Moisture-resistant polyion elastomer for flexible pressure sensor

Abstract

The invention relates to a moisture-resistant polyion elastomer for a flexible pressure sensor, and belongs to the technical field of functional materials. The moisture-resistant polyion elastomer is prepared from a [DAAIM] [TFSI] ionic liquid monomer, a dithiol monomer and a cross-linking agent as raw materials through a photo-initiation polymerization reaction, and has a four-cross-linked network structure; the polyion elastomer can still keep stable electrical properties and mechanical properties in a high-humidity environment or an underwater environment, and shows extremely low hysteresis and creep deformation; the invention further provides a flexible pressure sensor. The sensing layer of the flexible pressure sensor is made of the moisture-resistant polyion elastomer. The flexible pressure sensor has the advantages of high sensitivity, quick responsiveness, wide linear pressure response range and high fidelity, is suitable for pressure detection in high-humidity and underwater environments, and has wide application prospects in the fields of medical health monitoring, underwater sensing and communication, soft robots, intelligent materials, extreme environment monitoring and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and particularly relates to a moisture-resistant polyionic elastomer for flexible pressure sensors. Background Art

[0002] With the continuous progress of technology, flexible pressure sensing technology and its core device - flexible pressure sensors, have shown broad application prospects and huge industrial potential in emerging industries such as humanoid robots. Flexible pressure sensors, with their characteristics of ultra-thin, light weight, high sensitivity, and stretchability, have been widely used in the fields of human health monitoring, human-computer interaction, wearable devices, underwater soft robots, etc. However, with the continuous expansion of application scenario requirements, especially in humid environments, underwater environments, or scenarios with frequent human contact, the importance of moisture-resistant flexible pressure sensors has become increasingly prominent.

[0003] Ionic gels have good conductivity and flexibility and are widely used in the field of flexible sensors. However, they have significant defects in practical applications: Firstly, ionic gels contain a large amount of free ionic liquids, which are prone to absorb water and swell in high-humidity environments or freeze at low temperatures, resulting in performance degradation; Secondly, the encapsulation layer of ionic gels usually cannot completely isolate water vapor, affecting the environmental adaptability of the sensors; In addition, the mechanical properties of ionic gels are poor and they are prone to leakage, further restricting their application in underwater or high-humidity environments.

[0004] As a new type of material, polyionic elastomers have the characteristic of no ionic leakage. However, most polyionic elastomer materials have a large polarity and are humidity-sensitive, and it is difficult to ensure the stability of conductivity and sensing performance in high-humidity or underwater environments. Summary of the Invention

[0005] To solve the above problems, one of the purposes of the present invention is to provide a moisture-resistant polyionic elastomer for flexible pressure sensors; through unique structural design and material selection, the moisture-resistant polyionic elastomer achieves excellent hydrophobic and moisture-resistant properties, improves stability in high-humidity environments while ensuring no risk of ionic leakage, and maintains good ionic conductivity.

[0006] Another purpose of the present invention is to provide a preparation method of a moisture-resistant polyionic elastomer for flexible pressure sensors. The preparation method is to mix an ionic monomer, a dithiol monomer, and a crosslinking agent evenly, and then crosslink the raw material components through a photoinitiated polymerization reaction to form a tetra-crosslinked network structure; the preparation method has simple technological steps, high raw material safety, good stability, and environmental friendliness.

[0007] A third object of the present invention is to provide a flexible pressure sensor, wherein the sensing layer material of the flexible pressure sensor is the anti-humid polyionic elastomer of the present invention; the flexible pressure sensor can work stably for a long time in high humidity and underwater environments and plays an important role in fields such as electronic skin, marine resource exploration, and real-time monitoring of human body conditions.

[0008] The present invention is achieved through the following technical solutions:

[0009] An anti-humid polyionic elastomer for a flexible pressure sensor, which is prepared by a photoinitiated polymerization reaction using an ionic liquid monomer, a dithiol monomer, and a crosslinking agent as raw materials;

[0010] Among them, the ionic liquid monomer is 1,3-diallylimidazolium bis(trifluoromethylsulfonyl)imide ([DAAIM][TFSI]); the cationic structure (DAAIM) in the ionic liquid monomer has a high degree of symmetry, which can significantly reduce the polarity of the ionic liquid monomer, and the anion is the fluorine-containing organic large group bis(trifluoromethylsulfonyl)imide (TFSI), which greatly improves the hydrophobicity of the molecule while providing conductivity.

[0011] The anti-humid polyionic elastomer has a four-crosslinked network structure.

[0012] Preferably, the dithiol monomer is 1,8-octanedithiol; the multi-carbon chain structure of 1,8-octanedithiol endows the obtained anti-humid polyionic elastomer with excellent hydrophobicity, which can effectively prevent water penetration in high humidity or underwater environments, thereby maintaining the mechanical and electrical properties of the anti-humid polyionic elastomer;

[0013] The crosslinking agent is pentaerythritol tetra(mercaptoacetate); pentaerythritol tetra(mercaptoacetate) as a crosslinking agent can make the obtained anti-humid polyionic elastomer form a stable four-crosslinked network structure. The four-crosslinked network structure not only improves the mechanical strength and elasticity of the anti-humid polyionic elastomer, but also significantly reduces the hysteresis and creep of the anti-humid polyionic elastomer by restricting the movement of [DAAIM][TFSI] chain segments in the anti-humid polyionic elastomer.

[0014] A preparation method of the anti-humid polyionic elastomer for a flexible pressure sensor of the present invention, the preparation method comprising the following steps:

[0015] Under ultraviolet light irradiation conditions, the ionic liquid monomer, the dithiol monomer, the crosslinking agent, and the photoinitiator are mixed evenly, and an anti-humid polyionic elastomer with a four-crosslinked network structure is obtained through a photoinitiated polymerization reaction;

[0016] The amount of the ionic liquid monomer is a mmol, the amount of the dithiol monomer is b mmol, and the amount of the crosslinking agent is c mmol. a, b, and c satisfy the following equation: 2a = 2b + 4c; c / (a + b + c) = X; X is the molar ratio of the crosslinking agent, and X = 0.05 - 0.2.

[0017] Preferably, X is the molar ratio of the crosslinking agent, and X = 0.05 - 0.1.

[0018] Preferably, the specific steps of the preparation method are as follows:

[0019] Step 1: Mechanically mix the ionic liquid monomer, dithiol monomer, crosslinking agent, and photoinitiator evenly, and apply ultraviolet light irradiation while mixing to perform prepolymerization to obtain a homogeneous polyion elastomer prepolymer solution.

[0020] Step 2: Place the release film and the frosted glass sheet parallel to each other, and pad a substrate between them to form a sandwich structure with a predetermined gap. The substrate is placed in the relative end regions of the sandwich, and the thickness of the substrate is the gap size of the sandwich structure; then drop the prepolymer solution obtained in Step 1 into the gap of the sandwich structure.

[0021] Step 3: Place the sandwich structure dropped with the prepolymer solution in Step 2 under ultraviolet light irradiation to perform a polymerization reaction until curing to obtain a transparent film, and peel it off to obtain the moisture-resistant polyion elastomer for the flexible pressure sensor of the present invention. The moisture-resistant polyion elastomer film prepared by the above method retains the rough microstructure of the frosted glass surface, has a large number of raised particles dispersed on the surface of the film, and there are many voids dispersed between the particles; the moisture-resistant polyion elastomer with the microstructure is applied to the flexible pressure sensor, which can effectively expand the pressure sensing range.

[0022] More preferably, in Step 1, the ionic liquid monomer, dithiol monomer, crosslinking agent, and photoinitiator are evenly mixed by magnetic stirring. The magnetic stirring speed is 500 rpm - 1000 rpm, and the stirring time is 2 min - 4 min; the ultraviolet light irradiation time is 2 min - 4 min, and the light power is 10 W - 20 W.

[0023] More preferably, in Step 2, the release film is a glass sheet with a polytetrafluoroethylene (PTFE) film adhered to the surface; the substrate is a polydimethylsiloxane (PDMS) film, and the thickness of the polydimethylsiloxane (PDMS) film is 100 μm - 200 μm.

[0024] More preferably, in Step 3, the ultraviolet light irradiation curing time is 10 min - 20 min, and the curing power is 30 W - 45 W.

[0025] Preferably, the ionic liquid monomer ([DAAIM][TFSI]) is prepared by the following method:

[0026] (1) Dissolve imidazole and 4-bromo-1-propene in acetonitrile, add sodium bicarbonate, heat under reflux at 75 °C to 90 °C for 10 h to 14 h, filter the suspension after cooling, and perform rotary evaporation to obtain a crude product;

[0027] Among them, the mass ratio of imidazole, 4-bromo-1-propene, sodium bicarbonate and acetonitrile is (5 - 8):(30 - 35):(9 - 12):(70 - 100);

[0028] (2) Dissolve the crude product obtained in step (1) with chloroform, add anhydrous magnesium sulfate, filter to precipitate solids, and then perform rotary evaporation on the filtrate to obtain a viscous oily crude product [DAAIM]Br; add deionized water to dissolve soluble impurities in [DAAIM]Br, separate the organic phase, and wash it successively with ethyl acetate, hexane and ether;

[0029] (3) Add an excessive amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to the organic phase washed in step (2) to obtain a yellow oily precipitate; freeze-dry the precipitate to obtain the ionic liquid monomer. Step two

[0030] A flexible pressure sensor, which successively includes an upper encapsulation layer, an upper electrode, a sensing layer, a lower electrode and a lower encapsulation layer from top to bottom; wherein, the material of the sensing layer is the anti-moisture polyionic elastomer of the present invention;

[0031] The upper electrode layer and the lower electrode layer form an electrode layer, and the electrode layer is in contact with the sensing layer for transmitting electrical signals; the upper encapsulation layer and the lower encapsulation layer form an encapsulation layer, and the encapsulation layer covers the sensing layer and the electrode layer for protecting the flexible sensor from the influence of the external environment.

[0032] Preferably, both the upper encapsulation layer and the lower encapsulation layer are PDMS films, and both the upper electrode and the lower electrode are PI-Cu films.

[0033] More preferably, the thickness of the PDMS film of the upper encapsulation layer is 100 μm to 200 μm, and the thickness of the PDMS film of the lower encapsulation layer is 100 μm to 200 μm; in the PI-Cu film of the upper electrode, the thickness of the Cu layer is 18 μm and the thickness of the PI layer is 25 μm; in the PI-Cu film of the lower electrode, the thickness of the Cu layer is 18 μm and the thickness of the PI layer is 25 μm.

[0034] Preferably, the flexible pressure sensor is applicable to pressure detection in high humidity and underwater environments.

[0035] A preparation method of the flexible pressure sensor according to the present invention includes the following steps: Align the upper encapsulation layer, upper electrode, sensing layer, lower electrode, and lower encapsulation layer from top to bottom and encapsulate them in a sandwich structure to obtain the flexible pressure sensor.

[0036] Preferably, the upper sensing layer and the lower sensing layer are respectively and independently obtained with customized patterns by laser cutting; the upper encapsulation layer and the lower encapsulation layer are respectively and independently obtained with customized sizes by laser cutting; in the flexible pressure sensor, the interfaces between adjacent layers are cleaned by a plasma machine to achieve stable bonding of each interface.

[0037] More preferably, the laser cutting parameters are a power of 30W - 60W, a cutting number of 8 - 20 times, and a laser frequency of 40% - 60%; the cleaning time of the plasma cleaning machine in a nitrogen atmosphere is 30s - 60s.

[0038] Beneficial effects

[0039] (1) The present invention provides a moisture-resistant polyionic elastomer for a flexible pressure sensor. Through unique material selection and structural design, the moisture-resistant polyionic elastomer achieves excellent hydrophobic and moisture-resistant properties and can maintain stable conductivity and mechanical properties in a high-humidity or underwater environment: The moisture-resistant polyionic elastomer is prepared by a photoinitiated polymerization reaction using an ionic liquid monomer, a dithiol monomer, and a crosslinking agent as raw materials; among them, the ionic liquid monomer material is a low-polarity 1,3-diallylimidazolium bis(trifluoromethylsulfonyl)imide ([DAAIM][TFSI]) designed and synthesized for the first time in the present invention. The cationic structure DAAIM in this monomer molecule has high symmetry, significantly reducing the polarity of the ionic liquid monomer. The anionic structure is a fluorine-containing organic large group bis(trifluoromethylsulfonyl)imide (TFSI), which greatly improves the hydrophobicity of the molecule while providing conductivity; the dithiol monomer material also has excellent hydrophobic properties. The moisture-resistant polyionic elastomer formed by their polymerization under the action of a crosslinking agent has a stable crosslinked network structure. This crosslinked network structure design not only improves the mechanical strength and elasticity of the polyionic elastomer but also can limit the outward diffusion and loss of cations by means of the elasticity of the network, significantly reducing the hysteresis and creep of the material.

[0040] (2) The present invention provides a moisture-resistant polyion elastomer for a flexible pressure sensor, wherein the dithiol monomer material is 1,8-octanedithiol. The multi-carbon chain structure of 1,8-octanedithiol gives the moisture-resistant polyion elastomer obtained by polymerization excellent hydrophobicity, which can effectively prevent moisture penetration in high humidity or underwater environments, thereby maintaining the mechanical and electrical properties of the polyion elastomer; the cross-linking agent is pentaerythritol tetrakis(thioglycollate). Pentaerythritol tetrakis(thioglycollate) is a four-cross-linking cross-linking agent, which can enable the polyion elastomer to form a stable four-cross-linked network structure, and further suppress the creep behavior of the polyion elastomer by increasing the cross-linking density.

[0041] (3) The present invention provides a method for preparing a moisture-resistant polyion elastomer for a flexible pressure sensor, the method comprising: firstly mixing an ionic liquid monomer, a dithiol monomer, a cross-linking agent and a photoinitiator under ultraviolet light irradiation to obtain a prepolymerization solution, and then polymerizing the prepolymerization solution on a frosted glass surface to obtain a moisture-resistant polyion elastomer having a four-cross-linked network structure through a photoinitiated polymerization reaction; the method has simple steps, high safety, good stability and environmental friendliness; the prepolymerization solution process can mix the raw material components to form a uniform phase, thereby improving the polymerization efficiency of the dithiol monomer and the ionic liquid monomer in the polymerization step; the polymerization on the frosted glass surface can enable the surface of the prepared moisture-resistant polyion elastomer to retain the microstructure of the frosted glass surface, with many protruding particles dispersed on the entire surface, and many gaps dispersed between the particles, so that the use of the flexible pressure sensor can effectively expand the range of pressure sensing.

[0042] (4) The present invention provides a flexible pressure sensor, the sensing layer material of the flexible pressure sensor is the moisture-resistant polyion elastomer described in the present invention; the sensing layer has a high modulus and can maintain structural integrity when subjected to pressure, while having low hysteresis and low creep characteristics, ensuring that the sensor has consistent response and stable performance during repeated use; the flexible pressure sensor has high sensitivity, fast responsiveness, a wide linear pressure response range and high fidelity, and its preparation method is convenient, green, non-toxic and pollution-free, and is suitable for large-scale production and wide application.

[0043] (5) The present invention provides a flexible pressure sensor, which is suitable for pressure detection in high humidity and underwater environments, and has broad application potential in the fields of medical health monitoring, underwater sensing and communication, soft robots, smart materials, and extreme environment monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The accompanying drawings are used to provide further understanding of the present disclosure and constitute a part of the specification. They are used to explain the present disclosure together with the following detailed description, but do not constitute a limitation of the present disclosure.

[0045] Figure 1Water contact angle of the moisture-resistant polyionic elastomer described in Example 1;

[0046] Figure 2 Mass change of the moisture-resistant polyionic elastomer described in Example 1 after soaking in water for 24 h;

[0047] Figure 3 Conductivity of the moisture-resistant polyionic elastomer described in Example 1 before and 1 h after soaking in water;

[0048] Figure 4 Modulus and strength of the moisture-resistant polyionic elastomer described in Example 1 before and 6 h after soaking in water;

[0049] Figure 5 10 h cyclic creep of the moisture-resistant polyionic elastomer described in Example 1;

[0050] Figure 6 1000-cycle hysteresis of the moisture-resistant polyionic elastomer described in Example 1;

[0051] Figure 7 Sensitivity of the pressure sensor made of the moisture-resistant polyionic elastomer described in Example 1 before and 1 h after soaking in water;

[0052] Figure 8 Schematic diagram of the morphological structure of the moisture-resistant polyionic elastomer described in Example 1;

[0053] Figure 9 Schematic diagram of the morphological structure of the frosted glass surface.

[0054] Figure 10 Schematic diagram of the preparation method of the moisture-resistant polyionic elastomer described in Example 1. Detailed implementation manners

[0055] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and examples, where the methods are conventional methods unless otherwise specified, and the raw materials can be obtained from public commercial channels unless otherwise specified.

[0056] Example 1

[0057] A moisture-resistant polyionic elastomer for a flexible pressure sensor in this example, the moisture-resistant polyionic elastomer is prepared by a photoinitiated polymerization reaction using an ionic liquid monomer, a dithiol monomer, and a crosslinking agent as raw materials;

[0058] Among them, the ionic liquid monomer is 1,3-diallylimidazolium bis(trifluoromethylsulfonyl)imide ([DAAIM][TFSI]); the dithiol monomer is 1,8-octanedithiol; the crosslinking agent is pentaerythritol tetra(mercaptoacetate); the moisture-resistant polyionic elastomer has a four-crosslinked network structure.

[0059] A preparation method of the moisture-resistant polyionic elastomer described in this embodiment is as follows Figure 10 shown, and the method steps are as follows:

[0060] Step 1: Mix 10.5 mmol of ionic liquid monomer, 7.5 mmol of dithiol monomer, 2 mmol of crosslinking agent and photoinitiator evenly by magnetic stirring under ultraviolet light irradiation. While mixing, apply ultraviolet light irradiation for prepolymerization. The magnetic stirring speed is 500 rpm, and the stirring time is 4 min; the ultraviolet light irradiation time is 4 min, and the light power is 10 W to obtain a homogeneous polyionic elastomer prepolymer solution; the molar ratio X of the crosslinking agent is 0.1;

[0061] Among them, the ionic liquid monomer is prepared by the following method:

[0062] (1) Dissolve 6.8 g of imidazole and 30 g of 4-bromo-1-propene in 70 g of acetonitrile, add 9 g of sodium bicarbonate, heat and reflux in an 82 °C oil bath for 12 h, cool and filter the suspension and perform rotary evaporation to obtain a crude product;

[0063] (2) Dissolve the crude product obtained in step (1) with chloroform, add 5 g of anhydrous magnesium sulfate, filter out the solid and then rotary evaporate the filtrate to obtain a viscous oily crude product [DAAIM]Br; add 8 mL of deionized water to dissolve the soluble impurities in [DAAIM]Br, separate the organic phase, and then wash it successively with 3×3 mL of ethyl acetate, 3 mL of hexane and 3 mL of ether;

[0064] (3) Add 20 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to the organic phase washed in step (2) to obtain a yellow oily precipitate; place the precipitate in a freeze dryer for drying to obtain the ionic liquid monomer;

[0065] Step 2: Place the release film and the frosted glass sheet parallel to each other, and pad a substrate between them to form a sandwich structure with a predetermined gap. The substrate is placed in the relative end regions of the sandwich, and the four sides are protected by silicone gaskets. The thickness of the substrate is the gap size of the sandwich structure; then drop the prepolymer solution obtained in step 1 into the gap of the sandwich structure;

[0066] The release film is a glass sheet with a polytetrafluoroethylene (PTFE) film adhered to the surface; the substrate is a polydimethylsiloxane (PDMS) film, and the thickness of the polydimethylsiloxane (PDMS) film is 200 μm;

[0067] Step 3, the sandwich structure after the prepolymer solution is dripped in step 2 is placed under ultraviolet light for polymerization reaction until it is cured to obtain a transparent film, the ultraviolet light curing time is 10 minutes, and the curing power is 45W; peeling off to obtain the moisture-resistant polyion elastomer for flexible pressure sensor; using scanning electron microscopy, the surface microstructure of the moisture-resistant polyion elastomer prepared by the method is tested, and the results are as follows Figure 8 As shown in the figure, it can be observed that the surface of the moisture-resistant polyion elastomer has many protruding particles, which are dispersed throughout the surface and there are many gaps between the particles, which is similar to the microstructure of the frosted glass surface (such as Figure 9 shown).

[0068] The hydrophobicity of the moisture-resistant polyionic elastomer described in Example 1 was tested. Figure 1 The water contact angle (CA) of the material was measured by a contact angle meter to be 101.31°; a moisture-resistant polyion elastomer with a diameter of 9 mm and a thickness of 0.27 mm was soaked in deionized water. Figure 2 As shown, the mass is almost unchanged before and after soaking in water for 24 hours, indicating that the moisture-resistant polyion elastomer has hydrophobic and anti-swelling properties.

[0069] The conductivity of the moisture-resistant polyionic elastomer described in Example 1 was tested using a broadband dielectric impedance spectrometer. The results are as follows: Figure 3 As shown, the conductivity of the moisture-resistant polyion elastomer in Example 1 before soaking in water is 6.21×10 -6 S cm -1 , the conductivity after soaking in water for 1 hour is 1.01×10 -5 S cm -1 The conductivity changes by less than one order of magnitude before and after soaking in water, indicating that the conductive properties of the moisture-resistant polyion elastomer are less affected by the underwater environment.

[0070] The moisture-resistant polyion elastomer described in Example 1 was subjected to a tensile test using a universal testing machine. The results are as follows: Figure 4 As shown, after soaking in water for 6 hours, the Young's modulus decreased by 6.2% and the breaking strength decreased by 4.1%, indicating that the mechanical properties of the moisture-resistant polyion elastomer are less affected by the underwater environment and can maintain structural integrity when subjected to high humidity or underwater pressure.

[0071] A high-precision mechanical testing machine was used to perform a 198 kPa compression test on the moisture-resistant polyion elastomer described in Example 1. The results are as follows: Figure 5As shown in the figure, the initial strain and the strain after 10 hours were calculated from the stress-strain curve changing with time: after 10 hours, the strain of the moisture-resistant polyionic elastomer increased from 18.58% to 18.76%, and the creep was 0.97%, with a small change, indicating that the moisture-resistant polyionic elastomer described in Example 1 has the characteristic of low creep; as Figure 6 shown, under a cyclic tensile force of 198 kPa, the cyclic hysteresis for 1000 cycles was approximately 4%, indicating that the moisture-resistant polyionic elastomer described in Example 1 has the characteristic of low hysteresis.

[0072] Example 2

[0073] A flexible pressure sensor, which successively includes an upper encapsulation layer, an upper electrode, a sensing layer, a lower electrode, and a lower encapsulation layer from top to bottom; wherein, the sensing layer is the moisture-resistant polyionic elastomer described in Example 1;

[0074] The thickness of the upper encapsulation layer PDMS film is 200 μm, and the thickness of the lower encapsulation layer PDMS film is 200 μm; in the upper electrode and lower electrode PI-Cu films, the thickness of the Cu layer is 18 μm and the thickness of the PI layer is 25 μm;

[0075] The upper sensing layer and the lower sensing layer are respectively independently laser-cut to obtain a customized pattern with a length of 2 cm, a width of 1 mm, and diameters of 5 mm and 3 mm at both ends; the upper encapsulation layer and the lower encapsulation layer are respectively independently laser-cut to obtain a customized size with a length of 6 cm and a width of 3 cm; in the flexible pressure sensor, the interfaces between adjacent layers are cleaned by a plasma machine to achieve stable bonding of each interface.

[0076] The parameters of the laser cutting are a power of 60 W, a cutting number of 8 times, and a laser frequency of 55%; the cleaning time of the plasma cleaning machine in a nitrogen atmosphere is 30 s.

[0077] Using a universal testing machine and a high-precision capacitance meter, the sensitivity of the flexible pressure sensor described in Example 2 was tested under the conditions of not being soaked in water, being soaked in water for 1 hour, and being soaked in water for 6 hours. The results are as Figure 6 shown, the sensitivity of the flexible pressure sensor has high consistency, and the influence of soaking water on the sensitivity of the sensor is very small.

[0078] Example 3

[0079] A moisture-resistant polyionic elastomer for a flexible pressure sensor described in this example, which is prepared by a photoinitiated polymerization reaction using an ionic liquid monomer, a dithiol monomer, and a crosslinking agent as raw materials;

[0080] Among them, the ionic liquid monomer is 1,3-diallylimidazolium bis(trifluoromethylsulfonyl)imide ([DAAIM][TFSI]); the dithiol monomer is 1,8-octanedithiol; the crosslinking agent is pentaerythritol tetra(mercaptoacetate); the moisture-resistant polyionic elastomer has a four-crosslinked network structure.

[0081] A preparation method of the moisture-resistant polyionic elastomer described in this embodiment, the method steps are as follows:

[0082] Step 1: Mix 21 mmol of ionic liquid monomer, 15 mmol of dithiol monomer, 4 mmol of crosslinking agent and photoinitiator evenly by magnetic stirring under ultraviolet light irradiation. While mixing, apply ultraviolet light irradiation for pre-polymerization. The magnetic stirring speed is 1000 rpm, and the stirring time is 2 min; the ultraviolet light irradiation time is 2 min, and the light power is 20 W to obtain a uniform polyionic elastomer prepolymer solution; the molar ratio X of the crosslinking agent is 0.05;

[0083] Among them, the ionic liquid monomer is prepared by the following method:

[0084] (1) Dissolve 8 g of imidazole and 35 g of 4-bromo-1-propene in 100 g of acetonitrile, add 12 g of sodium bicarbonate, heat and reflux in an oil bath at 90 °C for 14 h, filter the suspension after cooling and perform rotary evaporation to obtain a crude product;

[0085] (2) Dissolve the crude product obtained in step (1) with chloroform, add 5 g of anhydrous magnesium sulfate, filter to precipitate solids and then rotary evaporate the filtrate to obtain a viscous oily crude product [DAAIM]Br; add 8 mL of deionized water to dissolve soluble impurities in [DAAIM]Br, separate the organic phase, and then wash it successively with 3×3 mL of ethyl acetate, 3 mL of hexane and 3 mL of ether;

[0086] (3) Add 30 g of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) to the organic phase washed in step (2) to obtain a yellow oily precipitate; place the precipitate in a freeze dryer for drying to obtain the ionic liquid monomer;

[0087] Step 2: Place the release film and the frosted glass sheet parallel to each other, pad a substrate between them to form a sandwich structure with a predetermined gap. The substrate is placed in the relative end regions of the sandwich, and the substrate thickness is the gap size of the sandwich structure; then drop the prepolymer solution obtained in step 1 into the gap of the sandwich structure;

[0088] The release film is a glass sheet with a polytetrafluoroethylene (PTFE) film adhered to its surface; the substrate is a polydimethylsiloxane (PDMS) film, and the thickness of the polydimethylsiloxane (PDMS) film is 100 μm;

[0089] Step three, place the sandwich structure after the prepolymer liquid is dropped in step two under ultraviolet light for polymerization reaction until it is cured to obtain a transparent film, the ultraviolet light curing time is 20 minutes, and the curing power is 30W; peel off to obtain the moisture-resistant polyion elastomer for flexible pressure sensor.

[0090] The hydrophobicity of the moisture-resistant polyion elastomer described in Example 3 was tested, and the water contact angle (CA) of the material measured by a contact angle meter was 95°; the moisture-resistant polyion elastomer with a diameter of 9 mm and a thickness of 0.27 mm was soaked in deionized water, and the mass remained almost unchanged before and after soaking in water for 24 hours, indicating that the moisture-resistant polyion elastomer has hydrophobic and anti-swelling properties.

[0091] The conductivity of the moisture-resistant polyion elastomer described in Example 3 was tested using a broadband dielectric impedance spectrometer. The conductivity of the moisture-resistant polyion elastomer before soaking in water was 5.81×10 -6 S cm -1 , the conductivity after soaking in water for 1 hour is 1.21×10 -5 Scm -1 The conductivity changes by less than one order of magnitude before and after soaking in water, indicating that the conductive properties of the moisture-resistant polyion elastomer are less affected by the underwater environment.

[0092] The moisture-resistant polyion elastomer described in Example 3 was subjected to a tensile test using a universal testing machine. After being soaked in water for 6 hours, the Young's modulus decreased by 8.3% and the breaking strength decreased by 6.1%, indicating that the mechanical properties of the moisture-resistant polyion elastomer are less affected by the underwater environment and can maintain structural integrity when subjected to high humidity or underwater pressure.

[0093] Using a high-precision mechanical testing machine, the moisture-resistant polyion elastomer described in Example 3 was subjected to a 198 kPa compression test, and its initial strain and the strain after 10 hours were calculated through the stress-strain curve changing over time: after 10 hours, the strain (Strain) of the moisture-resistant polyion elastomer increased from 27.65% to 28.32%, and the creep (Creep) was 2.4%, with a small change, indicating that the moisture-resistant polyion elastomer described in Example 3 has the characteristic of low creep; under a cyclic tensile force of 198 kPa, the cycle hysteresis of 1000 cycles is approximately 6%, indicating that the moisture-resistant polyion elastomer described in Example 3 has the characteristic of low hysteresis.

[0094] Example 4

[0095] A flexible pressure sensor, the sensor comprising, from top to bottom, an upper packaging layer, an upper electrode, a sensing layer, a lower electrode and a lower packaging layer; wherein the sensing layer is the moisture-resistant polyion elastomer described in Example 3;

[0096] The thickness of the upper encapsulation layer PDMS film is 100 μm, and the thickness of the lower encapsulation layer PDMS film is 100 μm; in the upper electrode and lower electrode PI-Cu films, the thickness of the Cu layer is 18 μm and the thickness of the PI layer is 25 μm;

[0097] The upper sensing layer and the lower sensing layer are respectively and independently obtained by laser cutting to obtain customized patterns with a length of 2 cm, a width of 1 mm, and diameters of 5 mm and 3 mm at both ends; the upper encapsulation layer and the lower encapsulation layer are respectively and independently obtained by laser cutting to obtain customized sizes with a length of 6 cm and a width of 3 cm; in the flexible pressure sensor, the interfaces between adjacent layers are cleaned by a plasma machine to achieve stable bonding of each interface;

[0098] The laser cutting parameters are a power of 30 W, a cutting frequency of 20 times, and a laser frequency of 40%; the cleaning time of the plasma cleaner in a nitrogen atmosphere is 60 s;

[0099] Step 3: Assembly of the device. Align the upper encapsulation layer - upper electrode - polyionic elastomer material with microstructures - lower electrode - lower encapsulation layer in sequence and encapsulate them in a sandwich structure. Among them, the bonding between each interface is processed by a plasma machine to achieve stable bonding of each interface.

[0100] Using a universal testing machine and a high-precision capacitance meter, test the sensitivity of the flexible pressure sensor described in Example 4 under the conditions of not being soaked in water, being soaked in water for 1 hour, and being soaked in water for 6 hours. The sensitivity consistency of the flexible pressure sensor decreases by 2.31%, which is still relatively consistent, and the influence of soaking in water on the sensor sensitivity is very small.

[0101] The present invention includes but is not limited to the above embodiments. Any equivalent replacement or partial improvement carried out under the spirit and principle of the present invention will be regarded as within the protection scope of the present invention.

Claims

1. An anti-humidity polyionic elastomer for a flexible pressure sensor, characterized in that, The moisture-resistant polyionic elastomer is prepared by a photoinitiated polymerization reaction using an ionic liquid monomer, a dithiol monomer, and a crosslinking agent as raw materials; wherein, the ionic liquid monomer is 1,3-diallylimidazolium bis(trifluoromethylsulfonyl)imide ([DAAIM][TFSI]); The moisture-resistant polyionic elastomer has a tetra-crosslinked network structure.

2. The anti - wet polyionic elastomer for a flexible pressure sensor according to claim 1, wherein, The dithiol monomer is 1,8-octanedithiol; The crosslinking agent is pentaerythritol tetra(mercaptoacetate).

3. A preparation method of a moisture-resistant polyionic elastomer for a flexible pressure sensor as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: Under ultraviolet light irradiation conditions, the ionic liquid monomer, the dithiol monomer, the crosslinking agent, and the photoinitiator are mixed evenly, and a moisture-resistant polyionic elastomer with a tetra-crosslinked network structure is obtained through a photoinitiated polymerization reaction; The amount of substance of the ionic liquid monomer is a mmol, the amount of substance of the dithiol monomer is b mmol, and the amount of substance of the crosslinking agent is c mmol. a, b, and c satisfy the following equation: 2a = 2b + 4c; c / (a + b + c) = X; X is the molar ratio of the crosslinking agent, and X = 0.05 - 0.

2.

4. The preparation method of a moisture-resistant polyionic elastomer for a flexible pressure sensor according to claim 3, characterized in that, The specific steps of the preparation method are as follows: Step 1: Mechanically mix the ionic liquid monomer, the dithiol monomer, the crosslinking agent, and the photoinitiator evenly, and apply ultraviolet light irradiation while mixing to perform prepolymerization to obtain a homogeneous prepolymer solution of polyionic elastomer; Step 2: Place the release film and the frosted glass sheet parallel to each other, and insert a substrate between them to form a sandwich structure with a predetermined gap. The substrate is placed in the relative end regions of the sandwich, and the thickness of the substrate is the gap size of the sandwich structure; then drop the prepolymer solution obtained in Step 1 into the gap of the sandwich structure; Step 3: Place the sandwich structure with the prepolymer solution dropped in Step 2 under ultraviolet light irradiation to carry out a polymerization reaction until it is cured to obtain a transparent film, and peel it off to obtain the moisture-resistant polyionic elastomer for the flexible pressure sensor.

5. The preparation method of a moisture-resistant polyionic elastomer for a flexible pressure sensor according to claim 4, characterized in that, In Step 1, the ionic liquid monomer, the dithiol monomer, the crosslinking agent, and the photoinitiator are mixed evenly by magnetic stirring. The magnetic stirring speed is 500 rpm - 1000 rpm, and the stirring time is 2 min - 4 min; the ultraviolet light irradiation time is 2 min - 4 min, and the light power is 10 W - 20 W; In Step 2, the release film is a glass sheet with a polytetrafluoroethylene film adhered to the surface; the substrate is a polydimethylsiloxane film, and the thickness of the polydimethylsiloxane film is 100 μm - 200 μm; In Step 3, the ultraviolet light irradiation curing time is 10 min - 20 min, and the curing power is 30 W - 45 W.

6. The preparation method of a moisture-resistant polyionic elastomer for a flexible pressure sensor according to claim 3, characterized in that, The ionic liquid monomer is prepared by the following method: (1) Dissolve imidazole and 4-bromo-1-propene in acetonitrile, add sodium bicarbonate, heat and reflux at 75 °C - 90 °C for 10 h - 14 h, cool and filter the suspension, and then perform rotary evaporation to obtain a crude product; wherein, the mass ratio of imidazole, 4-bromo-1-propene, sodium bicarbonate, and acetonitrile is (5 - 8):(30 - 35):(9 - 12):(70 - 100); (2) Dissolve the crude product in chloroform, add anhydrous magnesium sulfate, filter to precipitate the solid, and then rotary evaporate the filtrate again to obtain the crude product [DAAIM]Br in a viscous oily state; add deionized water to dissolve the soluble impurities in [DAAIM]Br, separate the organic phase, and then wash it successively with ethyl acetate, hexane and ether; (3) Add an excess of lithium bis(trifluoromethanesulfonyl)imide to the washed organic phase to obtain a yellow oily precipitate; freeze-dry the precipitate to obtain the ionic liquid monomer.

7. A flexible pressure sensor, which sequentially includes an upper encapsulation layer, an upper electrode, a sensing layer, a lower electrode, and a lower encapsulation layer from top to bottom; characterized in that, The sensing layer material is the anti-humidity polyionic elastomer described in any one of claims 1 to 6.

8. The flexible pressure sensor according to claim 7, wherein Both the upper encapsulation layer and the lower encapsulation layer are PDMS thin films, and both the upper electrode and the lower electrode are PI-Cu thin films.

9. The flexible pressure sensor according to claim 8, wherein, The thickness of the upper encapsulation layer PDMS thin film is 100 μm to 200 μm, and the thickness of the lower encapsulation layer PDMS thin film is 100 μm to 200 μm; in the upper electrode PI-Cu thin film, the thickness of the Cu layer is 18 μm and the thickness of the PI layer is 25 μm; in the lower electrode PI-Cu thin film, the thickness of the Cu layer is 18 μm and the thickness of the PI layer is 25 μm.

10. A flexible pressure sensor according to any one of claims 7 to 9, characterized in that, The flexible pressure sensor is suitable for pressure detection in high humidity and underwater environments.

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