A highly sensitive carbon nanotube-based flexible humidity sensor and its preparation method

Abstract

The present invention provides a highly sensitive carbon nanotube-based flexible humidity sensor and a method for preparing the same. A highly dispersed carbon nanotube conductive ink is impregnated onto a flexible non-woven fabric as a humidity-sensitive layer using a padding method, and nanofibers are sprayed onto the fabric using electrospinning technology as an encapsulation layer to prepare a highly sensitive carbon nanotube-based flexible humidity sensor. The carbon nanotube conductive ink used is uniformly dispersed by sodium heparin, and the presence of sodium heparin gives the sensor higher humidity sensitivity and biosafety. In addition, a viscose fiber non-woven fabric with a three-dimensional porous mesh structure is used as the flexible substrate, and a nanofiber layer is used as the encapsulation layer, both of which have good flexibility, hygroscopicity, breathability, and comfort. The sensor has the advantages of high sensitivity, fast response speed, and high biosafety, and has broad application prospects and market prospects in the fields of flexible sensing equipment, medical care, biosensing, agricultural environmental protection, and the like.

Description

Technical Field

[0001] The present invention belongs to the field of sensors, and in particular relates to a highly sensitive carbon nanotube-based flexible humidity sensor and a preparation method thereof. Background Art

[0002] With the rapid development of modern society, new disruptive technologies such as the Internet of Things and wearable medical devices have emerged, significantly improving people's well-being and quality of life. Flexible electronic sensors play a vital role in practical applications, such as electronic skin, human-computer interaction interfaces, and physiological signal detection. Compared to traditional silicon-based electronic devices, flexible electronic devices exhibit strong conformality to diverse interfaces, offering excellent adhesion to both soft and hard interfaces, and flat and curved surfaces. This unique advantage has led to extensive research and widespread application of flexible electronic sensors in various fields.

[0003] Flexible electronics and novel sensing materials have always played a crucial role in the development of flexible sensors. With the continuous advancement of research, researchers have achieved breakthroughs in this field, significantly contributing to the progress and development of human life. However, various challenges still exist during use. For example, existing flexible electronics suffer from low sensitivity and a narrow detection range, making them unable to accurately sense even small humidity changes. Furthermore, humidity fluctuations of 10% to 30% during storage can affect the detection quality of some products, even exceeding the detection limits of traditional flexible devices. Furthermore, some sensors can lose some functionality or even cease to function in extreme environments. These challenges pose significant challenges to the materials used in flexible electronics and sensors.

[0004] Carbon nanotubes (CNTs) are non-metallic conductive fillers with superior conductivity to copper, a price significantly lower than silver, superior thermal conductivity to diamond, and excellent elastic modulus, tensile strength, and fatigue resistance. Printing conductive inks on flexible electronic textiles holds great promise for widespread application. However, CNTs exhibit high surface energy, strong adsorption between particles, strong electrostatic and van der Waals forces between surface molecules and atoms, and π-π bond interactions, which cause commercial CNTs to aggregate and become difficult to disperse in liquids, particularly water. This self-aggregation of CNTs significantly hinders their development as conductive inks, reducing uniformity, shelf life, and processing performance. Furthermore, CNTs exhibit a degree of cytotoxicity, limiting their application in biological systems. Therefore, finding suitable materials to uniformly and stably disperse CNTs while simultaneously reducing their cytotoxicity and improving the sensitivity of humidity sensing materials would significantly expand the application of CNT conductive inks in biological systems, such as biosensors.

[0005] Heparin sodium is a mucopolysaccharide, the sodium salt of glucosamine sulfate extracted from the intestinal mucosa of pigs, cattle, and sheep. It is secreted by mast cells in the human body and naturally present in the blood. Research has shown that heparin sodium exhibits a significant negative charge in aqueous solution, similar to the function of a surfactant, yet possesses excellent biodegradability. When mixed and dispersed with carbon nanotubes in water, it exhibits excellent dispersion stability and biocompatibility. Developing carbon nanotube-based materials with excellent dispersion uniformity and biocompatibility is essential for promoting the application of carbon nanotubes in healthcare, biosensing, and other fields.

[0006] In addition, sodium heparin itself has excellent water absorption. When combined with carbon nanotubes, it imparts excellent conductivity and a certain degree of humidity sensitivity. Therefore, based on the conductivity of carbon nanotubes, the water absorption and biocompatibility of sodium heparin, and using a flexible and breathable viscose non-woven fabric as the flexible substrate, this new method attempts to construct a highly sensitive carbon nanotube-based flexible humidity sensor. This method is expected to improve the humidity sensor's detection range and biosafety. Summary of the Invention

[0007] To address the challenges of the existing technology, the present invention provides a highly sensitive carbon nanotube-based flexible humidity sensor and its preparation method. The flexible humidity sensor consists of a carbon nanotube-based viscose non-woven fabric, an electrospun nanofiber membrane, conductive silver glue, copper tape, and copper wire. A highly dispersed carbon nanotube conductive ink is impregnated onto the flexible non-woven fabric using a padding method to form a humidity-sensitive layer. The nanofibers are then spray-coated using electrospinning technology to form an encapsulation layer, resulting in a highly sensitive carbon nanotube-based flexible humidity sensor. The carbon nanotube conductive ink is uniformly dispersed with sodium heparin, which imparts enhanced humidity sensitivity and biosafety to the sensor. Furthermore, the flexible substrate, a viscose non-woven fabric with a three-dimensional porous mesh structure, and the encapsulation layer, a nanofiber layer, exhibit excellent flexibility, hygroscopicity, breathability, and comfort. This sensor boasts high sensitivity, fast response, and excellent biosafety, and has broad application and market prospects in flexible sensing devices, healthcare, biosensing, agricultural and environmental protection, and other fields.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor, comprising:

[0010] Step (1): adding heparin sodium to deionized water, stirring and dissolving to obtain a transparent heparin sodium solution, then adding multi-walled carbon nanotubes to the heparin sodium solution, stirring and mixing, and placing in an ice water bath for ultrasonic treatment to obtain a crude carbon nanotube dispersion, further centrifuging, collecting the supernatant and repeating the centrifugation to obtain a highly dispersed carbon nanotube conductive ink;

[0011] Step (2): immersing a non-woven fabric having a three-dimensional porous mesh fiber structure in the highly dispersed carbon nanotube conductive ink prepared in step (1), and performing two immersions and two rollings after immersion under a certain bath ratio condition, and obtaining a conductive carbon nanotube-based non-woven fabric after immersion, rolling and drying, using the conductive carbon nanotube-based non-woven fabric as a humidity sensitive layer and cutting it into a required size and shape, and then using a copper tape adhered with a conductive silver glue to adhere and connect two copper wires at the left and right ends of the carbon nanotube-based non-woven fabric, and the connected copper wires are used as lead electrodes for connecting a test instrument; when the humidity changes, the humidity sensitive layer absorbs moisture, causing the electrical properties of the humidity sensitive layer to change, thereby generating a changing electrical signal;

[0012] Step (3): polyurethane is dissolved in N, N-dimethylformamide, stirred at room temperature to obtain a polyurethane spinning solution, the polyurethane spinning solution is subjected to electrospinning, polyurethane nanofiber membranes are sprayed on the front and back sides of a carbon nanotube-based non-woven fabric connected to a copper wire, the polyurethane nanofiber membrane is used as an encapsulation layer, and after drying, a carbon nanotube-based flexible humidity sensor with high sensitivity is obtained.

[0013] Furthermore, the molecular weight of the heparin sodium in step (1) is 4500-28000, and the heparin sodium accounts for 0.75%-1.50% of the mass of the deionized water.

[0014] Furthermore, the mass ratio of the multi-walled carbon nanotubes to heparin sodium in step (1) is 1.0:(1.5-3.0).

[0015] Furthermore, the ultrasonic time in step (1) is 30 to 60 minutes.

[0016] Furthermore, in step (1), the centrifugal speed is 5000 r / min, each centrifugation is 10-15 min, and the centrifugation is repeated 1-3 times.

[0017] Furthermore, the non-woven fabric in step (2) is viscose fiber non-woven fabric.

[0018] Furthermore, in step (2), the bath ratio is 1:(30-50), the immersion time is 10-15 min, the liquid rate is controlled at 70%-100% by two immersions and two rollings, and the number of immersion-rolling-drying is 1-4 times.

[0019] Furthermore, in step (3), the mass fraction of the polyurethane spinning solution is 12% to 14%, and the stirring time is 6 to 8 hours.

[0020] Furthermore, the electrospinning conditions in step (3) are as follows: the spinning voltage is 16-25 kV, the total flow rate of the spinning solution is 0.04-0.08 mL / min, the vertical distance between the spinning needle and the receiving device is 15-20 cm, the spinning time is 2-6 h, and the receiving drum speed is 150 rpm / min.

[0021] The highly sensitive carbon nanotube-based flexible humidity sensor prepared by the preparation method of the present invention has high sensitivity and excellent biocompatibility.

[0022] The working principle of the carbon nanotube-based flexible humidity sensor described in the present invention is as follows: carbon nanotubes are widely used in humidity sensors as a humidity-sensitive material. Viscose fiber non-woven fabric is composed of a large number of cellulose molecular chains. When the viscose fiber non-woven fabric is impregnated with carbon nanoconductive ink uniformly dispersed with sodium heparin, the carbon nanotubes can be attached to the viscose fiber through non-covalent bond forces. The larger specific surface area of ​​the viscose fiber can increase the contact area between the carbon nanotubes and water vapor, providing conditions for improving the humidity-sensitive performance of the carbon nanotubes. However, the unevenness of the carbon nanotubes on the viscose non-woven fabric will make its conductive network unstable and the humidity response stability poor. The presence of sodium heparin can ensure that the carbon nanotubes are evenly distributed in the viscose non-woven fabric, and a stable and reliable carbon nanotube conductive sensing network can be obtained, thereby improving the stability of the humidity-sensitive response. At the same time, sodium heparin itself is also an excellent humidity-sensitive material, and its synergistic effect with carbon nanotubes can further enhance its humidity-sensitive performance.

[0023] The present invention has the following beneficial effects:

[0024] (1) The present invention creatively uses biocompatible sodium heparin dispersed carbon nanotube conductive ink to prepare a humidity sensor. The ink itself has good biocompatibility and is harmless to the human body. At the same time, it gives the carbon nanotube-based flexible humidity sensor good biocompatibility.

[0025] (2) The carbon nanotube-based flexible humidity sensor prepared by the present invention has a simple preparation process, a safe production process, high sensitivity and good flexibility. At the same time, the encapsulation of the polyurethane nanofiber membrane also gives the sensor excellent fit and wearability, and can be widely used in sensing detection of flexible interfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a photo of the highly dispersed carbon nanotube conductive ink in Example 1 of the present invention and a field emission scanning electron microscope image of the ink after it was dropped on aluminum foil and dried.

[0027] Figure 2The carbon nanotube-based viscose non-woven fabrics are obtained by dipping the viscose non-woven fabric in the highly dispersed carbon nanotube conductive ink of Example 1 and drying it for different times, which are 0 times, 1 time, 3 times, 5 times, and 7 times from left to right.

[0028] Figure 3 Conductive properties of carbon nanotube-based viscose nonwoven fabrics impregnated with different times.

[0029] Figure 4 This is the surface morphology of the carbon nanotube-based viscose non-woven fabric obtained in Example 1.

[0030] Figure 5 This is a schematic structural diagram of the humidity sensor prepared by the present invention.

[0031] Figure 6 1 is a cyclic response curve diagram of the humidity sensor in Example 1 of the present invention under relative humidity conditions of 43% (left) and 75% (right).

[0032] Figure 7 1 is a cyclic response curve diagram of the humidity sensor in Example 6 of the present invention under relative humidity conditions of 43% (left) and 75% (right).

[0033] Figure 8 The linear relationship between the resistance response and relative humidity of the humidity sensors in Example 1 (left) and Example 6 (right) of the present invention.

[0034] Figure 9 Fluorescence photos of cells after culturing with a blank sample (left) and the conductive ink prepared in Example 1 (right) for 24 hours.

[0035] Figure 10 These are the cell viability test results for the blank sample, viscose non-woven fabric, carbon nanotube-based non-woven fabric, and humidity sensor in Example 1. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Example 1

[0038] A method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor, comprising the following steps:

[0039] (1) 1.0 g of heparin sodium with a molecular weight of 6000 was added to 100 mL of deionized water and stirred to dissolve to obtain a transparent heparin sodium solution. Then, 0.5 g of multi-walled carbon nanotubes was added to the heparin sodium solution, stirred and mixed, and placed in an ice water bath for 50 min to obtain a crude carbon nanotube dispersion. The dispersion was further centrifuged at 5000 r / min for 15 min. The supernatant was collected and centrifuged twice to obtain a highly dispersed carbon nanotube conductive ink.

[0040] (2) Immerse 1.0 g of viscose fiber non-woven fabric in 40 mL of highly dispersed carbon nanotube conductive ink. After immersion for 12 minutes, perform two dips and two rolls, controlling the liquid rate at 80%. After one dip, roll, and dry cycle, a carbon nanotube-based non-woven fabric that has been impregnated once is obtained. Cut the carbon nanotube-based non-woven fabric into the required size and shape, and then use copper tape with conductive silver glue to adhere two copper wires to the left and right ends of the carbon nanotube-based non-woven fabric. The connected copper wires serve as lead electrodes for connecting to the test instrument.

[0041] (3) 6.5 g of polyurethane was dissolved in 50 g of N, N-dimethylformamide and stirred at room temperature for 7 h to obtain a polyurethane spinning solution with a mass fraction of 13%. The polyurethane spinning solution was sprayed on the front and back sides of the carbon nanotube-based non-woven fabric connected to the copper wire using an electrospinning device. The spinning voltage was controlled to 20 kV, the total flow rate of the spinning solution was 0.04 mL / min, the vertical distance between the spinning needle and the receiving device was 15 cm, the spinning was carried out for 6 h, the receiving drum speed was 150 rpm / min, and after drying, a carbon nanotube-based flexible humidity sensor with high sensitivity was obtained.

[0042] Example 2

[0043] A method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor, comprising the following steps:

[0044] (1) 1.0 g of heparin sodium with a molecular weight of 6000 was added to 100 mL of deionized water and stirred to dissolve to obtain a transparent heparin sodium solution. Then, 0.5 g of multi-walled carbon nanotubes was added to the heparin sodium solution, stirred and mixed, and placed in an ice-water bath for 60 min to obtain a crude carbon nanotube dispersion. The dispersion was further centrifuged at 5000 r / min for 10 min. The supernatant was collected and centrifuged twice to obtain a highly dispersed carbon nanotube conductive ink.

[0045] (2) Immerse 1.0 g of viscose fiber non-woven fabric in 30 mL of highly dispersed carbon nanotube conductive ink. After immersion for 15 min, perform two dips and two rolls, controlling the liquid rate at 80%. After one dip, roll, and dry cycle, a carbon nanotube-based non-woven fabric that has been impregnated once is obtained. Cut the carbon nanotube-based non-woven fabric into the required size and shape, and then use copper tape with conductive silver glue to adhere two copper wires to the left and right ends of the carbon nanotube-based non-woven fabric. The connected copper wires serve as lead electrodes for connecting to the test instrument.

[0046] (3) 7.0 g of polyurethane was dissolved in 50 g of N, N-dimethylformamide and stirred at room temperature for 8 h to obtain a polyurethane spinning solution with a mass fraction of 14%. The polyurethane spinning solution was sprayed on the front and back sides of the carbon nanotube-based non-woven fabric connected to the copper wire using an electrospinning device. The spinning voltage was controlled to 25 kV, the total flow rate of the spinning solution was 0.06 mL / min, the vertical distance between the spinning needle and the receiving device was 17 cm, the spinning was carried out for 4 h, the receiving drum speed was 150 rpm / min, and after drying, a carbon nanotube-based flexible humidity sensor with high sensitivity was obtained.

[0047] Example 3

[0048] A method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor, comprising the following steps:

[0049] (1) 1.0 g of heparin sodium with a molecular weight of 6000 was added to 100 mL of deionized water and stirred to dissolve to obtain a transparent heparin sodium solution. Then, 0.5 g of multi-walled carbon nanotubes was added to the heparin sodium solution, stirred and mixed, and placed in an ice water bath for ultrasonication for 50 min to obtain a crude carbon nanotube dispersion. The dispersion was further centrifuged at 5000 r / min for 12 min. The supernatant was collected and centrifuged twice to obtain a highly dispersed carbon nanotube conductive ink.

[0050] (2) Immerse 1.0 g of viscose fiber non-woven fabric in 50 mL of highly dispersed carbon nanotube conductive ink. After immersion for 10 min, perform two dips and two rolls, controlling the liquid rate at 80%. After one dip, roll, and dry cycle, a carbon nanotube-based non-woven fabric that has been impregnated once is obtained. Cut the carbon nanotube-based non-woven fabric into the required size and shape, and then use copper tape with conductive silver glue to adhere two copper wires to the left and right ends of the carbon nanotube-based non-woven fabric. The connected copper wires serve as lead electrodes for connecting to the test instrument.

[0051] (3) 6.0 g of polyurethane was dissolved in 50 g of N, N-dimethylformamide and stirred at room temperature for 6 h to obtain a polyurethane spinning solution with a mass fraction of 12%. The polyurethane spinning solution was sprayed on the front and back sides of the carbon nanotube-based non-woven fabric connected to the copper wire using an electrospinning device. The spinning voltage was controlled to 16 kV, the total flow rate of the spinning solution was 0.08 mL / min, the vertical distance between the spinning needle and the receiving device was 15 cm, the spinning was carried out for 2 h, the receiving drum speed was 150 rpm / min, and after drying, a carbon nanotube-based flexible humidity sensor with high sensitivity was obtained.

[0052] Example 4

[0053] A method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor, comprising the following steps:

[0054] (1) 1.5 g of sodium heparin with a molecular weight of 6000 was added to 100 mL of deionized water and stirred to dissolve to obtain a transparent sodium heparin solution. Then, 0.5 g of multi-walled carbon nanotubes was added to the sodium heparin solution, stirred and mixed, and placed in an ice water bath for ultrasonication for 50 min to obtain a crude carbon nanotube dispersion. The dispersion was further centrifuged at 5000 r / min for 15 min. The supernatant was collected and centrifuged twice to obtain a highly dispersed carbon nanotube conductive ink.

[0055] (2) Immerse 1.0 g of viscose fiber non-woven fabric in 30 mL of highly dispersed carbon nanotube conductive ink. After immersion for 15 min, perform two dips and two rolls, controlling the liquid rate at 70%. After two dips and rolls and drying, a double-impregnated carbon nanotube-based non-woven fabric is obtained. Cut the carbon nanotube-based non-woven fabric into the required size and shape, and then use copper tape with conductive silver glue to adhere to the left and right ends of the carbon nanotube-based non-woven fabric to connect two copper wires. The connected copper wires serve as lead electrodes for connecting to the test instrument.

[0056] (3) 7.0 g of polyurethane was dissolved in 50 g of N, N-dimethylformamide and stirred at room temperature for 8 h to obtain a polyurethane spinning solution with a mass fraction of 14%. The polyurethane spinning solution was sprayed on the front and back sides of the carbon nanotube-based non-woven fabric connected to the copper wire using an electrospinning device. The spinning voltage was controlled to 25 kV, the total flow rate of the spinning solution was 0.06 mL / min, the vertical distance between the spinning needle and the receiving device was 17 cm, the spinning was carried out for 4 h, the receiving drum speed was 150 rpm / min, and after drying, a carbon nanotube-based flexible humidity sensor with high sensitivity was obtained.

[0057] Example 5

[0058] A method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor, comprising the following steps:

[0059] (1) 0.75 g of sodium heparin with a molecular weight of 28,000 was added to 100 mL of deionized water and stirred to dissolve to obtain a transparent sodium heparin solution. Then, 0.5 g of multi-walled carbon nanotubes was added to the sodium heparin solution, stirred and mixed, and placed in an ice-water bath for ultrasonication for 30 min to obtain a crude carbon nanotube dispersion. The dispersion was further centrifuged at 5,000 r / min for 15 min. The supernatant was collected and centrifuged again once to obtain a highly dispersed carbon nanotube conductive ink.

[0060] (2) Immerse 1.0 g of viscose fiber non-woven fabric in 40 mL of highly dispersed carbon nanotube conductive ink. After immersion for 15 min, perform two dips and two rolls, controlling the liquid rate at 100%. After three dips, rolls, and drying, a three-times-impregnated carbon nanotube-based non-woven fabric is obtained. Cut the carbon nanotube-based non-woven fabric into the required size and shape, and then use copper tape with conductive silver glue to adhere two copper wires to the left and right ends of the carbon nanotube-based non-woven fabric. The connected copper wires serve as lead electrodes for connecting to the test instrument.

[0061] (3) 6.0 g of polyurethane was dissolved in 50 g of N, N-dimethylformamide and stirred at room temperature for 6 h to obtain a polyurethane spinning solution with a mass fraction of 12%. The polyurethane spinning solution was sprayed on the front and back sides of the carbon nanotube-based non-woven fabric connected to the copper wire using an electrospinning device. The spinning voltage was controlled to 16 kV, the total flow rate of the spinning solution was 0.04 mL / min, the vertical distance between the spinning needle and the receiving device was 25 cm, the spinning was carried out for 4 h, the receiving drum speed was 150 rpm / min, and after drying, a carbon nanotube-based flexible humidity sensor with high sensitivity was obtained.

[0062] Example 6

[0063] A method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor, comprising the following steps:

[0064] (1) 1.0 g of sodium heparin with a molecular weight of 4500 was added to 100 mL of deionized water and stirred to dissolve to obtain a transparent sodium heparin solution. Then, 0.5 g of multi-walled carbon nanotubes was added to the sodium heparin solution, stirred and mixed, and placed in an ice-water bath for ultrasonication for 50 min to obtain a crude carbon nanotube dispersion. The dispersion was further centrifuged at 5000 r / min for 15 min. The supernatant was collected and centrifuged three times to obtain a highly dispersed carbon nanotube conductive ink.

[0065] (2) Immerse 1.0 g of viscose fiber non-woven fabric in 50 mL of highly dispersed carbon nanotube conductive ink. After immersion for 10 min, perform two dips and two rolls, controlling the liquid rate at 80%. After four dips, rolls, and drying, a four-times-impregnated carbon nanotube-based non-woven fabric is obtained. Cut the carbon nanotube-based non-woven fabric into the required size and shape, and then use copper tape with conductive silver glue to adhere two copper wires to the left and right ends of the carbon nanotube-based non-woven fabric. The connected copper wires serve as lead electrodes for connecting to the test instrument.

[0066] (3) 6.5 g of polyurethane was dissolved in 50 mL of N, N-dimethylformamide and stirred at room temperature for 6 h to obtain a polyurethane spinning solution with a mass fraction of 13%. The polyurethane spinning solution was sprayed on the front and back sides of the carbon nanotube-based non-woven fabric connected to the copper wire using an electrospinning device. The spinning voltage was controlled to 20 kV, the total flow rate of the spinning solution was 0.08 mL / min, the vertical distance between the spinning needle and the receiving device was 15 cm, the spinning was carried out for 2 h, the receiving drum speed was 150 rpm / min, and the carbon nanotube-based flexible humidity sensor with high sensitivity was obtained after drying.

[0067] The carbon nanotube conductive ink prepared in Example 1 was photographed and the sample after being dropped on aluminum foil and dried was observed using a field emission scanning electron microscope. The results are as follows: Figure 1 As shown in FIG. , it can be seen that multi-walled carbon nanotubes can be uniformly dispersed in the heparin sodium solution.

[0068] The carbon nanotube-based viscose nonwoven fabrics were obtained by dipping the viscose nonwoven fabric in the highly dispersed carbon nanotube conductive ink of Example 1 and drying it for different times. From left to right, the photos are of dipping times 0, 1, 3, 5, and 7, as shown in FIG. Figure 2 As shown in the figure, it can be seen that the color of the carbon nanotube viscose non-woven fabric gradually turns black with the increase of the number of dipping times. After dipping for 5 times, the color no longer turns black, indicating that the carbon nanotubes on the surface of the viscose non-woven fabric have basically reached saturation after dipping for 5 times.

[0069] The resistance of carbon nanotube-based viscose non-woven fabrics impregnated with different times was tested using a digital source meter. The results are as follows: Figure 3 As shown in the figure, it can be seen that the resistance of the carbon nanotube-based non-woven fabric gradually decreases with the increasing number of impregnation times, which also indicates that there are more carbon nanotubes on the viscose non-woven fabric. However, after 5 impregnations, the resistance of the carbon nanotube-based non-woven fabric does not decrease significantly, which further confirms that the carbon nanotubes on the surface of the viscose non-woven fabric have basically reached saturation after 5 impregnations.

[0070] The surface morphology of the carbon nanotube-based viscose nonwoven fabric obtained in Example 1 was observed using a field emission scanning electron microscope. Figure 4The carbon nanotube non-woven fabric is cut into long strips, and two copper wires are attached to the two ends of the carbon nanotube-based non-woven fabric using copper tape with conductive silver glue. The polyurethane spinning solution is then sprayed onto the front and back of the carbon nanotube-based non-woven fabric connected to the copper wires through an electrospinning process. After drying, a humidity sensor is obtained. The structural diagram is shown in FIG. Figure 5 shown.

[0071] At room temperature, phosphorus pentoxide powder, saturated lithium chloride solution, saturated potassium acetate solution, saturated magnesium chloride solution, saturated potassium carbonate solution, saturated copper chloride solution, saturated sodium chloride solution, and saturated potassium chloride solution were placed in wide-mouth bottles. Under saturated conditions at room temperature, the humidity levels of these solutions represent 0%, 11%, 23%, 33%, 43%, 67%, 75%, and 85%, respectively. A digital source meter was used to measure the humidity-sensing performance of the prepared carbon nanotube-based flexible humidity sensor. The specific steps are: suspend the prepared carbon nanotube-based flexible humidity sensor in the prepared saturated solution wide-mouth bottle, connect it to a digital source meter via copper wires at both ends, and observe and record the resistance change.

[0072] The humidity sensors prepared in Example 1 and Example 6 were placed in wide-mouth bottles filled with saturated potassium carbonate solution and saturated sodium chloride solution respectively to measure the sensing performance. Figure 6 and Figure 7 As shown in the figure, it can be seen that the resistance of the humidity sensor can change rapidly with the change of ambient humidity, and has a fast response performance.

[0073] The resistance of the humidity sensor when not in the jar is recorded as R 0 , the resistance after testing in the wide-mouth bottle after stabilization is recorded as R , the sensitivity of the humidity sensor is △R / R 0 The sensitivity of the humidity sensors in Example 1 (left) and Example 6 (right) at different humidity levels was measured and calculated. The results are shown in FIG. Figure 8 It can be seen that the flexible humidity sensors prepared in Example 1 and Example 6 exhibit excellent sensitivity, good cycle stability and fast response in the entire humidity range.

[0074] Human umbilical vein endothelial cells (HUVECs) were used as the research object. 25 μL of blank sample and ink of Example 1 were added to 100 μL of DMEM containing 10% FBS at 37°C. HUVECs were then cultured in DMEM containing 10% FBS, 100 U / mL penicillin, and 100 μg / mL streptomycin. The temperature and humidity were controlled at 37°C and 95%, respectively, and 5% CO2 was introduced. HUVECs were cultured at a concentration of 5×10 3After the cells were inoculated into 96-well plates at a seeding density of 100 cells / well and cultured for 24 hours, the cell morphology was observed using a fluorescence microscope. Figure 9 As shown, it can be seen that HUVECs cells grow well in both the blank sample and the culture medium containing the ink of Example 1, and the cell viability is close to 100%, indicating that the heparin sodium dispersed carbon nanotube conductive ink has good biocompatibility.

[0075] The CCK-8 assay was used to evaluate the cytotoxicity of the blank sample, viscose nonwoven fabric, carbon nanotube-based nonwoven fabric, and humidity sensor in Example 1 using HUVECs as the research object. The specific operation was as follows: at 37°C, 10×10 mm 2 Sterilized viscose nonwoven fabric, carbon nanotube-based nonwoven fabric, and humidity sensor were immersed in 10 mL of DMEM containing 10% FBS for 24 h to obtain the extract. 25 μL of each sample was added to 100 μL of DMEM containing 10% FBS. HUVECs were then cultured in DMEM containing 10% FBS, 100 U / mL penicillin, and 100 μg / mL streptomycin. The temperature and humidity were controlled at 37 °C and 95%, respectively, and a 5% CO2 concentration was introduced. HUVECs were cultured at a concentration of 5 × 10 3 Cells were seeded into 96-well plates at a density of 100 μL per well. After culturing for 24 h, 100 μL of 10% CCK-8 solution was added to each well of the plate and cultured for 1.5 h. The absorbance of each well was measured at 450 nm in a microplate reader to calculate the cell viability. The results were as follows: Figure 10 It can be seen that the cell viabilities of the extracts of the blank sample, viscose non-woven fabric, carbon nanotube-based non-woven fabric, and humidity sensor in Example 1 of the present invention are all above 95%, indicating that they all have good biocompatibility.

[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor, characterized in that: include: Step (1): adding heparin sodium to deionized water, stirring and dissolving to obtain a transparent heparin sodium solution, then adding multi-walled carbon nanotubes to the heparin sodium solution, stirring and mixing, and placing in an ice water bath for ultrasonic treatment to obtain a crude carbon nanotube dispersion, further centrifuging, collecting the supernatant and repeating the centrifugation to obtain a highly dispersed carbon nanotube conductive ink; Step (2): immersing the non-woven fabric having a three-dimensional porous mesh fiber structure in the highly dispersed carbon nanotube conductive ink prepared in step (1), and performing two dipping and two rolling after dipping under a certain bath ratio condition, and obtaining a conductive carbon nanotube-based non-woven fabric after dipping, rolling and drying, and using the conductive carbon nanotube-based non-woven fabric as a humidity sensitive layer and cutting it into a required size and shape, and then using copper tape adhered with conductive silver glue to adhere two copper wires to the left and right ends of the carbon nanotube-based non-woven fabric, and the connected copper wires are used as lead electrodes for connecting a test instrument; Step (3): dissolving polyurethane in N, N-dimethylformamide, stirring at room temperature to obtain a polyurethane spinning solution, electrospinning the polyurethane spinning solution, spraying polyurethane nanofiber membranes on the front and back sides of a carbon nanotube-based non-woven fabric connected to a copper wire, respectively, using the polyurethane nanofiber membranes as an encapsulation layer, and drying to obtain a carbon nanotube-based flexible humidity sensor with high sensitivity; The non-woven fabric in step (2) is viscose fiber non-woven fabric.

2. The method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor according to claim 1, wherein: The molecular weight of the heparin sodium in step (1) is 4500-28000, and the heparin sodium accounts for 0.75%-1.50% of the mass of the deionized water.

3. The method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor according to claim 1, wherein: The mass ratio of the multi-walled carbon nanotubes to heparin sodium in step (1) is 1.0:(1.5-3.0).

4. The method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor according to claim 1, wherein: The ultrasonication time in step (1) is 30 to 60 minutes.

5. The method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor according to claim 1, wherein: In the step (1), the centrifugal speed is 5000 r / min, each centrifugation is 10-15 min, and the centrifugation is repeated 1-3 times.

6. The method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor according to claim 1, wherein: In the step (2), the bath ratio is 1:(30-50), the dipping time is 10-15 min, the liquid rate is controlled at 70%-100% by two dipping and two rolling, and the number of dipping-rolling-drying is 1-4 times.

7. The method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor according to claim 1, wherein: The mass fraction of the polyurethane spinning solution in step (3) is 12% to 14%, and the stirring time is 6 to 8 hours.

8. The method for preparing a highly sensitive carbon nanotube-based flexible humidity sensor according to claim 1, wherein: The electrospinning conditions in step (3) are as follows: the spinning voltage is 16-25 kV, the total flow rate of the spinning solution is 0.04-0.08 mL / min, the vertical distance between the spinning needle and the receiving device is 15-20 cm, the spinning time is 2-6 h, and the receiving drum speed is 150 rpm / min.

9. A highly sensitive carbon nanotube-based flexible humidity sensor prepared according to the preparation method according to any one of claims 1 to 8.

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