Controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel and preparation method thereof, flexible sensor

Abstract

The application belongs to the technical field of composite materials, and particularly relates to a controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel and a preparation method and a flexible sensor thereof, and comprises the following steps: S11, adding a block-shaped EGaIn into anhydrous ethanol, obtaining EGaIn particles after ultrasonic treatment, and placing the particles in a vacuum drying box after standing, sealing and reserving after complete evaporation of the ethanol; S12, dispersing acrylamide and N,N'-methylene bisacrylamide in deionized water, adding EGaIn particles as an initiator after stirring until all the solids are dissolved, and obtaining an EGaIn-PAM hydrogel pre-polymer solution; S13, ultrasonic treating the EGaIn-PAM hydrogel pre-polymer solution under an ice water bath condition, converting the polymer into a gel, and forming an EGaIn-PAM composite hydrogel; S14, freeze-drying the EGaIn-PAM composite hydrogel, then immersing the hydrogel in an AgNO3 solution and placing the hydrogel under a xenon lamp for light irradiation, and finally obtaining an Ag / EGaIn-PAM hydrogel; wherein the concentration of the AgNO3 solution in the step S14 ranges from 0.02M to 0.4M.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel and its preparation method, as well as a flexible sensor. Background Technology

[0002] Hydrogels have poor mechanical properties, low electrical conductivity, and low dielectric constant, which prevents hydrogel-based pressure sensors from accurately monitoring and identifying human physiological parameters and movement behaviors. Currently, fabricating flexible pressure sensors with high sensitivity and good mechanical properties remains a challenge.

[0003] The sensing performance of hydrogel-based pressure sensors can be effectively improved by increasing the dielectric constant of the hydrogel and increasing the contact area between the sensing material and the electrode. Increasing the dielectric constant increases the initial capacitance and relative capacitance change of the sensing layer, effectively improving the signal-to-noise ratio of capacitive sensors. Adding a certain amount of metal material to the hydrogel can effectively improve its conductivity and dielectric constant, as well as its mechanical properties. The three-dimensional network structure of the hydrogel allows metal nanomaterials to be dispersed within it, effectively solving the problem of easy aggregation of metal nanomaterials in water. Currently, metal materials used to improve the sensing performance of hydrogel pressure sensors include Au, Ag, and Cr. Among them, Ag nanomaterials not only possess excellent conductivity, a large dielectric constant, and good mechanical properties, but are also plasma-enhancing metal materials that can undergo plasma resonance (SPR) on their surface under light stimulation, generating a large number of hot electrons. Combining Ag nanomaterials with hydrogels can effectively increase the dielectric constant of the hydrogel material through "penetration." Furthermore, the adhesion of Ag nanomaterials to the hydrogel can increase the contact area between the hydrogel and the electrode, improving the pressure response of the sensor. Due to their high surface energy and large specific surface area, silver nanomaterials are easily attracted to each other and aggregate in water. Using photochemical reduction, Ag+ can be rapidly reduced to Ag. 0 This improves the dispersibility of silver nanomaterials in water and reduces agglomeration.

[0004] To date, achieving controllable structural growth of Ag nanomaterials on EGaIn-PAM hydrogels remains challenging, as Ag nanomaterials prepared by photochemical reduction in existing technologies are typically granular.

[0005] It should be noted that the information disclosed in this background section is only for understanding the background technology of the present application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention

[0006] This disclosure provides at least one controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel, its preparation method, and a flexible sensor.

[0007] In a first aspect, embodiments of this disclosure provide a method for preparing a controllable silver nanomaterial-modified liquid metal-polyacrylamide composite hydrogel, comprising the following steps: S11, adding blocky EGaIn to anhydrous ethanol, ultrasonically treating it to obtain EGaIn particles, allowing it to stand, and then drying it in a vacuum drying oven until the ethanol has completely evaporated, then sealing it for later use; S12, dispersing and dissolving acrylamide and N,N′-methylenebisacrylamide in deionized water, stirring until the solid is completely dissolved, then adding EGaIn particles as an initiator to obtain... S13: The EGaIn-PAM hydrogel prepolymer solution is obtained; S14: The EGaIn-PAM hydrogel prepolymer solution is ultrasonically treated under ice-water bath conditions to transform the polymer into a gel, forming an EGaIn-PAM composite hydrogel; S15: The EGaIn-PAM composite hydrogel is freeze-dried, then immersed in AgNO3 solution and irradiated under a xenon lamp to finally obtain Ag / EGaIn-PAM hydrogel; wherein, the concentration range of AgNO3 solution in step S14 is 0.02-0.4M.

[0008] In one optional embodiment, the mass ratio of EGaIn to anhydrous ethanol in step S11 is 2:15 to 1:30; the ultrasonic treatment time is 30 to 90 minutes; the particle size range of EGaIn particles in step S11 is 1 to 5 μm; wherein, the proportion of EGaIn particles with a particle size of less than 2 μm is not less than 75%.

[0009] In one optional embodiment, the mass ratio of EGaIn to acrylamide in step S12 is 0.5:1.

[0010] In one optional embodiment, the ultrasonic treatment time in step S13 is 15 to 60 minutes.

[0011] In one optional implementation, the freeze-drying time in step S14 is not less than 24 hours.

[0012] In one optional embodiment, the concentration range of the AgNO3 solution in step S14 is 0.02 ≤ a < 0.2 M, and the Ag in the Ag / EGaIn-PAM hydrogel is granular.

[0013] In one optional embodiment, the concentration range of the AgNO3 solution in step S14 is 0.2≤b≤0.4M, and the Ag in the Ag / EGaIn-PAM hydrogel is in sheet form.

[0014] Secondly, this disclosure also provides a controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel, which is prepared by the method described above. The controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel includes a chemical network structure, on which EGaIn particles and silver nanomaterials are attached; wherein the silver nanomaterials are in the form of particles or sheets.

[0015] Thirdly, this disclosure also provides a method for preparing a flexible sensor, comprising the following steps: Step S21, ultrasonically cleaning sandpaper in ethanol and allowing it to air dry for later use; Step S22, uniformly mixing PDMS main agent and curing agent and coating it onto the surface of the sandpaper treated in Step S21, placing it under vacuum until air bubbles are eliminated, heating and curing it in an 80°C oven, and peeling it off from the sandpaper to obtain a PDMS film with a pyramid structure; Step S23, cutting the PDMS film and sputtering gold ions on one side with the pyramid structure to obtain a flexible PDMS-Au electrode; Step S24, placing the controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel as described in claim 7 in the middle of the flexible PDMS-Au electrode to obtain a flexible sensor with a sandwich structure.

[0016] Fourthly, embodiments of this disclosure also provide an application of the flexible sensor described above in the field of skin-like materials.

[0017] The beneficial effects of this invention are as follows: the controllable silver nanomaterial modified liquid metal-polyacrylamide composite hydrogel and its preparation method, and the flexible sensor are based on the characteristics of EGaIn material. EGaIn is used as an acrylamide crosslinking agent to fix EGaIn in the polyacrylamide hydrogel by forming chemical bonds, thus preparing EGaIn-polyacrylamide composite hydrogel. At the same time, silver nitrate is introduced as the silver source. Taking advantage of the plasmon resonance effect of Ag nanomaterials, the controllable structure formation of silver nanomaterials is realized under light stimulation conditions. By forming silver nanomaterials with different structures, the sensitivity of the flexible sensor in different pressure ranges is improved.

[0018] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description and the drawings.

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 SEM image of the EGaIn-PAM hydrogel provided in the embodiments of this disclosure;

[0022] Figure 2 XRD pattern of Ag / EGaIn-PAM hydrogel provided in the embodiments of this disclosure;

[0023] Figure 3 Infrared spectrum of Ag / EGaIn-PAM hydrogel provided in the embodiments of this disclosure;

[0024] Figure 4 SEM image of Ag / EGaIn-PAM hydrogel prepared in 0.4M AgNO3 according to the embodiments of this disclosure;

[0025] Figure 5 EDS image of Ag / EGaIn-PAM hydrogel prepared in 0.4M AgNO3 according to the embodiments of this disclosure;

[0026] Figure 6 SEM image of Ag / EGaIn-PAM hydrogel prepared in 0.02M AgNO3 according to the embodiments of this disclosure;

[0027] Figure 7 SEM image of Ag / EGaIn-PAM hydrogel prepared in 0.1M AgNO3 according to the embodiments of this disclosure;

[0028] Figure 8 SEM image of Ag / EGaIn-PAM hydrogel prepared in 0.2M AgNO3 according to the embodiments of this disclosure;

[0029] Figure 9 A graph showing the capacitance response of the sheet-like Ag / EGaIn-PAM hydrogel sensor provided in this embodiment of the present disclosure to different pressure changes;

[0030] Figure 10 A graph showing the capacitance response of the sheet-like Ag / EGaIn-PAM hydrogel sensor provided in this embodiment of the present disclosure to different pressure changes;

[0031] Figure 11The capacitance response of the particulate Ag / EGaIn-PAM hydrogel sensor provided in this embodiment of the present disclosure to different pressure changes is shown in the graph.

[0032] Figure 12 A comparison of the pressure response performance of EGaIn-PAM hydrogel and sheet-like Ag / EGaIn-PAM hydrogel provided in the embodiments of this disclosure with and without light irradiation;

[0033] Figure 13 The ultraviolet absorption spectra of Ag / EGaIn-PAM and EGaIn-PAM hydrogels provided in the embodiments of this disclosure;

[0034] Figure 14 The ultraviolet absorption spectra of Ag / EGaIn-PAM and EGaIn-PAM hydrogels provided in the embodiments of this disclosure;

[0035] Figure 15 This is a schematic diagram illustrating the response of the light-enhanced Ag / EGaIn-PAM hydrogel pressure sensor provided in an embodiment of this disclosure. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.

[0038] In this document, exemplary embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. As used herein, expressions such as “at least one of…” modify the entire list of elements when following a list of elements, rather than individual elements in the list. For example, the expression “at least one of a, b, and c” should be understood to include only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.

[0039] The terminology used herein is for the purpose of describing specific exemplary configurations only and is not intended to be limiting. As used herein, the singular articles “a,” “an,” and “the” may also be intended to include plural forms unless otherwise clearly stated herein. The terms “comprising,” “including,” and “having” are inclusive and thus specify the presence of features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein should not be construed as requiring them to be performed in the specific order discussed or shown, unless specifically identified as such. Additional or alternative steps may be employed.

[0040] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0041] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0042] This disclosure provides a method for preparing a controllable silver nanomaterial-liquid metal-polyacrylamide composite hydrogel, comprising the following steps: S11, adding blocky EGaIn to anhydrous ethanol, ultrasonically treating it to obtain EGaIn particles, allowing it to stand, and then drying it in a vacuum drying oven until the ethanol is completely evaporated, then sealing it for later use; S12, dispersing and dissolving acrylamide and N,N′-methylenebisacrylamide in deionized water, stirring until the solid is completely dissolved, then adding EGaIn particles as an initiator to obtain an EGaIn-PAM hydrogel prepolymer; S13, ultrasonically treating the EGaIn-PAM hydrogel prepolymer under ice-water bath conditions to transform the polymer into a gel, forming an EGaIn-PAM composite hydrogel; S14, freeze-drying the EGaIn-PAM composite hydrogel, then immersing it in an AgNO3 solution and irradiating the hydrogel under a xenon lamp to finally obtain an Ag / EGaIn-PAM hydrogel; wherein, the concentration range of the AgNO3 solution in step S14 is 0.02-0.4M.

[0043] Specifically, polyacrylamide hydrogel is a polymer material with a three-dimensional network structure, offering adjustable mechanical properties and making it suitable for fabricating flexible pressure sensors. Pretreatment with EGaIn improves the uniformity of the composite material, further enhancing the pressure response of the EGaIn-polyacrylamide hydrogel. Composites with Ag nanomaterials can further improve the dielectric constant and pressure sensitivity of the hydrogel material.

[0044] This disclosure also provides a controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel, which is prepared by the method described above. The controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel includes a chemical network structure, on which EGaIn particles and silver nanomaterials are attached; wherein the silver nanomaterials are in the form of particles or sheets.

[0045] This disclosure also provides a method for preparing a flexible sensor, comprising the following steps: Step S21, ultrasonically cleaning sandpaper in ethanol and allowing it to air dry for later use; Step S22, uniformly mixing PDMS main agent and curing agent and coating it onto the surface of the sandpaper treated in Step S21, placing it under vacuum until air bubbles are eliminated, heating and curing it in an 80°C oven, and peeling it off from the sandpaper to obtain a PDMS film with a pyramid structure; Step S23, cutting the PDMS film and sputtering gold ions on one side with the pyramid structure to obtain a flexible PDMS-Au electrode; Step S24, placing the controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel as described in claim 7 in the middle of the flexible PDMS-Au electrode to obtain a flexible sensor with a sandwich structure.

[0046] Preferably, the electrodes at both ends of the flexible pressure sensor are connected to the data acquisition unit via wires. The flexible temperature sensor is placed under the pressure gauge, and the data acquisition unit records the response of the pressure sensor to changes in applied pressure.

[0047] This disclosure also provides an application of the flexible sensor described above in the field of skin-like materials.

[0048] Example 1: Preparation of EGaIn-PAM composite hydrogel by chemical composite method.

[0049] 1.777 g of acrylamide and 0.0085 g of N,N′-methylenebisacrylamide were added to 10 mL of deionized water. Then, EGaIn particles were added to the solution and mixed thoroughly to obtain a prepolymer solution for the chemically composite EGaIn-polyacrylamide hydrogel. The sample was sonicated in an ice-water bath for 30 min to obtain the chemically composite EGaIn-PAM hydrogel. The chemically composite EGaIn-PAM hydrogel prepared in Example 1 was characterized using SEM, as shown below. Figure 1 As shown, it exhibits a network structure, with EGaIn particles attached to the network.

[0050] Example 2: Preparation of Ag nanosheet composite EGaIn-PAM hydrogel

[0051] After freeze-drying the EGaIn-PAM hydrogel obtained in Example 1, it was immersed in AgNO3 solutions (0.4M) of different concentrations for 10 min to fill the pores of the hydrogel with AgNO3 solution. Subsequently, the AgNO3-treated PAM-EGaIn hydrogel was placed under xenon lamp irradiation for 30 min to remove AgNO3 through photochemical reduction. + Restored to Ag 0 The Ag / EGaIn-PAM hydrogel prepared in Example 2 was characterized, and its infrared spectrum is shown below. Figure 2 As shown, this composite hydrogel at 3200 cm⁻¹ -1 The absorption peak at 3340 cm⁻¹ is caused by the stretching vibration of -NH₂ in the PAM molecular chain; -1 The nearby absorption peak is caused by the stretching vibration of -OH; 1672 cm⁻¹ -1 The peak at 1459 cm⁻¹ is a characteristic absorption peak caused by the stretching vibration of the carbonyl group (C=O) in the amide group. -1 The characteristic peak at 1330 cm⁻¹ corresponds to the bending vibration of the methylene group (-CH₂), and is located at 1330 cm⁻¹. -1 The nearby peaks are due to stretching vibrations of CN bonds or bending vibrations of CH bonds, demonstrating that the infrared spectrum of the Ag / EGaIn-PAM composite hydrogel encompasses the characteristic peaks of PAM. The XRD pattern of this composite hydrogel is shown below. Figure 3 As shown, the material exhibits distinct peaks at 2θ = 38.12, 44.28, 64.43, and 77.47, consistent with the standard Ag card (PDF 04-0783), demonstrating that Ag nanomaterials can be composited into PAM-EGaIn hydrogel via photochemical reduction. SEM images of the Ag / EGaIn-PAM hydrogel obtained after immersion in 0.4 M AgNO3 are shown below. Figure 4 As shown, the Ag nanoparticles grown in situ on the EGaIn-PAM surface are in sheet-like form. The EDS of the Ag / EGaIn-PAM hydrogel obtained by soaking in 0.4M AgNO3 is as follows: Figure 5 As shown, Ag nanosheets are uniformly distributed within the hydrogel. With further increases in Ag ion concentration, the EGaIn particles in EGaIn-PAM may be completely encapsulated by the Ag nanomaterials, preventing the EGaIn particles from being exposed to form an effective microcapacitive structure in the sensor. Furthermore, during the preparation of the Ag / EGaIn-PAM hydrogel using the photochemical reduction method, Ag... + Restored to Ag 0There is an exothermic reaction. As the concentration of Ag ions increases further, the exothermic effect becomes significant, leading to severe water loss from the hydrogel carrier and damaging the overall structure of the composite hydrogel.

[0052] Example 3: Preparation of Ag nanoparticle composite EGaIn-PAM hydrogel

[0053] After freeze-drying the EGaIn-PAM hydrogel obtained in Example 1, it was immersed in AgNO3 solutions (0.02M) of different concentrations for 10 min to fill the pores of the hydrogel with AgNO3 solution. Subsequently, the AgNO3-treated PAM-EGaIn hydrogel was placed under xenon lamp irradiation for 30 min, and AgNO3 was removed by photochemical reduction. + Restored to Ag 0 The Ag / EGaIn-PAM hydrogel prepared in Example 3 was characterized, as follows: Figure 6 As shown, the Ag nanomaterials exhibit a granular structure on the surface of the composite hydrogel obtained after immersion in 0.02M AgNO3.

[0054] Example 5: Preparation of Ag nanoparticle composite EGaIn-PAM hydrogel

[0055] After freeze-drying the EGaIn-PAM hydrogel obtained in Example 1, it was immersed in AgNO3 solutions (0.2M) of different concentrations for 10 min to fill the pores of the hydrogel with AgNO3 solution. Subsequently, the AgNO3-treated PAM-EGaIn hydrogel was placed under xenon lamp irradiation for 30 min, and AgNO3 was removed by photochemical reduction. + Restored to Ag 0 The Ag / EGaIn-PAM hydrogel prepared in Example 5 was characterized, as follows: Figure 8 As shown, the Ag nanomaterials exhibit a granular structure on the surface of the composite hydrogel obtained after immersion in 0.2M AgNO3.

[0056] Example 5: Preparation of Ag nanoparticle composite EGaIn-PAM hydrogel

[0057] After freeze-drying the EGaIn-PAM hydrogel obtained in Example 1, it was immersed in AgNO3 solutions (0.2M) of different concentrations for 10 min to fill the pores of the hydrogel with AgNO3 solution. Subsequently, the AgNO3-treated PAM-EGaIn hydrogel was placed under xenon lamp irradiation for 30 min, and AgNO3 was removed by photochemical reduction. + Restored to Ag 0 The Ag / EGaIn-PAM hydrogel prepared in Example 5 was characterized, as follows: Figure 8As shown, the Ag nanomaterials exhibit a granular structure on the surface of the composite hydrogel obtained after immersion in 0.2M AgNO3.

[0058] Example 6: Preparation method of Ag / EGaIn-PAM composite hydrogel pressure sensor

[0059] First, commercial sandpaper was ultrasonically cleaned in ethanol for 30 minutes and allowed to air dry. PDMS prepolymer and curing agent were mixed at a 10:1 mass ratio and coated onto the cleaned sandpaper surface. The mixture was then placed in a vacuum environment for 20 minutes to eliminate air bubbles in the PDMS prepolymer solution. Subsequently, it was placed in an 80°C oven for 3 hours to cure the PDMS. Finally, the pyramid-structured PDMS film was peeled off the sandpaper. The PDMS film was cut to the desired size (15mm × 15mm), and the pyramid-structured side of the cut PDMS film was sputtered with gold ions to obtain a flexible PDMS-Au electrode. An Ag / EGaIn-PAM hydrogel was placed in the middle of the pressure Au-PDMS electrode to fabricate a flexible pressure sensor with a sandwich structure.

[0060] Example 7: Pressure response of Ag / EGaIn-PAM flexible sensor

[0061] (1) The upper and lower layers of the flexible pressure sensor are connected to the data acquisition device through wires. The flexible pressure sensor is placed under the pressure gauge, and the pressure change of the sensor is recorded by the data acquisition device.

[0062] (2) When the pressure is 0N, record the capacitance value of the sensor as C0.

[0063] (3) Record the capacitance of the sensor under a specific applied pressure.

[0064] (4) The measured capacitance response is recorded as ΔC / C0, where C0 is the baseline capacitance at 0N, and ΔC is the capacitance change relative to the baseline capacitance after the pressure change.

[0065] The above test results were analyzed, such as... Figure 9 The figure shows the capacitance response of the Ag / EGaIn-polyacrylamide composite hydrogel to different pressures. The monitoring range of this pressure sensor is 89.5 Pa - 15.5 kPa. The capacitance increases with increasing pressure and decreases with decreasing pressure.

[0066] Example 8: Response of Ag / EGaIn-PAM (sheet-like) flexible sensor to pressure under light stimulation

[0067] (1) The upper and lower layers of the flexible pressure sensor are connected to the data acquisition device through wires. The flexible pressure sensor is placed under the pressure gauge, and the pressure change of the sensor is recorded by the data acquisition device.

[0068] (2) When the pressure is 0N, record the capacitance value of the sensor as C0.

[0069] (3) Record the capacitance of the sensor under a specific applied pressure.

[0070] (4) The measured capacitance response is recorded as ΔC / C0, where C0 is the baseline capacitance at 0N, and ΔC is the capacitance change relative to the baseline capacitance after the pressure change.

[0071] The above test results were analyzed, such as... Figure 10 The figure shows the capacitance response of the Ag / EGaIn-polyacrylamide composite hydrogel to different pressures under 455nm laser irradiation. The monitoring range of this pressure sensor is 89.5Pa-14.9kPa. The capacitance increases with increasing pressure and decreases with decreasing pressure. Figure 12 As shown, compared to the pressure sensor in Example 7, the Ag / EGaIn-PAM hydrogel pressure sensor under laser irradiation stimulation has stronger pressure response performance.

[0072] Example 9: Response of Ag / EGaIn-PAM (granular) flexible sensor to pressure under light stimulation

[0073] (1) The upper and lower layers of the flexible pressure sensor are connected to the data acquisition device through wires. The flexible pressure sensor is placed under the pressure gauge, and the pressure change of the sensor is recorded by the data acquisition device.

[0074] (2) When the pressure is 0N, record the capacitance value of the sensor as C0.

[0075] (3) Record the capacitance of the sensor under a specific applied pressure.

[0076] (4) The measured capacitance response is recorded as ΔC / C0, where C0 is the baseline capacitance at 0N, and ΔC is the capacitance change relative to the baseline capacitance after the pressure change.

[0077] The above test results were analyzed, such as... Figure 11 The figure shows the capacitance response of the Ag / EGaIn-PAM (particulate) composite hydrogel to different pressures under 455nm laser irradiation. The monitoring range of this pressure sensor is 89.5Pa-9.4kPa. The capacitance increases with increasing pressure and decreases with decreasing pressure. However, compared to the pressure sensor in Example 8, the sheet-like Ag / EGaIn-PAM composite hydrogel sensor exhibits better pressure response performance under laser irradiation stimulation than the particulate Ag / EGaIn-PAM hydrogel pressure sensor.

[0078] Example 10: Investigation into the performance of light-enhanced pressure sensing

[0079] The Ag / EGaIn-PAM hydrogel prepared in Example 2 and the EGaIn-PAM hydrogel prepared in Example 1 were subjected to UV-NIR absorption spectroscopy and Raman spectroscopy. The test results were analyzed, such as... Figure 13 As shown, the PAM-EGaIn composite hydrogel exhibits a weak absorption peak in the 967-1003 nm range; after being combined with Ag nanomaterials, a stronger absorption peak is generated in the 412-468 nm range. Since Ag nanomaterials are plasmon-metallic materials, surface plasmon resonance (SPR) can occur on their surface under visible light stimulation. Figure 14 As shown, Raman spectra of Ag / PAM-EGaIn hydrogel and PAM-EGaIn hydrogel were tested under the same conditions, and the intensity of the characteristic peaks related to PAM was significantly enhanced. This is because Ag nanomaterials exhibit the SPR effect after photostimulation, generating a strong electromagnetic field, thereby amplifying the Raman signal. The main reason why irradiating the Ag / PAM-EGaIn composite hydrogel-based pressure sensor with a 455nm laser can enhance the pressure response capability of the sensor is as follows: Figure 15 As shown, upon light stimulation, electrons on the surface of the Ag nanomaterial undergo collective oscillation under the influence of the plasma effect, transforming into hot electrons. The formation of hot electrons results in more transferable charges and holes at the Ag-EGaIn interface, effectively increasing the charge quantity of the microcapacitor. Therefore, the pressure sensor fabricated from Ag / EGaIn-PAM hydrogel shows an increase in charge output from 8.06 pF to 12.7 pF before and after light exposure.

[0080] In summary, this controllable silver nanomaterial-modified liquid metal-polyacrylamide composite hydrogel and its preparation method, along with a flexible sensor, are based on the properties of EGaIn material. EGaIn is used as an acrylamide crosslinking agent, and the chemical bonds formed fix EGaIn within the polyacrylamide hydrogel, thus preparing the EGaIn-polyacrylamide composite hydrogel. Simultaneously, silver nitrate is introduced as the silver source, and the plasmon resonance effect of Ag nanomaterials is utilized to achieve controllable structure formation of silver nanomaterials under photostimulation conditions. By forming silver nanomaterials with different structures, the sensitivity of the flexible sensor is improved within different pressure ranges.

[0081] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel, characterized in that, Includes the following steps: S11, add blocky EGaIn to anhydrous ethanol, and after ultrasonic treatment, obtain EGaIn particles. After standing, put them into a vacuum drying oven to dry. After the ethanol has completely evaporated, seal them for later use. S12, Acrylamide and N,N′-methylenebisacrylamide are dispersed and dissolved in deionized water, stirred until all solids are dissolved, and then EGaIn particles are added as initiators to obtain EGaIn-PAM hydrogel prepolymer solution; S13, the EGaIn-PAM hydrogel prepolymer solution is ultrasonically treated under ice-water bath conditions to transform the polymer into a gel, forming an EGaIn-PAM composite hydrogel. S14, freeze-dry the EGaIn-PAM composite hydrogel, then soak it in AgNO3 solution and place the hydrogel under a xenon lamp for illumination to finally obtain Ag / EGaIn-PAM hydrogel; In step S14, the concentration of the AgNO3 solution ranges from 0.02 to 0.4 M. In step S14, the concentration range of the AgNO3 solution is 0.02 ≤ a ≤ 0.2 M, and the Ag in the Ag / EGaIn-PAM hydrogel is granular; or In step S14, the concentration range of the AgNO3 solution is 0.2 < b ≤ 0.4 M, and the Ag in the Ag / EGaIn-PAM hydrogel is in sheet form.

2. The preparation method according to claim 1, characterized in that, In step S11, the mass ratio of EGaIn to anhydrous ethanol is 2:15 to 1:

30. The duration of ultrasonic treatment is 30–90 min; The particle size range of EGaIn particles in step S11 is 1–5 μm; Among them, EGaIn particles with a diameter of less than 2 μm account for no less than 75%.

3. The preparation method according to claim 1, characterized in that, In step S12, the mass ratio of EGaIn to acrylamide is 0.5:

1.

4. The preparation method according to claim 1, characterized in that, The ultrasonic treatment time in step S13 is 15 to 60 minutes.

5. The preparation method according to claim 1, characterized in that, The freeze-drying time in step S14 shall not be less than 24 hours.

6. A controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel, characterized in that, The controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel prepared by the method according to any one of claims 1-5 includes a chemical network structure, on which EGaIn particles and silver nanomaterials are attached; The silver nanomaterial is in the form of particles or sheets.

7. A method of manufacturing a flexible sensor, characterized by, Includes the following steps: Step S21: Ultrasonically clean the sandpaper in ethanol, and let it air dry for later use. Step S22: Mix the PDMS main agent and curing agent evenly and coat them onto the sandpaper surface treated in step S21. Place the mixture under vacuum until the air bubbles are eliminated, then heat and cure it in an 80°C oven. Peel it off from the sandpaper to obtain a PDMS film with a pyramid structure. Step S23: Cut the PDMS film and perform gold ion sputtering on one side with the pyramid structure to obtain a flexible PDMS-Au electrode; Step S24: Place the controllable silver nanomaterial modified-liquid metal-polyacrylamide composite hydrogel as described in claim 6 in the middle of the flexible PDMS-Au electrode to obtain a flexible sensor with a sandwich structure.

8. An application of a flexible sensor prepared by the method described in claim 7 in the field of skin-like materials.

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