Ultra-sensitive capacitive flexible pressure sensor based on ionic migration confinement effect

Abstract

The invention relates to the field of sensors for realizing an ionic migration confinement effect by using silicon dioxide, and discloses an ultrasensitive capacitive flexible pressure sensor based on the ionic migration confinement effect, which comprises an upper electrode layer and a lower electrode layer, and a dielectric layer is arranged between the upper electrode layer and the lower electrode layer. The dielectric layer comprises an ion migration regulation and control layer and ion limiting composite layers arranged on the upper side and the lower side of the ion migration regulation and control layer; each ion confinement composite layer comprises an ion confinement composite film fixed on the electrode layer on the corresponding side, and a plurality of first micro bulges are arranged on the surface of one side, facing the ion migration regulation and control layer, of the ion confinement composite film; the ion migration regulation and control layer is a nano-channel fiber membrane containing an ion channel; a plurality of second micro bulges are arranged on the surfaces of the upper side and the lower side of the nano-channel fiber membrane; and the plurality of first micro bulges and the plurality of second micro bulges on the corresponding sides are mutually embedded to form an interlocking structure in a horizontal plane. The sensor provided by the invention has high sensitivity in a wide pressure range.

Description

Technical Field

[0001] The present invention relates to the field of sensors that utilize silica to achieve the ion migration confinement effect, and particularly to an ultrasensitive capacitive flexible pressure sensor based on the ion migration confinement effect. Background Art

[0002] Flexible capacitive pressure sensors have attracted much attention in the fields of robot touch, human-computer interaction, intelligent wearable devices, etc. due to their high sensitivity, high flexibility, low power consumption and other characteristics. By using a dielectric layer material with a smaller elastic modulus or microstructuring the dielectric layer material, a larger change in the electrode plate spacing can be generated under the same pressure, thereby improving the sensor sensitivity. Based on the above methods, scholars at home and abroad continue to explore and innovate, and develop various capacitive pressure sensors.

[0003] Patent application CN119147040A proposes a preparation method and application of a pressure and humidity integrated flexible sensor based on MXene, which is prepared by laser etching and magnetron sputtering. The pressure and humidity integrated flexible sensor has the characteristics of simultaneously responding to pressure and humidity signals and high sensitivity, greatly improving the accuracy of sensor detection.

[0004] Patent application CN118992967A proposes a flexible pressure sensor with dual microstructures and its preparation method. A flexible pressure sensor is obtained by assembling a conductive polymer composite material with dual microstructures and interdigital electrodes. The prepared flexible pressure sensor has both porous and surface micro-protrusion dual microstructures, and at the same time has a wide pressure response range, high sensitivity, and low detection limit, and can realize the detection of small object pressure, the acquisition of human biological signals, the transmission of Morse code, and the detection and recognition of sitting postures.

[0005] In the academic paper "Graphene oxide as high-performance dielectric materials for capacitive pressure sensors" published by the Shu Wan team in the journal "Carbon", by using graphene oxide foam with a low elastic modulus as the dielectric layer and utilizing its high relative dielectric constant and excellent elastic properties, a capacitive pressure sensor with high sensitivity, fast response time and low detection limit is realized.

[0006] In the academic paper "Rough-Surface-Enabled Capacitive Pressure Sensors with 3D Touch Capability" published by the Kilsoo Lee team in the journal Small, a high-performance paper-based capacitive pressure sensor was constructed by leveraging the natural design of the paper surface roughness and combining it with a diluted PDMS film. This sensor utilizes the rough surface of the paper to form microstructure-like air gaps, significantly improving the pressure sensitivity, while also featuring a fast response time, a low detection limit, and excellent bending stability.

[0007] In the academic paper "Transparent, Flexible, Conformal Capacitive Pressure Sensors with Nanoparticles" published by the Hyeohn Kim team in the journal Small, a capacitive pressure sensor with high transparency and high sensitivity was achieved by sandwiching a dielectric layer containing silica nanoparticles between transparent conductive polymers and utilizing the aggregation characteristics of the nanoparticles to form a microstructure surface.

[0008] However, capacitive pressure sensors usually exhibit low sensitivity due to the limited capacitance and the low compressibility of dielectric materials. Recently, a new class of pressure sensing mechanisms based on the electric double layer (EDL) effect has been developed. These sensors have high sensitivity while retaining the advantages of traditional capacitive sensors. Ionic gels or hydrogels, as the dielectric layer, have good ionic conductivity, and combined with the double layer theory, ultra-high sensitivity ionoelectric pressure sensors can be realized.

[0009] Patent application CN118687722A proposes an ion-electronic pressure sensor with a wide working range and its preparation method. By promoting the densification of the polymer network during the dehydration process to facilitate the formation of a dense hydrogen bond network in PVA, the constructed pressure sensor has high sensitivity, a wide working range, good responsiveness, resolution, and stability.

[0010] Patent application CN118794575A provides an ionoelectric flexible pressure sensor, a pressure detection device, and a method. The sensor includes: a first electrode layer, an ion layer, and a second electrode layer that are sequentially stacked and distributed. The side of the second electrode layer close to the ion layer is an elastic hemispherical protrusion array structure. By setting hemispherical protrusions with different radii, when the external force applied to the sensor changes, the contact area between the ion layer and the second electrode layer changes significantly, thereby enabling the sensor to have a high pressure detection sensitivity.

[0011] In the academic paper "Normal-Direction Graded Hemispheres for Ionic Flexible Sensors with a Record-High Linearity in a Wide Working Range" published by the Shaowei Wu team in the journal ACS Applied Materials & Interfaces, by stratifying the introduced spheres along the normal direction, the surface of the large hemisphere was effectively divided, improving the linearity of the sensor and achieving high sensitivity in a relatively wide response range.

[0012] In the academic paper "Biomimetic nanofiber-iongel composites for flexible pressure sensors with broad range and ultra-high sensitivity" published by the Xin Gou team in the journal Nano Energy, inspired by the tactile sensing mechanism and hierarchical structure of human skin, a nanofiber-agar composite with internal graded stiffness characteristics and surface semi-embedded microstructures was designed by applying electrospinning and droplet injection methods. The sensor made of this material has ultra-high sensitivity, a wide pressure range, and strong stability.

[0013] In summary, relevant researchers have carried out a lot of research work on triboelectric pressure sensors. These studies have improved the sensitivity characteristics of the sensors by improving the micro-nano structure to increase the EDL capacitance and the interfacial contact area, and improved the mechanical properties through material modification. However, there are still the following deficiencies: 1. The triboelectric pressure sensors reported currently usually use the microstructures on the surface of the dielectric layer to improve the sensitivity of the sensor and broaden the pressure measurement range. However, due to the lack of effective control of free-moving ions under the electric field, the ions will quickly migrate to the interface between the dielectric layer and the electrode, forming a double-layer structure. This rapid ion aggregation will lead to too high an ion concentration at the double-layer interface, resulting in too high an initial capacitance, which limits the improvement of the sensor sensitivity.

[0014] 2. The triboelectric pressure sensors reported currently convert the pressure change into an electrical signal by the change in the capacitance caused by the change in the contact area between the electrode and the dielectric layer when pressure is applied. When pressure is applied, the contact area between the electrode-dielectric layer varies with different microstructures. The larger this contact area change is, the larger the final capacitance Cp will be, thus affecting the sensor sensitivity. However, there is a problem that the final contact area is not large enough, which limits the improvement of the sensor sensitivity.

[0015] 3. The reported current off - electro pressure sensors transport signals by introducing ions as charge carriers. However, usually only anions or cations are introduced, so when forming the electric double layer, usually only the quantity of one kind of ion changes, which makes the capacitance change very little, ultimately limiting the improvement of the sensor sensitivity.

[0016] 4. The reported current off - electro pressure sensors usually introduce microstructures to optimize the change in contact area when an external force is applied. The microstructures are mostly single microstructures, which deform significantly under small pressure and the contact area quickly reaches saturation as the pressure increases, limiting the improvement of the linear working range of the sensor.

[0017] 5. The reported current off - electro pressure sensors' designs mainly rely on adopting disordered diffusion mechanisms or random pore structures. This design makes the ion flow path complex and inefficient, reducing the effective ion diffusion coefficient, resulting in a lower conversion rate from pressure change signals to electrical signals and reducing the sensor's response speed.

[0018] 6. The reported current off - electro pressure sensors usually introduce ion channels by using nanomaterials to improve the sensor's response speed. However, under long - term immersion, there is a problem that the ionic liquid penetrates into the interior of the nanomaterials, damaging their pore structure or layered structure, resulting in the collapse of the ion channels and a decrease in material strength, affecting the reliability and long - term stability of the sensor.

[0019] 7. The reported current off - electro pressure sensors improve conductivity by introducing ionic liquids. However, most ionic liquids have high viscosities, resulting in poor fluidity of the ionic liquids, and it is difficult to precisely control the film thickness and structure through traditional thin - film preparation processes (such as spin - coating, spraying).

[0020] 8. The reported current off - electro pressure sensors introduce ion gels as dielectric layers. However, ion gels usually use non - biodegradable organic polymer materials, and their degradation treatment process requires high - temperature treatment or the introduction of chemical reagents such as strong acids and strong bases, and it is easy to produce harmful substances, affecting the natural environment. Summary of the Invention

[0021] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an ultrasensitive capacitive flexible pressure sensor based on the ion migration confinement effect, in order to effectively improve the sensitivity of such capacitive flexible pressure sensors in a wide pressure range.

[0022] The purpose of the present invention is achieved by the following technical solutions: The present invention first provides a super-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect, which includes upper and lower electrode layers, and a dielectric layer is provided between the upper and lower electrode layers. The dielectric layer includes an ion migration regulation layer and ion confinement composite layers disposed on the upper and lower sides of the ion migration regulation layer. Each ion confinement composite layer includes an ion confinement composite thin film fixed on the corresponding side electrode layer. The ion confinement composite thin film is provided with first protruding microstructures on the surface facing the ion migration regulation layer. The first protruding microstructures include a plurality of first micro-protrusions. The ion migration regulation layer is a nano-channel fiber membrane containing ion channels. Second protruding microstructures are provided on the upper and lower surfaces of the nano-channel fiber membrane. The second protruding microstructures include a plurality of second micro-protrusions. The plurality of first micro-protrusions of the ion confinement composite layer and the plurality of second micro-protrusions on the corresponding side of the ion migration regulation layer are mutually interlocked to form an interlocking structure in the horizontal plane.

[0023] Further, the plurality of first micro-protrusions include a number of first large protrusions and a number of first small protrusions. The plurality of first micro-protrusions form a number of horizontal rows and a number of vertical rows that intersect horizontally and vertically on the surface of the ion confinement composite thin film. In each horizontal row and each vertical row, the first large protrusions and the first small protrusions are arranged at intervals in sequence. Four adjacent first micro-protrusions enclose an embedding gap; the plurality of second micro-protrusions on one side of the nano-channel fiber membrane are inserted one by one into a number of embedding gaps on the surface of the ion confinement composite layer on the corresponding side.

[0024] Further, the composition of each raw material for preparing the ion confinement composite thin film by mass percentage is as follows: tetraethyl orthosilicate TEOS 6-8%, ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide EMIM TFSI 5-7%, thermoplastic polyurethane elastomer TPU 10-15%, deionized water 3-5%, and the balance is N,N-dimethylformamide DMF.

[0025] Further, the composition of each raw material for preparing the nano-channel fiber membrane containing ion channels by mass percentage is as follows: graphene oxide GO 1-3%, nanocellulose CNFs 0.2-0.6%, deionized water 13-18%, KOH 1-5%, and the balance is polyvinyl alcohol PVA.

[0026] Further, the first micro-protrusion is composed of a frustum section and a spherical crown section that vertically extend along the surface of the ion confinement composite film and are coaxial. The size range of the first large protrusion is as follows: the radius of the spherical crown section is 40 μm to 60 μm, the height of the spherical crown section is 30 μm to 50 μm, the end face radius of the large end of the frustum section is 60 μm to 80 μm, and the height of the frustum section is 60 μm to 80 μm. The size range of the first small protrusion is as follows: the radius of the spherical crown section is 20 μm to 40 μm, the height of the spherical crown section is 15 μm to 20 μm, the end face radius of the large end of the frustum section is 40 μm to 60 μm, and the height of the frustum section is 40 μm to 60 μm; in the horizontal rows and vertical rows formed by multiple first micro-protrusions, the axial center distance between two adjacent first micro-protrusions is equal and is 80 μm to 160 μm.

[0027] Further, the second micro-protrusion is composed of a frustum section and a spherical crown section that vertically extend along the surface of the nanochannel fiber membrane and are coaxial. The size range of the second micro-protrusion is as follows: the radius of the spherical crown section is 20 μm to 40 μm, the height of the spherical crown section is 40 μm to 60 μm, the end face radius of the large end of the frustum section is 40 μm to 60 μm, and the height of the frustum section is 40 μm to 60 μm; in the horizontal rows and vertical rows formed by multiple second micro-protrusions, the axial center distance between two adjacent second micro-protrusions is equal and is 80 μm to 160 μm.

[0028] Further, the thickness of the ion confinement composite film is 20 μm to 30 μm, and the thickness of the nanochannel fiber membrane containing ion channels is 25 μm to 40 μm.

[0029] Further, the upper and lower electrode layers and the periphery of the dielectric layer are encapsulated by a PDMS flexible encapsulation layer.

[0030] The present invention also provides a preparation method of the ultra-sensitive capacitive flexible pressure sensor, including the following steps: Step 1, prepare an ion confinement composite layer Under the condition of heating at 40 to 60 °C: Add TEOS to deionized water, stir for 10 to 20 minutes to promote the hydrolysis reaction of TEOS, then dropwise add EMIM TFSI ionic liquid and continue to stir for 15 to 20 minutes to obtain a composite gel material; Subsequently, dropwise add hydrochloric acid to the composite gel material and continuously stir for 30 to 45 minutes to obtain an IL-SiO2 gel (where IL represents ionic liquid); Add TPU beads to DMF and continuously stir at 70 to 80 °C for 3 to 4 hours to obtain a TPU gel; Then dropwise add the IL-SiO2 gel to the TPU gel at 70 to 80 °C, and then continuously stir at 40 to 60 °C for 4 to 5 hours to obtain an IL-SiO2-TPU composite solution; Uniformly fill the IL-SiO2-TPU composite solution in the mold used for fabricating the ion confinement composite layer; spin-coat the IL-SiO2-TPU composite solution on the surface of the electrode layer, then place the electrode layer with the solution-spun side facing down above the mold, and demold after drying at room temperature, thus forming an ion confinement composite layer on the surface of the electrode layer; Repeat the fabrication to obtain two electrode layers with ion confinement composite layers formed thereon, which are used as the upper and lower electrode layers respectively.

[0031] Step 2: Prepare the ion migration regulation layer Add GO nanosheets into deionized water and disperse them evenly by ultrasonic treatment, then add the aqueous dispersion of CNFs and stir evenly at room temperature to obtain a composite dispersion; add PVA into the composite dispersion, stir at 90 - 100 °C until PVA is fully dissolved, then freeze and thaw, and add KOH solution and stir at 50 - 60 °C for 15 - 20 minutes to obtain the CNFs-GO / PVA-KOH composite solution; Uniformly fill the CNFs-GO / PVA-KOH composite solution in the mold for fabricating the ion migration regulation layer, then dry and demold to obtain the ion migration regulation layer.

[0032] Step 3: Prepare the PDMS flexible encapsulation film After mixing PDMS and the curing agent to form a PDMS solution, pour it on the surface of an acrylic plate, then cure it at 50 - 60 °C for 15 - 20 minutes in a vacuum drying oven, and peel to obtain the PDMS flexible encapsulation film; repeat the preparation to obtain two layers of PDMS flexible encapsulation films.

[0033] Step 4: Sensor assembly Stack the lower electrode layer with the ion confinement composite layer formed thereon, the ion migration regulation layer, and the upper electrode layer with the ion confinement composite layer formed thereon in sequence on one layer of the PDMS flexible encapsulation film, and then place another layer of the PDMS flexible encapsulation film; then use a coating rod to fill the sides of the two PDMS films with the PDMS solution and air-dry it, so as to form a complete PDMS flexible encapsulation layer around the upper and lower electrode layers and the dielectric layer, thus completing the assembly of the sensor.

[0034] Compared with the prior art, the beneficial effects of the present invention are reflected in the following aspects: 1. A super-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect provided by the present invention has a dielectric layer designed as a sandwich-like structure composed of two layers of ion confinement composite films and a nano-channel fiber membrane with ion channels in the middle. The ion confinement composite film contains ionic liquids participating in conduction, and the nano-channel fiber membrane contains ion channels, so that the ionic liquids are separated from the nano-conductive channels, avoiding problems such as the collapse of ion channels and the decrease of material strength caused by long-term immersion, and improving the long-term reliability and stability of the sensor. At the same time, a plurality of first micro-protrusions are provided on the surface of the ion confinement composite film, and a plurality of second micro-protrusions are provided on the upper and lower surfaces of the nano-channel fiber membrane. The two types of micro-protrusions are mutually embedded to form an interlocking structure in the horizontal plane. This structure setting has a higher pressure sensing range, a larger normalized contact area and capacitance change compared with a single structure, making the sensor have both high sensitivity and high linearity. The specific analysis is as follows: On the one hand, it increases the compressibility of the dielectric layer, avoiding the rapid contact between the two layers of ion confinement composite films and further enhancing the compressibility of the dielectric layer. The combined effect of the two broadens the linear working range of the sensor. On the other hand, it provides a larger contact area change range for the dielectric layer. During the contact process between the electrode layer and the dielectric layer, more ion channels can be provided, allowing many anions and cations to conduct through the membrane barrier to form an EDL. The ion confinement composite film increases the ionic conductivity while increasing the final capacitance Cp, thereby increasing the sensitivity of the sensor. On the other hand, the two types of micro-protrusions on the surfaces of the ion confinement composite film and the nano-channel fiber membrane are mutually embedded to form an interlocking structure in the horizontal plane, which can play a role in locking each other between adjacent membranes in the horizontal plane. In this interlocking structure, the contact area between several first large protrusions on the surface of the ion confinement composite film and the second micro-protrusions on the corresponding side surface of the nano-channel fiber membrane shows a significant increase under light load; under medium load, the first large protrusions are continuously compressed and the capacitance continuously increases; under heavy load, the change in the contact area of the first large protrusions gradually reaches saturation, and the contact area between several first small protrusions on the surface of the ion confinement composite film and the second micro-protrusions on the corresponding side surface of the nano-channel fiber membrane changes, improving the linear working range of the sensor.

[0035] 2. A super-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect provided by the present invention has specific raw material settings for the ion confinement composite film and the nano-channel fiber membrane with ion channels. The specific analysis is as follows: On the one hand, an ion-restricted composite film is prepared by the sol-gel method: using TEOS as the silicon source and the ionic liquid EMIM TFSI as the functional component, adding hydrochloric acid to promote the hydrolysis and condensation polymerization reaction of TEOS, generating a silanol intermediate and polymerizing to form a silica gel network, and then forming an IL-SiO2 gel through the interaction between ionic substances and the silica network. By introducing the ionic liquid, under the action of pressure and electric field applied to the sensor, the anions and cations in it migrate to the anode and cathode respectively to form an electric double layer. This strategy of synergistic migration of anions and cations effectively improves the problem of limited sensitivity caused by only single-ion conduction, enabling the sensor to achieve higher sensitivity. At the same time, using silica as the ion-restricted matrix to achieve the ion migration confinement effect: the anion [TFSI － in the ionic liquid interacts with the silanol groups (Si-OH) on the silica surface through hydrogen bonds and is surrounded by [EMIM ＋ cations. The [EMIM ＋ cations are driven by the Coulomb coupling force of the [TFSI － anions and the π-π stacking interaction of the imidazole ring, so that the ion pair is restricted on the surface of the silica microstructure through hydrogen bond-Coulomb interaction. This confinement effect enables the ions to remain on the surface of the silica microstructure without external force when a voltage is applied, and almost no free ions participate in the formation of capacitance, achieving a low initial capacitance, making the capacitance change more significant under pressure, thus improving the sensitivity of the pressure sensor. Further, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide is used as the ionic liquid, which has a low viscosity. This low viscosity not only enables it to better fill and distribute when combined with the silica microstructure, thereby forming a uniform ion conduction network, but also enables the preparation of a good structure through the spin-coating process.

[0036] On the other hand, a composite of GO and CNFs is used to prepare a nanochannel fiber membrane with ion channels through freezing and thawing: by incorporating GO into the nanochannel fiber membrane, a two-dimensional layered nanochannel is formed to transport ions. Under the pressure-free state, the ion transport in the two-dimensional layered nanochannel is weak to reduce the energy loss of the device in the standby mode. Under the regulation of external pressure, the size of the two-dimensional layered nanochannel is further reduced, and ions can rapidly transport in the confined nanochannel. This design optimizes the ion flow path, improves the ion mobility, and enables the sensor to have a wide linear range and a fast response speed. Further, due to the hydrogen bond interaction between CNFs and GO, the bonding between GO nanosheets is enhanced, and X-ray diffraction analysis shows that after adding CNFs to GO, the characteristic X-ray diffraction peaks shift to the left. Therefore, the addition of CNFs increases the layer spacing of GO nanosheets, significantly increases the thickness of the composite membrane, further improves the compressibility of the membrane, and doping GO in the nanochannel fiber membrane forms an ion channel, improves the ion mobility, and enables the sensor to have a wide linear range and a fast response speed.

[0037] On the other hand, materials such as PVA, TPU, and nano-cellulose used in the design of the flexible pressure sensor of the present invention can be naturally degraded or simply and greenly degraded, and have good biocompatibility and environmental friendliness. Brief Description of the Drawings

[0038] Figure 1 is a longitudinal sectional view of the capacitive flexible pressure sensor of the present invention.

[0039] Figure 2 is a top view of the lower ion confinement composite layer of the present invention.

[0040] Figure 3 is a top view of the ion migration regulation layer of the present invention.

[0041] Figure 4 is a partial structural schematic diagram of the first mold used to fabricate the ion confinement composite layer of the present invention.

[0042] Figure 5 is a partial structural schematic diagram of the lower mold of the second mold used to fabricate the ion migration regulation layer of the present invention.

[0043] Figure 6 is a schematic diagram of the reaction mechanism for fabricating the ion confinement composite layer of the present invention.

[0044] Figure 7 is the surface of the silica microstructure in the ion confinement composite film of the present invention for [EMIM ＋ and [TFSI － ion pair migration confinement effect schematic diagram.

[0045] Figure 8Frequency response of the ultrasensitive capacitive flexible pressure sensor based on ion migration confinement effect fabricated in Example 1 at 60 kPa.

[0046] Figure 9 It is the sensitivity comparison curve of the presence or absence of silica structure in the ion confinement composite layer of the present invention.

[0047] Figure 10 Pressure-capacitance change rate curve of the ultrasensitive capacitive flexible pressure sensor based on ion migration confinement effect fabricated in Example 1 in the pressure range of 0 - 650 kPa.

[0048] Figure 11 Dynamic loading-unloading cycle test of the ultrasensitive capacitive flexible pressure sensor based on ion migration confinement effect fabricated in Example 1 from 10 to 600 kPa.

[0049] Figure 12 Response and recovery time of the ultrasensitive capacitive flexible pressure sensor based on ion migration confinement effect fabricated in Example 1 at 60 kPa pressure.

[0050] Figure 13 Cyclic stability test of the ultrasensitive capacitive flexible pressure sensor based on ion migration confinement effect fabricated in Example 1 at 300 kPa pressure.

[0051] Reference numerals in the figure: 1 upper electrode layer; 2 lower electrode layer; 3 ion migration regulation layer; 4 upper ion confinement composite layer; 5 lower ion confinement composite layer; 6 first large protrusion; 7 first small protrusion; 8 frustum section; 9 spherical crown section; 10 second micro protrusion; 11 PDMS flexible encapsulation layer; 12 embedded void; 13 first mold; 14 lower mold. Specific embodiments

[0052] The following details the embodiments of the present invention. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0053] See Figures 1 to 3, this embodiment discloses a super-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect, which includes an upper electrode layer 1 and a lower electrode layer 2 arranged up and down. Both the upper and lower electrode layers use copper foil electrodes. A dielectric layer is provided between the upper and lower electrode layers. The dielectric layer includes an ion migration regulation layer 3 and ion confinement composite layers disposed on both the upper and lower sides of the ion migration regulation layer 3. The two ion confinement composite layers are respectively an upper ion confinement composite layer 4 and a lower ion confinement composite layer 5. The two ion confinement composite layers are symmetrically distributed up and down on both sides of the ion migration regulation layer 3. The upper and lower electrode layers and the periphery of the dielectric layer are encapsulated by a PDMS flexible encapsulation layer 11.

[0054] Each ion confinement composite layer includes an ion confinement composite thin film fixed on the corresponding side electrode layer. Among them, the ion confinement composite thin film is deposited on the surface of the electrode layer. The ion confinement composite thin film is provided with a first protruding microstructure on the surface facing the ion migration regulation layer 3. The first protruding microstructure includes a plurality of first micro-protrusions. The ion migration regulation layer 3 is a nano-channel fiber membrane containing ion channels. Second protruding microstructures are provided on both the upper and lower surfaces of the nano-channel fiber membrane. The second protruding microstructure includes a plurality of second micro-protrusions 10. The plurality of first micro-protrusions of the ion confinement composite layer and the plurality of second micro-protrusions 10 on the corresponding side of the ion migration regulation layer 3 are mutually interlocked to form an interlocking structure in the horizontal plane.

[0055] In the first protruding microstructure, the plurality of first micro-protrusions include a number of first large protrusions 6 and a number of first small protrusions 7. The plurality of first micro-protrusions form a number of horizontal rows and a number of vertical rows that cross horizontally and vertically on the surface of the ion confinement composite thin film. In each horizontal row and each vertical row, the first large protrusions 6 and the first small protrusions 7 are arranged at intervals in turn. Adjacent four first micro-protrusions enclose an embedding gap 12; in the second protruding microstructure on one side of the nano-channel fiber membrane, the plurality of second micro-protrusions 10 are inserted one by one into a number of embedding gaps 12 on the surface of the corresponding side ion confinement composite layer.

[0056] The thickness of the ion confinement composite thin film is 20μm - 30μm. The first micro-protrusion is composed of a frustum section 8 and a spherical crown section 9 that extend vertically along the surface of the ion confinement composite thin film and are coaxial. The size range of the first large protrusion 6 is: the radius of the spherical crown section 9 is 40μm - 60μm, the height of the spherical crown section 9 is 30μm - 50μm, the end face radius of the large end of the frustum section 8 is 60μm - 80μm, and the height of the frustum section 8 is 60μm - 80μm; the size range of the first small protrusion 7 is: the radius of the spherical crown section 9 is 20μm - 40μm, the height of the spherical crown section 9 is 15μm - 20μm, the end face radius of the large end of the frustum section 8 is 40μm - 60μm, and the height of the frustum section 8 is 40μm - 60μm; in the horizontal rows and vertical rows formed by the plurality of first micro-protrusions, the axial center distance between adjacent two first micro-protrusions is equal and is 80μm - 160μm.

[0057] The thickness of the nanochannel fiber membrane is 25 μm to 40 μm. The second microprotrusion 10 is composed of a frustum section 8 and a spherical crown section 9 that vertically extend from the surface of the nanochannel fiber membrane and are coaxial; the size range of the second microprotrusion 10 is: the radius of the spherical crown section 9 is 20 μm to 40 μm, the height of the spherical crown section 9 is 40 μm to 60 μm, the end face radius of the large end of the frustum section 8 is 40 μm to 60 μm, and the height of the frustum section 8 is 40 μm to 60 μm; in the horizontal rows and vertical rows formed by multiple second microprotrusions 10, the axial distance between adjacent two second microprotrusions 10 is equal and is 80 μm to 160 μm.

[0058] See Figure 4 , the cavity shape of the first mold 13 used to fabricate the ion confinement composite layer coincides with the shape of the ion confinement composite film with the first convex microstructure on the surface. See Figure 5 , the second mold used to fabricate the ion migration regulation layer 3 includes an upper mold and a lower mold 14 that are symmetric up and down, and the cavity of the second mold after the upper and lower molds are closed coincides with the overall shape of the nanochannel fiber membrane with the second convex microstructure on the upper and lower surfaces.

[0059] Example 1 This example provides a super-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect with specific dimensions, and its preparation raw materials and preparation steps are as follows: Preparation raw materials: The used EMIM TFSI was purchased from Anhui Cool Biological Engineering Co., Ltd. (AR, 98%). The used TEOS was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (GC, 99%). The used hydrochloric acid was purchased from Zhejiang Mingyuan Chemical Instrument Co., Ltd. (AR, mass concentration of 5%). The used TPU was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (AR, 99%). The used DMF was purchased from Sinopharm Chemical Reagent Co., Ltd. (AR, 99.5%). The used graphene oxide nanosheets were purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd. (purity 99%, sheet diameter 500 nm to 5 μm, thickness 0.8 to 1.2 nm). The aqueous dispersion of the used nanocellulose was purchased from Songhu Shenjian Technology (Dongguan) Co., Ltd. (mass concentration of 2%, diameter 1 to 50 nm, length 1 to 30 nm). The used polyvinyl alcohol was purchased from Shanghai Macklin Biochemical Co., Ltd. (type 1797, degree of alcoholysis 98.0 to 99.0 mol%, Mw~195000). The used KOH aqueous solution was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (mass concentration of 5%). The used PDMS was purchased from Shenzhen Songsen New Materials Technology Co., Ltd.

[0060] Preparation steps: Step 1, prepare the ion confinement composite layer Under the condition of heating at 40 °C: 0.5 g of TEOS was added to 0.25 g of deionized water, and continuously stirred for 10 minutes to promote the hydrolysis reaction of TEOS. Then, 0.4 g of EMIM TFSI ionic liquid was added dropwise, and the mixture was continuously stirred for 15 minutes while maintaining the temperature to ensure the full combination of the ionic liquid and the silica precursor, thus preparing a composite gel material. Subsequently, 0.05 g of hydrochloric acid was added dropwise to the composite gel material, and continuously stirred for 30 minutes to promote the formation of silica, obtaining an IL-SiO2 gel. 1 g of TPU beads were added to 5 g of DMF, and continuously stirred at 80 °C for 3 hours to ensure the full dissolution of TPU, obtaining a TPU gel. The IL-SiO2 gel was added dropwise to the TPU gel at 80 °C, and then continuously stirred at 40 °C for 4 hours to finally obtain a uniform and stable IL-SiO2-TPU composite solution, and its reaction mechanism is as Figure 6 shown.

[0061] The first mold 13 used for fabricating the ion confinement composite layer was uniformly filled with the IL-SiO2-TPU composite solution; the IL-SiO2-TPU composite solution was spin-coated on the surface of the copper foil serving as the electrode layer at a spin-coating speed of 300 rpm for 30 s. Then, the copper foil was placed with the solution-spin-coated side facing down above the first mold 13, and demolded after drying at room temperature for 36 hours, thus forming an ion confinement composite layer on the surface of the electrode layer; two copper foils formed with ion confinement composite layers were fabricated repeatedly and used as the upper and lower electrode layers 2 respectively. Specifically, in the ion confinement composite layer obtained in this embodiment, the thickness of the ion confinement composite film is 30 μm. The size of the first large protrusion 6 is: the radius of the spherical cap section 9 is 60 μm, the height of the spherical cap section 9 is 50 μm, the end face radius of the large end of the frustum section 8 is 80 μm, and the height of the frustum section 8 is 80 μm; the size range of the first small protrusion 7 is: the radius of the spherical cap section 9 is 40 μm, the height of the spherical cap section 9 is 20 μm, the end face radius of the large end of the frustum section 8 is 60 μm, and the height of the frustum section 8 is 60 μm; in the horizontal and vertical rows formed by multiple first micro-protrusions, the axial center distance between adjacent two first micro-protrusions is equal and is 120 μm.

[0062] Step 2: Prepare the ion migration regulation layer 3 0.2 g of GO nanosheets were weighed and added to 2 g of deionized water, ultrasonically dispersed for 30 minutes, then 2 g of an aqueous dispersion of CNFs with a mass concentration of 2% was added and stirred evenly at room temperature to obtain a composite dispersion. 6 g of PVA was added to the composite dispersion, and stirred at 98 °C for 2.5 hours to fully dissolve PVA. After being frozen at -24 °C for 12 hours and thawed at room temperature, 3 g of an aqueous KOH solution with a mass fraction of 5% was added and stirred at 60 °C for 20 minutes to obtain a CNFs-GO / PVA-KOH composite solution; The upper and lower dies 14 of the second mold for fabricating the ion migration regulation layer 3 are uniformly filled with the CNFs-GO / PVA-KOH composite solution, and then the upper and lower dies 14 are placed in a vacuum drying oven for 10 minutes to remove air bubbles. The uncured upper and lower dies 14 are aligned and buckled, and pressed to fit more tightly. Then, the second mold is placed in a drying oven and dried at 50 °C for 10 hours and then demolded to obtain the ion migration regulation layer 3. Specifically, in the ion migration regulation layer 3 prepared in this embodiment: the thickness of the nanochannel fiber membrane is 30 μm. The dimensions of the second micro-protrusions 10 are: the radius of the spherical crown section 9 is 40 μm, the height of the spherical crown section 9 is 60 μm, the end face radius of the large end of the frustum section 8 is 60 μm, and the height of the frustum section 8 is 60 μm; in the horizontal and vertical rows formed by multiple second micro-protrusions 10, the center distance between adjacent two second micro-protrusions 10 is equal and is 120 μm.

[0063] Step 3: Prepare the PDMS flexible encapsulation film After mixing 5 g of PDMS and 0.5 g of curing agent to form a PDMS solution, it is poured on the surface of an acrylic plate, and then cured at 60 °C for 15 minutes in a vacuum drying oven, and peeled off to obtain the PDMS flexible encapsulation film; the preparation is repeated to obtain two layers of PDMS flexible encapsulation films and cut into a size of 1 cm × 1 cm.

[0064] Step 4: Sensor assembly After sequentially stacking the lower electrode layer 2 with an ion confinement composite layer, the ion migration regulation layer 3, and the upper electrode layer 1 with an ion confinement composite layer on one layer of PDMS flexible encapsulation film, another layer of PDMS flexible encapsulation film is placed; then a coating rod is used to fill the sides of the two PDMS films with PDMS solution and air-dried, so that a complete PDMS flexible encapsulation layer 11 is formed around the upper and lower electrode layers and the dielectric layer, and the assembly of the sensor is completed.

[0065] Figure 7 For the schematic diagram of the interaction involved in the migration confinement effect of [EMIM ＋ and [TFSI － ion pairs on the surface of the silica microstructure in the ion confinement composite film. In the figure, for [EMIM ＋ and [TFSI － , the molecular structures, as well as the silanol groups of silica and the -CF3 groups in TFSI − ions form hydrogen bond interactions, and there are also Coulomb interactions between [EMIM ＋ and [TFSI － , and finally an ion migration confinement effect with silica as the confinement structure is formed.

[0066] Figure 8The frequency response of the ultrasensitive capacitive flexible pressure sensor based on the ion migration confinement effect fabricated in this embodiment at 60 kPa. In the figure, the ordinate capacitance change rate is the ratio of the capacitance change under pressure to the initial capacitance. At pressure loading frequencies of 1 Hz, 5 Hz, and 10 Hz, the sensor achieved stable capacitance output, indicating that the sensor has excellent frequency response performance.

[0067] To verify the restriction effect of silica on ions, the IL-SiO2-TPU composite solution prepared in Step 1 was coated on an acrylic plate and dried into a film, and then the sensitivity under pressure was tested. At the same time, a TPU solution containing only EMIMTFSI ionic liquid without SiO2 was formed into a film in the same way as a comparison. Among them, the preparation method of the TPU solution containing only EMIM TFSI ionic liquid without SiO2 is as follows: 1 gram of TPU beads was added to 5 grams of DMF, and continuously stirred at 80 °C for 3 hours to ensure the full dissolution of TPU, obtaining a TPU gel. 0.4 grams of EMIM TFSI ionic liquid was added to the TPU gel at 80 °C, and then continuously stirred at 40 °C for 4 hours.

[0068] Figure 9 It is the sensitivity comparison curve of the ion confinement composite layer with and without the silica structure. It can be seen that at the same amount of ionic liquid added, without the silica confinement structure, the maximum sensitivity is only 1.2 kPa -1 After introducing the silica confinement structure, the sensitivity reaches 18.7 kPa -1 , which is increased by about 18 times.

[0069] Figure 10 It is the pressure-capacitance change rate curve of the ultrasensitive capacitive flexible pressure sensor based on the ion migration confinement effect fabricated in this embodiment in the pressure range of 0 - 650 kPa. The obtained sensor was fixed on the measurement platform, and a stress of 0 - 650 KPa was applied to the sensor through the pulling and pressing machine ZQ990B, and the sensing capacitance of the sensor was measured using a precision LCR digital bridge TH2829. The sensitivity coefficient of this sensor is 66.7 kPa at 0 - 120 kPa -1 ; in the range of 120 - 400 kPa, the compressibility of the ion migration regulation layer 3 gradually increases, and the deformation of the first large protrusion 6 on the surface microstructure of the ion confinement composite layer gradually saturates. At this time, the sensitivity coefficient is 19.5 kPa -1 ; in the range of 400 - 650 kPa, the compressibility of the ion migration regulation layer 3 reaches the maximum, and the deformation of the first small protrusion 7 on the surface microstructure of the ion confinement composite layer gradually saturates. At this time, the sensitivity coefficient is 8.9 kPa -1 . As the pressure increases, the sensitivity gradually decreases.

[0070] Figure 11 The ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect manufactured for this embodiment was subjected to a dynamic loading-unloading cycle test from 10 to 600 kPa, and the pressure changes within this range had a high degree of recognition.

[0071] In order to evaluate the dynamic response speed of the sensor, a 600 g weight (equivalent pressure ~60 kPa) was gently placed on the flexible pressure sensor prepared in this example and then quickly released. Figure 12 The response and recovery time of the sensor under a pressure of 60 kPa. The results show that the response time and recovery time are 80 ms and 79 ms respectively.

[0072] Figure 13 The ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect produced in this embodiment was subjected to a cyclic stability test under a pressure of 60 kPa. After 1000 cycles of testing, the sensor still maintained a stable capacitive response, indicating that the sensor has good cyclic stability.

[0073] The above description is only an exemplary embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A super-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect, comprising upper and lower electrode layers, and a dielectric layer is provided between the upper and lower electrode layers, characterized in that: The dielectric layer includes an ion migration regulation layer and ion confinement composite layers disposed on both the upper and lower sides of the ion migration regulation layer; Each ion confinement composite layer includes an ion confinement composite thin film fixed on the corresponding side electrode layer. The ion confinement composite thin film is provided with first protruding microstructures on the surface facing the ion migration regulation layer, and the first protruding microstructures include a plurality of first micro protrusions; The ion migration regulation layer is a nanochannel fiber membrane containing ion channels. Second protruding microstructures are provided on both the upper and lower surfaces of the nanochannel fiber membrane, and the second protruding microstructures include a plurality of second micro protrusions; The plurality of first micro protrusions of the ion confinement composite layer and the plurality of second micro protrusions on the corresponding side of the ion migration regulation layer are mutually interlocked to form an interlocking structure in the horizontal plane.

2. The ultrasensitive capacitive flexible pressure sensor based on the ion migration confinement effect according to claim 1, wherein: The plurality of first micro protrusions include a number of first large protrusions and a number of first small protrusions. The plurality of first micro protrusions form a number of horizontal rows and a number of vertical rows that cross each other on the surface of the ion confinement composite thin film. In each horizontal row and each vertical row, the first large protrusions and the first small protrusions are arranged at intervals in sequence, and four adjacent first micro protrusions enclose an embedding gap; A plurality of second micro protrusions on one side of the nanochannel fiber membrane are inserted one by one into a number of embedding gaps on the surface of the ion confinement composite layer on the corresponding side.

3. The ultrasensitive capacitive flexible pressure sensor based on the ion migration confinement effect according to claim 1, wherein The composition of each raw material for preparing the ion confinement composite thin film by mass percentage is as follows: tetraethyl orthosilicate TEOS 6-8%, ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide EMIM TFSI 5-7%, thermoplastic polyurethane elastomer TPU 10-15%, deionized water 3-5%, and the balance is N,N-dimethylformamide DMF.

4. The ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect according to claim 1, characterized in that: The composition of each raw material for preparing the nanochannel fiber membrane containing ion channels by mass percentage is as follows: graphene oxide GO 1-3%, nanocellulose CNFs 0.2-0.6%, deionized water 13-18%, KOH 1-5%, and the balance is polyvinyl alcohol PVA.

5. The ultrasensitive capacitive flexible pressure sensor based on the ion migration confinement effect according to claim 2, wherein: The first micro protrusion is composed of a frustum section and a spherical crown section that extend vertically along the surface of the ion confinement composite thin film and are coaxial; The size range of the first large protrusion is: the radius of the spherical crown section is 40μm-60μm, the height of the spherical crown section is 30μm-50μm, the end face radius of the large end of the frustum section is 60μm-80μm, and the height of the frustum section is 60μm-80μm; The size range of the first small protrusion is: the radius of the spherical crown section is 20μm-40μm, the height of the spherical crown section is 15μm-20μm, the end face radius of the large end of the frustum section is 40μm-60μm, and the height of the frustum section is 40μm-60μm; in the horizontal rows and vertical rows formed by the plurality of first micro protrusions, the axial center distance between two adjacent first micro protrusions is equal and is 80μm-160μm.

6. The ultrasensitive capacitive flexible pressure sensor based on the ion migration confinement effect according to claim 5, wherein: The second micro protrusion is composed of a frustum section and a spherical crown section that extend vertically from the surface of the nanochannel fiber membrane and are coaxial; The size range of the second micro-protrusions is as follows: the radius of the spherical crown section is 20 μm to 40 μm, the height of the spherical crown section is 40 μm to 60 μm, the end face radius of the large end of the frustum section is 40 μm to 60 μm, and the height of the frustum section is 40 μm to 60 μm; in the horizontal rows and vertical rows formed by multiple second micro-protrusions, the axial center distance between two adjacent second micro-protrusions is equal and is 80 μm to 160 μm.

7. The ultrasensitive capacitive flexible pressure sensor based on the ion migration confinement effect according to claim 1, wherein: The thickness of the ion-restricting composite film is 20 μm to 30 μm, and the thickness of the nanochannel fiber membrane containing ion channels is 25 μm to 40 μm.

8. The ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect according to claim 1, wherein: The upper and lower electrode layers and the periphery of the dielectric layer are encapsulated by a PDMS flexible encapsulation layer.

9. The preparation method of the ultra-sensitive capacitive flexible pressure sensor according to any one of claims 1 to 8, characterized in that, It includes the following steps: Step 1, prepare an ion-restricting composite layer Under the condition of heating at 40 - 60 °C: Add TEOS to deionized water, stir for 10 - 20 minutes to promote the hydrolysis reaction of TEOS, then dropwise add EMIM TFSI ionic liquid and continue to stir for 15 - 20 minutes to obtain a composite gel material; subsequently, add hydrochloric acid to the composite gel material and continuously stir for 30 - 45 minutes to obtain IL-SiO2 gel; Add TPU beads to DMF and continuously stir at 70 - 80 °C for 3 - 4 hours to obtain TPU gel; then dropwise add IL-SiO2 gel to the TPU gel at 70 - 80 °C, and then continuously stir at 40 - 60 °C for 4 - 5 hours to obtain an IL-SiO2-TPU composite solution; Uniformly fill the IL-SiO2-TPU composite solution in the mold used for making the ion-restricting composite layer; spin-coat the IL-SiO2-TPU composite solution on the surface of the electrode layer, then place the electrode layer with the solution-spin-coated side facing down above the mold, and demold after drying at room temperature, that is, an ion-restricting composite layer is formed on the surface of the electrode layer; Repeat to fabricate two electrode layers formed with ion-restricting composite layers, which are used as the upper and lower electrode layers respectively; Step 2, prepare an ion migration regulation layer Add GO nanosheets to deionized water and ultrasonically disperse evenly, then add an aqueous dispersion of CNFs and stir evenly at room temperature to obtain a composite dispersion; add PVA to the composite dispersion, stir at 90 - 100 °C until PVA is fully dissolved, then after freezing and thawing, add KOH solution and stir at 50 - 60 °C for 15 - 20 minutes to obtain a CNFs-GO / PVA-KOH composite solution; Uniformly fill the CNFs-GO / PVA-KOH composite solution in the mold for making the ion migration regulation layer, and then after drying and demolding, obtain an ion migration regulation layer; Step 3, prepare a PDMS flexible encapsulation film After mixing PDMS and a curing agent to form a PDMS solution, pour it on the surface of an acrylic plate, and then cure at 50 - 60 °C in a vacuum drying oven for 15 - 20 minutes, and peel to obtain a PDMS flexible encapsulation film; repeat to prepare two layers of PDMS flexible encapsulation films; Step 4, sensor assembly After stacking a lower electrode layer with an ion confinement composite layer, an ion migration regulation layer, and an upper electrode layer with an ion confinement composite layer in sequence on a layer of PDMS flexible encapsulation film, another layer of PDMS flexible encapsulation film is placed; then a PDMS solution is filled into the sides of the two PDMS films using a coating rod and air-dried, so as to form a complete PDMS flexible encapsulation layer around the upper and lower electrode layers and the dielectric layer, and the assembly of the sensor is completed.

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