A method for preparing a bi-oriented nanocarbon fiber-based sensing yarn

Abstract

The application provides a preparation method of a bioriented nanocarbon fiber-based sensing yarn, aiming to solve the problem that existing flexible strain sensors are difficult to simultaneously have high sensitivity and wide strain detection range. The method realizes the characteristics of simultaneously having high sensitivity and wide strain detection range in the same sensor by regulating the orientation degree of nanofibers and combining high-temperature carbonization technology. The main steps include: preparing a polyamide acid solution, optimizing electrospinning parameters to prepare parallel arranged and disordered arranged nanofiber films, imidization and high-temperature carbonization treatment, and compounding the carbonized nanofiber film on an elastic yarn. The sensing yarn preparation method is simple, low in cost, suitable for large-scale popularization and application, and especially suitable for the field of flexible wearable electronics.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and particularly relates to a preparation method of a double-oriented nanocarbon fiber-based sensing yarn. BACKGROUND

[0002] In recent years, flexible wearable electronic devices have shown important application potential in human motion detection, personalized health monitoring, soft robots and human-computer interaction, and have attracted widespread attention. Wearable sensors, as a key component of flexible electronics, are mainly divided into physical, chemical and biological sensors, and play an important role in human physiological monitoring and external environment detection. These wearable sensors have good stretchability, light weight and human-friendly characteristics, and can be integrated on clothes or directly attached to human skin.

[0003] In order to detect the weak physiological signals and the violent limb movements of the human body, high-performance wearable sensors should not only have sensitive strain sensing ability, but also have a wide strain detection range. By compounding conductive nanomaterials with high-stretchable polymers, flexible sensors with a wide strain detection range can be obtained, but the structure of the conductive materials in these sensors does not change significantly under small strain, thereby making their sensitivity low. For example: Cheng et al. reported a graphene-based composite fiber strain sensor, which has a structure similar to a compression spring, which makes its strain detection range reach 100%, but the sensitivity coefficient is only 10 at 1% strain. In order to solve the problem of low sensitivity, the deformation mechanism of conductive nanomaterials, such as slip, crack propagation and breakage mechanism, can be adjusted to improve the sensitivity of the sensor. For example: Araromi et al. proposed a contact-separation type strain detection mechanism based on anisotropic resistance, they patterned the conductive microstructure into a curved shape and encapsulated it in a pre-stretched elastic film, thereby preparing a flexible sensor with a strain coefficient greater than 85,000 under low strain conditions (less than 5%).

[0004] However, for flexible sensors prepared by using the fracture mechanism or the slip mechanism, the resistance often changes greatly or is directly in an open circuit state under large strain conditions, which greatly limits the application range of flexible sensors in human interaction. Therefore, it is an urgent need to prepare flexible wearable strain sensors with high sensitivity and wide strain detection range.

[0005] Through the above analysis, the problems and defects of the prior art are: as a flexible strain sensor that needs to detect the weak physiological signals of the human body and the violent limb movements, it should have both sensitive strain sensing ability and wide strain detection range. However, the current flexible strain sensor often only has one of the two characteristics of ultra-sensitivity and wide strain detection range. Although new materials are continuously emerging through the composite and structural design optimization of flexible sensors, which has promoted the development of the field of flexible wearable electronics, but there are still few flexible sensors that have both ultra-high sensitivity and wide strain range. Therefore, it is very important to develop a new type of flexible sensor that has both high sensitivity and wide strain detection range. SUMMARY

[0006] The purpose of the present application is to solve the problem that the existing flexible strain sensor is difficult to have both high sensitivity and wide strain detection range. By controlling the orientation degree of nanofibers and combining high-temperature carbonization technology, the present application realizes the characteristics of having both high sensitivity and wide strain detection range in the same sensor. Among them, the parallel arranged nanocarbon fibers produce parallel cracks when stretched, which improves the sensitivity; while the disordered arranged nanocarbon fibers ensure the stretchability and continuous path characteristics under large strain. In addition, the preparation method of the sensing yarn is simple, low in cost, suitable for large-scale popularization and application, especially in the field of flexible wearable electronics.

[0007] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0008] The present application provides a preparation method of a double-oriented nanocarbon fiber-based sensing yarn, comprising the following steps:

[0009] Step 1, 0.5108g 4, 4'-diamino diphenyl ether is dissolved in 7.6ml N, N'-dimethylacetamide, and then 1.02:1 of phthalic anhydride is added to obtain a viscous polyamide acid solution; through optimization of electrospinning parameters, two kinds of nanofiber films with parallel arrangement and disordered arrangement are controllably prepared;

[0010] Step 2, the two kinds of nanofiber films with different orientation degrees are pressed by a glass sheet for imidization treatment, and then the imidized nanofiber film is pressed by two thin iron sheets and subjected to high-temperature carbonization in a mixed atmosphere of argon and hydrogen;

[0011] Step 3, covering a layer of polydimethylsiloxane on the elastic yarn, then uniformly coating the disordered arranged carbonized nanofiber film on the elastic yarn, spraying the polydimethylsiloxane solution diluted by n-hexane on the disordered fiber film, when the polydimethylsiloxane is in a semi-cured state, uniformly coating the parallel arranged carbonized nanofiber film, respectively connecting the flexible wires to the two ends of the parallel arranged carbonized nanofiber film and the disordered arranged carbonized nanofiber film by silver glue, connecting the two kinds of films in parallel, only 2 wires are needed, then uniformly coating the polydimethylsiloxane on the parallel arranged carbonized film, and obtaining the double-oriented nanocarbon fiber-based sensing yarn after curing.

[0012] In the above method, the optimized electrospinning parameters in step 1 are as follows:

[0013] The positive voltage and the negative voltage are respectively set to 18kV and -3kV, the flow rate of the push pump is 0.1mm / min, the needle diameter is 0.33mm, the distance from the needle to the receiving plate is 20cm, and the electrospinning process needs to control the environmental humidity to be lower than 50% to ensure that uniform electrospun nanofibers are obtained.

[0014] In the above method, the parallel arranged nanofiber film in step 1 adopts a high-speed birdcage collector, and the disordered arranged nanofiber film adopts a low-speed drum collector.

[0015] In the above method, the thickness of the parallel arranged nanofiber film is 50μm, and the thickness of the disordered arranged nanofiber film is 5μm.

[0016] In the above method, the imidization temperature in step 2 is 280℃, the carbonization temperature of the parallel arranged nanofiber film is 950℃, and the carbonization temperature of the disordered arranged nanofiber film is 750℃.

[0017] In the above method, the size of the carbonized nanofiber film in step 3 is 2.5*60mm2, so as to meet the size requirement of the flexible wearable electronic device.

[0018] In the above method, the volume ratio of polydimethylsiloxane to n-hexane in step 3 is 1:2, and this ratio ensures that the mixed solution can be sprayed.

[0019] The application provides a double-oriented nanocarbon fiber-based sensing yarn, which is prepared by using the preparation method of the double-oriented nanocarbon fiber-based sensing yarn.

[0020] Because the application adopts the above technical means, the following beneficial effects are achieved:

[0021] I. The preparation method of the present application is simple, ingenious, simple and low in cost, and is suitable for large-scale popularization and application. The present application designs two kinds of electrospun fiber films arranged in parallel and disorder, and the films have sensor function by high-temperature carbonization. The two kinds of fiber films with different orientation degrees are combined to obtain a composite flexible strain sensor with high sensitivity and wide strain detection range.

[0022] II. The technical solution of the present application fills the technical gap in the industry at home and abroad: At present, it is generally difficult to consider both ultra-sensitivity and wide strain detection range in the design of flexible sensors at home and abroad. By adjusting the orientation degree of nanofiber, the present application prepares two kinds of fiber films arranged in disorder and in parallel. In the stretching process, the nanocarbon fibers arranged in parallel will form parallel cracks, which makes the resistance of the fiber film increase sharply in a small strain range, so that it has very high sensitivity. The nanocarbon fibers arranged in disorder only move with the stretching of the flexible polymer without obvious cracks, and will not be disconnected even under large strain. By using high-temperature carbonization method to make the fiber film have conductive properties, and by using composite method to prepare a flexible sensor with high sensitivity and wide strain detection range. This design is the first time to use a single raw material to obtain a double-oriented flexible sensor with high sensitivity and wide strain detection range by adjusting the orientation degree of the fiber.

[0023] III. The technical solution of the present application overcomes the technical bias: For a long time, due to the limitation of its own sensing structure, flexible strain sensor is usually difficult to consider both ultra-sensitivity and wide strain detection range. The strain sensor based on crack sensing has high sensitivity, but the appearance of crack also limits the detection of large strain range of this kind of sensor. The strain sensor based on deformation sensing can change its resistance value with the change of strain under large strain condition, but its sensitivity is usually low. We innovatively combine the high sensitivity of parallel fiber film and the wide strain detection range of disordered fiber film to prepare a sensing yarn with high sensitivity and wide strain detection range.

[0024] IV. The two kinds of fiber films arranged in disorder and in parallel have the following advantages compared with single form:

[0025] Compared with inserting two yarns at the same time, the volume occupied by the fabric of the present application is reduced, and the information calculation amount and device cost of signal acquisition and analysis will be reduced. Using parallel detection can effectively reduce the cost. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The preparation method flow chart of the double-oriented nanocarbon fiber-based sensing yarn provided in the embodiments of the present application is provided.

[0027] Figure 2 Scanning electron microscope images of disordered and parallel polyimide nanofibers obtained in Example 1 of this invention;

[0028] Figure 3 Raman spectra of two carbonized polyimide nanofiber films obtained at different temperatures in Example 1 of this invention;

[0029] Figure 4 IV curves of two carbonized polyimide nanofiber films obtained in Example 1 of this invention at different temperatures;

[0030] Figure 5 The cracking of a strain sensor made of disordered and parallel nanofiber thin films when subjected to tension;

[0031] Figure 6 This is a structural diagram of the sensing yarn obtained in Embodiment 1 of the present invention;

[0032] Figure 7 Strain response of strain sensors made of disordered and parallel nanofiber thin films;

[0033] Figure 8 Sensitivity response diagram of the sensing yarn obtained in Embodiment 1 of the present invention;

[0034] Figure 9 The response of the sensing yarn obtained in Embodiment 1 of the present invention to ultra-small strain and ultra-large strain;

[0035] Figure 10 The response time of the sensing yarn obtained in Embodiment 1 of the present invention;

[0036] Figure 11 Stability diagram of the sensing yarn obtained in Embodiment 1 of the present invention. Detailed Implementation

[0037] The embodiments of the present invention will be described in detail below. Although the present invention will be described and illustrated in conjunction with some specific embodiments, it should be noted that the present invention is not limited to these embodiments. On the contrary, any modifications or equivalent substitutions made to the present invention should be covered within the scope of the claims of the present invention.

[0038] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art will understand that the present invention can be practiced without these specific details.

[0039] To demonstrate the inventiveness and technical value of the technical solution of this invention, this section provides specific product or related technology application examples of the technical solution claimed.

[0040] The flexible pressure sensor prepared by the method for fabricating ultrasensitive, wide strain detection range bi-oriented carbon nanofiber-based sensing yarn provided in this invention can be applied in fields such as soft robotics, electronic skin, human-computer interaction, and life monitoring. This invention has achieved some positive results during research and development or use, and indeed has significant advantages compared to existing technologies. The following description combines experimental data and figures.

[0041] Example 1

[0042] This invention provides a method for preparing a dual-oriented nanofiber carbon fiber-based sensing yarn, comprising the following steps:

[0043] Step 1: First, 4,4'-diaminodiphenyl ether is dissolved in N,N'-dimethylacetamide, and then pyromellitic dianhydride with a molar ratio of 1.02:1 to 4,4'-diaminodiphenyl ether is added to obtain a viscous polyamic acid solution. Electrospinning parameters are optimized, including the applied voltage, the extrusion speed of the spinning solution, the distance between the needle and the collector, and the rotational speed of the collecting roller. By controlling the electric field distribution through the collector, controllable preparation of two types of nanofiber films—parallel and disordered—is achieved.

[0044] Step 2: Press two nanofiber films with different orientations onto a glass plate for imidization treatment. Then, press the imidized nanofiber films onto two thin iron plates and perform high-temperature carbonization in a mixed atmosphere of argon and hydrogen.

[0045] Step 3: Cover the elastic yarn with a layer of polydimethylsiloxane, then uniformly wrap the yarn with a randomly arranged carbonized nanofiber film. Spray a polydimethylsiloxane solution diluted with n-hexane onto the randomly arranged fiber film. When the polydimethylsiloxane is in a semi-cured state, uniformly wrap the parallel-arranged carbonized nanofiber film. Connect flexible wires to both ends of the carbonized film (the randomly arranged carbonized nanofiber film and the parallel-arranged carbonized nanofiber film are connected together in parallel) with silver paste. Then uniformly coat the carbonized film with polydimethylsiloxane. After curing, a bi-oriented carbon nanofiber based sensing yarn with ultra-sensitive and wide strain detection range is obtained.

[0046] Furthermore, in step one, the positive voltage and negative voltage are set to 18 and -3kV respectively, the flow rate of the propulsion pump is 0.1mm / min, the needle diameter is 0.33mm, the distance from the needle to the receiving plate is 20cm, and the ambient humidity during the electrospinning process needs to be controlled below 50% to ensure that uniform electrospun nanofibers are obtained.

[0047] Furthermore, in step one, the parallel-arranged nanofiber films employ a high-speed birdcage collector, while the disordered nanofiber films employ a low-speed roller collector. The birdcage collector, due to the parallel arrangement of the rods, has an electric field perpendicular to the crossbars, thus ensuring the parallel arrangement of the electrospun fibers. In contrast, the roller collector, still stretched onto the cylindrical plane by the electric field in the form of a Taylor cone, exhibits a disordered arrangement.

[0048] Furthermore, the parallel-arranged nanofiber film in step 1 has a thickness of 50 μm, which ensures that the sensor made from the carbonized film can generate parallel cracks when stretched; the disordered nanofiber film has a thickness of 5 μm, which ensures that the sensor made from the carbonized film has greater stretchability.

[0049] Furthermore, in step 2, the imidization temperature is 280°C, the carbonization temperature of the parallel-arranged nanofiber film is 950°C, and the thickness of the disordered nanofiber film is 750°C. These two carbonization temperature settings enable the composite sensor to have a sensing gradient.

[0050] Furthermore, the carbonized nanofiber films in step 3 are all 2.5*60mm in size. 2 To meet the size requirements of flexible wearable electronic devices.

[0051] Furthermore, in step 3, the volume ratio of PDMS to n-hexane is 1:2, which ensures that the mixed solution can be sprayed.

[0052] The ultrasensitive inorganic non-metallic sensing yarn prepared according to Example 1 is applied in the field of flexible electronics. The specific flowchart is as follows: Figure 1 As shown. Figure 2 As shown, the nanofiber films collected by the low-speed drum collector are randomly arranged, while those collected by the birdcage collector are parallel arranged. The diameters of both types of fibers with different orientations are concentrated between 200 nm and 300 nm. To construct a sensing gradient, this invention employs differentiated high-temperature carbonization: the disordered nanofiber film is carbonized at 700 °C, and the parallel nanofiber film is carbonized at 950 °C. Figure 3 As shown, the Raman spectra of two carbonized nanofiber films with different degrees of orientation are both at 1590 cm⁻¹. -1 1348cm -1 The appearance of G and D peaks at this point is mainly due to the presence of sp. 2 The vibrations generated by the hybridized crystalline carbon produce this peak, which proves the successful conversion of conductive graphite. Meanwhile, the G and D peaks appear more prominent after carbonization at 950℃, because the higher the carbonization temperature, the higher the crystallinity after carbonization. Figure 4The figure shows the IV curves of two films carbonized at different temperatures under the same size conditions. It can be seen from the figure that the resistivity of the nanofiber film carbonized at 950℃ is much lower than that of the nanofiber film carbonized at 700℃. Furthermore, this invention reduces the thickness of the disordered film to only 5μm, much smaller than the 50μm thickness of the parallel nanofiber film. This treatment further increases the stretchable length of the disordered film; while the thicker parallel nanofiber film also ensures that cracks do not appear during stretching, thus improving its sensing sensitivity. Figure 5 As shown, when a 100% strain is applied to a sensor made of disordered nanofiber thin film, no cracks appear. This characteristic allows the sensor made of disordered nanofiber thin film to sense strains exceeding 100%. However, when a 1% strain is applied to a parallel nanofiber thin film, obvious parallel cracks appear on its surface. This characteristic gives the sensor made of parallel nanofiber thin film extremely high sensitivity. Both types of carbonized nanofiber thin films with different orientations were cut into 2.5*60mm pieces. 2 The process involves coating an elastic yarn with a layer of polydimethylsiloxane (PDMS), then uniformly covering the yarn with a randomly arranged carbonized nanofiber film. A PDMS solution diluted with n-hexane is sprayed onto the disordered fiber film. While the PDMS is in a semi-cured state, a parallel-arranged carbonized nanofiber film is then uniformly covered on top. Flexible wires are attached to both ends of the carbonized film with silver paste. PDMS is then uniformly coated onto the carbonized film. After curing, a highly sensitive, wide-range strain detection bi-oriented carbon nanofiber-based sensing yarn is obtained. The specific structural diagram is shown below. Figure 6 As shown in the figure. Studies on flexible strain sensors with different degrees of orientation revealed that the sensor composed of parallel nanofiber thin films can detect strain as small as 0.005% and exhibits high sensitivity across the entire sensing range, but its maximum detectable strain value is only 5%. In contrast, the sensor composed of disordered nanofiber thin films has a minimum detectable strain range of only 0.25%, but can detect a maximum strain change of 100%. These test results are as follows. Figure 7 As shown. By compositing two nanofiber films with different orientations, this invention yields a dual-oriented nanofiber-based sensing yarn that possesses both ultra-sensitive properties and a wide strain detection range. We applied different strains to both ends of the sensing yarn to study its strain-sensing sensitivity characteristics, such as... Figure 8 and Figure 9 As shown, we found that the sensing yarn can achieve stable sensing of strain as low as 0.005%, with a maximum strain detection range of 100%. Furthermore, the sensor's sensitivity (GF value) across the entire sensing range is higher than 3200, reaching a maximum of 4179. This indicates that the sensing yarn has extremely high application value in sensing both fine deformation and large-scale motion. Figure 10As shown, although the flexible sensing yarn is coated with PDMS, it still exhibits an extremely fast response time of approximately 200ms. However, due to the presence of multiple elastomers in the sensing yarn, creep occurs during the stretching and recovery process, resulting in a longer recovery time of approximately 1000ms. This invention tested the stability of the sensing yarn. After more than 1000 cycles, the yarn's strain response showed no significant change. Specific results are as follows... Figure 11 As shown, this demonstrates that this ultra-sensitive, wide strain detection range dual-oriented carbon nanofiber-based sensing yarn exhibits good stability in strain detection and can be widely applied in the field of flexible wearables.

Claims

1. A method for the preparation of a bi-oriented nanocarbon fiber-based sensing yarn, characterized by, The method comprises the following steps: Step 1: 0.5108 g of 4,4'-diaminodiphenyl ether is dissolved in 7.6 ml of N,N'-dimethylacetamide, and then 1.02:1 of phthalic anhydride is added to obtain a viscous polyamic acid solution; and parallel arrangement and disordered arrangement of two kinds of nanofiber films are controllably prepared by optimizing electrospinning parameters; Step 2: the nanofiber films with different degrees of orientation are pressed by glass sheets for imidization treatment, and then the imidized nanofiber films are pressed by two thin iron sheets and subjected to high-temperature carbonization in a mixed atmosphere of argon and hydrogen; Step 3: a layer of polydimethylsiloxane is coated on the elastic yarn, the disordered carbonized nanofiber film is uniformly coated on the elastic yarn, a polydimethylsiloxane solution diluted with n-hexane is sprayed on the disordered fiber film, when the polydimethylsiloxane is in a semi-cured state, the parallel arranged carbonized nanofiber film is uniformly coated, the flexible wires are connected to both ends of the parallel arranged carbonized nanofiber film by silver glue, and then the polydimethylsiloxane is uniformly coated on the parallel arranged carbonized film, and a double-orientation nanocarbon fiber-based sensing yarn is obtained after curing.

2. A method of making a bi-oriented nanocarbon fiber based sensing yarn as claimed in claim 1, wherein, The optimized electrospinning parameters in step 1 are as follows: The positive voltage and the negative voltage are set to 18 kV and -3 kV respectively, the flow rate of the push pump is 0.1 mm / min, the needle diameter is 0.33 mm, the distance from the needle to the receiving plate is 20 cm, and the electrospinning process needs to control the environmental humidity to be less than 50% to ensure that uniform electrospun nanofibers are obtained.

3. A method of making a bi-oriented nanocarbon fiber based sensing yarn as claimed in claim 1, wherein, The parallel arranged nanofiber film in step 1 is collected by a high-speed birdcage collector, and the disordered arranged nanofiber film is collected by a low-speed drum collector.

4. A method of making a bi-oriented nanocarbon fiber based sensing yarn as claimed in claim 1, wherein, The thickness of the parallel arranged nanofiber film is 50 μm, and the thickness of the disordered arranged nanofiber film is 5 μm.

5. The method for preparing the dual-oriented carbon nanofiber-based sensing yarn as described in claim 1, characterized in that, The imidization temperature in step 2 is 280℃, the carbonization temperature of the parallel arranged nanofiber film is 950℃, and the carbonization temperature of the disordered arranged nanofiber film is 750℃.

6. A method of making a bi-oriented nanocarbon fiber based sensing yarn as claimed in claim 1, wherein, The carbon nanofiber film size in step 3 is 2.5*60mm 2 to meet the size requirements as flexible wearable electronic devices.

7. A method of making a bi-oriented nanocarbon fiber based sensing yarn as claimed in claim 1, wherein, The volume ratio of polydimethylsiloxane to n-hexane in step 3 is 1:

2.

8. A bi-oriented nanocarbon fiber-based sensing yarn, characterized by, The double-orientation nanocarbon fiber-based sensing yarn is prepared by the preparation method of any one of claims 1-7.

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