A method for preparing flexible double-encrypted hydrogel film by 3D printing

Abstract

A method for preparing a flexible double-encrypted hydrogel film by 3D printing belongs to the field of responsive functional films. The method mainly comprises the following steps: (1) selecting a flexible transparent hydrogel as a support layer; (2) using a fluorescent material with light response, adding it to the hydrogel film, and processing it into a microstructured two-dimensional code hydrogel film with photochromic function using maskless photolithography technology to form an information storage and first encryption layer; (3) selecting two polymers with hydrogen bond complexation and pH-responsive hydrogen bond density, and processing them into an opaque flexible hydrogel film using maskless photolithography to construct a second encryption layer; (4) the above three-layer structure forms a flexible double-encrypted hydrogel film; the prepared flexible double-encrypted hydrogel film has high security level, fast response, easy integration and good flexibility, and can be used for encryption in the fields of medicine, currency, precious goods, military, electronics, etc.

Description

Technical field:

[0001] The invention relates to a preparation method and application of a 3D-printed flexible double-layer hydrogel film with reversible response for double encryption, and belongs to the field of responsive functional films. Background technology:

[0002] Information encryption is closely related to human health, social stability, and national security, and is widely used in medicine, currency, valuable commodities, military affairs, electronics, and other fields. The development of advanced anti-counterfeiting technologies with high security levels is crucial. Physical encryption technology, due to its multiple encryption and decryption paths, holds great promise for application. However, most current encryption methods remain in the single-encryption stage, and their slow encryption and decryption speeds, lack of flexibility, and integrability limit their application.

[0003] Hydrogel materials are flexible, transparent, and stimuli-responsive, producing reversible physical changes in response to a variety of environmental signals, such as light, pH, solvents, force, temperature, and ions, making them ideal for information encryption. Typically, fluorescent materials such as organic dyes, semiconductor quantum dots, and carbon dots (CDs) are used for information storage, while transparent hydrogels serve as carriers for information encryption. When exposed to light of a specific wavelength, the stored material emits visible light, enabling decryption. However, this single-layer encryption technique suffers from low security and is easily cracked.

[0004] To address these issues, researchers have proposed building devices with dual encryption features to enhance the security of information encryption. By leveraging the time-scale effect of the material's stimulus-response process, researchers have developed a "time-locked" information encryption technology (Wang, Q., et al., Advanced Functional Materials. 2022, 32, 2208865). This means that the material exhibits different states at different times, and the information obtained at a specific time point is the correct information. Furthermore, by leveraging the material's shape memory function, an encryption device with a complex 3D structure has been developed (Zhu, CN, et al., Advanced Materials. 2021, 33, 2102023). This device requires two steps to unlock: 1) changing the temperature to restore the shape; 2) obtaining information through illumination. These technologies significantly improve the security of encryption, but their long encryption-decryption time, large encryption membrane volume, cumbersome operation, and difficulty integrating into different devices make them unsuitable for users eager to obtain information. Therefore, the development of functional membranes with fast encryption-decryption, easy integration, convenient operation and high encryption degree is of great significance for meeting the needs of multiple current fields (such as health monitoring, electronic information, currency, military, etc.).

[0005] The present invention utilizes the hydrogel membrane phase separation mechanism and prepares a double-layer flexible hydrogel membrane with an opaque upper layer and a transparent lower layer through 3D printing, which is embedded with a QR code for high-security encryption. Figure 4 As shown, a microstructured two-dimensional code with photochromic function (the first information encryption layer) is formed in the lower transparent hydrogel film by 3D printing; the upper layer is constructed by in-situ 3D printing to construct an opaque hydrogel film (the second information encryption layer). During the decryption process, the prepared encrypted hydrogel film first increases the pH (by coating with sodium hydroxide aqueous solution) to induce its reversible phase transformation, achieving an opaque-transparent transition and enabling light transmission; secondly, ultraviolet light is used to induce the two-dimensional code layer to emit light; relevant information can be obtained by scanning the QR code; when the ultraviolet light is removed and the pH is lowered (by coating with an acidic solution), the dual encryption function is restored, and the process can be completed in just a few minutes. Therefore, the proposed double-layer flexible hydrogel film encryption technology has the characteristics of high security (double encryption), simple and fast operation, small area and easy integration. It is expected to be used in a variety of encryption applications and has important scientific value and application prospects. Summary of the invention:

[0006] The purpose of the present invention is to use 3D printing technology to prepare a flexible hydrogel membrane with dual encryption function. A transparent flexible hydrogel membrane is used as a support layer, and a photochromic two-dimensional code is embedded using 3D printing technology for information storage and the first encryption layer. A pH-induced reversible phase separation flexible hydrogel membrane is used as the second encryption layer (opaque layer) to obtain a hydrogel membrane with dual encryption function for high-security information encryption. The dual-encryption flexible hydrogel membrane prepared by this method has highly secure information storage and is easy to integrate, and can be used in a variety of information encryption applications.

[0007] The preparation of the double-encrypted hydrogel film includes the following steps:

[0008] (1) dissolving the acrylic monomer in deionized water, adding a crosslinking agent and a photoinitiator, stirring thoroughly until fully dissolved, and setting aside;

[0009] (2) Mixing acrylic monomers with carbon dots (CDs) aqueous dispersion, adding crosslinking agent and photoinitiator, stirring thoroughly until fully dissolved, and setting aside;

[0010] (3) dissolving the acrylic monomer and hydrogen bond acceptor polymer in deionized water in a certain proportion, adding a crosslinker and a photoinitiator, stirring thoroughly until fully dissolved, and setting aside;

[0011] (4) taking the solution stirred evenly in step (1) to a maskless photolithography platform and polymerizing it under ultraviolet light to obtain a supporting layer PAA hydrogel film;

[0012] (5) taking the solution stirred evenly in step (2) and adding it dropwise to the surface of the hydrogel film in step (4), polymerizing it under ultraviolet light to obtain a PAA-CDs hydrogel film with a two-dimensional code structure; that is, using the solution in step (2) to prepare the corresponding two-dimensional code structure image information;

[0013] (6) The uniformly stirred solution obtained in step (3) is added dropwise to the surface of the hydrogel film in step (5), and polymerized under ultraviolet light to obtain an upper opaque PAA / hydrogen bond receptor polymer hydrogel film.

[0014] The three-layer hydrogel film obtained in steps (4) (5) (6) constitutes a double-encrypted flexible hydrogel film.

[0015] The mass percentage of the acrylic acid monomer in step (1) of the present invention is 40 to 100%;

[0016] In step (2), the content of the carbon dot aqueous dispersion can be 10% to 60% of the total mass fraction of the final mixed solution, and the concentration of the carbon dot (CDs) aqueous dispersion is 0.25 g / L; the acrylic monomer is 40% to 90% of the total mass fraction of the final mixed solution, and the mass content of the crosslinker and photoinitiator is not included in the total weight of the final mixed solution as long as they can crosslink, or can be ignored.

[0017] In step (3), the deionized water content is 60% of the total mass fraction of the solution, and the amount of the acrylic acid monomer and the hydrogen bond acceptor polymer is such that the molar ratio of the acrylic acid monomer to the hydrogen bond acceptor polymer is 0.25 to 2:1.

[0018] The ultraviolet light used for light focusing has a light power density of 10-100 mW cm -2 .

[0019] The acrylic monomer may be selected from acrylic acid, methacrylic acid, ethacrylic acid, and alginic acid; the hydrogen bond acceptor polymer may be selected from polyvinyl pyrrolidone, polyethylene oxide, polyvinyl pyridine, and polyvinyl oxazoline.

[0020] The double-encrypted flexible double-layer hydrogel film prepared by the present invention has good information storage and information encryption functions. The double-encrypted flexible double-layer hydrogel film is evaluated by treating it with an alkaline solution coupled with ultraviolet light to induce the photoresponse of carbon dots, and its feasibility is confirmed by scanning the QR code information with an electronic device.

[0021] Technical principle of the present invention

[0022] This invention uses 3D printing technology to fabricate a photochromic two-dimensional code microstructure into a transparent flexible hydrogel film as the lower layer. It then in-situ prints a flexible hydrogel film with reversible phase transitions as the upper layer, creating a flexible double-layer hydrogel film with dual encryption. The QR code in the lower layer serves as both information storage and primary encryption. The transparent flexible hydrogel film acts as a carrier for the QR code. When exposed to ultraviolet light, the QR code changes color, allowing information to be retrieved through scanning. In the upper layer, pH is used to regulate the ionization of weak acid molecules, thereby altering the hydrogen bonding between polymer segments and achieving a reversible transparent-opaque transition in the hydrogel film. At low pH, the weak acid protonates, forming hydrogen bonds and rendering the hydrogel film opaque, thus performing a secondary encryption on the lower layer. At high pH, ​​the weak acid deprotonates, breaking hydrogen bonds and rendering the hydrogel film transparent, allowing decryption. Due to rapid phase separation and photochromic changes, the dual encryption-decryption process can be completed within minutes. Furthermore, the proposed flexible double-layer hydrogel encryption film can be integrated into various devices using 3D printing technology. Description of the drawings:

[0023] Figure 1 This is the fluorescence photo of PAA / CDs hydrogel under UV light;

[0024] Figure 2 Photos of PAA / PVP hydrogels after treatment at different pH values;

[0025] Figure 3 This is a diagram of the double encryption process in Example 1;

[0026] Figure 4 Schematic diagram of preparing flexible double-encrypted hydrogel membrane for 3D printing Specific implementation method:

[0027] The present invention is described in detail below with reference to specific examples, but the present invention is not limited to the following examples.

[0028] Example 1

[0029] (1) Dissolve AA in deionized water, add crosslinker and photoinitiator, stir thoroughly until fully dissolved, and set aside;

[0030] (2) AA was dissolved in CDs aqueous dispersion (the concentration of CDs aqueous dispersion was 0.25 g / L, and the mass ratio of AA to CDs aqueous dispersion was 4:6), and a crosslinker and a photoinitiator were added. The mixture was stirred until fully dissolved and set aside.

[0031] (3) AA and PVP are dissolved in deionized water at a monomer molar ratio of 1:1, and a crosslinker and a photoinitiator are added, stirred thoroughly until fully dissolved, and set aside;

[0032] (4) taking the solution stirred evenly in step (1) to a maskless photolithography platform and polymerizing it under ultraviolet light to obtain a supporting layer PAA hydrogel film;

[0033] (5) adding the uniformly stirred solution from step (2) dropwise to the surface of the hydrogel film from step (4), polymerizing under ultraviolet light to obtain a PAA-CDs hydrogel film having a two-dimensional code structure;

[0034] (6) adding the uniformly stirred solution obtained in step (3) dropwise to the surface of the hydrogel film in step (5), polymerizing under ultraviolet light to obtain an upper opaque PAA / PVP hydrogel film;

[0035] The three-layer hydrogel film obtained in steps (4), (5), and (6) constitutes a double-encrypted flexible hydrogel film. It is used for information decryption and reading tests, and the operation is as follows:

[0036] Add alkaline pH = 14 NaOH solution to the top layer of the hydrogel and wait for 4 minutes; use filter paper to treat the residual NaOH solution and irradiate it with a 365nm UV lamp. You can obtain information by scanning the code with your mobile phone; if you need to restore the double encryption function again, remove the UV light and add acidic pH = 0 HCl solution to the top layer of the hydrogel and wait for 1 minute.

[0037] Example 2

[0038] (1) Dissolve AA in deionized water, add crosslinker and photoinitiator, stir thoroughly until fully dissolved, and set aside;

[0039] (2) AA was dissolved in CDs aqueous dispersion (the concentration of CDs aqueous dispersion was 0.25 g / L, and the mass ratio of AA to CDs aqueous dispersion was 4:6), and a crosslinker and a photoinitiator were added. The mixture was stirred until fully dissolved and set aside.

[0040] (3) AA and PVP are dissolved in deionized water at a monomer molar ratio of 0.75:1, and a crosslinker and a photoinitiator are added, stirred thoroughly until fully dissolved, and set aside;

[0041] (4) taking the solution stirred evenly in step (1) to a maskless photolithography platform and polymerizing it under ultraviolet light to obtain a supporting layer PAA hydrogel film;

[0042] (5) adding the uniformly stirred solution from step (2) dropwise to the surface of the hydrogel film from step (4), polymerizing under ultraviolet light to obtain a PAA-CDs hydrogel film having a two-dimensional code structure;

[0043] (6) adding the uniformly stirred solution obtained in step (3) dropwise to the surface of the hydrogel film in step (5), polymerizing under ultraviolet light to obtain an upper opaque PAA / PVP hydrogel film;

[0044] The three-layer hydrogel film obtained in steps (4), (5), and (6) constitutes a double-encrypted flexible hydrogel film. It is used for information decryption and reading tests, and the operation is as follows:

[0045] Add alkaline pH = 14 NaOH solution to the top layer of the hydrogel and wait for 7 minutes; use filter paper to treat the residual NaOH solution and irradiate it with 365nm UV light. You can obtain information by scanning the code with your mobile phone; if you need to restore the double encryption function again, remove the UV light and add acidic pH = 0 HCl solution to the top layer of the hydrogel and wait for 1.5 minutes.

[0046] Example 3

[0047] (1) Dissolve AA in deionized water, add crosslinker and photoinitiator, stir thoroughly until fully dissolved, and set aside;

[0048] (2) AA was dissolved in CDs aqueous dispersion (the concentration of CDs aqueous dispersion was 0.25 g / L, and the mass ratio of AA to CDs aqueous dispersion was 4:6), and a crosslinker and a photoinitiator were added. The mixture was stirred until fully dissolved and set aside.

[0049] (3) AA and PVP are dissolved in deionized water at a monomer molar ratio of 0.5:1, and a crosslinker and a photoinitiator are added, stirred thoroughly until fully dissolved, and set aside;

[0050] (4) taking the solution stirred evenly in step (1) to a maskless photolithography platform and polymerizing it under ultraviolet light to obtain a supporting layer PAA hydrogel film;

[0051] (5) adding the uniformly stirred solution from step (2) dropwise to the surface of the hydrogel film from step (4), polymerizing under ultraviolet light to obtain a PAA-CDs hydrogel film having a two-dimensional code structure;

[0052] (6) adding the uniformly stirred solution obtained in step (3) dropwise to the surface of the hydrogel film in step (5), polymerizing under ultraviolet light to obtain an upper opaque PAA / PVP hydrogel film;

[0053] The three-layer hydrogel film obtained in steps (4), (5), and (6) constitutes a double-encrypted flexible hydrogel film. It is used for information decryption and reading tests, and the operation is as follows:

[0054] Add alkaline pH = 14 NaOH solution to the top layer of the hydrogel and wait for 10 minutes; use filter paper to treat the residual NaOH solution and irradiate it with a 365nm ultraviolet lamp. You can obtain information by scanning the code with your mobile phone; if you need to restore the double encryption function again, remove the ultraviolet light and add acidic pH = 0 HCl solution to the top layer of the hydrogel and wait for 1.5 minutes.

[0055] Example 4

[0056] (1) Dissolve AA in deionized water, add crosslinker and photoinitiator, stir thoroughly until fully dissolved, and set aside;

[0057] (2) AA was dissolved in CDs aqueous dispersion (the concentration of CDs aqueous dispersion was 0.25 g / L, and the mass ratio of AA to CDs aqueous dispersion was 4:6), and a crosslinker and a photoinitiator were added. The mixture was stirred until fully dissolved and set aside.

[0058] (3) AA and PVP are dissolved in deionized water at a monomer molar ratio of 0.25:1, and a crosslinker and a photoinitiator are added, stirred thoroughly until fully dissolved, and set aside;

[0059] (4) taking the solution stirred evenly in step (1) to a maskless photolithography platform and polymerizing it under ultraviolet light to obtain a supporting layer PAA hydrogel film;

[0060] (5) adding the uniformly stirred solution from step (2) dropwise to the surface of the hydrogel film from step (4), polymerizing under ultraviolet light to obtain a PAA-CDs hydrogel film having a two-dimensional code structure;

[0061] (6) adding the uniformly stirred solution obtained in step (3) dropwise to the surface of the hydrogel film in step (5), polymerizing under ultraviolet light to obtain an upper opaque PAA / PVP hydrogel film;

[0062] The three-layer hydrogel film obtained in steps (4), (5), and (6) constitutes a double-encrypted flexible hydrogel film. It is used for information decryption and reading tests, and the operation is as follows:

[0063] Add alkaline pH = 14 NaOH solution to the top layer of the hydrogel and wait for 20 minutes; use filter paper to treat the residual NaOH solution and irradiate it with a 365nm UV lamp. You can obtain information by scanning the code with your mobile phone; if you need to restore the double encryption function again, remove the UV light and add acidic pH = 0 HCl solution to the top layer of the hydrogel and wait for 2 minutes.

[0064] Example 5

[0065] (1) Dissolve AA in deionized water, add crosslinker and photoinitiator, stir thoroughly until fully dissolved, and set aside;

[0066] (2) AA was dissolved in CDs aqueous dispersion (the concentration of CDs aqueous dispersion was 0.25 g / L, and the mass ratio of AA to CDs aqueous dispersion was 4:6), and a crosslinker and a photoinitiator were added. The mixture was stirred until fully dissolved and set aside.

[0067] (3) AA and PVP are dissolved in deionized water at a monomer molar ratio of 2:1, and a crosslinker and a photoinitiator are added, stirred thoroughly until fully dissolved, and set aside;

[0068] (4) taking the solution stirred evenly in step (1) to a maskless photolithography platform and polymerizing it under ultraviolet light to obtain a supporting layer PAA hydrogel film;

[0069] (5) adding the uniformly stirred solution from step (2) dropwise to the surface of the hydrogel film from step (4), polymerizing under ultraviolet light to obtain a PAA-CDs hydrogel film having a two-dimensional code structure;

[0070] (6) adding the uniformly stirred solution obtained in step (3) dropwise to the surface of the hydrogel film in step (5), polymerizing under ultraviolet light to obtain an upper opaque PAA / PVP hydrogel film;

[0071] The three-layer hydrogel film obtained in steps (4), (5), and (6) constitutes a double-encrypted flexible hydrogel film. It is used for information decryption and reading tests, and the operation is as follows:

[0072] Add alkaline pH = 14 NaOH solution to the top layer of the hydrogel and wait for 2 minutes; use filter paper to treat the residual NaOH solution and irradiate it with a 365nm UV lamp. You can obtain information by scanning the code with your mobile phone; if you need to restore the double encryption function again, remove the UV light and add acidic pH = 0 HCl solution to the top layer of the hydrogel and wait for 1 minute.

[0073] Example 6

[0074] (1) Methacrylic acid (MAA) is dissolved in deionized water, and a crosslinker and a photoinitiator are added. The mixture is stirred until fully dissolved and set aside.

[0075] (2) MAA was dissolved in CDs aqueous dispersion (the concentration of CDs aqueous dispersion was 0.25 g / L, and the mass ratio of MAA to CDs aqueous dispersion was 4:6), and a crosslinker and a photoinitiator were added. The mixture was stirred thoroughly until fully dissolved and set aside.

[0076] (3) MAA and PVP are dissolved in deionized water at a monomer molar ratio of 1:1, and a crosslinker and a photoinitiator are added, stirred thoroughly until fully dissolved, and set aside;

[0077] (4) taking the solution stirred evenly in step (1) to a maskless photolithography platform and polymerizing it under ultraviolet light to obtain a supporting layer PAA hydrogel film;

[0078] (5) adding the uniformly stirred solution from step (2) dropwise to the surface of the hydrogel film from step (4), polymerizing under ultraviolet light to obtain a PAA-CDs hydrogel film having a two-dimensional code structure;

[0079] (6) adding the uniformly stirred solution obtained in step (3) dropwise to the surface of the hydrogel film in step (5), polymerizing under ultraviolet light to obtain an upper opaque PAA / PVP hydrogel film;

[0080] The three-layer hydrogel film obtained in steps (4), (5), and (6) constitutes a double-encrypted flexible hydrogel film. It is used for information decryption and reading tests, and the operation is as follows:

[0081] Add alkaline pH = 14 NaOH solution to the top layer of the hydrogel and wait for 8 minutes; use filter paper to treat the residual NaOH solution and irradiate it with 365nm UV light. You can obtain information by scanning the code with your mobile phone; if you need to restore the double encryption function again, remove the UV light and add acidic pH = 0 HCl solution to the top layer of the hydrogel and wait for 1.5 minutes.

[0082] Example 7

[0083] (1) Dissolve AA in deionized water, add crosslinker and photoinitiator, stir thoroughly until fully dissolved, and set aside;

[0084] (2) AA was dissolved in CDs aqueous dispersion (the concentration of CDs aqueous dispersion was 0.25 g / L, and the mass ratio of AA to CDs aqueous dispersion was 4:6), and a crosslinker and a photoinitiator were added. The mixture was stirred until fully dissolved and set aside.

[0085] (3) AA and polyethylene oxide (PEO) were dissolved in deionized water at a monomer molar ratio of 1:1, and a crosslinker and a photoinitiator were added. The mixture was stirred until fully dissolved and set aside.

[0086] (4) taking the solution stirred evenly in step (1) to a maskless photolithography platform and polymerizing it under ultraviolet light to obtain a supporting layer PAA hydrogel film;

[0087] (5) adding the uniformly stirred solution from step (2) dropwise to the surface of the hydrogel film from step (4), polymerizing under ultraviolet light to obtain a PAA-CDs hydrogel film having a two-dimensional code structure;

[0088] (6) adding the uniformly stirred solution obtained in step (3) dropwise to the surface of the hydrogel film in step (5), polymerizing under ultraviolet light to obtain an upper opaque PAA / PVP hydrogel film;

[0089] The three-layer hydrogel film obtained in steps (4), (5), and (6) constitutes a double-encrypted flexible hydrogel film. It is used for information decryption and reading tests, and the operation is as follows:

[0090] Add alkaline pH = 14 NaOH solution to the top layer of the hydrogel and wait for 8 minutes; use filter paper to treat the residual NaOH solution and irradiate it with 365nm UV light. You can obtain information by scanning the code with your mobile phone; if you need to restore the double encryption function again, remove the UV light and add acidic pH = 0 HCl solution to the top layer of the hydrogel and wait for 1.5 minutes.

[0091] Example 8

[0092] (1) Dissolve AA in deionized water, add crosslinker and photoinitiator, stir thoroughly until fully dissolved, and set aside;

[0093] (2) AA was dissolved in CdSe / ZnS quantum dot aqueous dispersion (the concentration of CdSe / ZnS aqueous dispersion was 0.25

[0094] g / L, the mass ratio of AA to CdSe / ZnS aqueous dispersion is 4:6), and a crosslinker and a photoinitiator are added, stirred thoroughly until fully dissolved, and set aside;

[0095] (3) AA and PVP are dissolved in deionized water at a monomer molar ratio of 1:1, and a crosslinker and a photoinitiator are added, stirred thoroughly until fully dissolved, and set aside;

[0096] (4) taking the solution stirred evenly in step (1) to a maskless photolithography platform and polymerizing it under ultraviolet light to obtain a supporting layer PAA hydrogel film;

[0097] (5) adding the uniformly stirred solution from step (2) dropwise to the surface of the hydrogel film from step (4), polymerizing under ultraviolet light to obtain a quantum dot-doped PAA hydrogel film having a two-dimensional code structure;

[0098] (6) adding the uniformly stirred solution obtained in step (3) dropwise to the surface of the hydrogel film in step (5), polymerizing under ultraviolet light to obtain an upper opaque PAA / PVP hydrogel film;

[0099] The three-layer hydrogel film obtained in steps (4), (5), and (6) constitutes a double-encrypted flexible hydrogel film. It is used for information decryption and reading tests, and the operation is as follows:

[0100] Add alkaline pH = 14 NaOH solution to the top layer of the hydrogel and wait for 4 minutes; use filter paper to treat the residual NaOH solution and irradiate it with a 365nm UV lamp. You can obtain information by scanning the code with your mobile phone; if you need to restore the double encryption function again, remove the UV light and add acidic pH = 0 HCl solution to the top layer of the hydrogel and wait for 1 minute.

Claims

1. A method for preparing a flexible double-encrypted hydrogel film by 3D printing, characterized in that: The following steps are involved: (1) Dissolve the acrylic monomer in deionized water, add the crosslinker and photoinitiator, stir thoroughly until fully dissolved, and set aside; (2) Mix the acrylic monomer with the carbon dots (CDs) aqueous dispersion, add the crosslinker and photoinitiator, stir thoroughly until fully dissolved, and set aside; (3) Dissolve the acrylic monomer and hydrogen bond acceptor polymer in deionized water in a certain proportion, add a crosslinker and a photoinitiator, stir thoroughly until fully dissolved, and set aside; (4) taking the solution stirred evenly in step (1) to a maskless photolithography platform and polymerizing it under ultraviolet light to obtain a supporting layer PAA hydrogel film; (5) The uniformly stirred solution of step (2) is added dropwise to the surface of the hydrogel film of step (4), and polymerized under ultraviolet light to obtain a PAA-CDs hydrogel film having a two-dimensional code structure; that is, the solution of step (2) is used to prepare the corresponding two-dimensional code structure image information; (6) The uniformly stirred solution obtained in step (3) is added dropwise to the surface of the hydrogel film in step (5), and polymerized under ultraviolet light to obtain an upper opaque PAA / hydrogen bond receptor polymer hydrogel film; In step (3), the deionized water content is 60% of the total mass fraction of the solution, and the amount of the acrylic acid monomer and the hydrogen bond acceptor polymer is such that the molar ratio of the acrylic acid monomer to the hydrogen bond acceptor polymer is 0.25 to 2:1; The acrylic monomer is selected from acrylic acid, methacrylic acid, and ethacrylic acid; the hydrogen bond acceptor polymer is selected from polyvinyl pyrrolidone, polyethylene oxide, polyvinyl pyridine, and polyvinyl oxazoline.

2. The method according to claim 1, characterized in that The mass percentage of the acrylic acid monomer in step (1) is 40-100%.

3. The method according to claim 1, characterized in that The content of the carbon dot aqueous dispersion in step (2) can be 10% to 60% of the total mass fraction of the final mixed solution, and the concentration of the carbon dot (CDs) aqueous dispersion is 0.25 g / L; the acrylic monomer is 40% to 90% of the total mass fraction of the final mixed solution, and the mass content of the crosslinker and photoinitiator is not included in the total weight of the final mixed solution as long as they can crosslink, or can be ignored.

4. The method according to claim 1, characterized in that The ultraviolet light used for light focusing has a light power density of 10-100 mW cm -2 .

5. A flexible double-encrypted hydrogel film prepared according to the method according to any one of claims 1 to 4.

6. Use of the flexible double-encrypted hydrogel film prepared by the method according to any one of claims 1 to 4 in encryption devices.

7. The use according to claim 6, characterized in that During the decryption process, the pH is first increased to induce its reversible phase transformation, achieving an opaque-transparent transition and enabling light transmission; secondly, ultraviolet light is used to induce the QR code layer to luminesce; relevant information can be obtained by scanning the QR code; when the ultraviolet light is removed and the pH is lowered, the double encryption function is restored, and the process can be completed in just a few minutes.

8. The use according to claim 7, characterized in that The pH is increased by coating with a sodium hydroxide aqueous solution; the pH is decreased by coating with an acidic solution.

Images