the smallest blue-shift, resulting in a yellow hydrogel.

[0055] like Figure 6 The figure below compares the mechanical properties of solvent-responsive hydrogels produced using different organic solvents. As can be seen from the figure, different organic solvents enhance the mechanical properties of the super-strong hydrogels to varying degrees. The elastic modulus and tensile strength increase, while the elongation at break decreases, following stimulation with methanol, ethanol, and propanol. The hydrogel produced with propanol exhibits the strongest mechanical properties.

[0056] In summary, the hydrogel prepared by the present invention has both structural color characteristics and super-strong mechanical properties after organic solvent stimulation. The addition of cellulose nanocrystals and different organic solvent stimulations jointly control the maximum mechanical properties and color wavelength range of the hydrogel. This controllable preparation process makes solvent-responsive hydrogels have a wider application prospect in functional materials.

[0057] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for preparing a solvent-responsive hydrogel with structural color characteristics, characterized by: The steps of the method are: S1, using absorbent cotton as raw material, and preparing cellulose nanocrystals with negative surface charge through chemical treatment; S2. Dispersing 3 wt% to 5 wt% of a hydrogel monomer having solvent stimulus responsive properties and 6 wt% to 10 wt% of the cellulose nanocrystals in 80 wt% to 90 wt% of a solvent to obtain a dispersion, wherein the hydrogel monomer is one or more of acrylamide, N,N-dimethylacrylamide, N-tert-butylacrylamide, and methacrylamide; S3, adding 0.01wt% to 0.03wt% of a crosslinking agent, 0.5wt% to 1.2wt% of a photoinitiator, and 0.005wt% to 0.009wt% of a black fiber material to the dispersion obtained in S2, and mixing thoroughly to obtain a precursor solution; S4, heating and evaporating the precursor solution obtained in S3 to a solid content of 50% to 70%, and then polymerizing the solution under LED ultraviolet light to prepare a hydrogel with structural color characteristics, and then immersing the hydrogel in deionized water to obtain a soft hydrogel; S5. The soft hydrogel in the above state is taken out from the deionized water and immersed in an organic solvent for stimulation to obtain a solvent-responsive hydrogel with structural color characteristics.

2. The method for preparing a solvent-responsive hydrogel having structural color characteristics according to claim 1, characterized in that: The S1 chemical treatment is one or more of acid hydrolysis, enzyme hydrolysis, TEMPO oxidation, and ionic liquid method.

3. The method for preparing a solvent-responsive hydrogel having structural color characteristics according to claim 1, characterized in that: The negatively charged zeta potential of the S1 cellulose nanocrystals is -70 to -40 mV.

4. The method for preparing a solvent-responsive hydrogel having structural color characteristics according to claim 1, wherein: The S1 cellulose nanocrystals are one or more of sulfonate cellulose nanocrystals, carboxy cellulose nanocrystals, and carboxymethyl cellulose nanocrystals; the S2 solvent is deionized water; the S3 cross-linking agent is one or more of N,N-methylenebisacrylamide and polyethylene glycol dimethacrylate; the S3 photoinitiator is one or more of HMPP1173, HMPP2959, HMPP4265, HMPP500, and HMPP819DW; the S3 black fiber material is one or more of carbon nanotubes, black cellulose nanofibers, and carbon fibers.

5. The method for preparing a solvent-responsive hydrogel having structural color characteristics according to claim 1, wherein: The S3 mixing method is one or more of magnetic stirring, shaking, and ultrasound.

6. The method for preparing a solvent-responsive hydrogel having structural color characteristics according to claim 1, wherein: The wavelength of the S4LED ultraviolet light is one of 365nm, 395nm, and 405nm.

7. The method for preparing a solvent-responsive hydrogel having structural color characteristics according to claim 1, wherein: The S5 organic solvent is one or more of ethylene glycol, methanol, ethanol, n-propanol, and acetone, and the stimulation time of the organic solvent is 5 minutes to 12 hours.

8. A solvent-responsive hydrogel with structural color characteristics, characterized in that: The method is prepared by any one of claims 1 to 7.

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