Preparation method of force-responsive flexible hydrogel, product and application thereof

Abstract

The application discloses a preparation method of a force-responsive tough hydrogel, and the method comprises the following steps: (1) mixing a hydrophobic monomer, a hydrophilic monomer, a force-sensitive group crosslinking agent and an initiator in a solvent to obtain a prepolymer solution, and performing free radical polymerization on the prepolymer solution to obtain an organic gel; and (2) soaking the organic gel in deionized water to obtain a stable force-responsive tough hydrogel. The application further discloses the force-responsive tough hydrogel obtained by the above preparation method and application of the force-responsive tough hydrogel in the fields of mechanical sensing, information encryption, anti-counterfeiting identification or structural health monitoring. The method can quickly prepare the force-responsive tough hydrogel without using a surfactant.

Description

Technical Field

[0001] This invention belongs to the field of hydrogel technology, and specifically relates to a method for preparing a force-responsive tough hydrogel, its products, and applications. Background Technology

[0002] Mechanochromatic hydrogels are hydrogel materials that undergo detectable chemical / optical changes when subjected to mechanical forces (tension, compression, shear, etc.). These changes typically manifest as alterations in color, fluorescence, or other signals, originating from the chemical or structural responses of internal mechanochromatic groups under the influence of force. Existing mechanochromatic hydrogels based on mechanochromatic groups are mainly classified into two categories: micellar hydrogels and dual-network hydrogels.

[0003] For micellar hydrogel systems, the general preparation method involves mixing the hydrophilic monomer acrylamide and the hydrophobic monomer methyl acrylate containing a photoinitiator, thoroughly mixing them under the emulsifying action of the surfactant Tween 80 to form a homogeneous emulsion, and then photopolymerizing to form a hydrogel. This hydrogel has the following shortcomings in terms of performance, applications, and preparation method: 1) Application Limitations: The prepared hydrogel is in a non-swelling equilibrium state, therefore its actual water content is generally below 50%. Although the water content of the fully swollen hydrogel can reach over 60%, the gel strength is very weak at this point, lacking mechanical responsiveness, thus greatly limiting its application in aquatic environments. Furthermore, due to the presence of hydrophobic units, it quickly loses water and becomes brittle in air, causing it to lose its mechanical responsiveness and limiting its application in low-humidity air environments. In summary, the inherent properties of this hydrogel—poor water retention and a narrow force response window—significantly limit its practical applications.

[0004] 2) Low transmittance: In its preparation method, the presence of Tween 80 can induce micelle formation in the emulsion. However, the size control mechanism of the micelles is not yet clear. The resulting micron-sized micelle particles exhibit significant light scattering characteristics, leading to low gel transmittance. This results in poor mechanochromic performance and limits its practical application. Furthermore, the introduction of the surfactant TWEEN 80 affects the gel's properties, inevitably causing migration during swelling and resulting in the polarization and destruction of spiropyran molecules.

[0005] 3) System and functional limitation: This hydrogel system has a clear orientation towards the types of comonomers and mechanosensitive groups, and the applicable monomers and mechanosensitive groups are limited to a few known types. This limits the expansion of the system and its functions.

[0006] The preparation method for dual-network hydrogel systems has the following significant drawbacks: the preparation process involves two steps—preparing the first network and the second network—which results in a long preparation cycle, making it unsuitable for mass production. Furthermore, the network often uses three or four monomer components, making it difficult to precisely control the network performance through component content, and limiting the range of physicochemical property regulation, such as the glass transition temperature. The two-step preparation method also makes it difficult to achieve programmed mechanochromism; moreover, surfactants are still required to assist in the dissolution of the mechanosensitive groups. Over time, due to the diffusion of surfactants, the mechanosensitive groups are induced to become ineffective by water molecule polarization, which is detrimental to preservation.

[0007] Force-responsive materials are a class of smart materials capable of structural or property changes under external mechanical action, with important applications in mechanical sensing, information encryption, anti-counterfeiting, and structural health monitoring. Existing force-responsive hydrogels typically rely on flexible polymer chains to transmit high chain tension under large deformation conditions to activate force-sensitive groups, thus generally suffering from high activation thresholds, low activation efficiency of force-responsive groups, and insensitivity to loading conditions. Furthermore, in aqueous environments, some force-sensitive groups are susceptible to non-mechanically induced transformations due to solvent polarity, further limiting their stable application in hydrogel systems. Therefore, developing a hydrogel material that achieves efficient and controllable force response under relatively small macroscopic deformations while maintaining stability in aqueous environments is a pressing technical problem in this field. Existing methods for preparing force-responsive hydrogels generally suffer from limited universality, inconvenient preparation methods, or insensitive force responses. Therefore, developing hydrogels with simple preparation methods, efficient and sensitive force responses, and controllable activation of force-sensitive groups is particularly necessary and important. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing a force-responsive tough hydrogel, as well as its products and applications. This method can rapidly prepare a tough hydrogel with high force response without the need for surfactants.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for preparing a force-responsive toughness hydrogel, the method comprising the following steps: (1) A prepolymer solution is obtained by mixing a hydrophobic monomer, a hydrophilic monomer, a mechanosensitive crosslinking agent and an initiator in a solvent, and the prepolymer solution is subjected to free radical polymerization to obtain an organic gel; (2) The organic gel was soaked in deionized water to obtain a stable force-responsive tough hydrogel.

[0010] This invention employs a simple and efficient preparation method. The preparation process utilizes a one-step photopolymerization method combined with a solvent exchange strategy to rapidly prepare a tough hydrogel with high mechanical response, without the need for surfactants. Specifically, it employs a hydrophobic monomer, phenyl acrylate, with functional side groups, combined with a solvent exchange strategy. During solvent exchange, hydrophobic aggregation and π-π interactions form a local glassy phase region, protecting the hydrophobic methanophores and making them less susceptible to damage by polar solvents. Therefore, the preparation method provided by this invention not only eliminates the need for surfactants but also creates a phase-separated structure where glassy and rubbery phase regions coexist during solvent exchange. This allows for efficient stress transmission to the methanophores, resulting in a hydrogel with high mechanical response. Furthermore, by simply adjusting the ratio of the two comonomers, flexible and rapid selective control of mechanical properties and mechanical response performance can be achieved.

[0011] In step (1), the molar ratio of hydrophobic monomers to hydrophilic monomers in the prepolymer solution is 1:1 to 1:5. This invention adjusts the hydrogel by controlling the proportion of the introduced hydrophobic monomers. T g It provides mechanical strength while effectively protecting SP molecules from polarization and ring opening.

[0012] In step (1), the total concentration of hydrophobic and hydrophilic monomers in the prepolymer solution is 4~6 mol / L.

[0013] In the method for preparing hydrogels provided by this invention, the range of selectable system components is wide, thus enabling flexibility and diversity in properties and functions. The choice of monomers is diverse, with hydrophobic and hydrophilic monomers having a wider range of applications. The choice of methanophores is also diverse, thus enabling precise control of the activation-induced color change response. For example, programmed activation can be achieved by utilizing different initial activation strains, realizing mechanochromatic patterning and information encryption functions.

[0014] In step (1), the hydrophobic monomer is selected from one or more of phenyl acrylate, cyclohexyl acrylate, naphthyl acrylate or anthracene acrylate, and the hydrophilic monomer is selected from one or more of acrylamide AAm, sodium acrylate or hydroxyethyl acrylate.

[0015] In step (1), the mechanistic crosslinking agent is selected from one or more of acrylate double-bonded spiropyran, rhodamine, or anthracene-maleimide adducts.

[0016] In step (1), the free radical polymerization can be initiated by ultraviolet light or by thermal initiation. If thermal initiation is used, the mechanosensitive group can be anthracene-maleimide adduct and its derivatives.

[0017] In step (1), the solvent is miscible with water, and the solvent is selected from dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF).

[0018] In step (1), the preparation method further includes: injecting the prepolymer liquid into a glass plate mold with a silicone pad of a certain thickness, and then placing it under an ultraviolet LED surface light source with an emission wavelength of 395nm and a light intensity of 10 mW / cm². 2 The photopolymerization process is carried out for 30 minutes. After the photopolymerization is completed, the gel sample taken out of the glass interlayer is the target organic gel.

[0019] Furthermore, the preparation method of the force-responsive toughness hydrogel includes the following steps: (1) Phenyl acrylate PhA, acrylamide AAm and spiropyran crosslinking agent SP were subjected to free radical polymerization in dimethyl sulfoxide DMSO solvent system to obtain an organic gel of phenyl acrylate-acrylamide copolymer P(PhA-co-AAm); (2) The organic gel containing SP crosslinking was soaked in deionized water and the water was changed every 12 hours. After 3 days, a stable force-responsive tough hydrogel was obtained.

[0020] The present invention also provides a force-responsive tough hydrogel obtained by the above preparation method.

[0021] The present invention also provides an application of the above-mentioned force-responsive tough hydrogel in the field of mechanical sensing.

[0022] Furthermore, by employing responsive toughness hydrogels with two or more hydrophobic monomer contents, programmed response (programmed mechanochromic color change) is achieved under external force compression conditions; furthermore, by employing force-responsive hydrogels with two or more different hydrophobic monomer contents, programmed response (programmed mechanochromic color change) is achieved under external force compression conditions.

[0023] Compared with the prior art, the present invention has the following beneficial effects: 1. In the method for preparing hydrogels provided by this invention, the solvent exchange strategy is crucial for forming a glassy state. After solvent exchange, local glassy microregions (glassy phase microregions) are formed due to hydrophobic aggregation, hydrogen bonding, or π-π interactions. This not only protects chromophores (such as spiropyran and rhodamine) from being destroyed by polar solvents, but also shortens the profile length, achieving the effect of efficiently transferring stress. This is a new mechanism and preparation method.

[0024] 2. The preparation method of the hydrogel provided by the present invention is based on the supramolecular interaction between the hydrophobic groups of the side chains of the hydrophobic monomer. Since the supramolecular interaction is not limited to hydrophobic association interaction, it also includes hydrogen bonding or π-π interaction, etc. Therefore, it solves the problem of poor universality in the existing system and is applicable to a variety of monomers, such as anthracene acrylate, pentafluorophenyl acrylate, etc.

[0025] 3. The preparation method provided by this invention does not require the introduction of surfactants, thus avoiding interference such as performance instability caused by the use of surfactants. It also solves the problem of surfactant diffusion during the swelling process of hydrogel systems in water. In contrast, conventional force-responsive hydrogels must use surfactants due to the strong hydrophobicity of the chromophores. As the swelling process proceeds, the surfactants diffuse, leading to unstable hydrogel performance and problems such as decreased mechanical properties and deactivation of chromophores.

[0026] 4. The preparation method provided by this invention solves the problems of narrow control window and low activation efficiency of existing hydrogels: The hydrogel prepared by this invention adjusts the stress distribution of the network to the glass phase region through the phase separation mechanism formed by the solvent exchange process, thereby improving the stress transmission efficiency and activation efficiency; while the mechanical properties of traditional hydrogels are generally weak, so the strain range of the mechanic response is limited. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process for preparing the hydrogel in the example; Figure 2 The fluorescence spectra, tensile mechanical properties, and loss tangent values ​​of Examples 1-5 and Comparative Example 1 are characterized. Figure 3 Physical photographs and fluorescence photographs of the mechanical responses of Examples 1, 5, 6 and 7; Figure 4 Physical photographs of the procedural force responses in Application Examples 1 and 2. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0029] Example 1: Preparation of P(PhA- co -AAm)-40% hydrogel The preparation process in this embodiment is as follows: Figure 1As shown, a DMSO prepolymer solution was first prepared, containing 2.0 M PhA (phenyl acrylate) and 3.0 M AAm (acrylamide), as well as 0.02 M spiropyran SP crosslinking agent (0.4 mol% of total monomers) and 0.01 M TPO-L (ethyl 2,4,6-trimethylbenzoylphenylphosphonate) photoinitiator, with a total solution volume of 5.0 mL. This precursor solution was then injected into a reaction chamber separated by two glass plates and a 0.5 mm thick silicone pad. These gels were then immersed in deionized water at room temperature for solvent exchange, with the deionized water replaced every 12 h. After repeating the water exchange for 3 days, the desired force-responsive hydrogel was obtained.

[0030] Example 2: Preparation of P(PhA- co -AAm)-33% hydrogel First, a DMSO prepolymer solution was prepared, containing 1.67 M PhA and 3.33 M AAm, as well as 0.02 M crosslinking agent SP (0.4 mol% of the total monomers) and 0.01 M TPO-L photoinitiator, with a total solution volume of 5.0 mL. The photocrosslinking and solvent exchange procedures were the same as in Example 1.

[0031] Example 3: Preparation of P(PhA- co -AAm)-25% hydrogel First, a DMSO prepolymer solution was prepared, containing 1.25 M PhA and 3.75 M AAm, as well as 0.02 M crosslinking agent SP (0.4 mol% of the total monomers) and 0.01 M TPO-L photoinitiator, with a total solution volume of 5.0 mL. The photocrosslinking and solvent exchange procedures were the same as in Example 1.

[0032] Example 4: Preparation of P(PhA- co -AAm)-20% hydrogel First, a DMSO prepolymer solution was prepared, containing 1.0 M PhA and 4.0 M AAm, as well as 0.02 M crosslinking agent SP (0.4 mol% of the total monomers) and 0.01 M TPO-L photoinitiator, with a total solution volume of 5.0 mL. The photocrosslinking and solvent exchange procedures were the same as in Example 1.

[0033] Example 5: Preparation of P(PhA- co -AAm)-17% hydrogel First, a DMSO prepolymer solution was prepared, containing 0.85 M PhA and 4.15 M AAm, as well as 0.02 M crosslinking agent SP (0.4 mol% of the total monomers) and 0.01 M TPO-L photoinitiator, with a total solution volume of 5.0 mL. The photocrosslinking and solvent exchange procedures were the same as in Example 1.

[0034] Example 6 First, a DMSO prepolymer solution was prepared, containing 2.0 M PhA and 3.0 M AAm, as well as 0.02 M crosslinking agent Rho (rhodamine, accounting for 0.4 mol% of the total monomers) and 0.01 M TPO-L photoinitiator, with a total solution volume of 5.0 mL. The photocrosslinking and solvent exchange procedures were the same as in Example 1.

[0035] Example 7 First, a DMSO prepolymer solution was prepared, containing 1.67 M PhA and 3.33 M AAm, as well as 0.02 M An-Ma crosslinking agent (anthraynylene-maleimide adduct, accounting for 0.4 mol% of the total monomers) and 0.01 M TPO-L photoinitiator, with a total solution volume of 5.0 mL. The photocrosslinking and solvent exchange procedures were the same as in Example 1.

[0036] Comparative Example 1 First, a DMSO prepolymer solution was prepared, containing 5 M AAm (acrylamide), 0.02 M crosslinking agent SP (spiropyran accounting for 0.4 mol% of the total monomers), and 0.01 M TPO-L photoinitiator (ethyl 2,4,6-trimethylbenzoylphenylphosphonate, accounting for 0.2 mol% of the total monomers), with a total solution volume of 5.0 mL. The photocrosslinking and solvent exchange procedures were the same as in Example 1.

[0037] Application Example 1: First, three prepolymer solutions, a, b, and c, are prepared. Prepolymer solution a is the same as P(PhA-) in Example 2. co Prepolymer solution b was prepared as the prepolymer solution for the Rho crosslinked hydrogel of Example 7, containing 2.0 M PhA (phenyl acrylate) and 3.0 M AAm, as well as 0.02 M crosslinking agent HDDA (1,6-hexanediol diacrylate, accounting for 0.4 mol% of the total monomers) and 0.01 M TPO-L photoinitiator, with a total solution volume of 10.0 mL. After the prepolymer solution was prepared, prepolymer solution a was injected into the stem portion in a reaction chamber separated by two pre-prepared glass plates and a concave flower-patterned silicone pad (2 mm thick), and then photocrosslinked to obtain a stem-shaped organic gel. After polymerization, prepolymer solution b was injected into the petal portion, and photopolymerization was performed again to obtain a petal-shaped organic gel. After polymerization, prepolymer solution c was injected into the remaining portion, and photopolymerization was performed again to obtain a complete organic gel. The solvent exchange procedure was the same as in Example 1. It exhibits a programmed response under external compression, meaning that the stem turns blue when the compressive strain is 20%, and the petals turn red when the compressive strain is 80%, presenting an overall pattern of a complete flower.

[0038] Application Example 2: First, two prepolymer solutions, a and b, are prepared. Prepolymer solution a is the same as P(PhA-) in Example 2. co -AAm)-40% hydrogel prepolymer solution, prepolymer solution b is the same as P(PhA- in Example 3) co A prepolymer solution of 33% (AAm) hydrogel was prepared. After the prepolymer solution was prepared, it was injected into the H-shaped portion of a reaction chamber separated by two pre-prepared glass plates and a silicone pad (2 mm thick) with an H-shaped letter pattern. Photocrosslinking was then performed to obtain an H-shaped organic gel. After polymerization, prepolymer solution b was injected into the remaining blank portion, and photopolymerization was performed again to obtain the target organic gel. The solvent exchange procedure was the same as in Example 1. The prepared gel exhibited a programmed response under external compression; that is, the H-shaped portion turned blue when the compressive strain was 20%, and the entire gel turned blue when the compressive strain was 50%.

[0039] like Figure 2 The figures show the fluorescence spectra, tensile mechanical properties, and loss tangent properties of Examples 1-5 and Comparative Example 1. From... Figure 2 It can be seen that, Figure 2 (a) in the figure shows the physical photographs of Example 1 and Comparative Example 1 in equilibrium under DMSO and water conditions. In the comparative example, the spiropyran molecules in the PAAm gel undergo ring-opening due to the polarization effect of water, while the hydrophobic protection and glass transition effect of the PhA monomer achieve protection of SP. Figure 2 Figure (b) shows the fluorescence emission spectra of gels with different PhA contents (0%, 17%, 20%, 25%, 33%, 40%). Pure PAAm gel (0% PhA) shows a strong fluorescence peak at 650-700 nm, while the fluorescence intensity of the PhA-containing copolymer gel is significantly reduced, and the fluorescence intensity further decreases with increasing PhA content, indicating that the introduction of PhA effectively protects SP molecules from being destroyed by polar water. Figure 2 (c) shows the stress-strain curves of gels with different PhA contents (Examples 1-5). As the PhA content increases from 17% to 40%, the fracture stress of the gel increases from about 3 MPa to about 8 MPa, and the Young's modulus increases from 2 MPa to 100 MPa, indicating that the introduction of PhA enhances the mechanical strength of the gel. Figure 2 In the figure, (d) represents the curve of loss tangent (tanδ) versus temperature for gels with different PhA contents. The tanδ peak corresponds to the glass transition temperature of the gel. T g As PhA content increases from 17% to 40%, T g The temperature gradually increased from 28.2℃ to 64.3℃, resulting in a gradual transition and transformation from a rubbery state to a glassy state. In summary, the introduction of the hydrophobic monomer PhA improved the gel's... Tg As the temperature rises, the mechanical strength increases, and at the same time, fewer SP molecules are polarized and open their rings.

[0040] like Figure 3 The images shown are photographs of the mechanical responses of Examples 1, 5, 6, and 7. Figure 3 As shown in (a), when the PhA content is 40%, the activation strain of SP in the gel is 20%, while when the PhA content is 17%, the activation strain is 340%, indicating that the vitrification effect greatly reduces the activation strain and improves the activation efficiency of SP. Furthermore, in Figure 3 (b) and Figure 3 In (c), replacing the chromophore with rhodamine and anthracene-maleimide adduct both achieved tensile force-induced activation, fully demonstrating the good universality of the hydrogel.

[0041] Figure 4 Physical photographs of the procedural responses to Application Examples 1 and 2. Figure 4 It can be seen that the programmed force response of hydrogels can be achieved through reasonable design. Figure 4 As can be seen in (a), the spiropyran hydrogel is activated at approximately 20% strain as the compressive strain increases. Figure 4 As shown in (b), the rhodamine hydrogel is activated at approximately 80% strain. By utilizing the difference in activation strain between the two, flowers with different activation strain portions were prepared, such as... Figure 4 As shown in (c), a spatiotemporally selective programmed response was achieved, where the petal turns blue upon 20% compressive strain (activated by spiropyran) and red upon 80% compressive strain (activated by rhodamine). Figure 4 As shown in (d), by utilizing the difference in activation strain of hydrogels with different PhA concentrations, hydrogels containing the letter "H" were prepared, thus achieving the same programmed response effect.

Claims

1. A method for preparing a force-responsive toughness hydrogel, characterized in that, The method includes the following steps: (1) A prepolymer solution is obtained by mixing a hydrophobic monomer, a hydrophilic monomer, a mechanosensitive crosslinking agent and an initiator in a solvent, and the prepolymer solution is subjected to free radical polymerization to obtain an organic gel; (2) The organic gel was soaked in deionized water to obtain a stable force-responsive tough hydrogel.

2. The method for preparing a force-responsive tough hydrogel according to claim 1, characterized in that, In step (1), the molar ratio of hydrophobic monomers to hydrophilic monomers in the prepolymer solution is 1:1 to 1:

5.

3. The method for preparing the force-responsive toughness hydrogel according to claim 1, characterized in that, In step (1), the total concentration of hydrophobic and hydrophilic monomers in the prepolymer solution is 4~6 mol / L.

4. The method for preparing the force-responsive toughness hydrogel according to claim 1, characterized in that, In step (1), the hydrophobic monomer is selected from one or more of phenyl acrylate, cyclohexyl acrylate, naphthyl acrylate or anthracene acrylate, and the hydrophilic monomer is selected from one or more of acrylamide AAm, sodium acrylate or hydroxyethyl acrylate.

5. The method for preparing the force-responsive toughness hydrogel according to claim 1, characterized in that, In step (1), the mechanistic crosslinking agent is selected from one or more of acrylate double-bonded spiropyran, rhodamine, or anthracene-maleimide adducts.

6. The method for preparing the force-responsive toughness hydrogel according to claim 1, characterized in that, In step (1), the solvent is miscible with water, and the solvent is selected from dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF).

7. A force-responsive tough hydrogel obtained by the preparation method according to any one of claims 1-6.

8. The application of the force-responsive toughness hydrogel of claim 7 in mechanical sensing.

9. The application according to claim 8, characterized in that, By employing responsive toughness hydrogels with contents of two or more hydrophobic monomers, programmed response is achieved under external force compression conditions.

10. The application according to claim 8, characterized in that, By employing responsive toughness hydrogels with contents of two or more hydrophobic monomers, programmed response is achieved under external force compression conditions.

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