Ultrasensitive capacitive flexible pressure sensor based on ion migration confinement effect

Abstract

The present invention relates to the field of sensors that utilize silicon dioxide to achieve the ion migration confinement effect. Disclosed is an ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect. The sensor comprises upper and lower electrode layers, with a dielectric layer disposed between the upper and lower electrode layers. The dielectric layer comprises an ion migration control layer and ion confinement composite layers disposed above and below the ion migration control layer. Each ion confinement composite layer comprises an ion confinement composite film fixed to the corresponding electrode layer, the ion confinement composite film having a plurality of first micro-protrusions on the side facing the ion migration control layer. The ion migration control layer comprises a nanochannel fiber membrane containing ion channels, with a plurality of second micro-protrusions disposed on both the upper and lower surfaces of the nanochannel fiber membrane. The plurality of first micro-protrusions interlock with the plurality of second micro-protrusions on the corresponding side to form an interlocking structure in a horizontal plane. The sensor of the present invention exhibits high sensitivity over a wide pressure range.

Description

Technical Field

[0001] The present invention relates to the field of sensors that utilize silicon dioxide to realize an ion migration confinement effect, and in particular to an ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect. Background Art

[0002] Flexible capacitive pressure sensors, due to their high sensitivity, flexibility, and low power consumption, have attracted significant attention in fields such as robotic tactile sensing, human-machine interaction, and smart wearable devices. By employing dielectric materials with lower elastic moduli or microstructuring the dielectric materials, the sensor can achieve a greater variation in the spacing between the electrode plates under the same pressure, thereby improving sensor sensitivity. Based on these approaches, researchers at home and abroad continue to innovate and develop various capacitive pressure sensors.

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

[0004] Patent application CN118992967A proposes a flexible pressure sensor with a dual microstructure and its fabrication method. The flexible pressure sensor is assembled from a conductive polymer composite material with a dual microstructure and interdigitated electrodes. The resulting flexible pressure sensor features a dual microstructure with both porous and micro-protruded surfaces. It exhibits a wide pressure response range, high sensitivity, and a low detection limit. This allows for pressure detection of small objects, collection of human biosignals, Morse code transmission, and detection and recognition of sitting postures.

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

[0006] In their academic paper, "Rough-Surface-Enabled Capacitive Pressure Sensors with 3D Touch Capability," published in the journal Small, Kilsoo Lee's team demonstrated a high-performance paper-based capacitive pressure sensor by leveraging the natural surface roughness of paper and combining it with a thin PDMS film. This sensor utilizes the rough surface of paper to create microstructured air gaps, significantly improving pressure sensitivity while also exhibiting fast response time, low detection limits, and excellent bending stability.

[0007] In their academic paper, "Transparent, Flexible, Conformal Capacitive Pressure Sensors with Nanoparticles," published in the journal Small, Hyeohn Kim's team achieved a highly transparent and sensitive capacitive pressure sensor by sandwiching a dielectric layer containing silica nanoparticles between transparent conductive polymers and exploiting the aggregation properties of the nanoparticles to form a microstructured surface.

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

[0009] Patent application CN118687722A proposes an ionic electronic pressure sensor with a wide working range and its preparation method. The densification of the polymer network during the dehydration process is used to promote 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 ion-type flexible pressure sensor, pressure detection equipment and method. The sensor includes: a first electrode layer, an ion layer and a second electrode layer stacked in sequence. 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 has a significant change, thereby making the sensor have a higher pressure detection sensitivity.

[0011] In their academic paper "Normal-Direction Graded Hemispheres for Ionic Flexible Sensors with a Record-High Linearity in a Wide Working Range," published in ACS Applied Materials & Interfaces, Shaowei Wu's team introduced spheres layered along the normal direction, effectively dividing the surface of the large hemisphere. This improved the linearity of the sensor while achieving high sensitivity over a wide response range.

[0012] In their paper, "Biomimetic nanofiber-iongel composites for flexible pressure sensors with broad range and ultra-high sensitivity," published in the journal Nano Energy, Xin Gou's team drew inspiration from the tactile sensing mechanism and layered structure of human skin. By applying electrospinning and droplet injection, they designed a nanofiber-agar composite with internal graded stiffness and a semi-embedded surface microstructure. The resulting sensor exhibits ultrahigh sensitivity, a wide pressure range, and exceptional stability.

[0013] In summary, relevant researchers have carried out a lot of research work on ionized pressure sensors. These studies have improved the sensitivity characteristics of the sensor by improving the micro-nano structure, increasing the EDL capacitance and interface contact area, and improving the mechanical properties by material modification. However, there are still the following shortcomings:

[0014] 1. Currently reported ion-type pressure sensors typically utilize microstructures on the dielectric surface to enhance sensor sensitivity and broaden the pressure measurement range. However, due to a lack of effective control over the free-moving ions in the electric field, the ions rapidly migrate to the interface between the dielectric layer and the electrode, forming a double layer structure. This rapid ion aggregation leads to excessively high ion concentration at the double layer interface, resulting in excessively high initial capacitance, which limits the improvement of sensor sensitivity.

[0015] 2. Currently reported ionization pressure sensors convert pressure changes into electrical signals by varying capacitance due to changes in the contact area between the electrode and the dielectric layer when pressure is applied. When pressure is applied, the electrode-dielectric contact area varies depending on the microstructure. A greater change in this contact area increases the final capacitance Cp, thus affecting sensor sensitivity. However, the final contact area is often insufficient, limiting improvements in sensor sensitivity.

[0016] 3. Currently reported ionization-based pressure sensors use ions as charge transfer substances to transport signals. However, typically only anions or cations are introduced, so when forming the double layer, the amount of only one type of ion changes, resulting in minimal capacitance change, ultimately limiting improvements in sensor sensitivity.

[0017] 4. Currently reported ionization pressure sensors usually introduce microstructures to optimize the change in contact area when external force is applied. The microstructures are mostly single microstructures, which deform significantly under small pressures. As the pressure increases, the contact area quickly reaches saturation, limiting the improvement of the linear working range of the sensor.

[0018] 5. The design of the ion-type pressure sensor reported so far mainly relies on the use of disordered diffusion mechanism or random pore structure. This design makes the ion flow path complex and inefficient, reduces the effective ion diffusion coefficient, and leads to a low conversion rate from pressure change signal to electrical signal, which reduces the response speed of the sensor.

[0019] 6. Currently reported ionization pressure sensors usually use nanomaterials to introduce ion channels to improve the response speed of the sensor. However, under long-term immersion, there is a problem that ionic liquids penetrate into the nanomaterials and destroy their pore structure or layered structure, causing the ion channels to collapse and the material strength to decrease, affecting the reliability and long-term stability of the sensor.

[0020] 7. Currently reported ionized pressure sensors improve conductivity by introducing ionic liquids, but most ionic liquids have high viscosity and poor fluidity, making it difficult to accurately control the film thickness and structure through traditional thin film preparation processes (such as spin coating and spray coating).

[0021] 8. The ionized pressure sensors reported so far use ion gel as the dielectric layer. However, ion gel usually uses organic polymer materials that are not easily degraded. Its degradation process requires high-temperature treatment or the introduction of strong acids, strong bases and other chemical reagents, and is prone to produce harmful substances, affecting the natural environment. Summary of the Invention

[0022] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect, so as to effectively improve the sensitivity of such capacitive flexible pressure sensor under a wide pressure range.

[0023] The purpose of the present invention is achieved through the following technical solutions:

[0024] The present invention first provides an ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect, comprising two upper and lower electrode layers, with a dielectric layer disposed between the upper and lower electrode layers, the dielectric layer comprising an ion migration control layer and an ion confinement composite layer disposed on the upper and lower sides of the ion migration control layer. Each ion confinement composite layer comprises an ion confinement composite film fixed to the corresponding electrode layer, the ion confinement composite film having a first protruding microstructure on the surface facing the ion migration control layer, the first protruding microstructure comprising a plurality of first micro-protrusions. The ion migration control layer is a nanochannel fiber membrane containing ion channels, the upper and lower surfaces of the nanochannel fiber membrane being provided with a second protruding microstructure, the second protruding microstructure comprising 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 control layer interlock with each other to form an interlocking structure in a horizontal plane.

[0025] Furthermore, the multiple first micro-protrusions include several first large protrusions and several first small protrusions, and the multiple first micro-protrusions form several horizontal rows and several vertical rows that cross each other on the surface of the ion-restricted composite film. In each horizontal row and each vertical row, the first large protrusions and the first small protrusions are arranged in sequence, and the four adjacent first micro-protrusions form an embedded gap; the multiple second micro-protrusions on one side of the nanochannel fiber membrane are inserted one by one into the several embedded gaps on the surface of the ion-restricted composite layer on the corresponding side.

[0026] Furthermore, the raw materials for preparing the ion-confined composite film are composed of 6-8% tetraethyl silicate TEOS, 5-7% ionic liquid 1-ethyl-3-methylimidazolinium bis(trifluoromethylsulfonyl)imide EMIM TFSI, 10-15% thermoplastic polyurethane elastomer TPU, 3-5% deionized water, and the balance N,N-dimethylformamide DMF.

[0027] Furthermore, the raw materials for preparing the nanochannel fiber membrane containing ion channels are composed of the following by mass percentage: 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.

[0028] Furthermore, the first micro-protrusions are composed of a truncated cone segment and a spherical crown segment extending vertically and coaxially along the surface of the ion-confined composite film. The size range of the first large protrusion is: the spherical crown segment radius is 40μm to 60μm, the spherical crown segment height is 30μm to 50μm, the end face radius of the large end of the truncated cone segment is 60μm to 80μm, and the truncated cone segment height is 60μm to 80μm. The size range of the first small protrusions is: the spherical crown segment radius is 20μm to 40μm, the spherical crown segment height is 15μm to 20μm, the end face radius of the large end of the truncated cone segment is 40μm to 60μm, and the truncated cone segment height is 40μm to 60μm. In the horizontal and vertical rows formed by multiple first micro-protrusions, the axial center distance between two adjacent first micro-protrusions is equal and is both 80μm to 160μm.

[0029] Furthermore, the second micro-protrusions are composed of concentric truncated cone segments and spherical cap segments extending vertically from the surface of the nanochannel fiber membrane. The dimensions of the second micro-protrusions are as follows: the spherical cap segment has a radius of 20 μm to 40 μm, a height of 40 μm to 60 μm, an end face radius of 40 μm to 60 μm at the large end of the truncated cone segment, and a height of 40 μm to 60 μm. In horizontal and vertical rows of multiple second micro-protrusions, the axial center distances between adjacent second micro-protrusions are equal and range from 80 μm to 160 μm.

[0030] Furthermore, the thickness of the ion-restricted 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.

[0031] Furthermore, the upper and lower electrode layers and the periphery of the dielectric layer are encapsulated by a PDMS flexible encapsulation layer.

[0032] The present invention also provides a method for preparing the ultra-sensitive capacitive flexible pressure sensor, comprising the following steps:

[0033] Step 1: Preparation of ion-confined composite layer

[0034] Under heating conditions of 40-60° C., TEOS was added to deionized water and stirred for 10-20 minutes to promote the hydrolysis reaction of TEOS, and then EMIM TFSI ionic liquid was added dropwise and stirred for 15-20 minutes to obtain a composite gel material; then, hydrochloric acid was added dropwise to the composite gel material and stirred for 30-45 minutes to obtain an IL-SiO2 gel (where IL represents ionic liquid);

[0035] The TPU beads were added to DMF and stirred continuously at 70-80°C for 3-4 hours to obtain a TPU gel; then, the IL-SiO2 gel was added dropwise to the TPU gel at 70-80°C and stirred continuously at 40-60°C for 4-5 hours to obtain an IL-SiO2-TPU composite solution;

[0036] The IL-SiO2-TPU composite solution is evenly filled in a mold used to prepare the ion-confined composite layer; the IL-SiO2-TPU composite solution is spin-coated on the surface of the electrode layer, and then the electrode layer is placed on the mold with the solution-coated side facing down. After drying at room temperature, the layer is demoulded to form the ion-confined composite layer on the surface of the electrode layer;

[0037] Repeatedly make two electrode layers with ion-confined composite layers, which serve as upper and lower electrode layers respectively.

[0038] Step 2: Preparation of ion migration control layer

[0039] GO nanosheets were added to deionized water and ultrasonically dispersed uniformly, and then an aqueous dispersion of CNFs was added and stirred uniformly at room temperature to obtain a composite dispersion; PVA was added to the composite dispersion, stirred at 90-100°C until the PVA was fully dissolved, and then frozen and thawed, and then a KOH solution was added and stirred at 50-60°C for 15-20 minutes to obtain a CNFs-GO / PVA-KOH composite solution;

[0040] The CNFs-GO / PVA-KOH composite solution is evenly filled in a mold for making an ion migration regulating layer, and then dried and demolded to obtain the ion migration regulating layer.

[0041] Step 3: Preparation of PDMS flexible encapsulation film

[0042] After mixing PDMS and a curing agent to form a PDMS solution, pour it onto the surface of an acrylic plate, then cure it in a vacuum drying oven at 50-60°C for 15-20 minutes, and peel it off to obtain a PDMS flexible encapsulation film; repeat this process to prepare two layers of PDMS flexible encapsulation film.

[0043] Step 4: Sensor assembly

[0044] After stacking the lower electrode layer with an ion-restricted composite layer, the ion migration regulation layer, and the upper electrode layer with an ion-restricted composite layer in sequence on a layer of PDMS flexible packaging film, another layer of PDMS flexible packaging film is placed; then, a coating rod is used to fill the sides of the two PDMS films with PDMS solution and air-dry, so that the upper and lower electrode layers and the periphery of the dielectric layer form a complete PDMS flexible packaging layer, thus completing the assembly of the sensor.

[0045] Compared with the prior art, the beneficial effects of the present invention are embodied in the following aspects:

[0046] 1. The present invention provides an ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect. The dielectric layer is designed as a sandwich structure consisting of two layers of ion-restricted composite films and a nanochannel fiber membrane containing ion channels in the middle. The ion-restricted composite film contains an ionic liquid that participates in conductivity, and the nanochannel fiber membrane contains ion channels, so that the ionic liquid and the nanoconductive channels are separated, avoiding problems such as ion channel collapse and material strength degradation caused by long-term immersion, thereby 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-restricted composite film, and a plurality of second micro-protrusions are provided on the upper and lower surfaces of the nanochannel fiber membrane. The two micro-protrusions are interlocked with each other to form an interlocking structure in the horizontal plane. Compared with a single structure, this structural setting has a higher pressure sensing range, a larger normalized contact area and capacitance change, so that the sensor has both high sensitivity and high linearity. The specific analysis is as follows:

[0047] On the one hand, the compressibility of the dielectric layer is increased, which not only avoids the rapid contact between the two layers of ion-confined composite films, but also further improves the compressibility of the dielectric layer. The synergistic effect of the two broadens the linear operating range of the sensor.

[0048] On the other hand, it provides a larger contact area variation range for the dielectric layer, and can provide more ion channels during the contact process between the electrode layer and the dielectric layer, allowing many anions and cations to conduct through the membrane barrier to form EDL. The ion-limited composite film increases the final capacitance Cp while increasing the ionic conductivity, thereby increasing the sensitivity of the sensor.

[0049] On the other hand, the two types of micro-protrusions on the surface of the ion-confined composite film and the nanochannel fiber membrane are interlocked with each other to form an interlocking structure in the horizontal plane, which can play a role in locking adjacent membranes in the horizontal plane. This interlocking structure shows a significant enhancement in the contact area between several first large protrusions on the surface of the ion-confined composite film and the second micro-protrusions on the corresponding side surface of the nanochannel fiber membrane under light load; under medium load, the first large protrusion is continuously compressed and the capacitance is continuously increased; under heavy load, the change in the contact area of ​​the first large protrusion gradually reaches saturation, and the contact area between several first small protrusions on the surface of the ion-confined composite film and the second micro-protrusions on the corresponding side surface of the nanochannel fiber membrane changes, thereby improving the linear working range of the sensor.

[0050] 2. The present invention provides an ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect. The ion confinement composite film and the nanochannel fiber membrane containing ion channels are made of specific raw materials. The specific analysis is as follows:

[0051] On the one hand, the sol-gel method is used to prepare the ion-restricted composite film: TEOS is used as the silicon source and the ionic liquid EMIM TFSI is used as the functional component. Hydrochloric acid is added to promote the hydrolysis and condensation polymerization of TEOS to generate silicon hydroxyl intermediates and polymerize to form a silica gel network. Then, IL-SiO2 gel is formed through the interaction between the ionic substance 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 therein migrate to the anode and cathode respectively to form a double layer. This strategy of using the coordinated migration of anions and cations effectively improves the problem of limited sensitivity caused by the participation of only a single ion in conduction, so that the sensor achieves higher sensitivity. At the same time, silica is used as the ion-restricted matrix to achieve the ion migration confinement effect: the anions in the ionic liquid [TFSI － ] interacts with the silanol groups (Si-OH) on the surface of silica through hydrogen bonds and is surrounded by [EMIM ＋ ] cations surrounded, [EMIM ＋ ] cation is composed of [TFSI － ] The Coulomb coupling force of the anion and the π-π stacking interaction of the imidazole ring drive the ion pairs to be confined to the surface of the silica microstructure through hydrogen bond-Coulomb interaction. This confinement allows the ions to remain on the surface of the silica microstructure when there is no external force acting on the voltage, and almost no free ions participate in the formation of capacitance, achieving a low initial capacitance, making the capacitance change more significant under pressure, thereby improving the sensitivity of the pressure sensor. Furthermore, 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide is used as the ionic liquid, which has a low viscosity. This low viscosity not only allows it to be better filled and distributed when combined with the silica microstructure, thereby forming a uniform ion conduction network, but also enables it to be prepared with a good structure through a spin coating process.

[0052] On the other hand, a nanochannel fiber membrane containing ion channels was prepared by freezing and thawing a composite of GO and CNFs. GO was incorporated into the nanochannel fiber membrane to form two-dimensional layered nanochannels for ion transport. Under no-pressure conditions, ion transport within the two-dimensional layered nanochannels is weak, minimizing energy loss in the device during standby mode. Under external pressure, the dimensions of the two-dimensional layered nanochannels are further reduced, allowing for rapid ion transport within the confined nanochannels. This design optimizes the ion flow path and improves ion mobility, resulting in a sensor with a wide linear range and fast response speed. Furthermore, hydrogen bonding between CNFs and GO strengthens the bonding between GO nanosheets. X-ray diffraction analysis shows that the addition of CNFs to GO shifts the characteristic X-ray diffraction peak to the left. This indicates that the addition of CNFs increases the interlayer spacing of the GO nanosheets, significantly increasing the thickness of the composite membrane and further enhancing its compressibility. Furthermore, GO doping within the nanochannel fiber membrane forms ion channels, enhancing ion mobility and contributing to the sensor's wide linear range and fast response speed.

[0053] On the other hand, the materials used in the flexible pressure sensor designed by the present invention, such as PVA, TPU, nanocellulose, etc., can be naturally degraded or simply green-degraded, and have good biocompatibility and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a longitudinal cross-sectional view of the capacitive flexible pressure sensor of the present invention.

[0055] Figure 2 1 is a top view of the lower ion confinement composite layer of the present invention.

[0056] Figure 3 4 is a top view of the ion migration regulating layer of the present invention.

[0057] Figure 4 It is a partial structural schematic diagram of the first mold used in the production of the ion confinement composite layer of the present invention.

[0058] Figure 5 It is a partial structural schematic diagram of the lower mold of the second mold used for manufacturing the ion migration regulating layer of the present invention.

[0059] Figure 6 It is a schematic diagram of the reaction mechanism of the present invention for preparing the ion-confined composite layer.

[0060] Figure 7 The silicon dioxide microstructure surface in the ion-restricted composite film of the present invention is [EMIM ＋ ] and [TFSI － ] Schematic diagram of the migration confinement effect of ion pairs.

[0061] Figure 8The frequency response of the ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect produced in Example 1 at 60 kPa.

[0062] Figure 9 It is a sensitivity comparison curve of the presence or absence of a silicon dioxide structure in the ion confinement composite layer of the present invention.

[0063] Figure 10 The pressure-capacitance change rate curve of the ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect produced in Example 1 in the pressure range of 0~650 kPa.

[0064] Figure 11 The ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect produced in Example 1 was subjected to a dynamic loading-unloading cycle test at 10-600 kPa.

[0065] Figure 12 The response and recovery time of the ultrasensitive capacitive flexible pressure sensor based on the ion migration confinement effect produced in Example 1 under a pressure of 60 kPa.

[0066] Figure 13 This is a cyclic stability test of the ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect produced in Example 1 under a pressure of 300 kPa.

[0067] Numbers 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 segment; 9 spherical crown segment; 10 second micro protrusion; 11 PDMS flexible encapsulation layer; 12 embedded gap; 13 first mold; 14 lower mold. DETAILED DESCRIPTION

[0068] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0069] See also Figures 1 to 3This embodiment discloses an ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect, including an upper electrode layer 1 and a lower electrode layer 2 arranged in an upper and lower manner. 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 arranged on 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 on the upper and lower sides of the ion migration regulation layer 3. The upper and lower electrode layers and the dielectric layer are encapsulated by a PDMS flexible encapsulation layer 11.

[0070] Each ion-confining composite layer comprises an ion-confining composite thin film fixed to the corresponding electrode layer. The ion-confining composite thin film is deposited on the surface of the electrode layer and has a first protruding microstructure on the side facing the ion mobility regulating layer 3. The first protruding microstructure comprises a plurality of first micro-protrusions. The ion mobility regulating layer 3 is a nanochannel fiber membrane containing ion channels. The nanochannel fiber membrane has a second protruding microstructure on both its upper and lower surfaces. The second protruding microstructure comprises a plurality of second micro-protrusions 10. The plurality of first micro-protrusions on the ion-confining composite layer interlock with the plurality of second micro-protrusions 10 on the corresponding side of the ion mobility regulating layer 3, forming an interlocking structure within a horizontal plane.

[0071] In the first protrusion microstructure, the multiple first micro protrusions include several first large protrusions 6 and several first small protrusions 7. The multiple first micro protrusions form several horizontal rows and several vertical rows that cross each other on the surface of the ion-restricted composite film. In each horizontal row and each vertical row, the first large protrusions 6 and the first small protrusions 7 are arranged in sequence, and the four adjacent first micro protrusions form an embedded gap 12; in the second protrusion microstructure on one side of the nanochannel fiber membrane, the multiple second micro protrusions 10 are inserted one by one into the several embedded gaps 12 on the surface of the ion-restricted composite layer on the corresponding side.

[0072] The thickness of the ion-confining composite film is 20μm to 30μm. The first micro-protrusions are composed of a truncated cone segment 8 and a spherical crown segment 9 extending vertically and coaxially along the surface of the ion-confining composite film. The dimensions of the first large protrusions 6 are as follows: the radius of the spherical crown segment 9 is 40μm to 60μm, the height of the spherical crown segment 9 is 30μm to 50μm, the end face radius of the large end of the truncated cone segment 8 is 60μm to 80μm, and the height of the truncated cone segment 8 is 60μm to 80μm. The dimensions of the first small protrusions 7 are as follows: the radius of the spherical crown segment 9 is 20μm to 40μm, the height of the spherical crown segment 9 is 15μm to 20μm, the end face radius of the large end of the truncated cone segment 8 is 40μm to 60μm, and the height of the truncated cone segment 8 is 40μm to 60μm. In the horizontal and vertical rows formed by multiple first micro-protrusions, the axial center distance between two adjacent first micro-protrusions is equal and is both 80μm to 160μm.

[0073] The nanochannel fiber membrane has a thickness of 25 μm to 40 μm. The second micro-protrusions 10 are composed of a truncated cone segment 8 and a spherical crown segment 9 extending vertically from the surface of the nanochannel fiber membrane and having the same axis. The dimensions of the second micro-protrusions 10 are as follows: the radius of the spherical crown segment 9 is 20 μm to 40 μm, the height of the spherical crown segment 9 is 40 μm to 60 μm, the end face radius of the large end of the truncated cone segment 8 is 40 μm to 60 μm, and the height of the truncated cone segment 8 is 40 μm to 60 μm. In the horizontal and vertical rows formed by multiple second micro-protrusions 10, the axial center distance between two adjacent second micro-protrusions 10 is equal and is both 80 μm to 160 μm.

[0074] See also Figure 4 The shape of the cavity of the first mold 13 used to make the ion confinement composite layer matches the shape of the ion confinement composite film with the first protruding microstructure on the surface. Figure 5 The second mold used to make the ion migration regulating layer 3 includes an upper mold and a lower mold 14 that are symmetrical in upper and lower directions. After the upper and lower molds are combined, the mold cavity of the second mold is consistent with the overall shape of the nanochannel fiber membrane with the second protruding microstructure on the upper and lower surfaces.

[0075] Example 1

[0076] This embodiment provides an ultra-sensitive capacitive flexible pressure sensor of a specific size based on the ion migration confinement effect. The raw materials and preparation steps are as follows:

[0077] Raw materials: EMIM TFSI was purchased from Anhui Cool Bioengineering Co., Ltd. (AR, 98%). TEOS was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (GC, 99%). Hydrochloric acid was purchased from Zhejiang Mingyuan Chemical Instrument Co., Ltd. (AR, 5%). TPU was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (AR, 99%). DMF was purchased from Sinopharm Chemical Reagent Co., Ltd. (AR, 99.5%). Graphene oxide nanosheets were purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd. (purity 99%, sheet diameter 500 nm–5 μm, thickness 0.8–1.2 nm). Nanocellulose aqueous dispersion was purchased from Songhu Shenjian Technology (Dongguan) Co., Ltd. (mass concentration 2%, diameter 1–50 nm, length 1–30 nm). Polyvinyl alcohol was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. (1797, alcoholysis degree 98.0–99.0 mol%, Mw–195,000). The KOH aqueous solution used was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (mass concentration: 5%). The PDMS used was purchased from Shenzhen Songsen New Material Technology Co., Ltd.

[0078] Preparation steps:

[0079] Step 1: Preparation of ion-confined composite layer

[0080] Under heating conditions at 40°C: add 0.5 grams of TEOS to 0.25 grams of deionized water and stir continuously for 10 minutes to promote the hydrolysis reaction of TEOS. Then add 0.4 grams of EMIM TFSI ionic liquid, and continue to stir and keep warm for 15 minutes to ensure that the ionic liquid is fully combined with the silica precursor to prepare a composite gel material. Subsequently, add 0.05 grams of hydrochloric acid to the composite gel material and continue stirring for 30 minutes to promote the formation of silica to obtain IL-SiO2 gel. Add 1 gram of TPU beads to 5 grams of DMF and stir continuously at 80°C for 3 hours to ensure the full dissolution of TPU to obtain TPU gel. Add IL-SiO2 gel dropwise to TPU gel at 80°C, and continue stirring at 40°C for 4 hours to finally obtain a uniform and stable IL-SiO2-TPU composite solution. Its reaction mechanism is as follows: Figure 6 shown.

[0081] The first mold 13 used to form the ion-confined composite layer was uniformly filled with an 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 speed of 300 rpm for 30 seconds. The copper foil was then placed on top of the first mold 13, with the coating surface facing downward. After drying at room temperature for 36 hours, the mold was removed, forming an ion-confined composite layer on the surface of the electrode layer. This process was repeated to produce two copper foils each coated with an ion-confined composite layer, serving as the upper and lower electrode layers 2. Specifically, the ion-confined composite film obtained in this example had a thickness of 30 μm. The dimensions of the first large protrusion 6 are: the radius of the spherical crown segment 9 is 60 μm, the height of the spherical crown segment 9 is 50 μm, the end face radius of the large head end of the truncated cone segment 8 is 80 μm, and the height of the truncated cone segment 8 is 80 μm; the dimension range of the first small protrusion 7 is: the radius of the spherical crown segment 9 is 40 μm, the height of the spherical crown segment 9 is 20 μm, the end face radius of the large head end of the truncated cone segment 8 is 60 μm, and the height of the truncated cone segment 8 is 60 μm; in the horizontal and vertical rows formed by multiple first micro protrusions, the axial center distance between two adjacent first micro protrusions is equal and both are 120 μm.

[0082] Step 2: Preparation of ion migration control layer 3

[0083] 0.2 g of GO nanosheets were added to 2 g of deionized water and ultrasonically dispersed for 30 minutes. Then, 2 g of a 2% aqueous CNF dispersion was added and stirred 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 the PVA. After freezing at -24°C for 12 hours and thawing at room temperature, 3 g of a 5% aqueous KOH solution was added and stirred at 60°C for 20 minutes to obtain a CNFs-GO / PVA-KOH composite solution.

[0084] The CNFs-GO / PVA-KOH composite solution was evenly filled into the upper and lower molds 14 of the second mold for forming the ion migration control layer 3. The upper and lower molds 14 were then placed in a vacuum drying oven for 10 minutes to remove air bubbles. The uncured upper and lower molds 14 were aligned and snapped together, and pressed to form a tighter fit. The second mold was then dried in a drying oven at 50°C for 10 hours and demolded to obtain the ion migration control layer 3. Specifically, in the ion migration control layer 3 prepared in this embodiment, the nanochannel fiber membrane had a thickness of 30 μm. The dimensions of the second micro-protrusions 10 were as follows: the radius of the spherical cap segment 9 was 40 μm, the height of the spherical cap segment 9 was 60 μm, the end face radius of the large end of the truncated cone segment 8 was 60 μm, and the height of the truncated cone segment 8 was 60 μm. In the horizontal and vertical rows formed by the multiple second micro-protrusions 10, the axial center distance between two adjacent second micro-protrusions 10 was equal and both were 120 μm.

[0085] Step 3: Preparation of PDMS flexible encapsulation film

[0086] After mixing 5 grams of PDMS and 0.5 grams of curing agent to form a PDMS solution, pour it on the surface of the acrylic plate, then cure it in a vacuum drying oven at 60°C for 15 minutes, and peel it off to obtain a PDMS flexible packaging film; repeat the process to prepare two layers of PDMS flexible packaging film and cut them into a size of 1 cm × 1 cm.

[0087] Step 4: Sensor assembly

[0088] After stacking the lower electrode layer 2, the ion migration control layer 3 and the upper electrode layer 1 with an ion restriction composite layer on a layer of PDMS flexible packaging film, another layer of PDMS flexible packaging film is placed; then, the PDMS solution is filled into the sides of the two PDMS films using a coating rod and air-dried to form a complete PDMS flexible packaging layer 11 around the upper and lower electrode layers and the dielectric layer, thus completing the assembly of the sensor.

[0089] Figure 7 The surface of silica microstructure in ion confinement composite film [EMIM ＋ ] and [TFSI －]Schematic diagram of the interactions involved in the migration confinement effect of ion pairs, in which [EMIM ＋ ] and [TFSI － ] molecular structure and the silanol groups of silica and TFSI − The -CF3 groups in the ions form hydrogen bonds, and [EMIM ＋ ] and [TFSI － ] There is a Coulomb interaction, which ultimately forms an ion migration confinement effect with silicon dioxide as the limiting structure.

[0090] Figure 8 This figure shows the frequency response of the ultrasensitive capacitive flexible pressure sensor based on the ion migration confinement effect fabricated in this example at 60 kPa. The capacitance change rate on the vertical axis represents the ratio of the capacitance change under pressure to the initial capacitance. The sensor achieves stable capacitance output at pressure-applying frequencies of 1 Hz, 5 Hz, and 10 Hz, demonstrating its excellent frequency response.

[0091] To verify the ion-confining effect of silica, the IL-SiO2-TPU composite solution prepared in Step 1 was coated onto an acrylic plate and dried to form a film. The film's sensitivity under pressure was then tested. Simultaneously, a TPU solution containing only EMIM TFSI ionic liquid and no SiO2 was formed into a film using the same method for comparison. The TPU solution containing only EMIM TFSI ionic liquid and no SiO2 was prepared by adding 1 gram of TPU beads to 5 grams of DMF and stirring continuously at 80°C for 3 hours to ensure complete dissolution of the TPU, resulting in a TPU gel. 0.4 grams of EMIM TFSI ionic liquid was then added to the TPU gel at 80°C and stirred continuously at 40°C for 4 hours.

[0092] Figure 9 This is a sensitivity comparison curve with and without silica structure in the ion confinement composite layer. It can be seen that at the same ionic liquid addition amount, when there is no silica confinement structure, the maximum is only 1.2kPa -1 After the introduction of the silicon dioxide confinement structure, the sensitivity reached 18.7kPa -1 , increased by about 18 times.

[0093] Figure 10The pressure-capacitance change rate curve of the ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect produced in this embodiment is shown in the pressure range of 0-650 kPa. The obtained sensor is fixed on the measurement platform, and a stress of 0-650 kPa is applied to the sensor using a ZQ990B tensile press. The sensor capacitance is measured using a precision LCR digital bridge TH2829. The sensitivity coefficient of the sensor is 66.7 kPa at 0-120 kPa. -1 At 120~400kPa, the compressibility of the ion migration control layer 3 gradually increases, and the deformation of the first large protrusion 6 of the surface microstructure of the ion confinement composite layer gradually saturates. At this time, the sensitivity coefficient is 19.5kPa -1 At 400~650kPa, the compressibility of the ion migration control layer 3 reaches its 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 8.9kPa. -1 . As the pressure increases, the sensitivity gradually decreases.

[0094] Figure 11 The ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect produced in this embodiment was subjected to dynamic loading-unloading cycle tests from 10 to 600 kPa, and the pressure changes within this range showed high recognition.

[0095] 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 are shown in Figure 2. The response time and recovery time are 80 ms and 79 ms, respectively.

[0096] 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.

[0097] The above description is merely 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 shall be included in the scope of protection of the present invention.

Claims

1. An ultra-sensitive capacitive flexible pressure sensor based on the ion migration confinement effect comprises two upper and lower electrode layers with a dielectric layer disposed therebetween, characterized in that: The dielectric layer includes an ion migration regulating layer and an ion confinement composite layer disposed on the upper and lower sides of the ion migration regulating layer; Each ion-confining composite layer includes an ion-confining composite film fixed on the corresponding side electrode layer, and the ion-confining composite film is provided with a first protruding microstructure on a surface facing the ion migration regulating layer, and the first protruding microstructure includes a plurality of first micro protrusions; The ion migration regulating layer is a nanochannel fiber membrane containing ion channels, and the upper and lower surfaces of the nanochannel fiber membrane are both provided with a second protruding microstructure, and the second protruding microstructure includes 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 control layer are interlocked with each other to form an interlocking structure in a horizontal plane; The raw materials for preparing the ion-confined composite film are composed of 6-8% tetraethyl silicate (TEOS), 5-7% ionic liquid (1-ethyl-3-methylimidazolinium bis(trifluoromethylsulfonyl)imide (EMIM TFSI), 10-15% thermoplastic polyurethane (TPU), 3-5% deionized water, and the balance (N,N-dimethylformamide (DMF)).

2. The ultra-sensitive capacitive flexible pressure sensor based on ion migration confinement effect according to claim 1, characterized in that: The plurality of first micro-protrusions include a plurality of first large protrusions and a plurality of first small protrusions, the plurality of first micro-protrusions forming a plurality of horizontal rows and a plurality of vertical rows that intersect horizontally and vertically on the surface of the ion-confining composite film, wherein in each horizontal row and each vertical row, the first large protrusions and the first small protrusions are arranged in sequence and spaced apart, and four adjacent first micro-protrusions form an embedded gap; The plurality of second micro protrusions on one side of the nanochannel fiber membrane are inserted into the plurality of embedded gaps on the surface of the ion confinement composite layer on the corresponding side in a one-to-one correspondence.

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

4. The ultra-sensitive capacitive flexible pressure sensor based on ion migration confinement effect according to claim 2, characterized in that: The first micro protrusion is composed of a truncated cone segment and a spherical cap segment extending vertically along the surface of the ion-confined composite film and having the same axis; The size range of the first major protrusion is: the radius of the spherical crown segment is 40 μm to 60 μm, the height of the spherical crown segment is 30 μm to 50 μm, the end face radius of the large end of the frustum segment is 60 μm to 80 μm, and the height of the frustum segment is 60 μm to 80 μm; The size range of the first small protrusion is: the radius of the spherical crown segment is 20μm~40μm, the height of the spherical crown segment is 15μm~20μm, the end face radius of the large head end of the frustum segment is 40μm~60μm, and the height of the frustum segment is 40μm~60μm; in the horizontal and vertical rows formed by multiple first micro-protrusions, the axial center distance between two adjacent first micro-protrusions is equal and both are 80μm~160μm.

5. The ultra-sensitive capacitive flexible pressure sensor based on ion migration confinement effect according to claim 4, characterized in that: The second micro protrusions are composed of a truncated cone segment and a spherical cap segment extending vertically and coaxially on the surface of the nanochannel fiber membrane; The size range of the second micro-protrusions is: the radius of the spherical crown segment is 20μm~40μm, the height of the spherical crown segment is 40μm~60μm, the end face radius of the large head end of the frustum segment is 40μm~60μm, and the height of the frustum segment is 40μm~60μm; in the horizontal and vertical rows formed by multiple second micro-protrusions, the axial center distance between two adjacent second micro-protrusions is equal and both are 80μm~160μm.

6. The ultra-sensitive capacitive flexible pressure sensor based on ion migration confinement effect according to claim 1, characterized in that: The thickness of the ion-restricted 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.

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

8. A method for preparing the ultra-sensitive capacitive flexible pressure sensor according to any one of claims 1 to 7, characterized in that: The steps include: Step 1: Preparation of ion-confined composite layer Under heating conditions of 40-60° C., TEOS was added to deionized water and stirred for 10-20 minutes to promote the hydrolysis reaction of TEOS, and then EMIM TFSI ionic liquid was added dropwise and stirred for 15-20 minutes to obtain a composite gel material; subsequently, hydrochloric acid was added dropwise to the composite gel material and stirred for 30-45 minutes to obtain an IL-SiO2 gel; The TPU beads were added to DMF and stirred continuously at 70-80°C for 3-4 hours to obtain a TPU gel; then, the IL-SiO2 gel was added dropwise to the TPU gel at 70-80°C and stirred continuously at 40-60°C for 4-5 hours to obtain an IL-SiO2-TPU composite solution; The IL-SiO2-TPU composite solution is evenly filled in a mold used to prepare the ion-confined composite layer; the IL-SiO2-TPU composite solution is spin-coated on the surface of the electrode layer, and then the electrode layer is placed on the mold with the solution-coated side facing down. After drying at room temperature, the layer is demoulded to form the ion-confined composite layer on the surface of the electrode layer; Repeatedly fabricating two electrode layers having ion-confined composite layers, serving as upper and lower electrode layers respectively; Step 2: Preparation of ion migration control layer GO nanosheets were added to deionized water and ultrasonically dispersed uniformly, and then an aqueous dispersion of CNFs was added and stirred uniformly at room temperature to obtain a composite dispersion; PVA was added to the composite dispersion, stirred at 90-100°C until the PVA was fully dissolved, and then frozen and thawed, and then a KOH solution was added and stirred at 50-60°C for 15-20 minutes to obtain a CNFs-GO / PVA-KOH composite solution; The CNFs-GO / PVA-KOH composite solution is evenly filled in a mold for making an ion migration regulating layer, and then dried and demolded to obtain the ion migration regulating layer; Step 3: Preparation of 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, then cure it in a vacuum oven at 50-60°C for 15-20 minutes, and peel it off to obtain a PDMS flexible encapsulation film. Repeat this process to prepare two layers of PDMS flexible encapsulation films. Step 4: Sensor assembly After stacking the lower electrode layer with an ion-restricted composite layer, the ion migration regulation layer, and the upper electrode layer with an ion-restricted composite layer in sequence on a layer of PDMS flexible packaging film, another layer of PDMS flexible packaging film is placed; then, a coating rod is used to fill the sides of the two PDMS films with PDMS solution and air-dry, so that the upper and lower electrode layers and the periphery of the dielectric layer form a complete PDMS flexible packaging layer, thus completing the assembly of the sensor.

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