Flexible capacitive pressure sensor and its preparation method and application

Abstract

The present invention relates to a flexible capacitive pressure sensor and its preparation method and application, belonging to the technical field of sensor devices. The flexible capacitive pressure sensor of the present invention comprises an upper flexible substrate, an upper electrode layer, a dielectric layer, a lower electrode layer and a lower flexible substrate in sequence; the dielectric layer is a liquid crystal core coaxial fiber composite dielectric layer. The polymer and liquid crystal selected in the present invention both have good elastic properties, and the liquid crystal has good dielectric anisotropy. The flexible capacitive pressure sensor based on liquid crystal core coaxial fiber is a multilayer composite structure in which liquid crystal core coaxial fiber is encapsulated by a polymer elastic matrix and flexible electrodes are attached to both sides of the encapsulation film. The fiber in the prepared device is a liquid crystal core coaxial fiber structure, the inner layer is a liquid crystal core, and the outer layer is a polymer sheath. The flexible capacitive pressure sensor device based on liquid crystal core coaxial fiber prepared by the present invention has good sensitivity and a wide pressure detection range.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensor devices, and in particular relates to a flexible capacitive pressure sensor based on liquid crystal core coaxial fiber, and a preparation method and application thereof. Background Art

[0002] With the rapid development of the Internet of Things, smart wearable devices, and human health monitoring technologies, the demand for lightweight, flexible, and high-performance sensors continues to increase. Traditional rigid sensors are often not adaptable to curved or complex surfaces, and cannot achieve a close fit with the human body or flexible electronic products. Therefore, flexible pressure sensors have emerged. Compared with piezoresistive sensors, capacitive sensors have higher sensitivity and accuracy, and are more resistant to interference.

[0003] Flexible capacitive pressure sensors have enormous potential for widespread application, particularly in areas such as smart health monitoring, flexible electronic devices, artificial intelligence robots, virtual reality, and wearable devices. However, existing flexible capacitive pressure sensors struggle with balancing sensitivity and range. For some conventionally designed flexible capacitive pressure sensors, sensitivity can drop by half or more when pressure exceeds a certain range, severely limiting their application in scenarios requiring high-pressure measurements. Summary of the Invention

[0004] The present invention aims to address the technical problem of existing flexible capacitive pressure sensors struggling to achieve both high sensitivity and a wide detection range. It provides a flexible capacitive pressure sensor based on a liquid crystal core coaxial fiber, as well as its preparation method and application. The flexible capacitive pressure sensor of the present invention achieves both high sensitivity and a wide pressure detection range through dielectric layer design and liquid crystal molecular orientation control, while also exhibiting excellent mechanical flexibility and environmental stability.

[0005] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0006] A flexible capacitive pressure sensor comprises an upper flexible substrate, an upper electrode layer, a dielectric layer, a lower electrode layer and a lower flexible substrate arranged in sequence from top to bottom;

[0007] The dielectric layer is a liquid crystal fiber core coaxial fiber composite dielectric layer, the inner layer of the liquid crystal fiber core coaxial fiber composite dielectric layer is a liquid crystal fiber core, and the outer layer is a polymer sheath layer.

[0008] In the above technical solution, preferably, the liquid crystal molecules in the liquid crystal core coaxial fiber composite dielectric layer are completely covered by the polymer and the liquid crystal molecules are arranged along the long axis of the fiber in the polymer sheath layer.

[0009] In the above technical solution, preferably, the diameter distribution of the liquid crystal core coaxial fiber is 200~800nm.

[0010] In the above technical solution, preferably, both the upper flexible substrate and the lower flexible substrate are flexible films made of high molecular polymer materials.

[0011] In the above technical solution, preferably, both the upper flexible substrate and the lower flexible substrate are polydimethylsiloxane flexible substrates.

[0012] In the above technical solution, preferably, both the upper electrode layer and the lower electrode layer are made of flexible materials with a resistance of less than 10Ω / sq.

[0013] In the above technical solution, it is further preferred that both the upper electrode layer and the lower electrode layer are made of polyester fiber conductive cloth.

[0014] A method for preparing a flexible capacitive pressure sensor comprises the following steps:

[0015] Step 1: preparing a high molecular polymer material into a flexible film, and using the flexible film as an upper flexible substrate and a lower flexible substrate;

[0016] Step 2: Select flexible materials with a resistance of less than 10Ω / sq as the upper electrode layer and the lower electrode layer respectively;

[0017] Step 3: Prepare a liquid crystal core coaxial fiber membrane using polymer and liquid crystal material to obtain a dielectric layer;

[0018] Step 4: Laminating and packaging the upper flexible substrate, the upper electrode layer, the dielectric layer, the lower electrode layer and the lower flexible substrate in this order, and respectively leading electrode leads from the upper electrode layer and the lower electrode layer to obtain the flexible capacitive pressure sensor.

[0019] In the above technical solution, preferably, step 3 is to use polymer and liquid crystal material to prepare liquid crystal core coaxial fiber membrane by coaxial electrospinning method.

[0020] A flexible capacitive pressure sensor is used in wearable motion monitoring, medical health monitoring, or human-machine interaction.

[0021] The beneficial effects of the present invention are:

[0022] The flexible capacitive pressure sensor of the present invention achieves a highly sensitive capacitance change response within a wide pressure range by selecting and designing the material and structure of the dielectric layer, using a liquid crystal core coaxial fiber with a liquid crystal core and a polymer sheath as the dielectric layer, and selecting and designing the materials of the upper flexible substrate, lower flexible substrate, upper electrode layer, and lower electrode layer. The flexible capacitive pressure sensor of the present invention was tested for pressure sensing, and the pressure sensing range of the sensor exceeded 0~240kPa, and the linearity within this wide pressure sensing range reached 0.99. Overall, the average sensitivity of the flexible capacitive pressure sensor of the present invention is 69.85×10 -3 kPa -1 , the highest reached 105.5×10 -3 kPa -1 The flexible capacitive pressure sensor of the present invention can not only accurately measure tiny pressure changes but also adapt to larger external pressure changes. It has excellent mechanical flexibility and stable performance and can be widely used in wearable sports monitoring, medical health monitoring, and human-machine interaction.

[0023] The flexible capacitive pressure sensor of the present invention selects a polymer with good elasticity and pressure-capacitive properties and a liquid crystal to prepare a dielectric layer with a liquid crystal core coaxial fiber structure. The selected polymer and liquid crystal both have good elastic properties, and the liquid crystal has good dielectric anisotropy. The flexible capacitive pressure sensor based on liquid crystal core coaxial fiber is a multilayer composite structure in which the liquid crystal core coaxial fiber is encapsulated by a polymer elastic matrix and flexible electrodes are attached to both sides of the encapsulation film. The fiber in the prepared sensor device is a liquid crystal core coaxial fiber structure, the inner layer is a liquid crystal core, and the outer layer is a polymer sheath. The flexible capacitive pressure sensor based on liquid crystal core coaxial fiber prepared by the present invention has good sensitivity and a wide pressure detection range. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] Figure 1 Schematic diagram of the structure of the flexible capacitive pressure sensor of the present invention;

[0026] Figure 2 The infrared absorption spectra of liquid crystal, polymer and liquid crystal core coaxial fiber in the embodiment;

[0027] Figure 3 This is a scanning electron microscope image of the liquid crystal core coaxial fiber membrane in the embodiment;

[0028] Figure 4 Graph showing the segmented sensitivity of the flexible capacitive pressure sensor prepared in the embodiment;

[0029] Figure 5 : is a sensitivity diagram of the flexible capacitive pressure sensor prepared in the embodiment;

[0030] Figure 6 2 is a comparison chart of the sensitivities of the flexible capacitive pressure sensors prepared in the embodiment and the comparative example;

[0031] Figure 7 This is a loading / unloading cycle stability diagram of the flexible capacitive pressure sensor prepared in the embodiment. DETAILED DESCRIPTION

[0032] The inventive concept of this invention is as follows: To address the difficulty of balancing sensitivity and range in existing flexible capacitive pressure sensors, this invention designs a flexible capacitive pressure sensor using liquid crystal core coaxial fiber as the dielectric layer, based on the idea of ​​optimizing the dielectric layer material and structure of the flexible capacitive pressure sensor. Testing shows that the sensor significantly improves sensitivity while maintaining a wide pressure sensing range and has high linearity. The selected polymer substrate material, electrode material, and dielectric layer material all have good flexibility and durability. The prepared flexible capacitive pressure sensor has a simple process and good wearability.

[0033] like Figure 1 As shown, the flexible capacitive pressure sensor of the present invention is a flexible capacitive pressure sensor prepared with a liquid crystal core coaxial fiber composite dielectric layer, and has flexible capacitive pressure sensing performance. The flexible capacitive pressure sensor of the present invention comprises an upper flexible substrate, an upper electrode layer, a dielectric layer, a lower electrode layer and a lower flexible substrate arranged in sequence from top to bottom; the dielectric layer is a liquid crystal core coaxial fiber composite dielectric layer, which is prepared using a liquid crystal core coaxial fiber; the liquid crystal core coaxial fiber composite dielectric layer has liquid crystal as the core and a polymer as the sheath, that is, the inner layer is the liquid crystal core and the outer layer is the polymer sheath; the liquid crystal molecules in the liquid crystal core coaxial fiber composite dielectric layer are completely coated by the polymer and most of the liquid crystal molecules in the polymer sheath are arranged along the long axis of the fiber; wherein the diameter distribution of the liquid crystal core coaxial fiber is 200~800nm; wherein the liquid crystal is selected as any liquid crystal with high dielectric anisotropy, and the polymer used can be any polymer material with certain flexibility and mechanical strength, such as thermoplastic polyurethane TPU. The upper and lower flexible substrates are flexible films made of polymer materials, providing excellent mechanical support and deformability. For example, polydimethylsiloxane (PDMS) is used. PDMS has an elastic modulus close to that of human skin and can withstand up to 120% tensile strain without breaking, making it suitable for the dynamic deformation requirements of wearable devices. The upper and lower electrode layers are made of low-resistance (resistance <10Ω / sq) flexible materials (such as polyester conductive fabric), which maintain high conductivity while exhibiting excellent mechanical flexibility and durability.

[0034] A method for preparing a flexible capacitive pressure sensor comprises the following steps:

[0035] Step 1: Prepare a high molecular polymer material into a flexible film, cut it into required sizes, and use the cut flexible films as an upper flexible substrate and a lower flexible substrate respectively;

[0036] Step 2: tightly attaching a low-resistance flexible electrode material to one side of the upper flexible substrate and the lower flexible substrate in step 1 in the required size to obtain an upper flexible substrate packaging sheet with an upper electrode layer and a lower flexible substrate packaging sheet with a lower electrode layer;

[0037] Step 3: Prepare a liquid crystal core coaxial fiber membrane using polymer and liquid crystal material to obtain a dielectric layer; place the dielectric layer on the side of the upper flexible substrate packaging sheet with the upper electrode layer obtained in step 2 and closely adhere to it;

[0038] Step 4: Lay the upper flexible substrate packaging sheet with the dielectric layer and the lower flexible substrate packaging sheet with the lower electrode layer together, and lead electrode leads from the upper electrode layer and the lower electrode layer respectively to obtain the above-mentioned flexible capacitive pressure sensor based on liquid crystal core coaxial fiber.

[0039] In the above preparation method, the preparation method of the liquid crystal core coaxial fiber membrane of the present invention in step 3 can use any method to prepare coaxial fibers. The present invention preferably selects the coaxial electrospinning method to prepare liquid crystal core coaxial fibers. The coaxial electrospinning technology can use different materials in the outer and inner layers of the fiber to form a double-layer structure, which makes it possible to combine liquid crystal materials (usually as core materials) with other materials (such as polymers, conductive materials, etc.). During the electrospinning process, the formation of the fibers is affected by the electric field, which can prompt the liquid crystal molecules to be oriented in a certain direction in the fibers.

[0040] A flexible capacitive pressure sensor is used in wearable motion monitoring, medical health monitoring, or human-machine interaction.

[0041] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0042] Example

[0043] Step 1. The main agent and curing agent contained in polydimethylsiloxane (PDMS) (PDMS model is DC184, purchased from Dow Corning, USA) are mixed in a mass ratio of 10:1 and stirred evenly. The mixture is then placed in a vacuum drying oven and defoamed at 0.08 MPa for 30 minutes. The mixture is spin-coated on a glass substrate at 1000 rpm for 45 seconds and cured on a heating plate at 65°C for 3 hours to prepare a polydimethylsiloxane flexible substrate.

[0044] Step 2: Peeling the polydimethylsiloxane flexible substrate obtained in step 1 from the glass substrate, subjecting the obtained film to ultraviolet ozone treatment for 10 minutes, cutting the film, and using the treated films as an upper flexible substrate and a lower flexible substrate, respectively; and cutting the polyester fiber conductive cloth and adsorbing and bonding it to the upper flexible substrate and the lower flexible substrate, respectively, to prepare an upper flexible substrate encapsulation sheet with an upper electrode layer and a lower flexible substrate encapsulation sheet with a lower electrode layer;

[0045] Step 3, 20 wt% thermoplastic polyurethane TPU (model 1185A, 100,000 molecular weight, purchased from BASF AG, Germany) was dissolved in a mixed solvent (DMF:THF mass ratio = 1:1), stirred at 70°C for 6 hours to prepare a polymer electrospinning precursor solution, the obtained polymer electrospinning precursor solution was placed in a 20mL syringe and connected to the outer layer of the coaxial needle through a transparent tetrafluoroethylene tube, the liquid crystal material (4-pentyl-4'-cyanobiphenyl (5CB), purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) was placed in a 1mL syringe and connected to the inner layer of the coaxial needle, the voltage was adjusted to 10~11kV, the spinning propulsion speed of the liquid crystal material was 0.03mL / h, the spinning propulsion speed of the polymer electrospinning precursor solution was 0.3mL / h, the receiving distance was 15cm, and the spinning time was 4h to prepare a composite dielectric layer;

[0046] Step 4: placing the composite dielectric layer on the upper electrode layer of the upper flexible substrate packaging sheet obtained in step 2, and laminating the composite dielectric layer to the conductive surface of the upper flexible electrode layer without glue;

[0047] Step 5: Encapsulate the upper flexible substrate packaging sheet with the composite dielectric layer and the lower flexible substrate packaging sheet obtained in step 2, and lead electrode leads from the upper electrode layer and the lower electrode layer to obtain a flexible capacitive pressure sensor based on liquid crystal core coaxial fiber.

[0048] Comparative Example:

[0049] A flexible capacitive pressure sensor is fabricated by electrospinning without adding liquid crystal material. The preparation method is as follows:

[0050] Step 1. The main agent and curing agent contained in polydimethylsiloxane (PDMS) are mixed in a mass ratio of 10:1 and stirred evenly. The mixture is then placed in a vacuum drying oven and defoamed at 0.08 MPa for 30 minutes. The mixture is spin-coated on a glass substrate at 1000 rpm for 45 seconds and cured on a heating table at 65°C for 3 hours to prepare a polydimethylsiloxane flexible substrate.

[0051] Step 2: Peeling the polydimethylsiloxane flexible substrate obtained in step 1 from the glass substrate, subjecting the obtained film to ultraviolet ozone treatment for 10 minutes, cutting the film, and using the treated films as an upper flexible substrate and a lower flexible substrate, respectively; and cutting the polyester fiber conductive cloth and adsorbing and bonding it to the upper flexible substrate and the lower flexible substrate, respectively, to prepare an upper flexible substrate encapsulation sheet with an upper electrode layer and a lower flexible substrate encapsulation sheet with a lower electrode layer;

[0052] Step 3: 20 wt% of thermoplastic polyurethane (TPU) was dissolved in a mixed solvent (DMF:THF mass ratio = 1:1), and stirred at 70°C for 6 hours to prepare a polymer electrospinning precursor solution. The obtained polymer electrospinning precursor solution was loaded into a 20 mL syringe connected to a needle, and the spinning voltage was adjusted to 10-11 kV, the propulsion speed was 0.3 mL / h, and the spinning receiving distance was 15 cm. The spinning time was set to 4 hours to prepare a dielectric layer.

[0053] Step 4: placing the dielectric layer on the upper electrode layer of the upper flexible substrate packaging sheet obtained in step 2, and laminating the dielectric layer to the conductive surface of the upper flexible electrode layer without glue;

[0054] Step 5: Encapsulate the upper flexible substrate packaging sheet with the dielectric layer and the lower flexible substrate packaging sheet obtained in step 2, and lead electrode leads from the upper electrode layer and the lower electrode layer to obtain a flexible capacitive pressure sensor.

[0055] like Figure 2 The infrared absorption spectra of the liquid crystal, polymer fiber and liquid crystal core coaxial fiber in the embodiment are shown. The liquid crystal material used in the figure has an infrared absorption spectrum of 2240 cm -1 There is a clear sharp absorption peak near the nitrile group (C≡N) (typical range: 2260–2220 cm -1 ). Liquid crystal core coaxial fiber at 2240 cm -1 There is also an obvious sharp absorption peak nearby, but it is weaker than the pure liquid crystal peak, which may be due to intermolecular interaction. The above proves that the liquid crystal core coaxial fiber can be successfully prepared by the coaxial electrospinning method.

[0056] like Figure 3 The following is a scanning electron microscope image of the liquid crystal core coaxial fiber in the embodiment. Figure 3 It can be seen that the liquid crystal core coaxial fibers are randomly stacked to form a porous network. In this embodiment, liquid crystal core coaxial fibers with a smooth surface and no beading are produced by an electrospinning method. The fiber diameter distribution is 200-800 nm.

[0057] In order to characterize the pressure sensing performance of the sensor in this embodiment, the relative capacitance change curves of the flexible capacitive pressure sensor under different pressures are measured as follows: Figure 4As shown in the figure, the sensor has a high sensitivity in the range of 0~20kPa, which is 61.14×10 -3 kPa -1 (See S1 in the figure). The present invention has certain advantages in capturing micro-pressure. As the pressure increases, the sensitivity of the sensor in the range of 20~120kPa is 54.66×10 -3 kPa -1 (See S2 in the figure); the sensor has the highest sensitivity in the range of 120~180kPa, reaching 105.5×10 -3 kPa -1 (See Figure S3); Even in the high pressure range of 160~240kPa, the sensitivity of the sensor remains at 60.05×10 -3 kPa -1 (See Figure S4).

[0058] like Figure 5 The figure shows the sensitivity of the flexible capacitive pressure sensor (represented by TPU / 5CB in the figure) prepared in the embodiment. Figure 5 It can be seen that the overall sensitivity of the sensor in the range of 0~240kPa is 69.85×10 - 3 kPa -1 (See S in the figure), the sensitivity of the sensor changes very slightly in the wide sensing range of 0~240kPa, making the sensor have ultra-high linearity (through Figure 5 The linearity of the sensor is R 2 is 0.99).

[0059] from Figure 6 It can be seen that the sensitivity of the sensor prepared in the embodiment is significantly improved compared with the sensor prepared in the comparative example. Since the polymer liquid crystal fiber film is based on a coaxial fiber structure, the polymer sheath layer protects and stabilizes the orientation of the liquid crystal, and the liquid crystal core contributes to a higher sensitivity of the entire device, which significantly improves the sensitivity of the sensor in a wide detection range.

[0060] like Figure 7 The figure shows the loading / unloading cycle stability of the flexible capacitive pressure sensor prepared in the examples, demonstrating that the sensor maintains relatively stable performance during repeated long-term use. Key performance indicators, such as capacitance change, remain relatively stable over 2,300 loading and unloading cycles, indicating that the sensor accurately and consistently senses pressure changes without significant performance drift or error due to prolonged use or frequent pressure applications. This provides reliable data support for related measurement and monitoring applications.

[0061] In summary, the present invention is a flexible capacitive pressure sensor based on a liquid crystal core coaxial fiber as a dielectric layer, which aims to solve the technical problem that existing flexible capacitive pressure sensors are difficult to achieve high sensitivity and wide detection range unity. Through the material selection and structural design of the flexible capacitive sensor dielectric layer, it is prepared from a flexible fiber membrane. The flexible fiber in the prepared device is a liquid crystal core coaxial fiber structure, the inner layer is a liquid crystal core, and the outer layer is a polymer sheath. The dielectric layer of the flexible capacitive pressure sensor is prepared using liquid crystal core coaxial fiber, which has a wider pressure sensing range and higher sensitivity than ordinary flexible capacitive sensor structures. The present invention achieves high sensitivity of the device within a wide pressure sensing range, while having good linearity, providing a new idea for the field of flexible pressure sensors.

[0062] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A flexible capacitive pressure sensor comprising, arranged in order from top to bottom, an upper flexible substrate, an upper electrode layer, a dielectric layer, a lower electrode layer, and a lower flexible substrate; It is characterized by: The dielectric layer is a liquid crystal core coaxial fiber composite dielectric layer, the inner layer of the liquid crystal core coaxial fiber composite dielectric layer is a liquid crystal core, and the outer layer is a polymer sheath layer.

2. The flexible capacitive pressure sensor according to claim 1, characterized in that: The liquid crystal molecules in the liquid crystal core coaxial fiber composite medium layer are completely covered by the polymer and the liquid crystal molecules are arranged along the long axis of the fiber in the polymer sheath layer.

3. The flexible capacitive pressure sensor according to claim 1, characterized in that: in, The diameter distribution of liquid crystal core coaxial fibers is 200~800nm.

4. The flexible capacitive pressure sensor according to claim 1, characterized in that: The upper flexible substrate and the lower flexible substrate are both flexible films made of high molecular polymer materials.

5. The flexible capacitive pressure sensor according to claim 4, characterized in that: The upper flexible substrate and the lower flexible substrate are both polydimethylsiloxane flexible substrates.

6. The flexible capacitive pressure sensor according to claim 4, characterized in that: The upper electrode layer and the lower electrode layer are both made of flexible materials with a resistance of less than 10Ω / sq.

7. The flexible capacitive pressure sensor according to claim 6, characterized in that: The upper electrode layer and the lower electrode layer are both polyester fiber conductive cloth.

8. A method for preparing the flexible capacitive pressure sensor according to claim 6, characterized in that: The following steps are involved: Step 1: preparing a high molecular polymer material into a flexible film, and using the flexible film as an upper flexible substrate and a lower flexible substrate; Step 2: Select flexible materials with a resistance of less than 10Ω / sq as the upper electrode layer and the lower electrode layer respectively; Step 3: Prepare a liquid crystal core coaxial fiber membrane using polymer and liquid crystal material to obtain a dielectric layer; Step 4: Laminating and packaging the upper flexible substrate, the upper electrode layer, the dielectric layer, the lower electrode layer and the lower flexible substrate in this order, and respectively leading electrode leads from the upper electrode layer and the lower electrode layer to obtain the flexible capacitive pressure sensor.

9. The preparation method according to claim 8, characterized in that Step 3 is to prepare a liquid crystal core coaxial fiber membrane by using polymer and liquid crystal material through a coaxial electrospinning method.

10. Application of the flexible capacitive pressure sensor according to any one of claims 1 to 7 in wearable sports monitoring, medical health monitoring, or human-machine interaction.

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