Graphene-coated plastic acicular substrate and method of making

Abstract

This application relates to the field of plastic modification technology, and more particularly to a graphene-coated plastic needle-like substrate and its preparation method. The method includes: S1, performing surface pretreatment and conductivity treatment on the plastic needle-like substrate to obtain a conductive substrate; S2, using the conductive substrate as a working electrode, performing electrophoretic deposition in a graphene oxide electrophoresis solution to obtain a graphene oxide-coated intermediate; S3, performing a reduction treatment on the intermediate to obtain the graphene-coated plastic needle-like substrate. The solution provided by this application can achieve uniform, firm, and controllable-thickness graphene coating on the surface of thermoplastic substrates while avoiding thermal damage. Furthermore, the conductivity of the final product can be precisely and bidirectionally controlled within a wide range through process parameters. It also has the advantages of strong process versatility, environmental friendliness, and low cost.

Description

Technical Field

[0001] This application relates to the field of plastic modification technology, and in particular to a graphene-coated plastic needle-like substrate and its preparation method. Background Technology

[0002] Plastic substrates, with their lightweight, simple molding process, low cost, and excellent chemical stability, have been widely used in fields such as micro-nano sensors, medical consumables, and electronic components. However, plastics themselves are insulating materials, and their lack of conductivity greatly limits their application in conductive applications. Graphene possesses ultra-high conductivity, excellent mechanical properties, and good surface compatibility. Uniformly coating the surface of plastic needle-like substrates with graphene can endow them with controllable conductivity, representing an important approach to functional modification of plastic substrates.

[0003] Currently, methods for coating graphene onto plastic substrates generally suffer from several technical defects: First, the uniformity of the coating layer is poor, making it difficult to ensure consistent circumferential and axial coating of the needle-like substrate, easily leading to problems such as exposed substrate, material accumulation, and cracks; second, the adhesion between graphene and the plastic substrate is weak, making it prone to detachment and affecting product stability; in addition, there is insufficient precision in controlling the coating layer thickness, lacking nanoscale precise thickness control methods; the conductivity control mode is singular, unable to achieve differentiated and precise control; some processes use high-temperature thermal reduction treatment, which easily causes the thermoplastic substrate to melt and deform, resulting in poor process versatility; and some methods require expensive specialized equipment, resulting in high preparation costs and making it difficult to achieve industrial application.

[0004] Therefore, developing a graphene coating method that is process-controllable, provides uniform coating, strong adhesion, and allows for precise bidirectional control of conductivity, while being compatible with various thermoplastic needle-like substrates, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To overcome the problems existing in related technologies, this application provides a method for preparing graphene-coated plastic needle-like substrates. This method can achieve uniform, firm, and thickness-controllable graphene coating on the surface of thermoplastic substrates without thermal damage. Furthermore, the conductivity of the final product can be precisely and bidirectionally controlled within a wide range of process parameters. It also has the advantages of strong process versatility, environmental friendliness, and low cost.

[0006] The first aspect of this application provides a method for preparing a graphene-coated plastic needle-like substrate, comprising the following steps: S1. Perform surface pretreatment and conductive treatment on the plastic needle-shaped substrate to obtain a conductive substrate; S2. Using the conductive substrate as the working electrode, electrophoretic deposition is performed in the graphene oxide electrophoresis solution to obtain an intermediate coated with graphene oxide. S3. The intermediate is reduced to obtain a graphene-coated plastic needle-like substrate.

[0007] In some embodiments, step S1 includes sequential cleaning, chemical roughening, and interface enhancement treatments.

[0008] In some embodiments, the cleaning process includes: ultrasonically cleaning the plastic needle-shaped substrate with an organic solvent, then rinsing it with deionized water, drying it with nitrogen, and drying it with hot air. The ultrasonic cleaning process uses a power of 150-200W, a temperature of 20-30℃, and a time of 10-20 minutes. The hot air drying process uses a temperature of 55-65℃.

[0009] In some embodiments, the chemical roughening treatment is as follows: the plastic needle-shaped substrate is immersed in an acidic roughening solution at 40-50°C for 5-10 minutes, and then rinsed with deionized water, dried with nitrogen, and dried with hot air. The acidic roughening solution is prepared by mixing 20g of chromic anhydride, 300mL of 75wt% sulfuric acid and 100mL of water.

[0010] In some embodiments, the interface enhancement treatment includes: immersing the chemically roughened plastic needle-like substrate in a silane coupling agent solution at room temperature for 5-10 minutes, and then removing it and sequentially drying it with nitrogen and hot air. The silane coupling agent solution is a mixture of KH550, ethanol and water, wherein the volume ratio of ethanol to water is (8-9):1, the mass of KH550 accounts for 1-3% of the total mass of the solution, and the pH value of the silane coupling agent solution is 4.5-5.5.

[0011] In some embodiments, in step S1, the conductive treatment includes: immersing the surface-pretreated plastic needle-shaped substrate in a conductive liquid using a dip-coating method, removing it, suspending it at room temperature to level it, and then drying it with hot air. The dip-coating method has an immersion speed and a lifting speed of 4-6 mm / s.

[0012] In some embodiments, in step S2, the graphene oxide electrophoresis solution is a mixture of magnesium nitrate, water and graphene oxide, wherein the concentration of graphene oxide is 0.2-1 mg / mL and the concentration of magnesium nitrate is 0.01-0.02 mol / L.

[0013] In some embodiments, in step S2, the electrophoretic deposition is performed under a DC voltage of 5-20V and a current of 1-10mA.

[0014] In some embodiments, step S3 includes the reduction process comprising: placing the intermediate in an L-ascorbic acid aqueous solution with a concentration of 8-12 mg / mL at 85-95°C for liquid-phase reduction for 1-6 hours, followed by washing and drying.

[0015] The second aspect of this application provides a graphene-coated plastic needle-like substrate, which is prepared by the above-described method.

[0016] The technical solution provided in this application may include the following beneficial effects: The method of this application first involves a synergistic surface pretreatment of the plastic needle-like substrate, including ultra-clean cleaning, chemical roughening and activation, and silane coupling agent bridging. This removes surface contaminants and increases surface roughness and activity. A chemical bridging layer is constructed on the substrate surface using a silane coupling agent, enhancing the interfacial bonding between the subsequent graphene oxide and the substrate. Next, the pretreated plastic needle-like substrate is conductiveized to prepare an ultrathin, uniform conductive substrate film. This addresses the core issues of plastic insulation and the inability to directly electrophoretically deposit graphene, providing a conductive substrate for subsequent deposition. Then, electrophoretic deposition is performed using this conductive substrate as the anode. A DC electric field drives the directional and uniform deposition of graphene oxide on the substrate surface, achieving precise control of the coating thickness at the nanometer level. Finally, an environmentally friendly L-ascorbic acid liquid-phase reduction method is used to efficiently convert graphene oxide into reduced graphene while avoiding thermal damage to the thermoplastic substrate, ultimately forming a functional conductive coating layer.

[0017] Using the above method, this application can obtain graphene-coated plastic needle-like substrates with a uniform, dense, defect-free surface coating, strong adhesion, excellent axial conductivity, and high circumferential uniformity. This method is process-controllable and has good repeatability; by adjusting deposition parameters and the degree of reduction, it can achieve a process range of 10⁻¹⁰. 6 Ω / sq enables precise, bidirectional control of the material's conductivity over a wide range, thereby meeting the differentiated needs of various application scenarios and possessing good process versatility and industrial application prospects. Detailed Implementation

[0018] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] The graphene oxide aqueous dispersion used in the embodiments of this application is a non-precipitated and non-agglomerated dispersion with a sheet diameter of 1-5 μm, 1-3 layers, a solid content of 10 mg / mL, and an absolute value of Zeta potential >40 mV; the aqueous ultrathin conductive carbon paste is a conventional product with a solid content of 5% and a particle size <1 μm; all chemical reagents are analytical grade, and the experimental water is deionized water; all instruments used are conventional laboratory instruments.

[0020] It should be noted that the needle-shaped substrate described in this application commonly has diameters ranging from micrometers to millimeters (e.g., 0.1mm-2mm) and lengths ranging from a few millimeters to a few centimeters. The specific specifications need to be determined based on the final application (e.g., sensor probes, microelectrodes, medical catheters, etc.).

[0021] Example 1 S1. Perform surface pretreatment and conductive treatment on the plastic needle-shaped substrate; S11. Cleaning treatment: Take a needle-shaped ABS substrate with a diameter of 1 mm and a length of 2 cm, hold both ends with PTFE tweezers, wipe the visible stains on the surface with anhydrous ethanol, then fix it vertically on a PTFE clamp and place it in 50 mL of anhydrous ethanol. Ultrasonically clean it for 15 min at 180 W and 25 °C. After removal, rinse three times with deionized water, then ultrasonically clean it again in deionized water for 5 min. Next, blow it vertically with high-purity nitrogen gas, and finally dry it in a 60 °C hot air dryer for 30 min. After removal, place it in a desiccator to cool to room temperature.

[0022] S12. Chemical roughening treatment: Prepare an acidic roughening solution. Add 20g of chromic anhydride to 100mL of deionized water, then slowly add 300mL of 75wt% concentrated sulfuric acid while stirring, stirring until completely dissolved. Immerse the cleaned needle-shaped ABS substrate in the above roughening solution and soak at 45℃ for 8 minutes. After removal, rinse with plenty of flowing deionized water for 5 minutes, then ultrasonically clean with deionized water for 3 minutes. After drying with high-purity nitrogen, dry with hot air at 60℃ for 30 minutes, and place in a desiccator to cool for later use.

[0023] S13, Interface Enhancement Processing: Prepare the silane coupling agent solution. Mix 90 mL of anhydrous ethanol with 10 mL of deionized water, add 1.6 g of silane coupling agent KH550, adjust the pH to 5.0 with glacial acetic acid, and continue stirring at room temperature for 30 min to ensure complete hydrolysis. Vertically immerse the chemically roughened needle-shaped ABS substrate into the silane coupling agent solution and soak at room temperature for 5 min. After removal, hang vertically and gently blow dry the excess liquid on the surface with high-purity nitrogen gas, then dry in a forced-air oven at 100℃ for 10 min, and cool in a desiccator.

[0024] S14, Conductivity treatment: Prepare the conductive liquid by mixing 1g of water-based ultrathin conductive carbon paste with a solid content of 5% and a particle size of <1μm with 9g of deionized water, stirring thoroughly, and then ultrasonically dispersing for 10min. Vertically fix the interface-reinforced needle-shaped ABS substrate onto a lifting machine, suspending the lower end of the needle and aligning it with the center of the liquid surface. Immerse and lift at a uniform speed of 5mm / s. After removal, allow to hang and level at room temperature for 2min, then dry in a forced-air oven at 60℃ for 15min. Use a digital multimeter to test the resistance at the upper, middle, and lower ends of the needle, ensuring the overall needle resistance is <1kΩ and the relative resistance deviation at different locations is <10%. Once the standard is met, the conductive substrate with a uniform conductive base film is obtained.

[0025] S2. Using the conductive substrate as the working electrode, electrophoretic deposition is performed in a graphene oxide electrophoresis solution. S21. Prepare graphene oxide electrophoresis buffer. Weigh 0.256 g of magnesium nitrate hexahydrate using an electronic analytical balance and place it in a 100 mL volumetric flask. Add 80 mL of deionized water and shake until completely dissolved. Pipette 5 mL of a 10 mg / mL graphene oxide aqueous dispersion into the volumetric flask and add deionized water to the 100 mL mark. Pour the mixture into a 250 mL beaker, place a polytetrafluoroethylene magnetic stir bar inside, and stir at 300 rpm at room temperature for 30 min. Then, ultrasonically disperse the mixture in a 300 W ice-water bath for 20 min to obtain a homogeneous graphene oxide electrophoresis buffer with a graphene oxide concentration of 0.5 mg / mL and a magnesium nitrate concentration of 0.01 mol / L.

[0026] S22. Using a 100mL glass beaker as the electrophoresis tank, pour in the above-mentioned graphene oxide electrophoresis solution and place a polytetrafluoroethylene (PTFE) magnetic stir bar inside. Two 1mm thick 304 stainless steel plates are vertically fixed to the sides of the electrophoresis tank as counter electrodes, with the electrode spacing adjusted to 7cm and their lower ends immersed 3cm below the liquid surface. The conductive substrate obtained in step S12 is vertically fixed to the PTFE clamp as the working electrode and placed in the center of the two pairs of electrodes, ensuring that its effective coating area is completely immersed in the electrophoresis solution and does not contact the tank wall or the stir bar. Connect a DC power supply, with the positive terminal connected to the conductive substrate and the negative terminal connected to the stainless steel electrode. Turn on the magnetic stir bar and set the speed to 100rpm. First, turn off the power output and zero the voltage and current. Then, slowly adjust the power output voltage to 10V. Once the current stabilizes at 3mA, start timing for deposition for 20 seconds. After deposition, immediately turn off the power, disconnect the circuit, remove the sample vertically, gently rinse it three times with deionized water in a parallel direction, blow it dry vertically downwards with high-purity nitrogen, and then vacuum dry it at 60°C for 20 minutes to obtain the graphene oxide-coated intermediate.

[0027] S3. Perform a reduction process on the intermediate; Prepare a 10 mg / mL L-ascorbic acid aqueous solution by weighing 1 g of L-ascorbic acid and dissolving it in 100 mL of deionized water, stirring until completely dissolved. Pour the solution into a 250 mL three-necked flask and heat it in an oil bath to 90 °C, maintaining a constant temperature. The graphene oxide-coated intermediate obtained in step S22 is vertically suspended in the flask, ensuring the needle is completely immersed in the solution without touching the flask walls or bottom. Seal the flask and reduce it at 90 °C for 1.5 h. After reduction, turn off the oil bath, remove the sample, and immediately rinse it vertically three times with 90 °C deionized water. After drying with high-purity nitrogen, vacuum dry it at 60 °C for 30 min to finally obtain the 5-10 nm ultrathin graphene-coated plastic needle-like substrate.

[0028] Example 2 S1. Perform surface pretreatment and conductive treatment on the plastic needle-shaped substrate; S11. Cleaning treatment: Take a needle-shaped ABS substrate with a diameter of 1 mm and a length of 2 cm, hold both ends with PTFE tweezers, wipe the visible stains on the surface with anhydrous ethanol, then fix it vertically on a PTFE clamp and place it in 50 mL of anhydrous ethanol. Ultrasonically clean it for 15 min at 180 W and 25 °C. After removal, rinse three times with deionized water, then ultrasonically clean it again in deionized water for 5 min. Next, blow it vertically with high-purity nitrogen gas, and finally dry it in a 60 °C hot air dryer for 30 min. After removal, place it in a desiccator to cool to room temperature.

[0029] S12, Chemical roughening treatment: Prepare an acidic roughening solution by adding 20g of chromic anhydride to 100mL of deionized water, followed by slowly adding 300mL of 75wt% concentrated sulfuric acid while stirring until completely dissolved. Immerse the cleaned needle-shaped ABS substrate in the above roughening solution and soak at a constant temperature of 45℃ for 8 minutes. After removal, rinse with plenty of flowing deionized water for 5 minutes, then ultrasonically clean with deionized water for 3 minutes. After drying with high-purity nitrogen, dry with hot air at 60℃ for 30 minutes, and then cool in a desiccator for later use.

[0030] S13, Interface Enhancement Processing: Prepare the silane coupling agent solution. Mix 90 mL of anhydrous ethanol with 10 mL of deionized water, add 1.6 g of silane coupling agent KH550, adjust the pH to 5.0 with glacial acetic acid, and continue stirring at room temperature for 30 min to ensure complete hydrolysis. Vertically immerse the chemically roughened needle-shaped ABS substrate into the silane coupling agent solution and soak at room temperature for 5 min. After removal, hang vertically and gently blow dry the excess liquid on the surface with high-purity nitrogen gas, then dry in a forced-air oven at 100℃ for 10 min, and cool in a desiccator.

[0031] S14, Conductivity treatment: Prepare the conductive liquid by mixing 1g of water-based ultrathin conductive carbon paste with a solid content of 5% and a particle size of <1μm with 9g of deionized water, stirring thoroughly, and then ultrasonically dispersing for 10min. Vertically fix the interface-reinforced needle-shaped ABS substrate onto a lifting machine, suspending the lower end of the needle and aligning it with the center of the liquid surface. Immerse and lift at a uniform speed of 5mm / s. After removal, allow to hang and level at room temperature for 2min, then dry in a forced-air oven at 60℃ for 15min. Use a digital multimeter to test the resistance at the upper, middle, and lower ends of the needle, ensuring the overall needle resistance is <1kΩ and the relative resistance deviation at different locations is <10%. Once the standard is met, the conductive substrate with a uniform conductive base film is obtained.

[0032] S2. Using the conductive substrate as the working electrode, electrophoretic deposition is performed in a graphene oxide electrophoresis solution. S21. Preparation of graphene oxide electrophoresis buffer: Weigh 0.256 g of magnesium nitrate hexahydrate using an electronic analytical balance, place it in a 100 mL volumetric flask, add 80 mL of deionized water, and shake until completely dissolved. Pipette 5 mL of a 10 mg / mL graphene oxide aqueous dispersion into the volumetric flask, and add deionized water to the 100 mL mark. Pour the mixture into a 250 mL beaker, place a polytetrafluoroethylene magnetic stir bar inside, stir at 300 rpm at room temperature for 30 min, and then sonicate in a 300 W ice-water bath for 20 min to obtain a homogeneous graphene oxide electrophoresis buffer with a graphene oxide concentration of 0.5 mg / mL and a magnesium nitrate concentration of 0.01 mol / L.

[0033] S22, Electrophoretic Deposition: Using a 100mL glass beaker as the electrophoresis tank, pour in the above-mentioned graphene oxide electrophoresis solution and place a polytetrafluoroethylene (PTFE) magnetic stir bar. Two 1mm thick 304 stainless steel plates are vertically fixed on both sides of the electrophoresis tank as counter electrodes, with the electrode spacing adjusted to 7cm and their lower ends immersed 3cm below the liquid surface. The conductive substrate obtained in step S1 is vertically fixed on the PTFE clamp as the working electrode and placed in the center of the two pairs of electrodes, ensuring that its effective coating area is completely immersed in the electrophoresis solution and does not contact the tank wall or the stir bar. Connect a DC power supply, with the positive terminal connected to the conductive substrate and the negative terminal connected to the stainless steel electrode. Turn on the magnetic stir bar and set the speed to 100rpm. First, turn off the power output and zero the voltage and current. Then, slowly adjust the power output voltage to 15V. Once the current stabilizes at 6mA, start timing and begin deposition for 5 minutes. After deposition, immediately turn off the power, disconnect the circuit, remove the sample vertically, gently rinse it three times with deionized water in a parallel direction, blow it dry vertically downwards with high-purity nitrogen, and then vacuum dry it at 60°C for 20 minutes to obtain the graphene oxide-coated intermediate.

[0034] S3. Perform a reduction process on the intermediate; Prepare a 10 mg / mL L-ascorbic acid aqueous solution by dissolving 1 g of L-ascorbic acid in 100 mL of deionized water and stirring until completely dissolved. Pour the solution into a 250 mL three-necked flask and heat it in an oil bath to 90 °C, maintaining a constant temperature. Suspend the graphene oxide-coated intermediate obtained in step S2 vertically in the flask, ensuring the needle is completely immersed in the solution without touching the flask walls or bottom. Seal the flask and reduce it at 90 °C for 3.5 h. After reduction, turn off the oil bath, remove the sample, and immediately rinse it vertically three times with 90 °C deionized water. After drying with high-purity nitrogen, vacuum dry it at 60 °C for 30 min to finally obtain the 50-100 nm graphene-coated plastic needle-like substrate.

[0035] Example 3 S1. Perform surface pretreatment and conductive treatment on the plastic needle-shaped substrate; S11. Cleaning treatment: Take a needle-shaped ABS substrate with a diameter of 1 mm and a length of 2 cm, hold both ends with PTFE tweezers, wipe the visible stains on the surface with anhydrous ethanol, then fix it vertically on a PTFE clamp and place it in 50 mL of anhydrous ethanol. Ultrasonically clean it for 15 min at 180 W and 25 °C. After removal, rinse three times with deionized water, then ultrasonically clean it again in deionized water for 5 min. Next, blow it vertically with high-purity nitrogen gas, and finally dry it in a 60 °C hot air dryer for 30 min. After removal, place it in a desiccator to cool to room temperature.

[0036] S12, Chemical roughening treatment: Prepare an acidic roughening solution. Add 20g of chromic anhydride to 100mL of deionized water, then slowly add 300mL of 75wt% concentrated sulfuric acid while stirring, stirring until completely dissolved. Immerse the cleaned needle-shaped ABS substrate in the above roughening solution and soak at a constant temperature of 45℃ for 8 minutes. After removal, rinse with a large amount of flowing deionized water for 5 minutes, then ultrasonically clean with deionized water for 3 minutes. After drying with high-purity nitrogen, dry with hot air at 60℃ for 30 minutes, and place in a desiccator to cool for later use.

[0037] S13, Interface Enhancement Processing: Prepare the silane coupling agent solution. Mix 90 mL of anhydrous ethanol with 10 mL of deionized water, add 1.6 g of silane coupling agent KH550, adjust the pH to 5.0 with glacial acetic acid, and continue stirring at room temperature for 30 min to ensure complete hydrolysis. Vertically immerse the chemically roughened needle-shaped ABS substrate into the silane coupling agent solution and soak at room temperature for 5 min. After removal, hang vertically and gently blow dry the excess liquid on the surface with high-purity nitrogen gas, then dry in a forced-air oven at 100℃ for 10 min, and cool in a desiccator.

[0038] S14. Conductivity Treatment: Prepare a conductive liquid by mixing 1g of water-based ultrathin conductive carbon paste with a solid content of 5% and a particle size of <1μm with 9g of deionized water. After stirring evenly, ultrasonically disperse for 10min. Vertically fix the interface-reinforced needle-shaped ABS substrate on a lifting machine, suspending the lower end of the needle and aligning it with the center of the liquid surface. Immerse and lift at a uniform speed of 5mm / s. After removal, hang and level at room temperature for 2min, then dry in a forced-air dryer at 60℃ for 15min. Use a digital multimeter to test the resistance of the upper, middle, and lower ends of the needle, ensuring that the overall needle resistance is <1kΩ and the relative deviation of resistance at different positions is <10%. Once the standard is met, it is ready for use, thus obtaining a conductive substrate with a uniform conductive base film.

[0039] S2. Using the conductive substrate as the working electrode, electrophoretic deposition is performed in a graphene oxide electrophoresis solution. S21. Preparation of graphene oxide electrophoresis solution: Weigh 0.512 g of magnesium nitrate hexahydrate using a 0.01 g analytical balance and place it in a 100 mL volumetric flask. Add 80 mL of deionized water and shake until completely dissolved. Pipette 10 mL of a 10 mg / mL graphene oxide aqueous dispersion into the same volumetric flask and add deionized water to the 100 mL mark. Pour the mixture into a 250 mL beaker, place a PTFE magnetic stir bar inside, and stir at 300 rpm at room temperature for 30 min. Then, sonicate the mixture in a 300 W ice-water bath for 20 min to obtain a homogeneous graphene oxide electrophoresis buffer with a graphene oxide concentration of 1.0 mg / mL and a magnesium nitrate concentration of 0.02 mol / L.

[0040] S22, Electrophoretic deposition: Using a 100mL glass beaker as the electrophoresis tank, pour in the above-mentioned graphene oxide electrophoresis solution and place a polytetrafluoroethylene (PTFE) magnetic stir bar inside. Two 1mm thick 304 stainless steel plates are vertically fixed to the sides of the electrophoresis tank as counter electrodes, with the electrode spacing adjusted to 7cm and their lower ends immersed 3cm below the liquid surface. The conductive substrate obtained in step S1 is vertically fixed to the PTFE clamp as the working electrode and placed in the center of the two pairs of electrodes, ensuring that its effective coating area is completely immersed in the electrophoresis solution and does not contact the tank wall or the stir bar. Connect a DC power supply, with the positive terminal connected to the conductive substrate and the negative terminal connected to the stainless steel electrode. Turn on the magnetic stir bar and set the speed to 100rpm. First, turn off the power output and zero the voltage and current. Then, slowly adjust the power output voltage to 20V. Once the current stabilizes at 10mA, start timing for deposition for 8 minutes. After deposition, immediately turn off the power, disconnect the circuit, remove the sample vertically, gently rinse it three times with deionized water in a parallel direction, blow it dry vertically downwards with high-purity nitrogen, and then vacuum dry it at 60°C for 20 minutes to obtain the graphene oxide-coated intermediate.

[0041] S3. Perform a reduction process on the intermediate; Prepare a 10 mg / mL L-ascorbic acid aqueous solution by dissolving 1 g of L-ascorbic acid in 100 mL of deionized water and stirring until completely dissolved. Pour the solution into a 250 mL three-necked flask and heat it in an oil bath to 90 °C, maintaining a constant temperature. Suspend the graphene oxide-coated intermediate obtained in step S2 vertically in the flask, ensuring the needle is completely immersed in the solution without touching the flask walls or bottom. Seal the flask and reduce it at 90 °C for 5.5 h. After reduction, turn off the oil bath, remove the sample, and immediately rinse it vertically three times with 90 °C deionized water. After drying with high-purity nitrogen, vacuum dry it at 60 °C for 30 min to finally obtain the 100-200 nm graphene-coated plastic needle-like substrate.

[0042] Performance testing The performance of the graphene-coated plastic needle-like substrates prepared in Examples 1-3 was characterized. The test items, methods, and results are as follows: 1. Conductivity continuity test The conductivity of the finished product was tested using a digital multimeter with an accuracy of 0.1Ω. The test results showed that there was full conductivity between any two points along the axial direction of the needle-like substrate, with no open circuit. Resistance measurements were taken at four points uniformly selected circumferentially on the substrate, and the relative deviation of the resistance values ​​was less than 10%. These results demonstrate that the graphene coating prepared in this application possesses good three-dimensional conductive network connectivity and excellent circumferential uniformity.

[0043] 2. Conductivity test The surface sheet resistance of the finished product was quantitatively tested using a four-probe sheet resistance tester. The test results are as follows: The sheet resistance of Example 1 is 10. 5 -10 6 Ω / sq.

[0044] The sheet resistance of Example 2 is 10. 2 -10 4 Ω / sq.

[0045] The sheet resistance of Example 3 is 10-10. 2 Ω / sq.

[0046] 3. Coating thickness and repeatability testing To quantitatively characterize the thickness of graphene and verify the controllability and repeatability of the preparation method, repeatability experiments were conducted on the processes of Examples 1-3, and cross-sectional morphology was analyzed by field emission scanning electron microscopy.

[0047] 3.1 Sample preparation: Five parallel samples were prepared independently according to the methods and parameters described in Examples 1, 2 and 3, for a total of 15 samples.

[0048] 3.2 Test Procedure: The prepared graphene-coated plastic needle-shaped substrate sample was subjected to brittle fracture in liquid nitrogen to obtain a clean cross-section.

[0049] The sample is fixed on the sample stage with the cross-section facing upwards and then sprayed with gold to increase conductivity.

[0050] The cross-sectional morphology was observed under FE-SEM. High-magnification images were taken at three different positions (top, middle, and bottom) for each sample, and the coating thickness was directly measured using the instrument's built-in scale software.

[0051] Five measurement points are randomly selected at each location, and the thickness of a single sample is the arithmetic mean of its 15 measurement points. The final thickness of each embodiment is the average of the thicknesses of its five parallel samples.

[0052] 3.3 Test Results SEM cross-sectional observations showed that the coating layers of all samples were continuous and dense, with clear bonding at the interface with the plastic substrate. Thickness measurement results are shown in the table below:

[0053] The results above demonstrate that the method for preparing a uniformly coated plastic needle-like substrate using graphene provided in this application, along with the resulting substrate, produces a graphene coating that is uniform, dense, crack-free, pinhole-free, agglomerated, and without exposed substrate. The sheets are flat and spread out, exhibiting strong adhesion to the plastic substrate and are not easily detached. The needle-like substrate is axially conductive throughout without any open circuits, exhibits high circumferential resistance uniformity (relative deviation <10%), and significantly improves coating consistency. The conductivity can be precisely controlled bidirectionally through the coating thickness and reduction degree, with a sheet resistance control range as wide as 10. 1 - 10 6 With a capacitance of Ω / sq, this method can meet the diverse conductivity requirements of various applications, including micro / nano sensors, electronic components, and medical conductive consumables. Furthermore, by controlling the deposition voltage and time, and establishing a time-thickness standard curve based on the single-factor variable principle, this application can precisely prepare coatings of arbitrary target thicknesses within the range of 5-200 nm. The deposition thickness exhibits a good linear relationship with process parameters, with high reproducibility of experimental data, strong process controllability, and good repeatability, which is beneficial for industrial-scale standardized production. In addition, this application forms a progressive synergistic system through surface pretreatment and conductivity treatment. The cleaning treatment avoids interference; chemical roughening and activation increase the surface roughness and active area of ​​the substrate; silane coupling agents bridge the interface to construct a chemically bonded layer; and conductivity treatment solves the insulation problem of plastics, providing a uniform conductive substrate for electrophoretic deposition. Through these multi-step synergy, the interfacial adhesion between the coating and the substrate is significantly enhanced, fundamentally preventing coating detachment.

[0054] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing a graphene-coated plastic needle-like substrate, characterized in that, Includes the following steps: S1. Perform surface pretreatment and conductive treatment on the plastic needle-shaped substrate to obtain a conductive substrate; S2. Using the conductive substrate as the working electrode, electrophoretic deposition is performed in the graphene oxide electrophoresis solution to obtain an intermediate coated with graphene oxide. S3. The intermediate is reduced to obtain a graphene-coated plastic needle-like substrate.

2. The method for preparing graphene-coated plastic needle-like substrate according to claim 1, characterized in that, In step S1, the surface pretreatment includes cleaning, chemical roughening and interface enhancement treatment performed sequentially.

3. The method for preparing graphene-coated plastic needle-like substrate according to claim 2, characterized in that, The cleaning process includes: ultrasonic cleaning of the plastic needle-shaped substrate with an organic solvent, followed by rinsing with deionized water, drying with nitrogen and hot air. The ultrasonic cleaning process uses a power of 150-200W, a temperature of 20-30℃, and a time of 10-20 minutes. The hot air drying process uses a temperature of 55-65℃.

4. The method for preparing graphene-coated plastic needle-like substrate according to claim 2, characterized in that, The chemical roughening treatment is as follows: the plastic needle-shaped substrate is immersed in an acidic roughening solution at 40-50℃ for 5-10 minutes, and then rinsed with deionized water, dried with nitrogen and hot air. The acidic roughening solution is prepared by mixing 20g of chromic anhydride, 300mL of 75wt% sulfuric acid and 100mL of water.

5. The method for preparing graphene-coated plastic needle-like substrate according to claim 2, characterized in that, The interface enhancement treatment includes: immersing the chemically roughened plastic needle-shaped substrate in a silane coupling agent solution at room temperature for 5-10 minutes, and then removing it and drying it with nitrogen and hot air in sequence. The silane coupling agent solution is a mixture of KH550, ethanol and water, wherein the volume ratio of ethanol to water is (8-9):1, the mass of KH550 accounts for 1-3% of the total mass of the solution, and the pH value of the silane coupling agent solution is 4.5-5.

5.

6. The method for preparing graphene-coated plastic needle-like substrate according to any one of claims 1-5, characterized in that, In step S1, the conductive treatment includes: immersing the surface-pretreated plastic needle-shaped substrate in a conductive liquid using a dip-coating method, removing it, suspending it at room temperature to level it, and then drying it with hot air. The dip-coating method has an immersion speed and a lifting speed of 4-6 mm / s.

7. The method for preparing graphene-coated plastic needle-like substrate according to claim 1, characterized in that, In step S2, the graphene oxide electrophoresis solution is a mixture of magnesium nitrate, water and graphene oxide, wherein the concentration of graphene oxide is 0.2-1 mg / mL and the concentration of magnesium nitrate is 0.01-0.02 mol / L.

8. The method for preparing graphene-coated plastic needle-like substrate according to claim 1 or 7, characterized in that, In step S2, the electrophoretic deposition is performed under a DC voltage of 5-20V and a current of 1-10mA.

9. The method for preparing graphene-coated plastic needle-like substrate according to claim 1, characterized in that, In step S3, the reduction treatment includes: placing the intermediate in an L-ascorbic acid aqueous solution with a concentration of 8-12 mg / mL at 85-95°C for liquid-phase reduction for 1-6 hours, followed by washing and drying.

10. A graphene-coated plastic needle-like substrate, characterized in that, It is prepared by any one of the preparation methods according to claims 1-9.

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