A method for large-area assembly of flexible nanowire orientation arrays

Abstract

This invention discloses a method for large-area assembly of flexible nanowire orientation arrays, belonging to the field of nanomaterial assembly technology. First, one-dimensional nanowires are prepared through liquid-phase synthesis. The nanowires are then sieved to their size and dispersed in water to prepare a solution of a specific concentration. A substrate is subjected to electrostatic treatment. The substrate is then slowly immersed in the nanowire solution. Due to electrostatic adsorption and substrate movement, hydrodynamic forces drive the nanowire orientation, forming a well-oriented nanowire array film on the substrate. This method is applicable to various ultralong one-dimensional nanomaterials and arbitrary substrates, suitable for the rapid large-area fabrication of array films, and can control multi-angle, multi-layer orientation networks of one-dimensional nanomaterials. This provides a solid industrial foundation for the fabrication of flexible electronic devices based on nanowires (NWs), including wearable energy storage devices, flexible displays, electronic sensors, and health monitors.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial assembly technology, and relates to an efficient, large-size assembly method for ultra-long and ultra-flexible one-dimensional nanomaterial orientation arrays, which can be applied to the fabrication and assembly of wafer-level thin films and electrical functional devices. Background Technology

[0002] One-dimensional nanomaterials have attracted widespread attention in numerous application fields due to their unique physicochemical properties and ease of mass production. In particular, aligning nanowires into a macroscopic thin-film network or complex micropatterns is a key challenge in the fabrication of flexible electronic devices based on nanowires (NWs), including wearable energy storage devices, flexible displays, electronic sensors, and health monitors. Large-area oriented nanowire arrays have broad implications for industrialized, integrated, and large-scale production. Currently, solution processing remains the most efficient nanowire alignment strategy, offering advantages such as mild operating conditions and large-scale production. Many methods for assembling oriented fibers have also been invented, such as LB assembly (Lagmuir-Blodgett), contact printing, electro / magnetic field induction, electrospinning, fluid flow guidance, and so on. Although significant progress has been made in improving the orientation and density of assembled nanofibers, many previous techniques required necessary preconditions, such as pre-grown vertical nanowire arrays, additional transfer processes, and device complexity due to the presence of fields. This limited the cost-effectiveness and large-scale production of nanowire assemblies with controllable orientation and high density. Meanwhile, the high aspect ratio (lengths up to 200 μm) of nanowires makes orientation assembly more challenging. For example, while the bloombubble film method can produce large-area oriented films, its very low line density (~0.3 nanowires / μm) is a serious problem. The Langmuir-Blodgett method, although capable of producing well-oriented structures, can only achieve dense unidirectional arrangements, cannot control the arrangement density of one-dimensional nanomaterial arrays, and places high demands on experimental procedures. Summary of the Invention

[0003] The purpose of this invention is to address the problems of complex assembly processes and difficulties in large-area fabrication of oriented arrays of one-dimensional nanofibers, and to provide a simple, easy-to-operate method for assembling long one-dimensional fibers that is suitable for large-area integration. This method is applicable to any substrate (including non-planar substrates) and provides a foundation for further development of devices based on oriented fiber assemblies.

[0004] This invention discloses a method for assembling a large-area array of one-dimensional nanomaterials oriented by electrostatic adsorption and hydrodynamics. First, one-dimensional flexible nanowires are prepared through liquid-phase synthesis. The nanowires are then sieved to size and dispersed in water to prepare a solution of a specific concentration. A substrate is positively charged. The substrate is then slowly immersed in the nanowire solution. Due to electrostatic adsorption and substrate movement, the nanowires are dragged, forming an oriented nanowire array film on the substrate. The method is characterized by the following steps:

[0005] (1) The one-dimensional nanomaterials to be arranged and assembled were dispersed in water to obtain a uniform dispersion of a specific concentration; and the zeta potential was measured by a dynamic light scattering (DLS) particle size analyzer to show negative / positive charge.

[0006] (2) The substrate is treated with oxygen plasma (O2-plasma) to make the surface of the substrate more hydrophilic.

[0007] (3) Place the substrate in a dispersion of positive / negative molecules. After a period of time, take the substrate out and rinse it with deionized water to remove excess positive / negative molecules, so that only a uniform monolayer of positive molecules exists on the substrate surface. Then dry the substrate surface with nitrogen.

[0008] (4) Clamp the substrate with a motion control instrument and immerse it in the nanowire solution at a certain speed. As the substrate is immersed in the solution, because the substrate is adsorbed with a layer of positively charged molecules and the nanowires are negatively charged, nanowires will be continuously adsorbed onto the substrate due to electrostatic attraction. Since the nanowires are long, one end or part of the nanowires will be adsorbed and anchored onto the substrate first due to electrostatic force. As the substrate moves downward, the nanowires move downward, thereby pulling the unadsorbed part downward as well. This part of the fiber will be subjected to the upward hydrodynamic force generated by the fluid due to the movement. This hydrodynamic force will make the fiber gradually vertically upward. Therefore, as the substrate moves downward, the nanowires gradually become vertically upward while being adsorbed, and an orientation array is formed on the substrate.

[0009] (5) After the substrate is basically completely immersed in the solution, the substrate is quickly pulled out, rinsed with water and dried with nitrogen to obtain a single-layer oriented nanowire thin film array.

[0010] (6) By changing the direction of the substrate immersion in the nanowire solution and then repeating steps (3) to (5), a nanowire array with arbitrary angles between multiple layers is obtained.

[0011] further,

[0012] The one-dimensional nanomaterial described in this invention is one of metal nanowires, semiconductor nanowires, or carbon nanotubes, and its length is greater than 5 μm. This invention enables large-area assembly of ultra-long nanowire arrays, with nanowire material lengths exceeding 200 μm.

[0013] The concentration of the specific concentration dispersion mentioned in step (1) is 10 mg / mL-50 mg / mL. The concentration is related to the density of adsorbed nanowires; the higher the concentration, the higher the nanowire density. The characterization of the Zeta potential is to demonstrate the electrical properties of the nanowires.

[0014] The substrate mentioned in step (2) can be a rigid substrate, a flexible substrate, or a stretchable substrate. Depending on the application, rigid substrates are preferably silicon wafers, silicon dioxide, or ordinary glass; flexible substrates are preferably polyethylene terephthalate (PET), polyimide (PI), etc.; and stretchable substrates are preferably polydimethylsiloxane (PDMS) and hydrogenated styrene-butadiene-styrene block copolymer (SEBS), etc. The oxygen plasma (O2-plasma) conditions can be adjusted according to the different substrates. The preferred conditions are 120W / 5min for rigid substrates and 100W / 1min for flexible and stretchable substrates.

[0015] The positively charged molecules mentioned in step (3) include, but are not limited to, polydiallyldimethylammonium chloride (PDDA), polyethyleneimine (PEI), and positively charged aqueous polyurethane (PU).

[0016] In step (4), the moving control platform can precisely control the speed at which the substrate is immersed in the solution. The specific speed is 1 μm / s-1 cm / s. The slower the speed, the higher the density of adsorbed nanowires and the better the orientation.

[0017] In step (5), because the nanowires are negatively charged, the positively charged molecules on the substrate surface can adsorb and anchor the nanowires, preventing them from being washed away. The outer nanowires that are not electrostatically adsorbed will be washed away, leaving only a single layer of well-aligned, electrostatically bonded fibers oriented on the substrate. The washing process is crucial for preparing single-layer oriented nanowires.

[0018] Furthermore, the electrostatic force between the substrate and the fibers is crucial for adsorption. The electrostatic forces between the substrate and the nanofibers are opposite in polarity; if the nanofibers are positively charged, the substrate can be negatively charged, and this approach is also applicable.

[0019] The beneficial effects of this invention are as follows: The method provided by this invention is simple and easy to implement, and suitable for large-area industrial production. The density of oriented one-dimensional nanowires can be controlled by adjusting the concentration of the nanowire solution and the substrate descent rate. Therefore, the performance of integrated devices based on oriented nanowires can be easily modulated. Furthermore, this method is compatible with different substrates, meeting the requirements for large-area integrated manufacturing of rigid high-performance devices, flexible devices, and stretchable wearable devices. The bottom-up assembly method fully utilizes nanowire materials, avoiding the waste of raw materials and chemical reagents caused by the etching process. This method is suitable for direct deposition on the substrate, avoiding complex subsequent transfer processes and reducing production costs. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the oriented nanowire thin film deposition process according to an embodiment of the present invention;

[0021] Figure 2 This is an analysis diagram of the orientation mechanism of nanowires in an embodiment of the present invention;

[0022] Figure 3 This is a characterization of the zate potential of the nanowires in an embodiment of the present invention;

[0023] Figure 4 This is an electron microscope image of the arrangement of tellurium nanowires on a silicon wafer substrate according to an embodiment of the present invention;

[0024] Figure 5 These are electron microscope images of the arrangement of multiple small-angle tellurium nanowires on a silicon wafer substrate according to an embodiment of the present invention;

[0025] Figure 6 This is an optical microscope image of tellurium nanowires oriented and arranged on a PDMS substrate according to an embodiment of the present invention.

[0026] Figure 7 This is an optical microscope image of tellurium nanowires oriented and arranged on a PET substrate according to an embodiment of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to embodiments. These descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention in any other way. Any person skilled in the art may make equivalent modifications to the disclosed technical content to create equivalent embodiments. Any simple modifications or equivalent changes made to the following embodiments based on the technical essence of the present invention without departing from the scope of the invention are all within the protection scope of the present invention.

[0028] Example 1: Preparation of tellurium nanowire oriented thin films on SiO2 / Si substrate.

[0029] Preparation of tellurium nanowire solution: 1 g PVP and 33 mL water were placed in a 50 mL reactor and stirred thoroughly. Then, 0.092 mg sodium tellurite (Na₂TeO₃), 1.67 mL ammonia water (NH₃·H₂O), and 3.33 mL hydrazine hydrate (N₂H₄·H₂O) were added, and the mixture was stirred with a magnetic stirrer for 10 minutes. The reactor was placed in an oven at 180 °C for 3 hours, and then allowed to cool naturally to room temperature to obtain the tellurium nanowire mother liquor. The tellurium nanowire mother liquor was centrifuged at 3000 rpm, and after sieving to remove flake and ribbon-like tellurium, it was dispersed in water to obtain the tellurium nanowire solution to be assembled.

[0030] Substrate pretreatment: The silicon wafer covered with 300nm silica was treated with oxygen plasma (120W, 5min) to give it strong hydrophilicity. Then it was placed in a 0.5wt% PDDA (polydiallyl dimethyl ammonium chloride) aqueous solution and left to stand for 3min. After removing the silicon wafer, it was rinsed with water and dried with nitrogen.

[0031] Deposition of oriented nanowire thin films: The substrate is fixed on a moving control platform fixture at a speed of 10 μm / s, allowing the substrate to be slowly immersed in the nanowire solution. When the substrate is almost completely immersed, the moving platform is controlled to rapidly lift the substrate; then, excess nanowires are rinsed off with deionized water and dried with nitrogen gas. This deposits a single layer of oriented nanofibers on the silicon wafer, such as... Figure 4 As shown.

[0032] Furthermore, the mechanism of nanowire orientation alignment is explained. For example... Figure 1 As shown, as the substrate is immersed in the solution, a layer of positively charged PDDA (polydiallyldimethylammonium chloride) is adsorbed on the substrate, while the tellurium nanowires are negatively charged (e.g., ...). Figure 3 As characterized, nanowires continuously adhere to the substrate due to electrostatic attraction. Because the nanowires are relatively long, one end or part of the nanowire will initially contact the substrate and be adsorbed and anchored there. As the substrate moves downwards, the nanowire moves downwards along with the substrate. This pulls the unadsorbed portions of the nanofibers downwards as well, and these unadsorbed portions are subjected to upward hydrodynamic forces generated by the fluid. Figure 2 As shown, this hydrodynamic force causes the fibers to gradually grow vertically upwards. Therefore, as the substrate moves downwards, the nanowires gradually grow vertically upwards while being adsorbed. This method allows for the production of large-area oriented fiber arrays.

[0033] To achieve nanowire arrays with arbitrary angles between multiple layers: Immerse a silicon wafer with a pre-prepared monolayer oriented fiber array in a PDDA aqueous solution and let it stand for 3 minutes. Remove the wafer, rinse it with water, and dry it with nitrogen. Then, immerse the wafer in the nanowire solution at a different angle. After rinsing and drying, an oriented nanowire array at a certain angle to the first layer can be obtained, such as... Figure 5 As shown. Based on the above method, the oriented nanowire array can be deposited in multiple layers, and the orientation angle of each layer can be adjusted.

[0034] Example 2: Prepare tellurium nanowire oriented thin films on stretchable PDMS (polydimethylsiloxane) substrates.

[0035] The tellurium nanowire mother liquor was centrifuged at 3000 rpm, and after sieving to remove flake and ribbon-like tellurium, it was dispersed in water to obtain the tellurium nanowire solution to be assembled. A certain mass of PDMS prepolymer and curing agent (mass ratio 10:1) was weighed and mixed uniformly. The mixture was then coated onto a glass plate using a 500 μm doctor blade. Afterwards, it was placed in a drying oven and cured at 100°C for 4 hours. Subsequently, the PDMS was treated with oxygen plasma (100W, 1 min) to make it hydrophilic. Then, it was placed in a 0.5 wt% PDDA aqueous solution and allowed to stand for 3 min. The PDMS was then removed, rinsed with deionized water, and dried with nitrogen. It was fixed on a moving control platform fixture, and a speed of 10 μm / s was set to slowly immerse the substrate in the nanowire solution. When the substrate was almost completely immersed in the solution, the moving platform was controlled to rapidly lift the substrate; then, excess nanowires were rinsed off with water and dried with nitrogen. In this way, a single layer of oriented nanofibers was deposited on the PDMS, such as... Figure 6 As shown.

[0036] Example 3: Nanowire-oriented thin films were prepared on a flexible PET (polyethylene terephthalate) substrate.

[0037] The tellurium nanowire mother liquor was centrifuged at 3000 rpm, and after sieving to remove flake and ribbon-like tellurium, it was dispersed in water to obtain the tellurium nanowire solution to be assembled. A certain amount of 2% polyethyleneimine (PEI) aqueous solution was prepared. The PET substrate was subjected to oxygen plasma treatment (80W, 1 min) to make it hydrophilic. Then it was placed in 2 wt% PEI aqueous solution and allowed to stand for 10 min. After removing the PET, it was rinsed with deionized water and dried with nitrogen. It was fixed on a moving control platform fixture, and the speed was set to 20 μm / s, so that the substrate was slowly immersed in the nanowire solution. When the substrate was about to be completely immersed in the solution, the moving platform was controlled to quickly lift the substrate; then the excess nanowires were rinsed off with water and dried with nitrogen. In this way, a single layer of oriented nanofibers was deposited on the PET flexible substrate, such as... Figure 7 As shown.

[0038] It should be noted that, as specific embodiments of this application, the above examples are merely for illustrating the implementation method of the technical solution of this application, and are not intended to limit the specific selection of materials and method steps. Other materials listed in the technical solution of this application can also achieve the purpose of this invention and achieve the same technical effect. Other modifications that fall within the technical concept of this invention and are obvious are also within the protection scope of this invention.

Claims

1. A method for large-area assembly of flexible nanowire orientation arrays, wherein one-dimensional nanowires are first prepared by liquid-phase synthesis, and the nanowires are then dispersed in water after size sieving to prepare a solution of a specific concentration; The substrate is subjected to electrochemical treatment; The substrate is slowly immersed in a nanowire solution. Due to electrostatic adsorption and substrate movement, the nanowires are hydrodynamically driven to form an oriented nanowire array film on the substrate. The method is characterized by the following steps: (1) Disperse the one-dimensional nanomaterials that need to be arranged and assembled into water to obtain a uniform dispersion of a specific concentration; and measure the Zeta potential by a dynamic light scattering particle size analyzer to indicate the negative / positive charge. (2) The substrate is treated with oxygen plasma to make the surface of the substrate more hydrophilic. (3) Place the substrate in a dispersion of positive / negative molecules, and after a period of time, take the substrate out and rinse it with deionized water so that only a uniform monolayer of positive / negative molecules exists on the surface of the substrate. Then dry the surface of the substrate with nitrogen. (4) Clamp the substrate with a motion control instrument and immerse it in the nanowire solution at a certain speed. As the substrate is immersed in the solution, nanowires are continuously adsorbed onto the substrate due to electrostatic attraction. As the substrate moves down, an oriented nanowire array is formed on the substrate. (5) After the substrate is basically completely immersed in the solution, the substrate is quickly pulled out, rinsed with deionized water and dried with nitrogen to obtain a single-layer oriented nanowire thin film array. (6) By changing the direction of the substrate immersion in the nanowire solution and then repeating steps (3) to (5), a nanowire array with arbitrary angles between multiple layers is obtained.

2. The method for large-area assembly of flexible nanowire orientation arrays according to claim 1, characterized in that: The electrostatic forces between the substrate and the nanofibers are opposite in polarity. If the nanofibers are positively charged, the substrate is treated to be negatively charged.

3. The method for large-area assembly of flexible nanowire orientation arrays according to claim 1, characterized in that: The substrate is a rigid substrate, a flexible substrate, or a stretchable substrate; the rigid substrate is a silicon wafer, silicon dioxide, or ordinary glass; the flexible substrate is polyethylene terephthalate (PET) or polyimide (PI); the stretchable substrate is polydimethylsiloxane (PDMS) or hydrogenated styrene-butadiene-styrene block copolymer (SEBS).

4. The method for large-area assembly of flexible nanowire orientation arrays according to claim 1, characterized in that: The ultra-long and ultra-flexible one-dimensional nanowire material is one of the following: metal nanowire, semiconductor nanowire or carbon nanotube, with a length greater than 5 mm.

5. The method for large-area assembly of flexible nanowire orientation arrays according to claim 1, characterized in that: In step (2), the substrate is subjected to hydrophilic treatment by methods including oxygen plasma treatment or 3-aminopropyltriethoxysilane APTES treatment.

6. The method for large-area assembly of flexible nanowire orientation arrays according to claim 1, characterized in that: In step (3), the positively charged molecules adsorbed on the substrate include one of polydiallyldimethylammonium chloride (PDDA), polyethyleneimine (PEI), and positively charged aqueous polyurethane (PU).

7. The method for large-area assembly of flexible nanowire orientation arrays according to claim 1, characterized in that: In step (4), the substrate moves at a speed of 1 mm / s to 1 cm / s.

8. The method for large-area assembly of flexible nanowire orientation arrays according to claim 1, characterized in that: In step (5), rinsing with deionized water will cause the upper fibers that are not electrostatically adsorbed to fall off due to the water washing, leaving only the single-layer fibers with good electrostatic bonding oriented and arranged on the substrate.

9. The method for large-area assembly of flexible nanowire orientation arrays according to claim 1, characterized in that: In step (6), the oriented nanowire array can be deposited in multiple layers, and the orientation angle of each layer can be adjusted.

10. The method for large-area assembly of flexible nanowire orientation arrays according to claim 1, characterized in that: The nanowires mentioned are tellurium nanowires.

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