Preparation method of visual electro-heating-strain sensing difunctional flexible device based on hollow conductive nanofiber yarn

Abstract

The invention discloses a preparation method of a visual electro-heating-strain sensing bifunctional flexible device based on hollow conductive nanofiber yarn, which comprises the following steps: firstly, taking water-soluble vinylon as core yarn, and continuously coating elastic nanofiber on the surface of the core yarn through conjugate electrostatic spinning to prepare elastic nanofiber / vinylon composite wrap yarn; then placing the core yarn in a hot water bath to dissolve the core yarn so as to obtain hollow nanofiber yarn; coating conductive treatment and pre-drafting treatment are synchronously carried out on the hollow nanofiber yarn through a roll-to-roll method, and the hollow conductive nanofiber yarn with a wrinkle structure is obtained; multiple pieces of hollow conductive nanofiber yarn are combined and twisted, and heat and moisture setting treatment is carried out to form yarn with an electric heating-strain sensing function; and finally, the surface of the yarn is coated with a mixed solution of waterborne polyurethane and thermochromic microcapsules to form a visual electro-heating-strain sensing dual-function flexible device, and the visual electro-heating-strain sensing dual-function flexible device can achieve collaborative monitoring of human body movement and physiological information and achieve the visual thermal therapy effect at the same time under the low working voltage. The method has a huge application prospect in the field of intelligent textiles.

Description

Technical Field

[0001] The present invention belongs to the technical field of novel fiber materials, and relates to a preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarns. Background Art

[0002] In recent years, flexible strain sensors, which are the core devices of intelligent textiles, have attracted much attention. Among them, one-dimensional fiber or yarn structures can be efficiently combined with textiles, and their excellent secondary processability has become a current research hotspot. At present, researchers mostly prepare flexible sensing yarns by compounding conductive materials with elastic polymers, and there are mainly three paths: (1) coating conductive materials on the surface of elastic fibers or yarns; (2) developing fibers or yarns by mixing conductive materials / elastic polymers; (3) twisting conductive fiber membranes into yarns. Among them, the second path has problems of poor sensing linearity and low sensitivity coefficient, while the third path has defects of poor continuity. Therefore, the first coating method is considered to be an effective path to realize the continuous preparation of high-performance strain sensing yarns. However, the sensors prepared by coating conductive materials on yarns at present have not been able to simultaneously achieve high sensitivity coefficient, high linearity and wide strain range. At the same time, the demand for multifunctional yarns for intelligent textiles has been gradually put forward. For example, multifunctional yarns that can monitor both human movement and physiological information and achieve efficient and safe visual electrothermal heating effects at low voltages have great development prospects in the fields of health training, assisted exercise and physiotherapy and health care. However, the current sensing yarns have insufficient performance and single functions and are difficult to meet various personalized needs at the same time.

[0003] Therefore, how to develop a visual electrothermal heating-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarns is a problem that needs to be solved at present. Summary of the Invention

[0004] The object of the present invention is to provide a preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarns, so as to solve the problems that existing flexible devices cannot simultaneously achieve high sensitivity coefficient, high linearity and wide strain range, etc.

[0005] The technical solution of the present invention is as follows:

[0006] A preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarns, comprising the following steps:

[0007] (1) Prepare a spinning solution using an elastic polymer. Using water-soluble vinylon as the core yarn, the elastic nanofibers in the spinning solution are coated on the surface of the core yarn by coaxial electrospinning to form an elastic nanofiber / vinylon composite coated yarn. The elastic nanofiber / vinylon composite coated yarn is placed in a hot water bath to dissolve, and the core yarn is removed to obtain hollow nanofiber yarns;

[0008] (2) Unwind the hollow nanofiber yarn from the unwinding device while maintaining a certain draw ratio, and then successively pass it through a yarn guiding device, a coating device, and a drying device to obtain a hollow conductive nanofiber yarn, and then wind it onto a collecting device;

[0009] (3) Combine and twist the hollow conductive nanofiber yarn and perform thermo-humid setting to obtain a yarn with electrothermal heating-strain sensing dual functions;

[0010] (4) Coat the surface of the yarn with electrothermal heating-strain sensing dual functions with a thermochromic solution to obtain a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn.

[0011] Further, in step (1), the elastic polymer is any one of thermoplastic polyurethane, butadiene-styrene block copolymer, and polydimethylsiloxane; the linear density of the water-soluble vinylon is 20S to 60S; the working voltage of the conjugate electrospinning is 13 kV to 19 kV, the flow rate is 0.8 mL / h to 1.4 mL / h, the spinning distance is 12 cm to 25 cm, and the collecting speed of the winding device for conjugate electrospinning is 0.1 m / min to 0.5 m / min.

[0012] Further, in step (1), the heating temperature of the hot water bath is 40°C to 80°C, and the heating time is 12 h to 36 h.

[0013] Further, in step (2), the draw ratio is 0 to 100%.

[0014] Further, in step (2), in the coating solution of the coating device, the conductive material is any one of silver nanowires, silver nanoparticles, gold nanowires, carbon nanotubes, graphene, carbon black nanoparticles, and polyaniline, and the mass percentage of the conductive material is 0.5% to 3%; the number of coating repetitions of the coating device is 2 to 12 times.

[0015] Further, in step (2), the temperature of the drying device is 40°C to 60°C.

[0016] Further, in step (3), during the combination and twisting process, the number of the hollow conductive nanofiber yarns is 2 to 5, and the twist is 300 turns / m to 800 turns / m.

[0017] Further, in step (3), the temperature of the humidification setting is 80°C to 120°C, and the time is 1 h to 4 h.

[0018] Further, in step (4), the number of coating times is 2 to 5 times.

[0019] Further, in step (4), the thermochromic solution is a mixed solution of waterborne polyurethane and thermochromic microcapsules. Among them, the mass fraction of the waterborne polyurethane is 25% - 35%. There are three types of the thermochromic microcapsules: the first type is that the thermochromic microcapsules change from colored to colorless at a temperature of 35°C; the second type is that the thermochromic microcapsules change from colorless to colored at a temperature of 40°C; the third type is that the thermochromic microcapsules change from colorless to colored at a temperature of 60°C. The mass ratio of the first type, the second type and the third type is any one of 4:2:4, 3:3:4 or 2:4:4. The total content of the thermochromic microcapsules is 25% - 35% of the waterborne polyurethane solute.

[0020] The present invention provides a preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on a hollow conductive nanofiber yarn. The prepared hollow nanofiber yarn can enable efficient and uniform attachment of a conductive material on the surface of a hydrophobic yarn, and constructs a hollow conductive nanofiber yarn with a wrinkled structure. Finally, the obtained flexible device has the characteristics of high strain-high sensitivity-high linearity, can achieve rapid heating and cooling under low voltage, synchronously realizes strain sensing, efficient electrothermal conversion and temperature response visualization functions, and has great application prospects in the field of intelligent textiles. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of a preparation device of an elastic nanofiber / vinylon composite coated yarn in the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on a hollow conductive nanofiber yarn according to the present invention;

[0022] Figure 2 It is an electron microscope image of the surface and cross-section of a hollow nanofiber yarn prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on a hollow conductive nanofiber yarn according to the present invention;

[0023] Figure 3 It is a comparison diagram of the wettability of a hollow nanofiber yarn and a non-hollow nanofiber yarn prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on a hollow conductive nanofiber yarn according to the present invention;

[0024] Figure 4 It is a schematic diagram of step (2) in the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on a hollow conductive nanofiber yarn according to the present invention;

[0025] Figure 5SEM image of the surface of the hollow conductive nanofiber yarn with a wrinkled structure prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn of the present invention;

[0026] Figure 6 SEM images of the surface and cross-section of the electrothermal heating-strain sensing dual-functional yarn prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn of the present invention;

[0027] Figure 7 Curves of strain-relative resistance change of the electrothermal heating-strain sensing dual-functional yarn prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn of the present invention under monotonic tension, curves of strain-relative resistance change at different tensile rates, and curves of relative resistance change under different cyclic tensile strains;

[0028] Figure 8 Temperature curves of the electrothermal heating-strain sensing dual-functional yarn prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn of the present invention under constant voltage, temperature curves under variable voltage, and response time diagrams of heating and cooling;

[0029] Figure 9 Color change effect diagrams of the visual electrothermal heating-strain sensing dual-functional flexible device prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn of the present invention at different temperatures. Detailed implementation manners

[0030] The object of the present invention is to provide a preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on a hollow conductive nanofiber yarn, and the specific steps are as follows:

[0031] Step 1, preparing a spinning solution using an elastic polymer, using water-soluble vinylon as the core yarn, please refer to Figure 1 , Figure 1 Schematic diagram of the preparation device of the elastic nanofiber / vinylon composite coated yarn in the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn of the present invention. As Figure 1As shown, elastic nanofibers are coated on the surface of the core yarn through conjugate electrospinning to form an elastic nanofiber / vinylon composite coated yarn. Subsequently, the coated yarn is placed in a hot water bath to dissolve and remove the core yarn, thereby obtaining a hollow nanofiber yarn. Among them, the elastic polymer can be any one of thermoplastic polyurethane, butadiene-styrene block copolymer, and polydimethylsiloxane; the linear density of the water-soluble vinylon is 20S to 60S; the heating temperature of the hot water bath is 40°C to 80°C, and the heating time is 12h to 36h; the working voltage of conjugate electrospinning is 13kV to 19kV, the flow rate is 0.8mL / h to 1.4mL / h, the spinning distance is 12cm to 25cm, and the collection speed of the winding device is 0.1m / min to 0.5m / min.

[0032] Please refer to Figure 2 and Figure 3 , Figure 2 are the SEM images of the surface and cross-section of the hollow nanofiber yarn prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn described in the present invention; Figure 3 is a comparison diagram of the wettability of the hollow nanofiber yarn and the non-hollow nanofiber yarn prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn described in the present invention. As Figure 2 shown, the hollow nanofiber yarn has a hollow structure. As Figure 3 shown, compared with the non-hollow nanofiber yarn, the hollow nanofiber yarn has excellent wetting properties.

[0033] Step 2: Unwind the hollow nanofiber yarn from the unwinding device while maintaining a certain draw ratio, and successively pass through a yarn guiding device, a coating device (an ethanol or water mixed solution containing a conductive material), and a drying device to obtain a hollow conductive nanofiber yarn, and then wind it onto a collecting device. Among them, the draw ratio is 0 to 100%; the conductive material in the coating solution can be any one of nanosilver wires, nanosilver particles, nanogold wires, carbon nanotubes, graphene, nanocarbon black, and polyaniline, and the mass fraction is 0.5% to 3%. The number of repetitions of this coating process is 2 to 12 times. Coating can be repeated under the process conditions of the same draw ratio, or coating can be repeated under the process conditions of different draw ratios; the temperature of the drying area of the drying device is 40°C to 60°C. Please refer to Figure 4 , Figure 4 is a schematic diagram of step (2) in the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn described in the present invention. As shown in the figure, under the condition of a certain draw ratio, the hollow nanofiber yarn uses the capillary action to efficiently and uniformly attach the conductive material to the surface of the yarn to form a hollow conductive nanofiber yarn with a wrinkled structure. Please refer to Figure 5 , Figure 5SEM image of the surface of the hollow conductive nanofiber yarn with a wrinkled structure prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn of the present invention. As Figure 5 shown, the construction of the wrinkled structure is beneficial to improving the strain range and linearity of the flexible device in strain sensing.

[0034] Step 3: Combine and twist the hollow conductive nanofiber yarn, and perform thermo-humid setting to obtain an electrothermal heating-strain sensing dual-functional yarn. The above-mentioned combining step can use the hollow conductive nanofiber yarns prepared under the same process conditions or the hollow conductive nanofiber yarns prepared under different process conditions. The number of combined yarns is 2 to 5, the twist is 300 turns / m to 800 turns / m, the setting temperature is 80°C to 120°C, and the setting time is 1h to 4h.

[0035] Please refer to Figures 6 to 8 , Figure 6 SEM images of the surface and cross-section of the electrothermal heating-strain sensing dual-functional yarn prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn of the present invention; Figure 7 Curves of strain-relative resistance change of the electrothermal heating-strain sensing dual-functional yarn prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn of the present invention under monotonic stretching, curves of strain-relative resistance change at different stretching rates, and curves of relative resistance change under different cyclic stretching strains; Figure 8 Temperature curves of the electrothermal heating-strain sensing dual-functional yarn prepared by the preparation method of a visual electrothermal heating-strain sensing dual-functional flexible device based on the hollow conductive nanofiber yarn of the present invention under constant voltage, temperature curves under variable voltage, and response time diagrams of heating and cooling. As Figure 6 shown, after twisting, the hollow conductive nanofiber yarn still retains the hollow structure, its structure is compact, and the setting effect is good. As Figure 7 shown, the device has the characteristics of high strain-high sensitivity-high linearity. The maximum sensing range is 80% to 140%. Under the strain of 0% to 70%, the linearity is 0.88 to 0.94, and the relative resistance change is 1.3 to 25.3. The signal is stable at different stretching speeds. Figure 8 shown, its structure also has excellent thermal conductivity, high electrothermal conversion efficiency, and good stability. When a voltage of 0.5V to 3V is applied to this structure, the surface temperature can reach 25°C to 65°C, and it maintains good stability within 120s. During the process of increasing and decreasing different voltages, the surface of the yarn shows the same temperature under the same voltage, having certain controllability.

[0036] Step 4: Coat the surface of the electrothermally heated - strain sensing yarn with a thermochromic solution for 2 - 5 times. After each coating, let it dry naturally and then carry out the next coating. The main components of the thermochromic solution are waterborne polyurethane and thermochromic microcapsules. The concentration of waterborne polyurethane is 25% - 35%, and there are three types of thermochromic microcapsules: colored to colorless at 35°C, colorless to colored at 40°C, and colorless to colored at 60°C. The ratio of the three is 4:2:4, 3:3:4, or 2:4:4, and the total content of thermochromic microcapsules is 25% - 35% of the waterborne polyurethane solute.

[0037] Please refer to Figure 9 , Figure 9 the color - changing effect diagrams of the visual electrothermally heated - strain sensing dual - functional flexible device prepared by the preparation method of a visual electrothermally heated - strain sensing dual - functional flexible device based on hollow conductive nanofiber yarn at different temperatures. As Figure 9 shown, at 25°C - 60°C, the color of the device shows colorful changes of yellow - colorless - blue - purple, which is beneficial to improving the convenience, visibility, safety, and sensing stability during electro - heating applications.

[0038] To make the above - mentioned objects, features, and advantages of the present invention more obvious and understandable, the technical solutions of the present invention will be further described below with specific embodiments. However, the present invention is not limited to the listed embodiments, and should also include any other well - known changes within the scope of the rights required by the present invention.

[0039] As used herein, "one embodiment" or "an embodiment" refers to a specific feature, structure, or characteristic that can be included in at least one implementation of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they separate or alternative embodiments that exclude each other.

[0040] Example 1

[0041] The following examples demonstrate a preparation method of a visual electrothermally heated - strain sensing dual - functional flexible device based on hollow conductive nanofiber yarn. The specific steps are as follows:

[0042] (1) Prepare a spinning solution using thermoplastic polyurethane. Using 20S water - soluble vinylon as the core yarn, coat the surface of the core yarn with elastic nanofibers through co - axial electrospinning to form an elastic nanofiber / vinylon composite coated yarn. Subsequently, place the coated yarn in an 80°C water bath and dissolve it for 12 hours to remove the core yarn, thereby obtaining hollow nanofiber yarn. Among them, the working voltage of co - axial electrospinning is 14 kV, the flow rate is 1 mL / h, the spinning distance is 16 cm, and the collection speed of the winding device is 0.1 m / min;

[0043] (2) The hollow nanofiber yarn is unwound from the unwinding device under the states of 100%, 50%, and 0% draw ratios respectively, and successively passes through a yarn guiding device, a coating device (including an ethanol mixed solution of silver nanowires), and a drying device to obtain a hollow conductive nanofiber yarn, and then is wound onto a collecting device. This coating process is repeated 8 times. Among them, the mass fraction of silver nanowires is 1%, and the temperature of the drying zone is 60 °C.

[0044] (3) The hollow conductive nanofiber yarns with three different draw ratios are combined, twisted, and heat and moisture set to obtain a yarn with electrothermal heating - strain sensing dual functions. Among them, the number of combined strands is 3, the twist is 300 turns / meter, the setting temperature is 100 °C, and the setting time is 2 h;

[0045] (4) A thermochromic solution is coated on the surface of the yarn with electrothermal heating - strain sensing dual functions to obtain a visible electrothermal heating - strain sensing dual - functional flexible device based on the hollow conductive nanofiber yarn. Among them, the concentration of water - borne polyurethane is 25%, and there are three kinds of thermochromic microcapsules: color changing from colored to colorless at 35 °C, color changing from colorless to colored at 40 °C, and color changing from colorless to colored at 60 °C. The ratio of the three is 4:2:4, and the total content of the thermochromic microcapsules is 25% of the water - borne polyurethane solute.

[0046] The maximum sensing range of the yarn with electrothermal heating - strain sensing dual functions is 110%. Under the strain of 0% - 70%, the linearity is higher than 0.94, the relative resistance change is greater than 10.1, and the signal is stable under different stretching speeds. This yarn also has excellent electrothermal heating performance and maintains good stability in 120 s; during the process of increasing and decreasing different voltages, the surface of this yarn shows the same temperature under the same voltage, with a certain degree of controllability; when a voltage of 0.5 V - 3 V is applied, the surface temperature can reach 25 °C - 65 °C, and rapid heating and cooling can be achieved. In addition, after coating the thermochromic layer, this flexible device can show four significant color changes of yellow - colorless - blue - purple at 25 °C - 60 °C.

[0047] Example 2

[0048] The following example demonstrates a preparation method of a visible electrothermal heating - strain sensing dual - functional flexible device based on a hollow conductive nanofiber yarn, and the specific steps are as follows:

[0049] (1) Prepare a spinning solution using a butadiene-styrene block copolymer. Use 40S water-soluble vinylon as the core yarn, and coat the surface of the core yarn with elastic nanofibers through conjugate electrospinning to form an elastic nanofiber / vinylon composite coated yarn. Subsequently, place the coated yarn in a 70°C water bath and dissolve it for 18 hours to remove the core yarn, thereby obtaining hollow nanofiber yarn. Among them, the working voltage of conjugate electrospinning is 16 kV, the flow rate is 1.4 mL / h, the spinning distance is 18 cm, and the collection speed of the winding device is 0.3 m / min;

[0050] (2) Unwind the hollow nanofiber yarn from the unwinding device under a draw ratio of 100%, and successively pass through a yarn guiding device, a coating device (an ethanol mixed solution containing silver nanowires), and a drying device to obtain a hollow conductive nanofiber yarn, and then wind it onto a collection device. This coating process is repeated 8 times. Among them, the draw ratio for the 1st - 2nd time is 100%, the draw ratio for the 3rd - 4th time is 75%, the draw ratio for the 5th - 6th time is 50%, the draw ratio for the 7th - 8th time is 25%, and the mass fraction of silver nanowires is 1.2%; the temperature in the drying zone is 50°C;

[0051] (3) Combine, twist, and heat and humidity set the hollow conductive nanofiber yarn to obtain a yarn with electrothermal heating - strain sensing dual functions. Among them, the number of combined strands is 2, the twist density is 600 turns / m, the setting temperature is 120°C, and the setting time is 1.5 h;

[0052] (4) Coat a thermochromic solution on the surface of the yarn with electrothermal heating - strain sensing dual functions to obtain a visual electrothermal heating - strain sensing dual - function flexible device based on the hollow conductive nanofiber yarn. Among them, the concentration of waterborne polyurethane is 35%, the thermochromic microcapsules are three types: colored to colorless at 35°C, colorless to colored at 40°C, and colorless to colored at 60°C, and the ratio of the three is 3:3:4. The total content of thermochromic microcapsules is 30% of the waterborne polyurethane solute.

[0053] The maximum sensing range of the yarn with electrothermal heating - strain sensing dual functions is 104%. Under a strain of 0% - 70%, the linearity is higher than 0.88, the relative resistance change is greater than 17.5, and the signal remains stable at different stretching speeds. This yarn also has excellent electrothermal heating performance and maintains good stability within 120 s; during the process of increasing and decreasing different voltages, the surface temperature of the yarn is the same under the same voltage, showing certain controllability; when a voltage of 0.5 V - 3 V is applied, the surface temperature can reach 25°C - 50°C, and rapid heating and cooling can be achieved. In addition, after coating the thermochromic layer, this flexible device can exhibit four significant color changes: yellow - colorless - blue - purple at 25°C - 60°C.

[0054] Example 3

[0055] The following examples demonstrate a preparation method for a visual electrothermal - strain sensing dual - function flexible device based on hollow conductive nanofiber yarns. The specific steps are as follows:

[0056] (1) Prepare a spinning solution using dimethyl silicone. Use 60S water - soluble vinylon as the core yarn, and through co - axial electrospinning, coat elastic nanofibers on the surface of the core yarn to form elastic nanofiber / vinylon composite coated yarn. Subsequently, place the coated yarn in a 60 °C hot water bath and dissolve it for 24 h to remove the core yarn, thereby obtaining hollow nanofiber yarns. Among them, the working voltage of co - axial electrospinning is 17 kV, the flow rate is 1.2 mL / h, the spinning distance is 16 cm, and the collection speed of the winding device is 0.15 m / min;

[0057] (2) Unwind the hollow nanofiber yarns from the unwinding device in the states of 0% and 100% draw ratios respectively, and successively pass through a yarn guiding device, a coating device (ethanol mixed solution containing carbon nanotubes), and a drying device to obtain hollow conductive nanofiber yarns, and then wind them onto the collection device. This coating process is repeated 10 times. Among them, the mass fraction of carbon nanotubes is 2%; the temperature of the drying zone is 45 °C;

[0058] (3) Combine, twist, and thermally and hydrophilically set the hollow conductive nanofiber yarns to obtain electrothermal - strain sensing dual - function yarns. Among them, the number of combined yarns is 3, including 2 hollow conductive nanofiber yarns with a draw ratio of 0% and 1 hollow conductive nanofiber yarn with a draw ratio of 100%. The twist is 320 turns / m, the setting temperature is 105 °C, and the setting time is 1.8 h;

[0059] (4) Coat a thermochromic solution on the surface of the electrothermal - strain sensing dual - function yarns to obtain a visual electrothermal - strain sensing dual - function flexible device based on hollow conductive nanofiber yarns. Among them, the concentration of water - borne polyurethane is 30%. There are three types of thermochromic microcapsules: colored to colorless at 35 °C, colorless to colored at 40 °C, and colorless to colored at 60 °C. The ratio of the three is 4:2:4, and the total content of thermochromic microcapsules is 30% of the water - borne polyurethane solute.

[0060] The maximum sensing range of the electrothermally heated-strain sensing dual-functional yarn is 108%. Under a strain of 0% to 70%, the linearity is higher than 0.92, the relative resistance change is greater than 25.3, and the signal is stable at different stretching speeds. The yarn also has excellent electrothermal heating performance, maintaining good stability within 120 s; during the process of increasing and decreasing different voltages, the surface of the yarn shows the same temperature at the same voltage, with certain controllability; when a voltage of 0.5 V to 3 V is applied, the surface temperature can reach 25°C to 60°C, and rapid heating and cooling can be achieved. In addition, after coating with a thermochromic layer, the flexible device can exhibit four significant color changes of yellow - colorless - blue - purple at 25°C to 60°C.

[0061] Example 4

[0062] The following examples demonstrate a preparation method for a visual electrothermally heated-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarn, and the specific steps are as follows:

[0063] (1) Prepare a spinning solution using thermoplastic polyurethane. Using 40S water-soluble vinylon as the core yarn, elastic nanofibers are coated on the surface of the core yarn through coaxial electrospinning to form an elastic nanofiber / vinylon composite coated yarn. Subsequently, the coated yarn is placed in a 40°C water bath and dissolved for 36 h to remove the core yarn, thereby obtaining hollow nanofiber yarn. Among them, the working voltage of coaxial electrospinning is 18 kV, the flow rate is 0.9 mL / h, the spinning distance is 15 cm, and the collection speed of the winding device is 0.18 m / min;

[0064] (2) The hollow nanofiber yarn is unwound from the unwinding device under a draw ratio of 100%, and successively passes through a yarn guiding device, a coating device (including an aqueous mixed solution of polyaniline), and a drying device to obtain hollow conductive nanofiber yarn, which is then wound onto a collection device. This coating process is repeated 6 times. Among them, the mass fraction of polyaniline is 1.5%; the temperature of the drying zone is 50°C;

[0065] (3) The hollow conductive nanofiber yarn is combined and twisted, and heat and moisture set to obtain an electrothermally heated-strain sensing dual-functional flexible device. Among them, the number of combined strands is 2, the twist is 700 turns / m, the setting temperature is 115°C, and the setting time is 1.2 h;

[0066] (4) Coat a thermochromic solution on the surface of the electrothermally heated-strain sensing dual-functional yarn to obtain a visual electrothermally heated-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarn. Among them, the concentration of aqueous polyurethane is 30%, and there are three types of thermochromic microcapsules: colored to colorless at 35°C, colorless to colored at 40°C, and colorless to colored at 60°C. The ratio of the three is 2:4:4, and the total content of thermochromic microcapsules is 35% of the aqueous polyurethane solute.

[0067] The maximum sensing range of the electrothermally heated-strain sensing dual-functional yarn is 140%. Under a strain of 0% to 70%, the linearity is higher than 0.94, the relative resistance change is greater than 1.3, and the signal remains stable at different stretching speeds. The yarn also has excellent electrothermal heating performance and maintains good stability within 120 s; during the processes of increasing and decreasing voltages at different levels, the surface temperature of the yarn is the same under the same voltage, showing certain controllability; when a voltage of 0.5 V to 3 V is applied, the surface temperature can reach 25°C to 40°C, and rapid heating and cooling can be achieved. In addition, after coating with a thermochromic layer, the flexible device can exhibit four distinct color changes of yellow - colorless - blue - purple at 25°C to 60°C.

[0068] In summary, for the preparation method of a visual electrothermally heated-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarns described in the present invention, the developed hollow nanofiber yarns enable efficient and uniform attachment of conductive materials on the surface of hydrophobic yarns, constructing hollow conductive nanofiber yarns with a wrinkled structure. The developed functional device has the characteristics of high strain - high sensitivity - high linearity, can achieve rapid heating and cooling at low voltages, and simultaneously realizes visual functions such as strain sensing, efficient electrothermal conversion, and temperature response.

[0069] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A preparation method of a visual electrothermal-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarns, characterized in that, It includes the following steps: (1) Prepare a spinning solution using an elastic polymer. Use water-soluble vinylon as the core yarn, and through conjugate electrospinning, coat the elastic nanofibers in the spinning solution on the surface of the core yarn to form an elastic nanofiber / vinylon composite coated yarn. Place the elastic nanofiber / vinylon composite coated yarn in a hot water bath to dissolve it, and remove the core yarn to obtain hollow nanofiber yarn; (2) Unwind the hollow nanofiber yarn from the unwinding device while maintaining a certain draw ratio, and then successively pass through a yarn guiding device, a coating device, and a drying device to obtain a hollow conductive nanofiber yarn, and then wind it onto a collecting device; (3) Combine, twist, and heat and humidify the hollow conductive nanofiber yarn to obtain a yarn with electrothermal heating-strain sensing dual functions; (4) Coat the surface of the yarn with electrothermal heating-strain sensing dual functions with a thermochromic solution to obtain a visual electrothermal heating-strain sensing dual-functional flexible device based on a hollow conductive nanofiber yarn.

2. The preparation method of a visual electrothermal-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarn according to claim 1, characterized in that: In step (1), the elastic polymer is any one of thermoplastic polyurethane, butadiene-styrene block copolymer, and polydimethylsiloxane; the linear density of the water-soluble vinylon is 20S to 60S; the working voltage of the conjugate electrospinning is 13 kV to 19 kV, the flow rate is 0.8 mL / h to 1.4 mL / h, the electrospinning distance is 12 cm to 25 cm, and the collection speed of the winding device for conjugate electrospinning is 0.1 m / min to 0.5 m / min.

3. The preparation method of a visual electrothermal-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarn according to claim 1, characterized in that: In step (1), the heating temperature of the hot water bath is 40°C to 80°C, and the heating time is 12 h to 36 h.

4. The preparation method of a visual electrothermal-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarn according to claim 1, characterized in that: In step (2), the draw ratio is 0 to 100%.

5. The preparation method of a visual electrothermal-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarn according to claim 1, characterized in that: In step (2), in the coating solution of the coating device, the conductive material is any one of silver nanowires, silver nanoparticles, gold nanowires, carbon nanotubes, graphene, carbon nanoblack, and polyaniline, and the mass percentage of the conductive material is 0.5% to 3%; the number of coating repetitions of the coating device is 2 to 12 times.

6. The preparation method of a visual electrothermal-strain sensing dual-functional flexible device based on hollow conductive nanofiber yarn according to claim 1, characterized in that: In step (2), the temperature of the drying device is 40°C to 60°C.

7. The preparation method of a visual electrothermal-strain sensing dual-functional flexible device based on a hollow conductive nanofiber yarn according to claim 1, characterized in that: In step (3), during the combination and twisting process, the number of hollow conductive nanofiber yarns is 2 to 5, and the twist is 300 twists / m to 800 twists / m.

8. The preparation method of a visual electrothermal-strain sensing dual-functional flexible device based on a hollow conductive nanofiber yarn according to claim 1, characterized in that: In step (3), the temperature for heat and humidity setting is 80°C to 120°C, and the time is 1 h to 4 h.

9. The preparation method of a visual electrothermal-strain sensing dual-functional flexible device based on a hollow conductive nanofiber yarn according to claim 1, characterized in that: In step (4), the number of coating times is 2 to 5 times.

10. The preparation method of a visual electrothermal-strain sensing dual-functional flexible device based on a hollow conductive nanofiber yarn according to claim 1, characterized in that: In step (4), the thermochromic solution is a mixed solution of waterborne polyurethane and thermochromic microcapsules. Among them, the mass fraction of the waterborne polyurethane is 25% - 35%. There are three types of the thermochromic microcapsules: the first type is that the thermochromic microcapsules change from colored to colorless at a temperature of 35°C; the second type is that the thermochromic microcapsules change from colorless to colored at a temperature of 40°C; the third type is that the thermochromic microcapsules change from colorless to colored at a temperature of 60°C. The mass ratio of the first type, the second type and the third type is any one of 4:2:4, 3:3:4 or 2:4:

4. The total content of the thermochromic microcapsules is 25% - 35% of the waterborne polyurethane solute.

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