Flexible underwater pressure sensor and preparation method and application thereof

Abstract

The invention belongs to the technical field of flexible sensors, and relates to a flexible underwater pressure sensor and a preparation method and application thereof. The flexible underwater pressure sensor comprises a conductive sensing layer with a pyramid microstructure on the surface, wherein the conductive sensing layer comprises a polydimethylsiloxane thin film with a pyramid microstructure unit and a silver nanowire thin film which is uniformly and conformally attached to the surface of the polydimethylsiloxane thin film; the electrode layer is located on the surface of the side, with the microstructure, of the conductive sensing layer; and the packaging layer is used for performing waterproof packaging on the sensor. The sensor provided by the invention adopts a flexible piezoresistive sensing technology, can work underwater, can at least detect the water depth of 4.5 cm, and has stable response to the water depth of 5mm. Moreover, the preparation process is simple, large-scale preparation can be realized, and the preparation method has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible sensors, in particular to a flexible underwater pressure sensor and a preparation method and application thereof. Background Art

[0002] In recent years, with the rapid development of marine resource development and underwater environmental monitoring, higher performance requirements have been placed on underwater pressure sensors. Traditional underwater pressure sensors are mostly made of rigid materials, which have many limitations in practical applications, such as poor flexibility, insufficient biocompatibility, and limited sensitivity. These limitations have severely restricted the application scope and development prospects of underwater pressure sensors.

[0003] The rise of flexible electronics offers a new avenue for addressing these challenges. Flexible sensors, with their exceptional flexibility, biocompatibility, and high sensitivity, have become a research hotspot in underwater sensing. Elastomeric conductive polymer composites (ECPCs), composed of elastomeric polymers and conductive nanofillers, have been widely used in flexible piezoresistive sensors. Ideal ECPC-based flexible sensors should exhibit a wide detection range and high sensitivity. To achieve this wide detection range, a dense conductive network must be constructed within the ECPCs to ensure that the material maintains structural integrity under large strains. However, this dense conductive network typically requires a high nanofiller loading, making it difficult for the material to undergo significant structural changes under small strains, thereby reducing sensitivity. Furthermore, the doping process and material preparation requirements for the conductive fillers are demanding, and the conductive edges of the conductive elastomer composites exhibit minimal change under low pressure. Consequently, these sensors often exhibit low sensitivity, lack of reproducibility, and long response times.

[0004] Despite significant progress in the development of flexible underwater pressure sensors, they still face several technical challenges. For example, insufficient long-term stability, a need for improved sensitivity, and weak anti-interference capabilities limit their widespread adoption in practical applications. Therefore, developing a flexible underwater pressure sensor with high sensitivity, high stability, and strong anti-interference capabilities is of great practical significance. Summary of the Invention

[0005] To address the shortcomings of the prior art, the present invention provides a flexible underwater pressure sensor, its preparation method, and its application. The sensor has the advantages of high sensitivity, good stability, and a simple preparation process. It can detect underwater pressure to a depth of at least 4.5 cm and maintains a stable response to a depth of 5 mm.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a flexible underwater pressure sensor. The flexible underwater pressure sensor comprises: a conductive sensing layer having a pyramid microstructure on its surface, the conductive sensing layer comprising a polydimethylsiloxane film having pyramid microstructure units and a silver nanowire film uniformly and conformally attached to the surface of the polydimethylsiloxane film; an electrode layer located on the microstructured side of the conductive sensing layer; and an encapsulation layer for waterproofing the sensor.

[0008] Preferably, the side length of the pyramid microstructure unit is 25 to 500 micrometers, and the height is 15 to 350 micrometers. For example, the side length of the pyramid microstructure unit is 250 micrometers, and the height is 175 micrometers.

[0009] Preferably, the distance between adjacent pyramid microstructure units is 25 to 500 micrometers. For example, the distance between two adjacent pyramid microstructure units is 500 micrometers.

[0010] Preferably, the size of the conductive sensing layer is 5-10 mm x 10-20 mm. For example, the size of the conductive sensing layer is 20 mm x 15 mm.

[0011] Preferably, the thickness of the polydimethylsiloxane film having the pyramid microstructure units is 0.1 to 1 mm. For example, the thickness of the polydimethylsiloxane film having the pyramid microstructure units is 1 mm.

[0012] Preferably, the electrodes are interdigitated electrodes. For example, the electrodes include a first electrode and a second electrode located in the same plane, and the first electrode and the second electrode are not in contact.

[0013] Preferably, the material of the encapsulation layer is silicone rubber; preferably, the silicone rubber is one of silicone rubber 706 or silicone rubber 704 .

[0014] In a second aspect, the present invention provides a method for preparing a conductive sensing layer having a pyramid microstructure on its surface. The preparation method comprises the following steps: S1. Preparing a microstructured polydimethylsiloxane film: mixing a polydimethylsiloxane prepolymer with a curing agent to obtain a polydimethylsiloxane preformed liquid; pouring the polydimethylsiloxane preformed liquid into a mold having a pyramid microstructure to form a film, and thermally curing the film to obtain a polydimethylsiloxane film having pyramid microstructure units; S2. Preparation of piezoresistive layer: Injecting an ethanol dispersion of silver nanowires at the water / n-hexane interface and assembling into a silver nanowire film, then uniformly attaching the silver nanowire film to the surface of the polydimethylsiloxane film. After vacuum treatment and drying, the silver nanowire film is conformally and uniformly attached to the surface of the polydimethylsiloxane film having pyramid microstructure units, thereby obtaining a conductive sensing layer having a pyramid microstructure on the surface.

[0015] In a third aspect, the present invention provides a method for preparing the flexible underwater pressure sensor. The method comprises the following steps: S1. Preparing a microstructured polydimethylsiloxane film: mixing a polydimethylsiloxane prepolymer with a curing agent to obtain a polydimethylsiloxane preformed liquid; pouring the polydimethylsiloxane preformed liquid into a mold having a pyramid microstructure to form a film, and thermally curing the film to obtain a polydimethylsiloxane film having pyramid microstructure units; S2. Preparing a piezoresistive layer: injecting an ethanol dispersion of silver nanowires at the water / n-hexane interface to assemble a silver nanowire film, then uniformly attaching the silver nanowire film to the surface of a polydimethylsiloxane film. After vacuuming and drying, the silver nanowire film is conformally and uniformly attached to the surface of the polydimethylsiloxane film having pyramidal microstructure units, thereby obtaining a conductive sensing layer having a pyramidal microstructure on the surface. S3. Encapsulate the sensor: tightly fit the microstructured side of the conductive sensing layer to the electrode layer, and then use silicone rubber to waterproof the sensor to obtain a flexible underwater pressure sensor.

[0016] Preferably, the ethanol dispersion of silver nanowires is uniformly injected into the water / n-hexane interface. After a uniform and stable silver nanowire film is formed, the injection is stopped. The n-hexane is completely evaporated at room temperature to obtain a silver nanowire film floating on the water surface. The silver nanowire film is then removed from the water using a polydimethylsiloxane film containing pyramid microstructure units, and uniformly attached to the surface of the polydimethylsiloxane film. After vacuum treatment and drying, a conductive sensing layer is obtained in which the silver nanowire film is conformally and uniformly attached to the surface of the polydimethylsiloxane film.

[0017] Preferably, the concentration of the silver nanowire dispersion in ethanol is 7-15 mg / mL.

[0018] In a third aspect, the present invention provides an application of the flexible underwater pressure sensor in underwater pressure monitoring.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] (1) The present invention creatively designs a piezoresistive flexible underwater pressure sensor with a microstructured surface. By assembling a uniform, stable, and complete silver nanowire film at the water / n-hexane interface, and then using a polydimethylsiloxane (PDMS) film with a microstructured surface to scoop up the silver nanowire film, the silver nanowire film can be completely attached to the microstructured PDMS film, resulting in a conductive sensing layer with a pyramidal microstructure on the surface. This can reduce contact resistance and effectively improve the sensitivity of the sensor.

[0021] (2) The flexible underwater pressure sensor prepared by the present invention can work underwater, can detect a water depth of at least 4.5 cm, and has a stable response to a water depth of 5 mm.

[0022] (3) The present invention adopts flexible piezoresistive sensing technology, which has a simple preparation process and can be produced in large quantities. Compared with capacitive sensing technology, it has stronger anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an optical photograph of the microstructured PDMS film prepared in Example 1 of the present invention; Figure 2 This is a magnified microscope photograph of the microstructured PDMS film prepared in Example 1 of the present invention; Figure 3 This is an optical photograph of the conductive sensing layer prepared in Example 1 of the present invention; Figure 4 This is the minimum detection limit result of the flexible underwater pressure sensor prepared in Example 1 of the present invention in water; Figure 5 This is a curve showing the resistance change versus pressure change of the flexible underwater pressure sensor prepared in Example 1 of the present invention in water; Figure 6 Schematic diagram of the structure of the flexible underwater pressure sensor prepared by the present invention, 1-encapsulation layer, 2-microstructure PDMS, 3-conductive sensing layer, 4-interdigitated electrode layer. DETAILED DESCRIPTION

[0024] The present invention is further described by the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, not to limit the present invention. The following exemplifies the flexible underwater pressure sensor and its preparation method and application.

[0025] To overcome the limitations of existing flexible sensors, such as low sensitivity, lack of reproducibility, and long response times, this paper proposes a design based on a mechanism that varies interfacial contact resistance. This mechanism achieves pressure detection by varying the contact resistance between conductive layers, exhibiting high sensitivity within a narrow pressure range. This represents a promising piezoresistive pressure sensor design.

[0026] The sensor based on the interface contact resistance change mechanism consists of two parts: one part is the conductive layer. The existing technology usually uses metal nanowires, carbon nanotubes, graphene or other conductive metal particles to prepare the conductive layer. In the present invention, silver nanowires (AgNWs) as a key material, due to its excellent conductivity, flexibility and transparency, play an important role in improving the sensitivity and stability of flexible sensors. The introduction of silver nanowires not only enhances the signal transmission capability of the sensor, but also improves its long-term stability and reliability in complex environments. The other part is an elastic substrate material, which is used to support the conductive layer and achieve pressure response. The sensor of the present invention uses polydimethylsiloxane (PDMS) as a flexible substrate and silver nanowires as a conductive material.

[0027] Flexible piezoresistive sensors achieve enhanced sensitivity by fabricating microstructures. These structures create an air gap between the electrodes. When the two electrodes are pressed together, the contact area increases, improving the sensor's sensitivity. Photolithography and etching of rigid silicon can be used to create molds with microstructures, such as pyramidal, cylindrical, and hemispherical structures. The dimensions of the microstructure units, including but not limited to the diameter (side length), spacing, and shape of the periodic structure, significantly influence the sensor's sensing performance.

[0028] The flexible underwater pressure sensor includes a conductive sensing layer with a pyramidal microstructure on its surface. The conductive sensing layer comprises a polydimethylsiloxane film with the pyramidal microstructure and a silver nanowire film uniformly and conformally adhered to the surface of the polydimethylsiloxane film. The introduction of this structure into the conductive sensing layer significantly improves the sensitivity of the sensor. The conformal adhesion within the conductive sensing layer allows the silver nanowire film to be loaded not only on the microstructured surface of the polydimethylsiloxane film but also on the surface of the non-microstructured areas of the polydimethylsiloxane film. Because the silver nanowires are only tens of nanometers in diameter, they are difficult to clearly and completely visualize under an optical microscope. However, a combination of magnified microscopy and optical photographs reveals that the silver nanowire film uniformly and conformally covers the entire surface of the polydimethylsiloxane film with the pyramidal microstructure.

[0029] The side length of the pyramid microstructure unit is 25 to 500 microns, and the height is 15 to 350 microns. For example, the side length of the pyramid microstructure unit is 250 microns, and the height is 175 microns. The spacing between adjacent (two) pyramid microstructure units is 25 to 500 microns. For example, the spacing between adjacent (two) pyramid microstructure units is 500 microns. By reasonably setting the unit parameters of the pyramid microstructure, it is easy to achieve high sensitivity and a wide detection range of the flexible underwater pressure sensor.

[0030] The PDMS film containing the pyramid microstructure units has an overall thickness of approximately 0.1 to 1 mm. For example, the PDMS film containing the pyramid microstructure units has an overall thickness of approximately 1 mm. The conductive sensing layer has a dimension of 5 to 10 mm x 10 to 20 mm. For example, the conductive sensing layer has a dimension of 20 mm x 15 mm.

[0031] The thickness of the silver nanowire film is on the nanometer scale, for example, the thickness of the silver nanowire film is 10 to 80 nm.

[0032] This invention proposes a novel method for preparing a conductive sensing layer with a pyramidal microstructure on its surface. A PDMS film with the pyramidal microstructure is prepared using a mold containing the microstructure as a template. A silver nanowire film is then prepared through interfacial assembly. The silver nanowire film is then uniformly and conformally loaded onto the PDMS film, resulting in a conductive sensing layer with the pyramidal microstructure on its surface.

[0033] Prepare a PDMS preform liquid. Mix the PDMS prepolymer and the curing agent in a mass ratio of 5 to 20:1 to obtain a PDMS preform liquid. In an optional embodiment, the PDMS prepolymer and the curing agent are mixed in a mass ratio of 10:1 and stirred for 10 minutes to obtain a PDMS preform liquid.

[0034] Prepare a PDMS film with a microstructure. Pour the polydimethylsiloxane prefabricated liquid into a mold with a pyramid microstructure to form a film, and after thermal curing, obtain a polydimethylsiloxane film with a pyramid microstructure. The mold can be a silicon wafer mold. The thermal curing temperature can be 80 to 120°C, and the thermal curing time can be 0.5 to 2 hours. In an optional embodiment, slowly pour the PDMS prefabricated liquid into the silicon wafer mold with a pyramid microstructure, place it in a vacuum oven after leveling, remove bubbles, and place it in an 80°C oven for thermal curing for 2 hours. After the PDMS is completely cured, take out the PDMS film to obtain a PDMS film containing a pyramid microstructure.

[0035] An ethanol dispersion of silver nanowires is injected at the water / n-hexane interface to assemble into a silver nanowire film. In an alternative embodiment, deionized water is added to a container, followed by n-hexane. After the water and n-hexane separate, a water / n-hexane interface is formed. The ethanol dispersion of silver nanowires is evenly injected into the water / n-hexane interface. Once a uniform and stable silver nanowire film is formed, injection is stopped and the container is placed in a ventilated environment. The n-hexane is allowed to evaporate completely at room temperature, resulting in a silver nanowire film floating on the water surface. The concentration of the ethanol dispersion of silver nanowires can be 7 to 15 mg / mL.

[0036] The silver nanowire film is then uniformly attached to the surface of the polydimethylsiloxane film (the side with the microstructure). After vacuuming and drying, the silver nanowire film is uniformly and conformally attached to the surface of the polydimethylsiloxane film with the pyramid microstructure, thereby obtaining a piezoresistive layer having a pyramid microstructure on the surface. In an optional embodiment, the silver nanowire film is removed from the water and uniformly attached to the surface of the PDMS film containing the pyramid microstructure. The film is then allowed to stand at room temperature and then vacuumed (for example, after standing at room temperature for 30 minutes, it is placed in a vacuum oven for 5 minutes) to achieve a closer fit. Finally, the film is placed in an oven for drying to obtain a piezoresistive layer having a pyramid microstructure on the surface.

[0037] The present invention achieves uniform, conformal loading of silver nanowires onto the surface of a microstructured polydimethylsiloxane film by forming a silver nanowire film and then transferring it. During the retrieval process, the silver nanowire film is transferred to the microstructured PDMS film. In other words, the microstructured PDMS film serves as the transfer substrate for the silver nanowire film. The method described herein enables uniform, conformal coverage of silver nanowires onto the surface of the pyramid-microstructured PDMS film, achieving precise coverage and promoting the formation of a complete and continuous conductive path, thereby improving the sensitivity and cyclic stability of the piezoresistive flexible underwater pressure sensor.

[0038] The inventors previously attempted to prepare a silver nanowire layer on the surface of a PDMS film with a pyramidal microstructure by spray coating. However, the silver nanowires could not be uniformly and conformally loaded onto the pyramidal microstructured PDMS film, making it difficult to form a uniform and stable conductive electrode layer. This led to the conductive layer easily falling off and the coating cracking during subsequent use, significantly affecting the conductive properties and mechanical stability of the film material.

[0039] The following is an exemplary description of a method for preparing the flexible underwater pressure sensor.

[0040] The microstructured side of the conductive sensing layer is tightly bonded to the electrode layer. The electrodes may be interdigitated electrodes. Interdigitated electrodes are electrodes with a periodic pattern within their surface, such as finger-like or comb-like shapes. These electrodes are used to generate capacitance associated with an electric field that can penetrate the sample material and the sensitive coating. In some embodiments, the electrode material may be a PI-Cu electrode, i.e., a copper-plated polyimide (PI) film.

[0041] The electrodes include a first electrode and a second electrode. The first electrode and the second electrode are located in the same plane. The electrodes maintain contact with the top of the pyramid microstructure. A distance is maintained between the two electrodes. The first electrode and the second electrode form a conductive loop. Furthermore, the first electrode and the second electrode are disposed on a common conductive substrate. The conductive substrate is made of PI copper foil.

[0042] Encapsulate the sensor. The encapsulation layer is a conventional method in this field. The encapsulation layer can be arranged on the periphery of the flexible underwater pressure sensor. It should be understood that any sensor encapsulation material commonly used in this field is applicable to the present invention. In an optional embodiment, the sensor is waterproofly encapsulated using silicone rubber to obtain a flexible underwater pressure sensor. The silicone rubber can be one of 706 or 704 silicone rubbers. By uniformly coating the silicone rubber on the entire surface of the conductive sensing layer and the interdigitated electrode layer and the sides in contact with each other, the pressure sensor is ensured to be well encapsulated as a whole, thereby avoiding device failure caused by water infiltration during underwater testing.

[0043] The present invention also provides application of the flexible underwater pressure sensor in underwater pressure monitoring.

[0044] In summary, the existing technology for constructing a pressure sensor with a micro-pyramid structure is mainly through a capacitive and resistive composite sensor for pressure and strain detection. Moreover, the electrodes are mainly prepared on the microstructure by coating methods such as suspension coating, but this method is difficult to ensure a uniform conformal load on the electrode (such as graphene oxide) on the microstructure. The present invention is directed to a flexible underwater pressure sensor, and a silver nanowire film is assembled at the water / n-hexane interface. This method can ensure that the thickness of the prepared conductive film is at the nanometer level, the overall distribution of the conductive film is uniform, and it can be tightly conformally fitted with the pyramid microstructure PDMS film, and the preparation is simple. Moreover, the sensor of the present invention adopts a piezoresistive structure for underwater pressure detection, and utilizes a pyramid microstructure PDMS film and a silver nanowire film array to form a conductive sensing layer. The underwater pressure is measured by the resistance change caused by the pressure change, and the sensitivity is high.

[0045] Based on the common sense in the art, the above preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention. The reagents and raw materials used in the present invention are all commercially available.

[0046] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0047] Example 1

[0048] (1) Preparation of microstructured PDMS film: PDMS prepolymer (Dow Corning DC184) and curing agent were mixed at a mass ratio of 10:1 and stirred for 10 minutes to obtain a PDMS prefabricated liquid. The PDMS prefabricated liquid was slowly poured into a silicon wafer mold with a pyramid microstructure. After leveling, it was placed in a vacuum oven. After removing bubbles, it was placed in an 80°C oven for thermal curing for 2 hours. After the PDMS was completely cured, the PDMS film was removed to obtain a PDMS film with a pyramid microstructure.

[0049] (2) Preparation of a conductive sensing layer: 300 mL of deionized water was added to a container, followed by 100 mL of n-hexane. After the water and n-hexane separated, an interface was formed with water at the bottom and n-hexane at the top. A 10 mg / mL ethanol dispersion of silver nanowires was evenly injected into the water / n-hexane interface. After a uniform and stable silver nanowire film was formed, the injection was stopped and the container was placed in a fume hood. The n-hexane was completely evaporated at room temperature to obtain a silver nanowire film floating on the water surface. The silver nanowire film was removed from the water using a PDMS film containing a pyramid microstructure and evenly attached to the PDMS film. The film was then allowed to stand at room temperature for 30 minutes and then placed in a vacuum oven for 5 minutes to evacuate the film for a tighter fit. The film was then placed in an oven for drying to obtain a conductive sensing layer with a pyramid microstructure on the surface.

[0050] (3) Encapsulating the sensor: The microstructured side of the conductive sensing layer is tightly fitted to the interdigital electrode layer (PI-Cu electrode), and finally the sensor is waterproof encapsulated using silicone rubber 706 to obtain a flexible underwater pressure sensor.

[0051] Example 2

[0052] Compared with Example 1, except that the ethanol dispersion of silver nanowires in step (2) is 8 mg / mL, the other operations and conditions are the same as those in Example 1.

[0053] Example 3

[0054] Compared with Example 1, except that the ethanol dispersion of silver nanowires in step (2) is 13 mg / mL, the other operations and conditions are the same as those in Example 1.

[0055] Example 4

[0056] Compared with Example 1, except that the silicone rubber in step (3) is 704 silicone rubber, the other operations and conditions are the same as those in Example 1.

[0057] Morphological characterization

[0058] The optical photograph of the microstructured PDMS film prepared in Example 1 is as follows: Figure 1 As shown in FIG, the area of ​​the microstructured PDMS film is 20 mm × 15 mm. The magnified microscope photo of the microstructured PDMS film prepared in Example 1 is shown in FIG. Figure 2 As shown in FIG, it can be seen that the prepared microstructured PDMS film has a pyramid microstructure, the side length of the pyramid microstructure unit is 250 microns, the tower height is 175 microns, and the distance between two adjacent pyramid microstructure units is 500 microns. The optical photograph of the conductive sensing layer prepared in Example 1 is shown in FIG. Figure 3 As shown. Figure 3It can be seen that the silver nanowire film is uniformly and conformally attached to the surface of the PDMS film.

[0059] Performance test and analysis of flexible underwater pressure sensor under water.

[0060] The flexible underwater pressure sensor prepared in Example 1 was placed in a bucket with the water surface covering the sensor surface. The sensor was connected to an electrochemical workstation and the voltage was set to 1V. Water was pumped into the bucket in sequence with the water level increasing by 5mm each time. The current curve of the sensor in response to each water level change was measured, and the sensor resistance change curve was obtained through data analysis. The results are shown in Figure 2. Figure 4 As shown in the figure, as the water depth increases, the resistance change of the sensor gradually decreases, indicating that the sensor can recognize a water depth of 5 mm. Therefore, the minimum detection limit of the sensor in water is about 50 Pa.

[0061] Figure 5 The curve of the resistance change of the flexible underwater sensor in water with the increase of linear pressure is shown in Figure 2. The piecewise linear fitting analysis shows that the sensitivity of the flexible underwater pressure sensor is -0.0015Pa in the pressure range of 0-100Pa. -1 , the sensitivity of the flexible underwater pressure sensor is -3.00699*10 in the pressure range of 100-200Pa -4 Pa -1 , the sensitivity of the flexible underwater pressure sensor is -8.3075*10 in the pressure range of 200-250Pa -4 Pa -1 , the sensitivity of the flexible underwater pressure sensor is -1.9574*10 in the pressure range of 250-450Pa -4 Pa -1 Compared to sensors without microstructures, when pressure is applied to the sensor described in the present invention, the sensor containing the pyramid microstructure produces a greater deformation, thereby providing a larger contact area, thereby reducing contact resistance and improving sensor sensitivity. The above test results demonstrate that this flexible underwater pressure sensor has great potential for underwater monitoring applications.

[0062] Although specific embodiments of the present invention have been described above, those skilled in the art will appreciate that these are merely illustrative and that the scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, and such changes and modifications are intended to fall within the scope of the present invention.

Claims

1. A flexible underwater pressure sensor, characterized in that: The flexible underwater pressure sensor includes: a conductive sensing layer with a pyramid microstructure on its surface, the conductive sensing layer comprising a polydimethylsiloxane film with pyramid microstructure units and a silver nanowire film uniformly and conformally attached to the surface of the polydimethylsiloxane film; an electrode layer located on the surface of the conductive sensing layer on the side with the microstructure; and an encapsulation layer for waterproofing the sensor.

2. The flexible underwater pressure sensor according to claim 1, characterized in that: The side length of the pyramid microstructure unit is 20 to 500 micrometers, and the height is 15 to 350 micrometers; the distance between adjacent pyramid microstructure units is 20 to 500 micrometers.

3. The flexible underwater pressure sensor according to claim 1 or 2, characterized in that: The electrodes are interdigitated electrodes; preferably, the electrodes include a first electrode and a second electrode located in the same plane, and the first electrode and the second electrode are not in contact.

4. The flexible underwater pressure sensor according to any one of claims 1 to 3, characterized in that: The material of the encapsulation layer is silicone rubber; preferably, the silicone rubber is one of silicone rubber 706 or silicone rubber 704 .

5. A method for preparing a conductive sensing layer having a pyramid microstructure on its surface, characterized in that: The following steps are involved: S1. Preparing a microstructured polydimethylsiloxane film: mixing a polydimethylsiloxane prepolymer with a curing agent to obtain a polydimethylsiloxane preformed liquid; pouring the polydimethylsiloxane preformed liquid into a mold having a pyramid microstructure to form a film, and thermally curing the film to obtain a polydimethylsiloxane film having pyramid microstructure units; S2. Preparation of piezoresistive layer: Injecting an ethanol dispersion of silver nanowires at the water / n-hexane interface and assembling into a silver nanowire film, then uniformly attaching the silver nanowire film to the surface of the polydimethylsiloxane film. After vacuum treatment and drying, the silver nanowire film is conformally and uniformly attached to the surface of the polydimethylsiloxane film having pyramid microstructure units, thereby obtaining a conductive sensing layer having a pyramid microstructure on the surface.

6. A method for preparing a flexible underwater pressure sensor according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Preparing a microstructured polydimethylsiloxane film: mixing a polydimethylsiloxane prepolymer with a curing agent to obtain a polydimethylsiloxane preformed liquid; pouring the polydimethylsiloxane preformed liquid into a mold having a pyramid microstructure to form a film, and thermally curing the film to obtain a polydimethylsiloxane film having pyramid microstructure units; S2. Preparing a piezoresistive layer: injecting an ethanol dispersion of silver nanowires at the water / n-hexane interface to assemble a silver nanowire film, then uniformly attaching the silver nanowire film to the surface of a polydimethylsiloxane film. After vacuuming and drying, the silver nanowire film is uniformly and conformally attached to the surface of the polydimethylsiloxane film having pyramidal microstructure units, thereby obtaining a conductive sensing layer having a pyramidal microstructure on the surface. S3. Encapsulate the sensor: tightly fit the surface of the conductive sensing layer with the microstructure to the electrode layer, and then use the encapsulation layer to waterproof the sensor to obtain a flexible underwater pressure sensor.

7. The preparation method according to claim 5 or 6, characterized in that: The mass ratio of the polydimethylsiloxane prepolymer to the curing agent is (5-20):

1.

8. The preparation method according to any one of claims 5 to 7, characterized in that An ethanol dispersion of silver nanowires is uniformly injected into the water / n-hexane interface. After a uniform and stable silver nanowire film is formed, the injection is stopped. The n-hexane is allowed to evaporate completely at room temperature to obtain a silver nanowire film floating on the water surface. The silver nanowire film is then removed from the water using a polydimethylsiloxane film containing pyramidal microstructure units and uniformly attached to the surface of the polydimethylsiloxane film. After vacuum treatment and drying, a conductive sensing layer is obtained in which the silver nanowire film is conformally and uniformly attached to the surface of the polydimethylsiloxane film.

9. The preparation method according to any one of claims 5 to 8, characterized in that The concentration of the silver nanowire ethanol dispersion is 7-15 mg / mL.

10. Use of the flexible underwater pressure sensor according to any one of claims 1 to 4 in underwater pressure monitoring.

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