Double-gradient hydrogel ion diode, preparation method and flexible pressure sensor

Abstract

The invention discloses a double-gradient hydrogel ion diode, a preparation method and application, and belongs to the field of polymer functional materials.The preparation method comprises the steps that 1, a cationic monomer, an anionic monomer, an acrylamide monomer, a photoinitiator and a cross-linking agent are dissolved in deionized water to prepare a uniform pre-polymerization solution; (2) injecting the pre-polymerization liquid into a mold, and inducing a cationic monomer and an anionic monomer to form gradient distribution in the pre-polymerization liquid under a direct-current electric field; and (3) carrying out polymerization reaction under an ultraviolet lamp to prepare the double-gradient hydrogel ion diode. According to the preparation method provided by the invention, the double-gradient hydrogel ion diode can be obtained, mechanical energy can be converted into a voltage signal to be output, the double-gradient hydrogel ion diode has the advantages of high sensitivity, high response speed and low detection lower limit, and a 5 * 5 array sensor can be further prepared to be used for simultaneously detecting stress at different positions and different magnitudes. And reference is provided for the development of the self-powered high-precision flexible pressure sensor.

Description

Technical Field

[0001] The invention belongs to the field of polymer functional materials, and in particular relates to a dual-gradient hydrogel ion diode, a preparation method and a flexible pressure sensor. Background Art

[0002] The booming development of smart wearable electronic products is rapidly changing our lifestyle in modern society. The application of next-generation wearable electronic devices urgently requires flexible sensors with precise sensing capabilities, self-powering and high safety. The use of self-powered sensors that can directly harvest ambient energy can avoid the use of bulky power equipment, thereby greatly expanding the scope of practical applications.

[0003] Hydrogel ion diodes are generally composed of two layers of hydrogels with opposite charges, which can convert external stimuli into signals such as resistance, capacitance, open circuit voltage and short circuit current. They also have good stretchability and biocompatibility, providing new ideas for expanding the preparation methods of wearable flexible sensors.

[0004] The Chinese patent application with publication number CN114720537A discloses a hydrogel ion diode including a cationic polyelectrolyte hydrogel and a cationic polyelectrolyte hydrogel heterojunction. The polyelectrolyte hydrogel ion diode includes a microfluidic chip and a hydrogel heterojunction. The microfluidic chip is provided with a microchannel, the microchannel includes a working microchannel and a reference microchannel, the working microchannel and the reference microchannel are connected through a bridge channel, and the working microchannel and the reference microchannel are respectively provided with electrode holes for installing a working electrode and a reference electrode; the hydrogel heterojunction includes a P-type hydrogel and an N-type hydrogel, both of which are arranged in the bridge channel, the P-type hydrogel is a cationic polyelectrolyte hydrogel, and the N-type hydrogel is an anionic polyelectrolyte hydrogel, and nucleic acids can be detected using electrical signals.

[0005] The Chinese patent document with publication number CN117279397A discloses an ionic diode device in which a MXene polyanion gel and a MXene polycation gel are assembled into a gel heterojunction. Since the MXene uniformly embedded in the gel can assist the ions in the polyelectrolyte gel to transport ions, the device has the rectification characteristics of the gel heterojunction while the forward current is also greatly improved, that is, it exhibits a high driving capability characteristic.

[0006] However, the sensitivity of the hydrogel ion diode in the above double-layer hydrogel structure is limited by the large interface resistance between the layers, resulting in low sensitivity of the diode sensor. Therefore, how to develop a hydrogel ion diode sensor with good stability and high sensitivity is a technical problem that needs to be solved urgently. Summary of the invention

[0007] In order to solve the problems of large interface resistance and low sensitivity between layers of double-layer hydrogel ion diode sensors in the prior art, the present invention provides a method for preparing a double-gradient hydrogel ion diode. The prepared double-gradient hydrogel ion diode can convert mechanical energy into voltage signal output, and has the advantages of high sensitivity, fast response speed and low detection limit. The 5×5 array sensor made of the double-gradient hydrogel ion diode can simultaneously detect stresses of different positions and sizes. It shows great application prospects in solving the challenges of high interface resistance and low sensitivity of hydrogel ion diodes, and broadens the application scope of the next generation of high-precision self-powered sensors.

[0008] The present invention provides a method for preparing a dual-gradient hydrogel ion diode, comprising the following steps:

[0009] (1) dissolving a cationic monomer, an anionic monomer, an acrylamide monomer, a photoinitiator and a crosslinking agent in deionized water to prepare a uniform prepolymer solution;

[0010] (2) injecting the prepolymer solution into a mold, and inducing the cationic monomer and the anionic monomer to form a gradient distribution in the prepolymer solution under a direct current electric field;

[0011] (3) A polymerization reaction is carried out under ultraviolet light to prepare a dual-gradient hydrogel ion diode.

[0012] Under a direct current electric field, cationic monomers and anionic monomers move in opposite directions due to their charge differences, causing the concentrations of cationic monomers and anionic monomers in the prepolymer solution to show a gradient change in space. Acrylamide monomers form a hydrogel matrix, and ultraviolet light activates the photoinitiator to initiate the polymerization reaction of the monomers. During the polymerization process, the gradient distribution is fixed in the hydrogel to form a stable dual-gradient structure. The dual-gradient structure makes the hydrogel directional in ion transport, similar to the unidirectional conductivity of a diode.

[0013] Preferably, the cationic monomer is one of methacryloyloxyethyl trimethyl ammonium chloride, acryloyloxyethyl trimethyl ammonium chloride, and (3-acrylamidopropyl) trimethyl ammonium chloride.

[0014] The above cationic monomers all contain quaternary ammonium salt groups, have permanent positive charges, can be completely ionized in water, and provide stable cationic properties. This strong cationic property enables it to migrate efficiently under a direct current electric field to form a significant concentration gradient, and the quaternary ammonium salt group has high chemical stability and is not easily affected by pH or environmental conditions. It can maintain stable cationic properties in a wide range of environments and improve the stability of the structure. The above cationic monomers all contain hydrophilic groups, which make them have excellent solubility in water and help to form a uniform hydrogel network during the polymerization process. The above cationic monomers all contain carbon-carbon double bonds, have high free radical polymerization reaction activity, and can be rapidly polymerized under ultraviolet light initiation.

[0015] Preferably, the anionic monomer is one of 3-sulfopropyl methacrylate potassium salt, sodium acrylate, and 2-acrylamido-2-methylpropanesulfonic acid sodium salt.

[0016] The above-mentioned anionic monomers all contain sulfonic acid groups (-SO3-) or carboxylic acid groups (-COO-), which can be completely ionized in water to provide a stable negative charge. The strong anionic properties enable them to migrate efficiently under a DC electric field and form a clear concentration gradient distribution with the cationic monomers. In addition, the sulfonic acid groups and carboxylic acid groups have high chemical stability and are not easily affected by pH or environmental conditions, and can maintain stable anionic properties in a wide range of environments.

[0017] Preferably, the photoinitiator is one of α-ketoglutaric acid, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, and 2-hydroxy-2-methylpropiophenone.

[0018] The above-mentioned photoinitiator can efficiently generate free radicals under ultraviolet light irradiation to initiate the polymerization reaction of the monomer, has good water solubility and biocompatibility, and is suitable for a hydrogel system.

[0019] Preferably, the cross-linking agent is one of N,N'-methylenebisacrylamide and trimethylolpropane.

[0020] The above cross-linking agents all contain multiple polymerizable double bonds, which can form a uniform three-dimensional cross-linking network with the monomers during the polymerization reaction, thereby enhancing the mechanical strength and stability of the hydrogel.

[0021] Preferably, based on the weight percentage of water, the cationic monomer is 10wt% to 40wt%, the anionic monomer is 10wt% to 40wt%, the acrylamide monomer is 20wt% to 30wt%, the crosslinking agent is 0.1wt% to 5wt%, and the initiator is 0.1wt% to 1wt%.

[0022] Preferably, in step (2), the mold is composed of ITO conductive glass and a silicone gasket.

[0023] The mold composed of ITO conductive glass and silicone gasket can obtain uniform electric field distribution, realize gradient distribution of monomers, and undergo efficient polymerization reaction under ultraviolet light. It can not only meet the preparation needs of hydrogel ion diodes, but the reusability of the mold also makes it cost-effective and has broad application prospects.

[0024] Further preferably, the mold specification is 40mm×40mm×2mm.

[0025] Preferably, in step (2), the DC electric field voltage is no higher than 1.23 V, and the power-on time is 10-50 min.

[0026] When the voltage is higher than 1.23V, water electrolysis reaction will occur, affecting the gradient distribution. Therefore, under the above-mentioned DC electric field voltage, the directional migration of charged monomers is driven by the electrophoresis effect to form a stable concentration gradient; the appropriate power-on time is selected to match the migration rate of the charged monomers to promote the formation of the concentration gradient; within the above-mentioned appropriate range, the steepness of the gradient distribution is controlled by adjusting the voltage or the power-on time.

[0027] Preferably, in step (3), the illumination intensity of the ultraviolet lamp is not less than 20W, and the light focusing time is not less than 1h.

[0028] The invention also provides a dual-gradient hydrogel ion diode prepared by the preparation method.

[0029] The dual-gradient hydrogel ion diode has gradient-distributed polycationic molecular chains and polyanionic molecular chains, and has high sensitivity, fast response speed and low detection limit.

[0030] Preferably, the dual-gradient hydrogel ion diode has a sensitivity of not less than 1000 mV / MPa, a response speed of not more than 0.2 s, and a detection limit of not more than 1 Pa.

[0031] The present invention also provides a flexible pressure sensor, which uses the dual-gradient hydrogel ion diode.

[0032] Preferably, the flexible pressure sensor comprises a first electrode layer, a second electrode layer and a dual gradient hydrogel ion diode, wherein the first electrode layer and the second electrode layer are gold, silver, copper or platinum.

[0033] Further preferably, the first electrode layer and the second electrode layer are platinum.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) Compared with existing hydrogel ion diode sensor materials, the dual-gradient hydrogel ion diode provided by the present invention has ultra-high sensitivity, extremely fast response speed and ultra-low detection limit, which provides a simple and effective strategy for improving the sensing performance of hydrogel ion diode sensors.

[0036] (2) The dual-gradient hydrogel ion diode of the present invention can be used as a flexible pressure sensor to convert mechanical energy into a voltage signal output, and has good stability and cycle performance, and can stably output a voltage signal under 2000 stress cycle stimulations.

[0037] (3) The flexible pressure sensor prepared by the dual-gradient hydrogel ion diode of the present invention can realize 5×5 array sensing and detect stresses of different positions and sizes, which greatly broadens the application scope of the hydrogel ion diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a physical picture of the dual gradient hydrogel ion diode in Example 1.

[0039] Figure 2 These are the test results of the dual-gradient hydrogel ion diode compression experiment in each embodiment.

[0040] Figure 3 This is a scanning electron microscope cross-sectional image of the dual gradient hydrogel ion diode in Example 1.

[0041] Figure 4 Schematic diagram of the structure of the self-supplied flexible pressure sensor of the embodiment and the comparative example.

[0042] Figure 5 The sensitivity test results of different hydrogel ion diode sensors in the embodiments and comparative examples are shown.

[0043] Figure 6 This is the response time test result of the dual gradient hydrogel ion diode sensor in Example 1.

[0044] Figure 7 This is the detection limit test result of the dual gradient hydrogel ion diode sensor in Example 1.

[0045] Figure 8 These are the test results of the cyclic performance of the dual gradient hydrogel ion diode sensor in Example 1.

[0046] Fig. 9 These are the test results of the dual gradient hydrogel ion diode 5×5 sensor array in Example 1. DETAILED DESCRIPTION

[0047] The present invention will be further described below in conjunction with the embodiments and drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0048] Example 1

[0049] (1) adding 10 wt % of methacryloyloxyethyl trimethylammonium chloride, 12 wt % of 3-sulfopropyl methacrylate potassium salt, 28 wt % of acrylamide, 0.5 wt % of photoinitiator α-ketoglutaric acid, and 0.5 wt % of crosslinking agent N,N'-methylenebisacrylamide into deionized water, and uniformly dispersing by ultrasonication to obtain a uniform prepolymer solution;

[0050] (2) The prepolymer solution was injected into the mold, induced under a 1V DC electric field for 40 minutes, and then placed under a 20W UV lamp for photopolymerization for 1 hour, and the unreacted monomers on the surface were removed to obtain a dual gradient hydrogel ion diode. Figure 1 As shown, the transparency of the actual picture is good.

[0051] The mechanical properties of the dual gradient hydrogel ion diode were tested. Figure 2 As shown, its compressive strength is 3.3MPa, the maximum compression rate is 93%, and the compression modulus is 246kPa.

[0052] The dual gradient pore size distribution of the dual gradient hydrogel ion diode cross section of this embodiment was observed by scanning electron microscopy ( Figure 3 ).Depend on Figure 3 It can be seen that the upper and lower sides have more positive or negative charges, and due to the effect of charge repulsion, they present a larger pore size distribution compared to the middle area with less charge.

[0053] like Figure 4 As shown, platinum foil is added as electrodes on the upper and lower sides of the dual gradient hydrogel ion diode, and compacted to ensure that the electrodes are completely attached to the hydrogel surface. At the same time, it also acts as a wire to conduct electrical signals to obtain a flexible pressure sensor. Its sensitivity is tested, and the results are shown in Figure 5 As shown, the sensitivity of the flexible pressure sensor in the range of 1 kPa-20 kPa is 1247.3 mV / MPa, and the sensitivity in the range of 20 kPa-100 kPa is 179.9 mV / MPa.

[0054] The response time and detection limit of the flexible pressure sensor prepared by the dual-gradient hydrogel ion diode were tested. Figure 6 As shown in FIG. 1 , the response time of the flexible pressure sensor is 0.14 s; Figure 7 As shown, the detection lower limit of the flexible pressure sensor is 0.8Pa.

[0055] like Figure 8As shown, the flexible pressure sensor prepared by the dual-gradient hydrogel ion diode was cyclically tested 2000 times at a frequency of 10 kPa and 0.02 Hz, and the change in output voltage could be maintained at about 32 mV, reflecting the repeatability and stability of the flexible pressure sensor in converting mechanical energy.

[0056] like Fig. 9 As shown, the dual-gradient hydrogel ion diode of this embodiment is used in a 5×5 sensor array. The results show that the flexible pressure sensor prepared by the dual-gradient hydrogel ion diode can realize accurate detection of pressures of different positions and sizes.

[0057] Example 2

[0058] The preparation method of this embodiment is the same as that of embodiment 1, except that 0.25 wt % of the cross-linking agent N,N'-methylenebisacrylamide is used to prepare a uniform prepolymer solution.

[0059] like Figure 2 As shown, the compressive strength of the dual gradient hydrogel ion diode prepared in this embodiment is 5.2 MPa, the maximum compression rate is 98%, and the compression modulus is 178 kPa.

[0060] Example 3

[0061] The preparation method of this embodiment is the same as that of embodiment 1, except that 1 wt % of the cross-linking agent N,N'-methylenebisacrylamide is used to prepare a uniform prepolymer solution.

[0062] like Figure 2 As shown, the compressive strength of the dual gradient hydrogel ion diode prepared in this embodiment is 2.4 MPa, the maximum compression rate is 90%, and the compression modulus is 279 kPa.

[0063] Example 4

[0064] The preparation method of this embodiment is the same as that of embodiment 1, except that 2 wt % of the cross-linking agent N,N'-methylenebisacrylamide is used to prepare a uniform prepolymer solution.

[0065] like Figure 2 As shown, the compressive strength of the dual gradient hydrogel ion diode prepared in this embodiment is 0.9 MPa, the maximum compression rate is 69%, and the compression modulus is 523 kPa.

[0066] Example 5

[0067] The preparation method of this embodiment is the same as that of embodiment 1, except that 4 wt % of the cross-linking agent N,N'-methylenebisacrylamide is used to prepare a uniform prepolymer solution.

[0068] like Figure 2As shown, the compressive strength of the dual gradient hydrogel ion diode prepared in this embodiment is 0.8 MPa, the maximum compression rate is 56%, and the compression modulus is 722 kPa.

[0069] Example 6

[0070] (1) adding 20 wt% of methacryloyloxyethyl trimethylammonium chloride, 24 wt% of 3-sulfopropyl methacrylate potassium salt, 28 wt% of acrylamide, 0.5 wt% of photoinitiator α-ketoglutaric acid, and 0.5 wt% of crosslinking agent N,N'-methylenebisacrylamide into deionized water, and uniformly dispersing by ultrasonication to obtain a uniform prepolymer solution;

[0071] (2) The prepolymer solution was injected into a mold, induced under a 1V DC electric field for 40 minutes, and then placed under a 20W UV lamp for photopolymerization for 1 hour to remove the unreacted monomers on the surface to obtain a dual-gradient hydrogel ion diode.

[0072] The sensitivity of the flexible pressure sensor was tested and the sensitivity was 1105mV / MPa in the range of 1kPa-20kPa and 158.3mV / MPa in the range of 20kPa-100kPa, which met the requirements for flexible sensors to detect stress.

[0073] Comparative Example 1

[0074] The preparation method of this comparative example is the same as that of Example 1, except that no direct current electric field is used to induce the prepolymer solution.

[0075] like Figure 5 As shown, the sensitivity of the hydrogel ion diode sensor prepared in this comparative example is 96.1mV / MPa in the range of 1kPa-20kPa, and the sensitivity in the range of 20kPa-100kPa is 5.3mV / MPa. The results show that the hydrogel ion diode sensor that does not use DC electric field to induce the formation of a dual gradient structure has low sensitivity and is not suitable as a flexible sensor for stress detection.

[0076] Comparative Example 2

[0077] (1) adding 20 wt % of methacryloyloxyethyl trimethyl ammonium chloride, 28 wt % of acrylamide, 0.5 wt % of a photoinitiator α-ketoglutaric acid, and 0.5 wt % of a crosslinking agent N,N'-methylenebisacrylamide into deionized water, and uniformly dispersing by ultrasonication to obtain a cationic monomer prepolymer solution;

[0078] (2) adding 24 wt % of 3-sulfopropyl methacrylate potassium salt, 28 wt % of acrylamide, 0.5 wt % of photoinitiator α-ketoglutaric acid, and 0.5 wt % of crosslinking agent N,N'-methylenebisacrylamide into deionized water, and uniformly dispersing by ultrasonication to obtain an anionic monomer prepolymer solution;

[0079] (3) The cationic monomer prepolymer solution and the anionic monomer prepolymer solution are injected into the mold respectively, placed under a 20W ultraviolet lamp for photopolymerization for 1 hour, and then the unreacted monomers on the surface are removed to obtain polycationic hydrogel and polyanionic hydrogel respectively. The two hydrogels are combined together by electrostatic interaction to obtain a double-layer hydrogel ion diode.

[0080] like Figure 5 As shown, the sensitivity of the double-layer hydrogel ion diode sensor in this comparative example is 403.1 mV / MPa in the range of 1 kPa-20 kPa, and the sensitivity in the range of 20 kPa-100 kPa is 47.7 mV / MPa. The results show that the sensitivity of the double-layer hydrogel ion diode sensor is lower than that of the double-gradient hydrogel ion diode.

[0081] It can be seen from the above embodiments, comparative examples and corresponding test results that the hydrogel ion diode with a dual gradient structure provided by the present invention has high sensitivity, and also has the advantages of fast response, low detection limit and good cycle performance, and is very suitable for preparing flexible pressure sensors; and the prepared flexible pressure sensor does not require an external power supply to work, and can also be used as an arrayed sensor to detect stresses of different positions and sizes, which greatly broadens the scope of use of current flexible sensors.

[0082] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a dual-gradient hydrogel ion diode, characterized in that: The following steps are involved: (1) dissolving a cationic monomer, an anionic monomer, an acrylamide monomer, a photoinitiator and a crosslinking agent in deionized water to prepare a uniform prepolymer solution; (2) injecting the prepolymer solution into a mold, and inducing the cationic monomer and the anionic monomer to form a gradient distribution in the prepolymer solution under a direct current electric field; (3) A polymerization reaction is carried out under ultraviolet light to prepare a dual-gradient hydrogel ion diode.

2. The preparation method according to claim 1, characterized in that: The cationic monomer is one of methacryloyloxyethyl trimethyl ammonium chloride, acryloyloxyethyl trimethyl ammonium chloride, and (3-acrylamide propyl) trimethyl ammonium chloride; The anionic monomer is one of 3-sulfonate propyl methacrylate potassium salt, sodium acrylate, and 2-acrylamide-2-methylpropanesulfonic acid sodium salt.

3. The preparation method according to claim 1, characterized in that: The photoinitiator is one of α-ketoglutaric acid, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, and 2-hydroxy-2-methylpropiophenone; The cross-linking agent is one of N, N'-methylenebisacrylamide and trimethylolpropane.

4. The preparation method according to claim 1, characterized in that: Calculated by weight percentage of water, the cationic monomer is 10wt% to 40wt%, the anionic monomer is 10wt% to 40wt%, the acrylamide monomer is 20wt% to 30wt%, the crosslinking agent is 0.1wt% to 5wt%, and the initiator is 0.1wt% to 1wt%.

5. The preparation method according to claim 1, characterized in that: In step (2), the DC electric field voltage is no higher than 1.23V, and the power-on time is 10-50 minutes.

6. The method for preparing a hydrogel ion diode with a dual gradient structure according to claim 1, characterized in that: In step (3), the ultraviolet light intensity is not less than 20W, and the light focusing time is not less than 1h.

7. A dual gradient hydrogel ion diode prepared according to the preparation method according to any one of claims 1 to 6.

8. The dual gradient hydrogel ion diode according to claim 7, characterized in that: The sensitivity of the hydrogel ion diode with a dual gradient structure is not less than 1000mV / MPa, the response speed is not higher than 0.2s, and the detection lower limit is not higher than 1Pa.

9. A flexible pressure sensor, comprising the dual gradient hydrogel ion diode according to claim 7 or claim 8.

10. The flexible pressure sensor according to claim 9, characterized in that: The invention comprises a first electrode layer, a second electrode layer and a dual-gradient hydrogel ion diode, wherein the first electrode layer and the second electrode layer are made of gold, silver, copper or platinum.

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