A flexible sensor with pressure and humidity sensing functions and a preparation method thereof

Abstract

The application discloses a flexible sensor with pressure and humidity sensing functions and a preparation method thereof, and relates to the technical field of flexible electronics and sensor devices, and comprises, from top to bottom, a microporous moisture-permeable protective layer, a dual-mode composite sensing layer, a pressure-sensitive microstructure layer, an elastomer protective layer and a film packaging layer, the dual-mode composite sensing layer comprises a humidity sensing layer, a film substrate and a pressure sensing electrode layer, the humidity sensing layer is arranged on one side of the film substrate, the pressure sensing electrode layer is arranged on the other side of the film substrate, the pressure sensing electrode layer is oppositely attached to the fingerprint-imitating microstructure of the pressure-sensitive microstructure layer, the pressure-sensitive microstructure layer is arranged in a notch of the elastomer protective layer, and the film packaging layer covers the pressure-sensitive microstructure layer and the elastomer protective layer. The flexible sensor provided by the application can efficiently sense pressure and humidity, and has a wide application prospect in the fields of robot interaction, intelligent artificial limbs and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible electronics and sensor devices, in particular to a flexible sensor with pressure and humidity sensing functions and a preparation method thereof. BACKGROUND

[0002] Non-contact sensing capability can perceive environmental changes before actual contact occurs, which is crucial for improving the environmental adaptability and interaction prediction capability of human-computer interaction systems. Although flexible sensors have made significant progress in contact pressure sensing, there are still many challenges in realizing high-performance contact and non-contact dual-mode sensing. Pressure and humidity, as core physical parameters, have become the focus of research in the field of flexible sensors. In this field, functional materials can efficiently convert external physical stimuli into measurable electrical signals through sensitive response to such stimuli, thereby achieving accurate sensing functions. In recent years, researchers have proposed various flexible sensors based on different response mechanisms. For example, flexible pressure sensors based on piezoelectric effect, piezoresistive effect, capacitive effect and triboelectric effect have been widely used in human health monitoring and robot tactile sensing. Humidity sensors mainly rely on the changes in electrical conductivity, dielectric constant and self-power supply of functional materials under different humidity conditions, and often use metal oxides, carbon-based materials (such as carbon nanotubes, conductive carbon black, graphene oxide, etc.), hydrophilic polymers and MXene as sensitive materials. The mechanical flexibility and high-performance response of these electronic devices make them important sensing components in various applications.

[0003] Although significant progress has been made in force sensing and humidity sensing devices in recent years, existing research still mainly focuses on single sensing function. From the perspective of sensing mode, force sensing usually relies on contact detection, while humidity can be sensed non-contact through the hygroscopic properties of materials. If both can be organically integrated, not only the multifunctionality of the device can be significantly improved, but also more comprehensive and reliable sensing can be achieved in complex environments. Although there have been some reports on pressure and humidity dual-mode sensors, most of the device structures still adopt separate design of sensing function units, or rely on multiple response characteristics of the same material (CN202411293404.4, CN202310062076.6, CN202410959699.8), and have not yet realized true integration. SUMMARY

[0004] To achieve the above object, the present application provides the following technical scheme: A flexible sensor with pressure and humidity sensing functions, comprising a microporous moisture-permeable protective layer, a dual-mode composite sensing layer, a pressure-sensitive microstructure layer, an elastomer protective layer and a film packaging layer sequentially attached from top to bottom, the dual-mode composite sensing layer comprises a humidity sensing layer, a film substrate and a pressure sensing electrode layer, the humidity sensing layer is arranged on one side of the film substrate, the pressure sensing electrode layer is arranged on the other side of the film substrate, the pressure sensing electrode layer is attached to the fingerprint-like microstructure of the pressure-sensitive microstructure layer, the pressure-sensitive microstructure layer is arranged in the notch of the elastomer protective layer, and the film packaging layer covers the pressure-sensitive microstructure layer and the elastomer protective layer.

[0005] Preferably, the microporous moisture-permeable protective layer is a polyethylene terephthalate film with a thickness of 50-100 µm, and the moisture-permeable micropores on the microporous moisture-permeable protective layer are processed by cutting, with a diameter of 1-1.5 mm.

[0006] Preferably, the film substrate of the dual-mode composite sensing layer is a polyethylene terephthalate material with a thickness of 200-300 µm, and the humidity sensing layer is a composite material prepared from MXene, silver nanowires and carboxylated cellulose nanofibers.

[0007] Preferably, the pressure-sensitive microstructure layer is composed of a high-molecular elastomer material and a conductive filler, and the pressure-sensitive microstructure layer comprises an elastomer and a fingerprint-like microstructure arranged on the elastomer, which is convex and in the form of a semi-cylindrical shape, with a cross-sectional height of 150 µm and a width of 300 µm.

[0008] Preferably, the material of the elastomer protective layer is polydimethylsiloxane, and the ratio of polydimethylsiloxane precursor solution to curing agent is 10-15:1.

[0009] Preferably, the material of the film packaging layer is polyethylene terephthalate or polyimide, with a thickness of 100-300 µm, and the adhesive side of the film packaging layer encapsulates the pressure-sensitive microstructure layer and the elastomer protective layer.

[0010] The present application also provides a preparation method of a flexible sensor with pressure and humidity sensing functions, which is used for preparing the flexible sensor with pressure and humidity sensing functions as described above, and specifically comprises the following steps:

[0011] Step 1: A polyethylene terephthalate film is processed into a preset pattern by laser cutting, and the surface of the film is formed with uniformly distributed moisture-permeable micropores by cutting, to constitute a microporous moisture-permeable protective layer.

[0012] Step 2, uniformly disperse MXene nanosheets in deionized water and stir for 12 hours or more to obtain a stable MXene dispersion; prepare silver nanowire dispersion by dispersing silver nanowires prepared by a hydrothermal method in ethanol and treating by ultrasonic dispersion, then mix equal mass of MXene dispersion and silver nanowire dispersion by ultrasonic for 15 minutes, and continue to stir for 6 hours, then add carboxylated cellulose nanofibers, the amount of carboxylated cellulose nanofibers is 5% to 10% of the total mass of MXene dispersion and silver nanowire dispersion, and continue to stir for 10 hours or more, thereby preparing a composite conductive ink; then print the composite conductive ink on one side of the hydrophilic treated film substrate, dry to form a humidity sensing layer, then prepare a pressure sensing electrode layer on the other side of the film substrate by combining a mask plate and a magnetron sputtering process; finally, obtain a dual-mode composite sensing layer by laser cutting.

[0013] Step 3, disperse the conductive filler in an organic solvent by ultrasonic dispersion, then add an elastomer base to the dispersion, stir well to obtain a mixture, heat the mixture during stirring to completely volatilize the organic solvent, then drop the composite liquid on the groove surface of the 3D printing template, and after curing, peel off to obtain a pressure-sensitive microstructure layer with a skin-like fingerprint protruding structure;

[0014] Step 4, mix the polydimethylsiloxane precursor solution and the curing agent in a ratio of 10 to 15:1, stir well, drop the mixture solution into the grooves of the 3D printing template, and after curing and peeling, obtain an elastomer protective layer;

[0015] Step 5, laser cut the polyethylene terephthalate film or polyimide film to obtain a preset pattern to obtain a film packaging layer;

[0016] Step 6, sequentially adhere the microporous moisture protection layer, dual-mode composite sensing layer, pressure-sensitive microstructure layer, elastomer protective layer, and film packaging layer from top to bottom to obtain a flexible sensor with pressure and humidity sensing functions.

[0017] Preferably, the concentration of the MXene dispersion in step 2 is 25 mg / mL, and the concentration of the silver nanowire dispersion is 10 mg / mL.

[0018] Preferably, the material of the pressure sensing electrode layer prepared by the magnetron sputtering process in step 2 is any one or a combination of more than one of silver, gold, copper, platinum, or nickel, and the pressure sensing electrode layer is relatively attached to the fingerprint-like microstructure of the pressure-sensitive microstructure layer in step 3.

[0019] As preferred, the conductive filler in step 3 is one or a combination of several of multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene, carbon black, MXene and carbon nanofiber; the elastomer base liquid in step 3 is one of polydimethylsiloxane, Ecoflex, water-based polyurethane, thermoplastic polyurethane, styrene-ethylene-butylene-styrene; the organic solvent in step 3 is one of n-hexane, isopropyl alcohol, toluene and chloroform.

[0020] The present application has the following advantages:

[0021] The fingerprint texture on the surface of human fingertips presents a unique periodic groove structure, which can enhance friction and force transmission when contacting external objects, thereby endowing the finger with sensitive tactile perception ability. In addition, the stratum corneum of the epidermis layer in human skin is rich in keratin, which not only has good mechanical strength and protective performance, but also can swell and change structure under high humidity environment, making the skin have excellent responsiveness to humidity changes. Inspired by this biological skin structure and perception strategy, the present application constructs a dual-mode flexible sensor integrating pressure and humidity. Among them, the fingerprint-inspired microstructure is used to realize the high-sensitivity response of the device to mechanical stimulation, and the humidity sensing layer uses MXene as the core material to mimic the "keratin" function to realize the rapid perception of environmental humidity changes. The flexible sensor can respond to pressure and humidity signals, and has high sensitivity and fast response characteristics, and has broad application potential in health detection, robot interaction and other fields.

[0022] The present application optimizes material selection and structural integration design, realizes rapid and non-crosstalk response of pressure and humidity through physical isolation and intermediate elastomer protection layer design, and also introduces a dual-mode composite sensing layer, which effectively avoids the device thickness and structural complexity brought by multi-mode sensors. The device size is close to the size of human fingertips, and has the characteristics of miniaturization and integration. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The structure diagram of the flexible sensor with pressure and humidity sensing functions of the present application.

[0024] Figure 2 The microporous moisture protection layer structure diagram of the flexible sensor with pressure and humidity sensing functions of the present application.

[0025] Figure 3 The SEM diagram of the humidity sensing layer of the flexible sensor with pressure and humidity sensing functions of the present application.

[0026] Figure 4 The wettability analysis of the humidity sensing layer of the flexible sensor with pressure and humidity sensing functions of the present application.

[0027] Figure 5 Structure diagram of the pressure sensitive microstructure layer of the flexible sensor with pressure and humidity sensing functions of the present application.

[0028] Figure 6 SEM diagram of the pressure sensitive microstructure layer of the flexible sensor with pressure and humidity sensing functions of the present application.

[0029] Figure 7 Compression mechanism of the pressure sensitive microstructure layer of the flexible sensor with pressure and humidity sensing functions of the present application.

[0030] Figure 8 Electrical signal response curve of the flexible sensor with pressure and humidity sensing functions of the present application under finger touch stimulation.

[0031] Figure 9 Electrical signal response curve of the flexible sensor with pressure and humidity sensing functions of the present application under humidification conditions when subjected to about 127 kPa loading-unloading cycles.

[0032] Figure 10 Non-contact response performance diagram of the flexible sensor with pressure and humidity sensing functions of the present application.

[0033] Figure 11 Response and recovery time diagram of the flexible sensor with pressure and humidity sensing functions of the present application under palm non-contact state.

[0034] Figure 12 Electrical signal change curve diagram of the flexible sensor with pressure and humidity sensing functions of the present application under continuous multiple cycle stimulation.

[0035] Figure 13 Electrical signal change curve diagram of the flexible sensor with pressure and humidity sensing functions of the present application under different breathing rates.

[0036] Figure 14 Recognition test diagram of the flexible sensor with pressure and humidity sensing functions of the present application for material surface humidity difference.

[0037] In the figure: 1, microporous moisture protection layer; 2, dual-mode composite sensing layer; 3, pressure sensitive microstructure layer; 4, elastomer protection layer; 5, thin film packaging layer; 21, humidity sensing layer; 22, thin film substrate; 23, pressure sensing electrode layer. DETAILED DESCRIPTION

[0038] The technical solutions of the embodiments 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, and 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.

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0040] Example 1: As Figure 1 As shown, a flexible sensor with both pressure and humidity sensing functions includes, from top to bottom, a microporous moisture-permeable protective layer 1, a dual-mode composite sensing layer 2, a pressure-sensitive microstructure layer 3, an elastomer protective layer 4, and a thin-film encapsulation layer 5. The dual-mode composite sensing layer 2 includes a humidity sensing layer 21, a thin-film substrate 22, and a pressure sensing electrode layer 23. The humidity sensing layer 21 is disposed on one side of the thin-film substrate 22, and the pressure sensing electrode layer 23 is disposed on the other side of the thin-film substrate 22. The pressure sensing electrode layer 23 is bonded to the fingerprint-like microstructure of the pressure-sensitive microstructure layer 3. The pressure-sensitive microstructure layer 3 is disposed within the notch of the elastomer protective layer 4 and is encapsulated and protected by the elastomer protective layer 4. The thin-film encapsulation layer 5 covers the pressure-sensitive microstructure layer 3 and the elastomer protective layer 4.

[0041] The pressure-sensitive microstructure layer 3 is composed of a polymer elastomer material and a conductive filler. The pressure-sensitive microstructure layer 3 includes an elastomer and a raised, semi-cylindrical fingerprint-like microstructure disposed on the elastomer. The overall morphology of the fingerprint-like microstructure is similar to that of a fingerprint structure. The cross-sectional height of the fingerprint-like microstructure is 150µm and the width is 300µm.

[0042] This embodiment also provides a method for fabricating a flexible sensor with both pressure and humidity sensing functions, used to fabricate the flexible sensor with both pressure and humidity sensing functions as described above, specifically including the following steps:

[0043] Step 1: A 100µm thick polyethylene terephthalate flexible film is laser-cut into a preset pattern. The surface of the film is cut to form uniformly distributed moisture-permeable micropores to form a microporous moisture-permeable protective layer 1.

[0044] Step 2, MXene nanosheets were uniformly dispersed in deionized water and stirred for more than 12 h to prepare a MXene dispersion with a concentration of 25 mg / mL; a silver nanowire dispersion was prepared by placing silver nanowires prepared by a hydrothermal method in ethanol and treating them with ultrasonic dispersion, with a concentration of 10 mg / mL, then equal amounts of MXene dispersion and silver nanowire dispersion were mixed and ultrasonically treated for 15 min, and then stirred for 6 h, on this basis, carboxylated cellulose nanofibers were added, the amount of carboxylated cellulose nanofibers added was 5% of the total amount of MXene dispersion and silver nanowire dispersion, and the mixture was stirred for more than 10 h, thereby preparing a composite conductive ink; the composite conductive ink was then printed on one side of the hydrophilic treated film substrate 22, dried to form a film to obtain a humidity sensing layer 21, and then a silver-based pressure sensing electrode layer 23 was prepared on the other side of the film substrate 22 by combining a mask and a magnetron sputtering process; finally, a dual-mode composite sensing layer 2 was obtained by laser cutting.

[0045] Step 3, multi-walled carbon nanotubes were placed in isopropyl alcohol and ultrasonically dispersed for 1 h, then polydimethylsiloxane precursor was added to the dispersion, the mass ratio of multi-walled carbon nanotubes to polydimethylsiloxane precursor was controlled to be 1:50, and the mixture was continuously stirred for more than 6 h to obtain a uniform mixture solution, then the mixture was heated during stirring to completely volatilize the organic solvent; on this basis, a curing agent was added to the mixture solution, the mass ratio of polydimethylsiloxane precursor to curing agent was 10:1, and the mixture was continuously stirred for 15 min, thereby preparing a polydimethylsiloxane / multi-walled carbon nanotube composite mixture, then the mixture was drop-coated on the groove surface of a 3D printing template, and after curing at 80°C for 2 h, a polydimethylsiloxane / multi-walled carbon nanotube pressure-sensitive microstructure layer 3 with a skin-like fingerprint protruding structure was obtained by peeling off;

[0046] Step 4, the polydimethylsiloxane precursor solution and the curing agent were mixed at a ratio of 10:1 and stirred thoroughly, the mixture solution was drop-coated in the grooves of a 3D printing template, and after curing and peeling off, an elastomer protective layer 4 was obtained;

[0047] Step 5, a polyethylene terephthalate flexible film with a thickness of 225 µm was laser cut into a predetermined pattern to obtain a film packaging layer 5;

[0048] Step 6, the microporous moisture protection layer 1, the dual-mode composite sensing layer 2, the pressure-sensitive microstructure layer 3, the elastomer protective layer 4, and the film packaging layer 5 were sequentially attached from top to bottom to obtain a flexible sensor with pressure and humidity sensing functions.

[0049] In step 1, the microporous moisture-permeable protective layer 1 adheres to the humidity sensing layer 21 of the double-mode composite sensing layer 2 in step 2, and the diameter of the moisture-permeable micropore is 1 mm; in step 2, the average length and diameter of the silver nanowire are about 20 μm and 50 nm respectively, the thickness of the polyethylene terephthalate film substrate 22 is 225 μm, and the humidity sensing layer 21 and the pressure sensing electrode layer 23 are bonded with copper tape at both ends of the lead wire; in step 3, the pressure-sensitive microstructure layer 3 is attached to the pressure sensing electrode layer 23, and the semi-cylindrical microstructure of the fingerprint-like microstructure is similar to the fingerprint texture, and the cross-sectional height of the fingerprint-like microstructure is about 150 μm and the width is about 300 μm (i.e. the cross-sectional shape is a semicircle with a radius of 150 μm); in step 4, the height of the elastomer protective layer 4 is 1 mm, which is consistent with the actual height of the pressure-sensitive microstructure layer 3 in step 3; in step 5, the film packaging layer 5 is packaged on the pressure-sensitive microstructure layer 3 and the elastomer protective layer 4.

[0050] As shown in Figure 2 , it is a schematic diagram of the microporous moisture-permeable protective layer 1 structure of the flexible sensor with pressure and humidity sensing function prepared in this embodiment, and the surface is distributed with moisture-permeable micropores with a diameter of 1 mm. This design not only makes water molecules more directly contact the humidity-sensitive layer to achieve fast response, but also effectively protects the humidity sensing layer.

[0051] As shown in Figure 3 , it is a SEM image of the humidity sensing layer of the flexible sensor with pressure and humidity sensing function prepared in this embodiment. In this humidity composite material system, MXene nanosheets and silver nanowires together form a stable mixed conductive network. Because MXene is rich in hydrophilic functional groups such as -OH, -O and -F on its surface, it has excellent moisture absorption performance, and silver nanowires as a highly conductive skeleton not only effectively reduce the initial resistance of the device, but also to some extent alleviate the problem of conductivity decrease of the composite material system caused by MXene oxidation. The synergistic effect of MXene and silver nanowires can improve the stability and mechanical durability of the conductive network. In addition, the introduction of carboxymethylated cellulose nanofibers can further improve the overall moisture absorption performance and structural stability of the composite material, and enhance the interfacial bonding strength between the sensing layer and the substrate.

[0052] As shown in Figure 4 , it is a wettability analysis of the humidity sensing layer (i.e. humidity sensing layer 21) of the flexible sensor with pressure and humidity sensing function prepared in this embodiment, and the water contact angle is 55.0°, showing good hydrophilicity, which is consistent with its excellent moisture absorption performance.

[0053] As shown in Figure 5Figure 3 shows a structural diagram of the pressure-sensitive microstructure layer 3 of the flexible sensor with pressure and humidity sensing functions prepared in this embodiment. The microstructure layer was prepared by 3D printing a reverse mold and one-time mold turning, and the surface of the microstructure layer formed regularly arranged semi-cylindrical microstructures (about 150 μm in height and about 300 μm in width) similar to the texture of human fingerprints.

[0054] As shown in Figure 4, the SEM image of the pressure-sensitive microstructure layer 3 of the flexible sensor with pressure and humidity sensing functions prepared in this embodiment shows that the microstructures are uniformly distributed and arranged, indicating that the microstructures have good forming precision and structural integrity. Figure 6 As shown in Figure 5, the compression mechanism of the pressure-sensitive microstructure layer 3 of the flexible sensor with pressure and humidity sensing functions prepared in this embodiment. The microstructure is based on the periodic groove features of the fingerprint of the human fingertip. In the initial state, the biomimetic microstructure only forms a limited linear contact with the electrode (i.e., the pressure sensing electrode layer 23), and the actual contact area of the interface is small, thereby showing a high interface resistance. As the external pressure increases, the microstructure undergoes reversible elastic compression, and the contact area increases significantly, thereby converting the increased pressure into a decreased resistance signal.

[0055] Figure 7 As shown in Figure 6, the electrical signal response curve of the flexible sensor with pressure and humidity sensing functions prepared in this embodiment under the stimulation of finger touch. The sensor can sensitively and quickly convert the touch stimulation into an electrical signal.

[0056] As shown in Figure 7, the electrical signal response curve of the flexible sensor with pressure and humidity sensing functions prepared in this embodiment under the loading-unloading cycle of about 127 kPa in the humidification condition. The sensor has a fast response and a stable waveform, indicating that the humidity change has no interference with the pressure detection. Figure 8 As shown in Figure 8, the non-contact response performance of the flexible sensor with pressure and humidity sensing functions prepared in this embodiment. It can be seen that in the process of the finger approaching and moving away from the sensor layer (i.e., the humidity sensing layer 21), the humidity sensing material can obviously distinguish the electrical signal changes caused by different contact distances. In contrast, the finger wearing gloves did not produce a significant humidity signal response.

[0057] Figure 9 As shown in Figure 9, the response and recovery time diagram of the flexible sensor with pressure and humidity sensing functions prepared in this embodiment in the non-contact state of the finger. The sensor shows a fast response time of 0.78 s.

[0058] As shown in Figure 10, the response and recovery time diagram of the flexible sensor with pressure and humidity sensing functions prepared in this embodiment in the non-contact state of the finger. The sensor shows a fast response time of 0.78 s. Figure 10 As shown in Figure 11, the response and recovery time diagram of the flexible sensor with pressure and humidity sensing functions prepared in this embodiment in the non-contact state of the finger. The sensor shows a fast response time of 0.78 s.

[0059] Figure 11 As shown in Figure 12, the response and recovery time diagram of the flexible sensor with pressure and humidity sensing functions prepared in this embodiment in the non-contact state of the finger. The sensor shows a fast response time of 0.78 s. ​​​

[0060] As shown in Figure 12 The flexible sensor prepared in the embodiment has stable and repeatable response waveform in continuous non-contact test, indicating that the humidity sensing performance has good reliability and stability.

[0061] As shown in Figure 13 The flexible sensor prepared in the embodiment has stable and repeatable response waveform in continuous non-contact test, indicating that the humidity sensing performance has good reliability and stability.

[0062] As shown in Figure 14 The flexible sensor prepared in the embodiment has stable and repeatable response waveform in continuous non-contact test, indicating that the humidity sensing performance has good reliability and stability.

[0063] In summary, the flexible sensor prepared in the embodiment can respond to pressure and humidity signals, has excellent pressure and humidity response performance, and provides a wide application prospect for health monitoring, intelligent robot interaction and other scenarios.

[0064] The present application optimizes material selection and structural integration design, realizes rapid and non-crosstalk response of pressure and humidity through physical isolation and intermediate elastomer protective layer design, and introduces a double-mode composite sensing layer, which effectively avoids the device thickness and structural complexity caused by multi-mode sensor.

[0065] Embodiment two: the flexible sensor prepared in the embodiment is prepared by the preparation method of the flexible sensor provided in embodiment one, and the difference between embodiment one and embodiment two is that the "silver-based" material in step 2 is replaced by other conductive metal, such as gold (Au), copper (Cu), platinum (Pt) or nickel (Ni). The other preparation methods are the same as those in embodiment one.

[0066] Example Three: This example is prepared by the preparation method of the flexible sensor with pressure and humidity sensing functions provided in Example One. On the basis of Example One, the difference from Example One is that the "multi-walled carbon nanotubes" in step 3 are replaced by other conductive materials, such as a combination of one or several of single-walled carbon nanotubes, graphene, carbon black, MXene, and carbon nanofibers. Other preparation methods are the same as Example One.

[0067] Example Four: This example is prepared by the preparation method of the flexible sensor with pressure and humidity sensing functions provided in Example One. On the basis of Example One, the difference from Example One is that the "polydimethylsiloxane" in step 3 is replaced by other high molecular elastic materials, such as Ecoflex, water-based polyurethane, thermoplastic polyurethane, styrene-ethylene-butylene-styrene. Other preparation methods are the same as Example One.

[0068] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A flexible sensor having both pressure and humidity sensing functions, characterized by, The flexible sensor comprises, from top to bottom, a microporous moisture-permeable protective layer (1), a dual-mode composite sensing layer (2), a pressure-sensitive microstructure layer (3), an elastomer protective layer (4), and a film packaging layer (5). The dual-mode composite sensing layer (2) comprises a humidity sensing layer (21), a film substrate (22), and a pressure sensing electrode layer (23). The humidity sensing layer (21) is arranged on one side of the film substrate (22), and the pressure sensing electrode layer (23) is arranged on the other side of the film substrate (22). The pressure sensing electrode layer (23) is attached to the fingerprint-like microstructure of the pressure-sensitive microstructure layer (3). The pressure-sensitive microstructure layer (3) is arranged in the notch of the elastomer protective layer (4). The film packaging layer (5) covers the pressure-sensitive microstructure layer (3) and the elastomer protective layer (4). The microporous moisture-permeable protective layer (1) is made of polyethylene terephthalate film. The film substrate (22) of the dual-mode composite sensing layer (2) is made of polyethylene terephthalate material. The humidity sensing layer (21) is a composite material made of MXene, silver nanowires, and carboxylated cellulose nanofibers. The pressure-sensitive microstructure layer (3) is composed of a high-molecular elastomer material and conductive fillers. The pressure-sensitive microstructure layer (3) comprises an elastomer and a fingerprint-like microstructure arranged on the elastomer, which is convex and in the shape of a semi-cylinder. 2.The flexible sensor with pressure and humidity sensing functions according to claim 1, wherein, The thickness of the microporous moisture-permeable protective layer (1) is 50-100 µm. The moisture-permeable micropores on the microporous moisture-permeable protective layer (1) are formed by cutting processing, with a diameter of 1-1.5 mm. 3.The flexible sensor with pressure and humidity sensing functions according to claim 2, wherein, The thickness of the dual-mode composite sensing layer (2) is 200-300 µm.

4. The flexible sensor with pressure and humidity sensing functions according to claim 3, wherein, The cross-sectional height of the fingerprint-like microstructure is 150 µm, and the width is 300 µm.

5. The flexible sensor with pressure and humidity sensing functions according to claim 4, wherein, The material of the elastomer protective layer (4) is polydimethylsiloxane. The mass ratio of the polydimethylsiloxane precursor solution to the curing agent is 10-15:

1.

6. The flexible sensor with pressure and humidity sensing functions according to claim 5, wherein, The material of the film packaging layer (5) is polyethylene terephthalate or polyimide, with a thickness of 100-300 µm. The adhesive side of the film packaging layer (5) encapsulates the pressure-sensitive microstructure layer (3) and the elastomer protective layer (4).

7. A method for preparing a flexible sensor having both pressure and humidity sensing functions, characterized by, The method for preparing the flexible sensor with pressure and humidity sensing functions as claimed in claim 6 comprises the following steps: Step 1: polyethylene terephthalate film is cut into a predetermined pattern by laser cutting, and the surface is formed with uniformly distributed moisture-permeable micropores to constitute the microporous moisture-permeable protective layer (1). Step 2, uniformly disperse MXene nanosheets in deionized water and stir for 12 hours or more to obtain a stable MXene dispersion; prepare a silver nanowire dispersion by placing silver nanowires prepared by a hydrothermal method in ethanol and dispersing by ultrasonic treatment, then mix equal amounts of the MXene dispersion and the silver nanowire dispersion by ultrasonic treatment for 15 minutes, and continue stirring for 6 hours, on this basis, add carboxylated cellulose nanofibers, the amount of carboxylated cellulose nanofibers added is 5% to 10% of the total mass of the MXene dispersion and the silver nanowire dispersion, and continue stirring for 10 hours or more, thereby preparing a composite conductive ink; then print the composite conductive ink on one side of a hydrophilic treated film substrate (22), dry to form a humidity sensing layer (21), and then prepare a pressure sensing electrode layer (23) on the other side of the film substrate (22) by combining a mask plate and a magnetron sputtering process; finally, laser cutting is performed to obtain a dual-mode composite sensing layer (2); Step 3, disperse the conductive filler in an organic solvent by ultrasonic treatment, then add an elastomer base liquid to the dispersion, stir thoroughly to obtain a mixture, heat the mixture during stirring to completely volatilize the organic solvent, then drop the mixture onto the groove surface of the 3D printing template, and after curing, peel off to obtain a pressure-sensitive microstructure layer (3) with a skin-like fingerprint protruding structure; Step 4, mix the polydimethylsiloxane precursor solution and the curing agent in a ratio of 10 to 15:1, stir thoroughly, drop the mixture solution into the grooves of the 3D printing template, and after curing and peeling, obtain an elastomer protective layer (4); Step 5, laser cut a polyethylene terephthalate film or a polyimide film into a predetermined pattern to obtain a film packaging layer (5); Step 6, sequentially adhere the microporous moisture protection layer (1), the dual-mode composite sensing layer (2), the pressure-sensitive microstructure layer (3), the elastomer protective layer (4), and the film packaging layer (5) from top to bottom to obtain a flexible sensor with pressure and humidity sensing functions.

8. The method of claim 7, wherein the flexible sensor having both pressure and humidity sensing functions is prepared by the steps of: In step 2, the concentration of the MXene dispersion is 25 mg / mL, and the concentration of the silver nanowire dispersion is 10 mg / mL.

9. The method of claim 8, wherein the flexible sensor having both pressure and humidity sensing functions is prepared by the steps of: (a) preparing a flexible substrate; (b) forming a first sensing layer on the flexible substrate; (c) forming a second sensing layer on the first sensing layer; and (d) forming a third sensing layer on the second sensing layer. In step 2, the pressure sensing electrode layer (23) prepared by magnetron sputtering process is made of any one or a combination of silver, gold, copper, platinum, or nickel, and the pressure sensing electrode layer (23) is oppositely attached to the fingerprint-like microstructure of the pressure-sensitive microstructure layer (3) in step 3.

10. The method of claim 9, wherein the flexible sensor having both pressure and humidity sensing functions is prepared by the steps of: In step 3, the conductive filler is one or a combination of multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene, carbon black, MXene, and carbon nanofibers; the elastomer base liquid is one of polydimethylsiloxane, Ecoflex, water-based polyurethane, thermoplastic polyurethane, and styrene-ethylene-butylene-styrene; and the organic solvent is one of n-hexane, isopropyl alcohol, toluene, and trichloromethane.

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