Multifunctional conductive nanofiber composite material as well as preparation method and application thereof

Abstract

According to the multifunctional conductive nanofiber composite material and the preparation method and application thereof, a conductive nanofiber membrane is prepared through an ultrasonic driving method, and the multifunctional conductive nanofiber composite material has the advantages of being low in filler content, adjustable in material conductivity, low in energy consumption, small in equipment occupied area and easy to operate; by adopting pre-stretching treatment, formation of an RGO scale structure on the surface of the fiber is facilitated, and modification of PDMS can improve the stability of an interface (RGO and the surface of the fiber) and can further guarantee the stability of the scale structure; due to the introduction of PDMS, the hydrophobic property of the material is improved, and the use of fluorine-containing low-surface-energy substances is avoided; according to the invention, hydrophobicity and photo-thermal properties of the material are combined, the application range of the material is greatly widened, and the material is used for stress sensing materials, photo-thermal materials or medical gauzes.

Description

Technical Field

[0001] The invention belongs to the technical field of conductive polymer composite materials, and specifically relates to a multifunctional conductive nanofiber composite material and a preparation method and application thereof. Background Art

[0002] Conductive nanofiber composites are widely used in smart wearable strain sensors due to their unique porous structure, excellent air permeability and controllable conductive network. In most cases, conductive nanofillers are assembled on the surface of elastomeric fibers to form a core-shell structure. In this core-shell structure, strong interfacial interactions become particularly important; otherwise, the conductive fillers may fall off from the fiber matrix, thereby reducing the mechanical properties and strain sensing performance. Typically, conductive nanofillers are modified on the fiber surface with the assistance of hydrogen bonding or ultrasound. For example, PU nanofiber membranes are immersed in carbon nanotube or RGO suspensions and then subjected to ultrasound treatment, during which the carbon nanofillers are modified on the nanofiber surface.

[0003] Although these nanofillers modified on the fiber surface can form excellent conductive networks, the prepared composites usually exhibit low strain sensing sensitivity, i.e., lower response sensitivities (GFs), because the formed perfect conductive network is not easily destroyed during stretching.

[0004] The patent with the publication number CN 109608688 A published on April 12, 2019 discloses a method for preparing a graphene sponge for efficient oil-water separation, the preparation method comprising: (1) clean polyurethane sponge; (2) preparation of graphene oxide; (3) preparation of graphene oxide dispersion; (4) preparation of 2 mg / ml graphene oxide ethanol suspension; (5) adding hydrazine hydrate and the clean melamine sponge obtained in step 1 to the graphene oxide ethanol suspension obtained in step (4), placing it in a microwave chemical reactor, microwave heating reaction for 30-60 minutes, and then placing it in an ultrasonic cleaner for ultrasonic dispersion for 30-50 minutes to increase the distribution uniformity of graphene oxide, taking out the sponge, washing it with deionized water, and drying it in an oven at 80-100°C; (6) preparation of polydimethylsiloxane / n-hexane solution; (7) preparation of graphene sponge for efficient oil-water separation. The prepared graphene sponge has excellent adsorption performance and good hydrophobicity. However, it is not disclosed how to improve its response sensitivity. Summary of the invention

[0005] The object of the present invention is to provide a multifunctional conductive nanofiber composite material and a preparation method thereof, wherein reduced graphene oxide RGO is adsorbed on the surface of a PU nanofiber membrane by ultrasonic driving, the prepared PU / RGO composite fiber membrane is pre-stretched to form a flaky structure on the surface of the material, and then immersed in a PDMS solution, thereby obtaining a super-hydrophobic conductive PU / RGO / PDMS nanofiber composite material. The prepared nanofiber composite material has excellent strain response performance, good stability, excellent cycle performance, wide application range, and high sensing sensitivity; and the material has super-hydrophobicity and photothermal effect, which broadens the application of the material in harsh environments.

[0006] Another object of the present invention is to provide an application of a multifunctional conductive nanofiber composite material, a stress sensing material, a photothermal material or a medical gauze.

[0007] The specific technical solutions of the present invention are as follows:

[0008] A method for preparing a multifunctional conductive nanofiber composite material comprises the following steps:

[0009] 1) immersing the PU nanofiber membrane in a reduced graphene oxide suspension solution, and driving RGO to adsorb on the surface of the PU nanofiber membrane by ultrasound to obtain a PU / RGO composite fiber membrane;

[0010] 2) Pre-stretching the PU / RGO composite fiber membrane;

[0011] 3) The pre-stretched PU / RGO composite fiber membrane is immersed in an alkane solution of PDMS and cured to obtain a multifunctional conductive PU / RGO / PDMS nanofiber composite material.

[0012] In step 1), the PU nanofiber membrane is prepared by electrospinning technology;

[0013] In the PU nanofiber membrane, the mass fraction of PU is 10-15%.

[0014] Preferably, in step 1), the method for preparing the PU nanofiber membrane is: dissolving polyurethane in a mixed solvent of N,N-dimethylformamide and tetrahydrofuran, heating and stirring to dissolve it to obtain a uniform solution; placing the solution on an electrospinning machine for spinning to prepare the PU nanofiber membrane.

[0015] In step 1), the cells are ultrasonically disrupted by an ultrasonic cell disruptor;

[0016] In step 1), the ultrasonic drive has an ultrasonic power of 30 to 150 W and an ultrasonic time of 1 to 90 min.

[0017] In step 1), the concentration of the reduced graphene oxide suspension solution is 1-5 mg / ml; and the solvent is anhydrous ethanol.

[0018] In step 2), the pre-stretching stretches the PU nanofiber membrane by 20%-80% of its original length;

[0019] In step 3), the concentration of the alkane solution of PDMS is 0.1-5 wt %; the alkane solvent is one of alkanes such as heptane, hexane, octane, etc.

[0020] In step 3), the pre-stretched PU / RGO composite fiber membrane is immersed in an alkane solution of polydimethylsiloxane (PDMS) at room temperature for 1 to 20 minutes; during the immersion process, the PU / RGO composite fiber membrane remains in a stretched state.

[0021] In step 3), the curing temperature is 60-100° C. and the time is 1-5 hours.

[0022] The invention provides a multifunctional conductive nanofiber composite material, which is prepared by the above method.

[0023] The present invention adsorbs reduced graphene oxide (RGO) on the surface of polyurethane (PU) nanofiber membrane by ultrasonic driving, and then immerses the pre-stretched PU / RGO nanofiber membrane into polydimethylsiloxane (PDMS) solution to obtain a super-hydrophobic conductive PU / RGO / PDMS nanofiber composite material. The nanofiber composite material prepared by the present invention has excellent strain response performance, good stability, excellent cycle performance, wide application range, and can be used for human motion monitoring; and due to the RGO flaky multi-level structure formed by pre-stretching, the material has super-hydrophobicity and photothermal effect, which broadens the application range of the material in harsh environments; in addition, excellent surface non-adhesion and biocompatibility make the nanofiber membrane applicable to non-invasive medical gauze, showing good hemostatic function; the material preparation process is simple, energy consumption is low, easy to operate, and has good application prospects.

[0024] The invention provides an application of a multifunctional conductive nanofiber composite material for stress sensing materials, photothermal materials or medical gauze.

[0025] In order to improve the sensing sensitivity, the present invention introduces a conductive network with a wrinkled or cracked structure. The structure inspired by biological scales in the present invention is designed for strain sensing. The RGO-modified PU nanofibers are first stretched and then immersed in a PDMS solution. After PDMS is cured, an RGO conductive network with a scale-like structure is constructed. PDMS can not only improve the interfacial interaction between RGO and PU and improve the surface stability, but also give the nanofiber composite material superhydrophobic properties. The superhydrophobic nanofiber composite material has excellent biocompatibility and hemostatic properties. The nanofiber composite strain sensor has a high GF, up to 49.1 in the strain range of 162%-325%.

[0026] Compared with the prior art, the present invention prepares conductive nanofiber membranes through an ultrasonic driving method, which has the advantages of low graphene filler content (low cost), adjustable material conductivity, low energy consumption, small equipment footprint and easy operation; the pre-stretching treatment is beneficial to the formation of RGO flake structure on the fiber surface, and the modification of PDMS can not only improve the stability of the interface (RGO and fiber surface) but also further ensure the stability of the flake structure; the introduction of PDMS improves the hydrophobicity of the material and avoids the use of fluorine-containing low surface energy substances; the present invention combines hydrophobicity with the photothermal properties of the material, which greatly broadens the application range of the material and is used for stress sensing materials, photothermal materials or medical gauze. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a scanning electron microscope image of the morphology of the PU / RGO nanofiber sample subjected to 150W ultrasound for 60 minutes in Example 2;

[0028] Figure 2 The morphology scanning electron microscope images of the samples prepared in the preparation process of the present invention and Example 2; wherein, (a) the preparation process of PU / RGO / PDMS nanofiber composite material; (b) the photo of flexible PU / RGO / PDMS nanofiber composite material; (c) the photo of water droplets on the surface of PU / RGO / PDMS nanofiber composite material in a stretched state; (d) the surface scanning electron microscope image of PU / RGO / PDMS nanofiber composite material; (e) the cross-section scanning electron microscope image of PU / RGO / PDMS nanofiber composite material;

[0029] Figure 3 Surface morphology of the fiber composite membrane after pre-stretching by 50% and soaking in PDMS solution for (a) 0 min; (b) 1 min; (c) 2 min; (d) 5 min;

[0030] Figure 4 The contact angle of the composite material prepared in Example 2 varies with PDMS modification time;

[0031] Figure 5 The response strength of the PU / RGO / PDMS nanofiber composite material prepared in Example 2 of the present invention changes with time under different tensile deformations, and the strain range is: 10%, 50%, 80%, 100%

[0032] (S-PU / RGO);

[0033] Figure 6 This is a graph showing the response signal of the product material of Example 2 used for human motion monitoring over time, a, b: facial expression changes, c: finger bending, d, e, f: different bending of the knee joint;

[0034] Figure 7 These are photos of the product use of Example 2; (a) cell live / dead staining image, (b) statistical graph of the number of active cells corresponding to different materials, (c) experimental graph of different materials used for wound gauze, and (d) image of gauze and fiber membrane used for mouse liver wound dressing. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the 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.

[0036] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0037] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0038] Example 1

[0039] A method for preparing a multifunctional conductive nanofiber composite material comprises the following steps:

[0040] 1) Preparation of PU nanofiber membrane: Take 5g of polyurethane particles and dissolve them in 45g of N, N-dimethylformamide and tetrahydrofuran mixed solvent (4:1w / w), heat and stir to dissolve them, and then obtain a uniform solution; place the solution on an electrospinning machine with a voltage of 12kv to prepare a PU nanofiber membrane. Then, the reduced graphene oxide RGO is dispersed in anhydrous ethanol, and a uniformly dispersed reduced graphene oxide suspension with a concentration of 1mg / ml is obtained under the ultrasonic action of an ultrasonic cell disruptor. The PU nanofiber membrane (8cm long and 4cm wide) is placed in 150mL of reduced graphene oxide suspension and ultrasonicated at 30W power for 1min; take it out, rinse it with deionized water and dry it under air conditions to obtain a PU / RGO composite fiber membrane;

[0041] 2) The PU / RGO composite fiber membrane was pre-stretched by 20%;

[0042] 3) Finally, the PU / RGO fiber membrane pre-stretched by 20% was kept stretched by 20% and immersed in 150mL of 0.1% PDMS solution. The solvent was hexane. The immersion time was 1min at room temperature. After the immersion, the material was placed in a 60°C oven for curing for 1h to obtain a PU / RGO / PDMS nanofiber composite.

[0043] Example 2

[0044] A method for preparing a multifunctional conductive nanofiber composite material comprises the following steps:

[0045] 1) Preparation of PU nanofiber particles: 5g of polyurethane particles were dissolved in 28.3g of N, N-dimethylformamide and tetrahydrofuran mixed solvent (4:1w / w), heated and stirred to dissolve, and then a uniform solution was obtained; the solution was placed on an electrospinning machine with a voltage of 12kv to prepare a PU nanofiber membrane. Then, the reduced graphene oxide RGO was dispersed in anhydrous ethanol, and a uniformly dispersed reduced graphene oxide suspension concentration of 5mg / ml was obtained under the ultrasonic action of an ultrasonic cell disruptor. The PU nanofiber membrane (8cm long and 4cm wide) was placed in 150mL of reduced graphene oxide suspension solution, and ultrasonicated again at a power of 150W for 60min, then taken out, rinsed with deionized water and dried under air conditions to obtain a PU / RGO composite fiber membrane, referred to as: PU / RGO.

[0046] 2) The PU / RGO composite fiber membrane was pre-stretched by 50%;

[0047] 3) The PU / RGO composite fiber membrane pre-stretched by 50% was always kept in a state of being stretched by 50% and immersed in 150 mL of a 0.5% PDMS solution, the solvent was heptane, and the immersion time was 5 min at room temperature. After the immersion, the material was placed in an oven at 80°C for 2 h to obtain a PU / RGO / PDMS nanofiber composite material, referred to as S-PU / RGO; Figure 2 As shown in photo b.

[0048] Figure 2 Middle c is a photo of a water drop on the surface of the stretched PU / RGO / PDMS nanofiber membrane. Figure 2 Figures d and e are scanning electron microscopy images of the fiber membrane surface and cross-section.

[0049] Figure 3 Surface morphology of PU / RGO fiber composite membranes pre-stretched by 50% and immersed in PDMS solution for (a) 0 min; (b) 1 min; (c) 2 min; and (d) 5 min. Figure 3 Soak in medium for 5 minutes Figure 2 d is the electron microscope image of the product of Example 2.

[0050] The contact angle of the nanofiber composite material was tested by a video optical contact angle measuring device. Specifically, the contact angle (CA) value was measured by placing a water droplet (5 μL) at a random position on the surface of the material, and the CA was obtained by averaging three test results. The conductivity of the material was tested by a conductivity meter, and the average value was obtained by averaging the test results at three positions. The conductivity and contact angle of the prepared PU / RGO / PDMS composite material changed with different PDMS immersion times as shown in the figure. Figure 4 As shown, the immersion time range is: 0-30min. Figure 4 This indicates that the optimal time for the fiber membrane to be immersed in the PDMS solution is about 5 minutes. At this time, the contact angle of the material is about 155° and the conductivity is about 0.5S / m. If the time is too short, the contact angle of the material is too low and the hydrophobicity is poor; if the time is too long, the conductivity of the material will drop too much.

[0051] The copper wire is adhered to both ends of the fiber membrane (length × width: 4cm × 1cm) through conductive silver paste, and the wire is connected to the resistance tester for strain sensing testing. The tensile strain size and rate of the nanofiber strain sensor are controlled by the tensile testing machine. The transient resistance of the strain sensor during the cyclic stretching-release process is recorded in real time using an insulation resistance meter. The stretching speed is 50mm / min; the response intensity of the prepared PU / RGO and S-PU / RGO under different tensile deformations changes with time as shown in the following figure. Figure 5 As shown, the strain range is: 10%, 50%, 80%, 100%. Figure 5It can be seen that as the tensile strain increases, the response intensity of the material also increases. In addition, under the same strain, the response signal of each cycle is basically the same, showing the excellent cyclic stability of the material.

[0052] Figure 6 Test and Figure 5 The test method is the same as that of the previous test, except that the fiber membrane is attached to different parts of the human body. The prepared PU / RGO / PDMS composite material has a motion monitoring response diagram for different parts of the human body. Figure 6 As shown in; Figures a and b show changes in facial expressions, where a shows an expression of surprise, b shows a puffed-up face; c shows bent fingers; d, e, f show different bending of the knee joints. Figure 6 The test results show that the fiber sensor can effectively monitor the movement of different parts of the human body and the response signals are basically the same under the same movement. In addition, it can effectively monitor the small movements of facial expressions. This shows the potential application of the material in human body detection sensors. When water, strong acid solution and strong alkali solution were dripped on the surface of the material during the bending process, the response signal intensity was basically the same.

[0053] In vitro coagulation experiment: using different types of gauze (PU / RGO / PDMS gauze and ordinary medical gauze; size: 20.0×20.0mm 2 ). Heparinized blood was mixed with 0.2M CaCl2 at a volume ratio of 10:1 to initiate coagulation, and blood samples were taken and dripped onto the surface of gauze until it was completely covered. A group with no gauze but an equal amount of blood was selected as a control group. After the samples were incubated at 37°C for 0, 3, and 5 minutes, 5.0 mL of deionized water was added to terminate coagulation. Uncoagulated red blood cells would hemolyze and release hemoglobin into the water. The absorbance of the sample supernatant at 540 nm was obtained using a spectrophotometer.

[0054] Coagulation experiment without blood loss: Imitation of a wound bandaged with medical gauze, an opening representing the wound was made on the silicone tube, and the PU / RGO / PDMS gauze was covered with medical tape, and a silicone tube wrapped with ordinary gauze was used as a control. Heparinized blood was mixed with CaCl2 solution to initiate coagulation. The activated blood was filled into the silicone tube and placed in a culture dish. After a period of time, the test tube was removed from the culture dish, and the weight increased in the culture dish due to blood leakage was measured as the amount of blood loss. The test was repeated 3 times (n=3) to obtain the average blood loss.

[0055] Cytotoxicity and cell proliferation assays:

[0056] The dead-live staining method was used to study the cytotoxicity of different groups of gauze (PU / RGO / PDMS gauze and ordinary medical gauze). Normal human liver cell suspension was implanted on the hydrogel and cultured for 1, 3 and 7 days. At the predetermined time point, the cells were stained with calcein acetoxymethyl ester / propidium iodide double staining kit for 10 minutes. Fluorescence images were obtained using an inverted fluorescence microscope. The cell counting method was used to qualitatively evaluate the cell proliferation rate of the extracts of different groups of gauze (PU / RGO / PDMS gauze and ordinary medical gauze).

[0057] Animal experiment: Before the experiment, prepare the gauze from different rows and cut them into the same size (20×20mm 2 ) and sterilized under ultraviolet light for 30 minutes. All instruments used in the operation were sterilized by high pressure. Male mice were selected to expose the liver through abdominal dissection, and a gap (1.0 cm) was made in the mouse liver. Different groups of hemostasis were used. After the material was placed on the liver wound for 3 minutes, it was opened and the bleeding and wound adhesion were observed. The experiment was repeated 3 times for each group to obtain the average value.

[0058] The prepared PU / RGO / PDMS composite material is used for medical gauze. Figure 7 As shown in the figure; (a) Cell live / dead staining image and (b) statistics of the number of active cells corresponding to different materials. (c) Experimental image of different materials used in wound gauze. (d) Image of gauze and fiber membrane used for mouse liver wound dressing. Control refers to the control group mentioned above Figure 7 The experimental description process includes Gauze gauze, Normal Gauze ordinary medical gauze; S-PU / RGO-5 refers to the sample soaked in PDMS solution for 5 minutes, and S-PU / RGO-30 refers to the sample soaked in PDMS solution for 30 minutes. The results of cytotoxicity and anticoagulation experiments show that PU / RGO / PDMS fiber membrane is non-toxic and can be used for medical gauze; in addition, due to its special hydrophobicity, it can effectively avoid secondary damage caused by gauze adhering to wounds when used in medical gauze.

[0059] Example 3

[0060] A method for preparing a multifunctional conductive nanofiber composite material comprises the following steps:

[0061] 1) Preparation of PU nanofiber particles: 5g of polyurethane particles were dissolved in 30.7g of N, N-dimethylformamide and tetrahydrofuran mixed solvent (4:1w / w), heated and stirred to dissolve, and then a uniform solution was obtained; the solution was placed on an electrospinning machine with a voltage of 12kv to prepare a PU nanofiber membrane. Then, the reduced graphene oxide RGO was dispersed in anhydrous ethanol, and a uniformly dispersed reduced graphene oxide suspension concentration of 1.5mg / ml was obtained under the ultrasonic action of an ultrasonic cell disruptor. The PU nanofiber membrane (8cm long and 4cm wide) was placed in 150mL of reduced graphene oxide suspension, and ultrasonicated again at 80W power for 90min, then taken out, rinsed with deionized water and dried under air conditions to obtain a PU / RGO composite fiber membrane.

[0062] 2) The PU / RGO composite fiber membrane is pre-stretched by 80%;

[0063] 3) The PU / RGO composite fiber membrane pre-stretched by 80% was always kept stretched by 80% and immersed in a PDMS solution with a mass concentration of 5wt%, the solvent was octane, and the immersion time at room temperature was 20 minutes. After the immersion, the material was placed in a 100°C oven for curing for 5 hours to obtain a PU / RGO / PDMS nanofiber composite.

[0064] Comparative Example 1

[0065] The preparation method of the PU / RGO / PDMS nanofiber composite material is the same as that described in Example 2, except that the PU / RGO / PDMS nanofiber membrane is not pre-stretched and is directly immersed in the PDMS solution.

[0066] The contact angle of the nanofiber composite material was tested by a video optical contact angle measuring device. The contact angle test result of the fiber membrane of Comparative Example 1, which was not pre-stretched, was about 120°, which did not reach super-hydrophobic performance (>150°), and the contact angle of Example 2 was about 155°. Therefore, pre-stretching can cause a large number of wrinkled structures to appear on the surface of the fiber membrane, effectively improving its surface roughness and giving the fiber membrane super-hydrophobic properties. Since the other applications of the fiber membrane of the present invention are all based on super-hydrophobic properties. Therefore, Comparative Example 1 did not perform other performance tests under the condition of not having super-hydrophobic properties.

[0067] The present invention adsorbs RGO on the surface of PU nanofiber membrane by ultrasonic drive, obtains a uniformly dispersed RGO ethanol solution under the action of ultrasound, and then puts the PU nanofiber film prepared by electrospinning into the RGO suspension. After a period of ultrasound, the RGO is anchored on the surface of the nanofiber, and the nanofiber membrane also changes from white to black. The typical microstructure of this polymer nanofiber composite material can be seen in Figure 1(Scanning electron microscope photo), as can be seen from the figure, the surface of the PU nanofiber is completely wrapped by the uniformly dispersed RGO, and the RGO is closely attached to the fiber surface. The principle of this method is: a large number of cavitation bubbles will be generated in the solution under the action of ultrasound, and these cavitation bubbles will burst to produce microjets, which will crush the RGO agglomerates in the solution, and the RGO will form a uniformly dispersed state; at the same time, the dispersed RGO will hit the polymer nanofiber at high speed, and at the interface between the fiber and RGO, the viscoelastic polymer nanofiber will soften or even partially melt under the action of instantaneous high temperature and high pressure. At this time, the RGO, which is extremely well dispersed under the action of ultrasound, is anchored in situ and adsorbed on the surface of the polymer nanofiber or penetrated into the fiber. These nanofibers with a large aspect ratio (diameter 300-500 nanometers, length from hundreds of microns to several centimeters) become conductive units after adsorbing RGO, and overlap each other to form a conductive network throughout the material. The construction of this conductive network gives the composite film excellent electrical properties. ) After that, the prepared PU / RGO composite fiber membrane is pre-stretched to different degrees by a pretreatment method to form a flaky structure on the surface of the material. In order to maintain the stability of the flaky structure, the pre-stretched membrane is then immersed in a PDMS solution to obtain a super-hydrophobic conductive PU / RGO / PDMS nanofiber composite material (see Figure 2 (SEM photos of d and e in the middle). The study shows that the scaly structure formed by the pre-stretching treatment can effectively increase the roughness of the material and further improve the hydrophobicity of the material. In addition, as a strain sensor, this conductive network connected by scaly RGO can also further improve the response sensitivity of the material.

[0068] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a multifunctional conductive nanofiber composite material, It is characterized in that The preparation method comprises the following steps: 1) immersing the PU nanofiber membrane in a reduced graphene oxide suspension solution, and driving RGO to adsorb on the surface of the PU nanofiber membrane by ultrasound to obtain a PU / RGO composite fiber membrane; 2) Pre-stretching the PU / RGO composite fiber membrane; 3) The pre-stretched PU / RGO composite fiber membrane is immersed in an alkane solution of PDMS and cured to obtain a multifunctional conductive PU / RGO / PDMS nanofiber composite material.

2. The preparation method according to claim 1, It is characterized in that In the PU nanofiber membrane, the mass fraction of PU is 10-15%.

3. The preparation method according to claim 1, It is characterized in that In step 1), the ultrasonic drive has an ultrasonic power of 30 to 150 W and an ultrasonic time of 1 to 90 min.

4. The preparation method according to claim 1 or 2, It is characterized in that In step 1), the concentration of the reduced graphene oxide suspension solution is 1 to 5 mg / ml.

5. The preparation method according to claim 1 or 2, It is characterized in that In step 2), the pre-stretching has a stretching range of 20% to 80%.

6. The preparation method according to claim 1, It is characterized in that In step 3), the concentration of the alkane solution of PDMS is 0.1-5%wt, and the alkane solvent is one of alkanes such as heptane, hexane, octane, etc.

7. The preparation method according to claim 1 or 6, It is characterized in that In step 3), the pre-stretched PU / RGO composite fiber membrane is immersed in an alkane solution of polydimethylsiloxane (PDMS) for 1 to 20 minutes.

8. The preparation method according to claim 1 or 6, It is characterized in that In step 3), the curing temperature is 60-100° C. and the time is 1-5 hours.

9. A multifunctional conductive nanofiber composite material prepared by the preparation method according to any one of claims 1 to 8.

10. An application of the multifunctional conductive nanofiber composite material according to claim 9, It is characterized in that Used for stress sensing materials, photothermal materials or medical gauze.

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