A vertically oriented continuous graphene film material and a preparation method and application thereof

Abstract

The application provides a vertically oriented continuous graphene film material and a preparation method and application thereof. By cooperating the flow field effect of the flow extrusion molding and the structure fixing effect of the hydrogel precursor, the drawbacks of the direct drying of the wet film in the traditional process are avoided, and the accurate and controllable orientation and arrangement of GO lamellar units are realized, so that the continuous mass production of the GO film is realized, the stable film layer quality is ensured, and the unit orientation is controllable, which provides a high-quality substrate for the subsequent heat treatment for preparing a specific oriented graphene skeleton and composite modification.

Description

Technical Field

[0001] This invention relates to the field of functional thin film materials, specifically to a vertically oriented continuous graphene film material, its preparation method, and its applications. Background Technology

[0002] GO sheets are rich in oxygen-containing functional groups, and GO films prepared from them exhibit excellent hydrophilicity, chemical stability, and functional tunability, showing broad application prospects in water treatment, flexible electronics, and other fields. Graphene films, obtained by heat-treating GO films, are also widely used in electronics and heat dissipation, new energy batteries, barrier and protection, and other fields. The core performance of both GO and graphene films is highly dependent on the ordered orientation of graphene units. The large-scale commercial application of these films relies heavily on efficient, stable, low-cost, and continuous preparation processes that enable the control of graphene unit orientation. Traditional batch preparation methods not only result in uneven film thickness and poor performance consistency but also fail to achieve directional control of graphene units, thus falling far short of the demands of industrial applications. Currently, the publicly disclosed continuous preparation processes in the industry mainly include roll-to-roll slit coating, spray deposition, electrophoretic deposition, evaporation-driven printing, self-assembly continuous film formation, and CVD. Although these processes have achieved continuous preparation of GO films, none of them can effectively control the orientation of graphene units. They also have insurmountable technical defects: roll-to-roll slit coating has strict requirements on the rheological properties of the dispersion, is prone to head clogging, and has many film defects, with GO flakes easily agglomerating and disordered; spray deposition wastes raw materials severely, and the atomization process leads to random stacking of graphene units, resulting in a chaotic film structure; electrophoretic deposition is only suitable for conductive substrates, has poor film uniformity, requires additional transfer, and cannot guide the orientation of units; evaporation-driven printing and self-assembly have extremely low industrialization efficiency, and the orientation of units is highly random and disordered; CVD has high equipment costs, high energy consumption, and the film transfer is easily damaged, and there is a lack of effective means to control the orientation of graphene units. In addition, various processes generally suffer from common problems such as low raw material utilization, heavy environmental burden, difficulty in controlling the overall structure of the membrane layer, and poor industrial adaptability. The lack of control over the orientation of graphene units directly leads to the degradation of the core performance of the produced membrane material and poor batch performance consistency, becoming a key bottleneck restricting the large-scale commercial application of GO membranes and subsequent graphene membranes.

[0003] The existing continuous GO film preparation processes generally face core challenges such as narrow process windows, poor controllability of film quality, low industrialization efficiency, high preparation costs, and poor environmental friendliness. Even when existing technologies attempt to control the orientation of graphene units in GO films through post-processing plasticizing and stretching, or centrifugal film formation, they can only achieve parallel orientation of the graphene units, failing to achieve precise and diversified control over their orientation. These interconnected problems not only hinder the large-scale commercialization of GO films and fail to meet the urgent demand for high-performance continuous GO films in various fields, but also severely restrict the subsequent heat treatment modification and performance optimization and commercial application of related derivatives due to the limitations in graphene unit orientation control. This further highlights the urgency of developing novel, efficient, continuous film preparation processes. Currently, there is no GO film preparation method in this field that allows for precise control of graphene unit orientation. Therefore, developing a continuous GO film preparation method that can precisely control the orientation of graphene units, has a wide process window, controllable film quality, high industrialization efficiency, low cost, and is environmentally friendly has become a pressing technical challenge for those skilled in the art. Summary of the Invention

[0004] To address the problems of uneven film thickness, numerous defects, and the inability to precisely control graphene units (resulting only in single parallel orientation) in existing continuous GO film fabrication processes, as well as low industrialization efficiency, significant raw material waste, heavy environmental burden, and high equipment costs, this invention provides a vertically oriented continuous graphene film material, its preparation method, and its applications. By synergistically utilizing the flow field effect of cast extrusion molding and the structural fixation effect of the hydrogel precursor, the drawbacks of direct drying of wet films in traditional processes are avoided, while achieving precise and controllable orientation alignment of GO wafer crystal units. This enables continuous mass production of GO films while ensuring stable film quality and controllable unit orientation, providing a high-quality substrate for subsequent heat treatment to prepare specifically oriented graphene frameworks and for composite modification.

[0005] One of the technical solutions of the present invention is to provide a method for preparing a vertically oriented continuous graphene film material, wherein an aqueous solution of graphene oxide is extruded through an extruder and then introduced into an expanded flow channel for casting to form a continuous gel film, followed by drying and heat treatment to graphitize it to obtain an oriented graphene film; the thickness of the expanded flow channel is not less than twice the thickness of the extruder, and the width of the expanded flow channel is the same as that of the extruder.

[0006] Furthermore, the width of the extrusion port is not less than 5cm and the thickness is not greater than 2mm.

[0007] Furthermore, the concentration of the aqueous graphene oxide solution is not less than 10 mg / g.

[0008] Furthermore, the drying process is performed at room temperature.

[0009] Furthermore, the temperature of the heat treatment is 2600-3000℃.

[0010] Furthermore, the aqueous solution of graphene oxide includes one or more of PAN, PAA, PVA, PVP, carbon nanotubes, and nanocellulose.

[0011] Further, the continuous gel membrane is immersed in a reducing agent, such as sodium ascorbate, hydroiodic acid, hydrobromic acid, tin dichloride solution, or hydrazine hydrate. After chemical reduction, the gel membrane can be freeze-dried or dried at room temperature to prepare a foam membrane. The foam membrane has a clearly visible vertical or parallel orientation of basic units, and its density is 7-800 mg / cm³. 3 .

[0012] A dense GO membrane was prepared by directly drying the gel membrane at room temperature. This GO membrane was then densified by high-temperature heat treatment and roll pressing to obtain a graphene membrane. The graphene membrane exhibited a structural history of vertically or parallelly oriented unit cell arrangements, and its density ranged from 1.64 to 1.95 g / cm³. 3 .

[0013] The second technical solution of the present invention is to provide an oriented graphene film prepared by the above method.

[0014] The graphene sheets in the graphene film are oriented perpendicular to the film surface, and at least some of the graphene sheets are arched along their length. The two ends of the arched graphene sheet overlap with the upper and lower surfaces of the adjacent graphene sheet or the graphene film.

[0015] The third technical solution of the present invention is to provide the application of the above-mentioned oriented graphene film.

[0016] The beneficial effects of this invention are as follows: (1) The present invention prepares a gel film by casting the nozzle of the membrane channel. By using the height ratio of the combined membrane nozzles to construct a double flow field in the thickness direction, the vertical orientation arrangement of GO units is controlled. After post-processing, a foam film or dense film with controllable unit orientation is obtained.

[0017] (2) The graphene oxide sheets in the gel film are in curved contact with the surface. The graphene oxide sheet structure has a certain curvature in the thickness direction. During the preparation of a dense graphene oxide film after direct room temperature drying, the vertical heat conduction channels can be maintained without breaking. After high-temperature heat treatment and roll pressing densification, a smooth graphene film is obtained, which has high biaxial thermal conductivity in both in-plane and inter-plane directions, and its strength is greatly increased, making it less prone to breakage. The inter-plane thermal conductivity of the densified graphene film can reach 24.7 W / (m·K), and the in-plane thermal conductivity can reach 1042.7 W / (m·K). In contrast, the inter-plane thermal conductivity of the vertically oriented graphene foam film can reach 334.6 W / (m·K), the in-plane thermal conductivity in the width direction can reach 281.4 W / (m·K), and the in-plane thermal conductivity in the length direction can reach 18.1 W / (m·K).

[0018] (3) Compared with the limitations of electrophoresis, the extremely low efficiency of self-assembly, and the complex equipment of CVD, this invention adopts an integrated continuous process of "nozzle extrusion-hydrogel molding-heating densification-winding and unwinding", which can be directly connected to existing roll-to-roll production lines. The linear speed and width are easily expanded, and no additional film transfer steps are required, which greatly improves production efficiency and solves the problem of large-scale production of existing processes.

[0019] (4) The present invention uses pure GO aqueous dispersion, which is not dependent on organic solvents and has a raw material utilization rate of nearly 100%, thus avoiding the serious problem of raw material waste in spray method. At the same time, the equipment has a simple structure (no need for vacuum, atomization, or electrochemical devices), low heating energy consumption, no toxic waste gas or strong acid waste liquid is generated, and the cleaning wastewater is easy to treat, which significantly reduces the preparation cost and environmental burden.

[0020] (5) High process tolerance and wide adaptability: Compared with the roll-to-roll coating method, which has strict requirements on the rheological properties of GO dispersion and is prone to clogging, the present invention has a wider range of adaptability to the solid content and viscosity of GO aqueous dispersion and is less prone to clogging of the nozzle; and it can be adapted to various flexible insulating substrates such as PET and PI without special treatment of the substrate, which facilitates the subsequent heat treatment to prepare graphene film and composite modification, and adapts to the application needs of multiple fields. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of an apparatus for the continuous casting of GO films.

[0022] Figure 2 This is a diagram illustrating the preparation mechanism of the present invention. Figure 2 (a) in the diagram is a schematic diagram of the extrusion port and the expansion channel. Figure 2 (b) in the figure is a diagram of the formation mechanism of the vertically oriented graphene film of the present invention.

[0023] Figure 3 This is a cross-sectional SEM image of the hydrogel membrane in Example 1.

[0024] Figure 4 This is a cross-sectional SEM image of the drying process of the hydrogel membrane in Example 1.

[0025] Figure 5 The image shows a surface SEM image of the GO dense film prepared in Example 3.

[0026] Figure 6 This is a diagram illustrating the preparation mechanism of Comparative Example 2. Figure 6 (a) in the diagram is a schematic diagram of the extrusion port and the expansion channel. Figure 6 (b) in the diagram shows the formation mechanism of the graphene film in Comparative Example 2. Detailed Implementation

[0027] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0028] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0029] The embodiments of the present invention will be further described below with reference to several examples.

[0030] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0031] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0032] Example 1 (1) Prepare a GO solution into a spinnable GO aqueous dispersion (concentration 10 mg / mL), place it in a vacuum homogenizer, and perform homogenization and degassing treatment at a speed of 1200 r / min for 6 min to remove bubbles in the solution and ensure the system is uniform. (2) After the prepared GO solution is extruded through the extruder, it is introduced into an expansion channel to form a continuous hydrogel film. The extrusion speed is adjusted to 18 mL / min, and the solution is extruded onto a PET substrate that moves continuously at a speed of 12 cm / min. The expansion flow field effect of the nozzle is used to guide the GO flakes to align vertically, forming a continuous vertically oriented GO gel film on the substrate. The width of both the extruder and the expansion channel is 5 cm, the thickness of the extruder is 1 mm, and the thickness of the expansion channel is 2 mm.

[0033] (3) The above vertically oriented GO gel film was peeled off from the PET substrate, immersed in a 4 wt% sodium ascorbate reducing solution, and reduced at room temperature for 4 h. After the reduction of GO was completed, it was taken out and freeze-dried (-50 ℃, vacuum degree 10 Pa, drying for 24 h) to obtain the vertically oriented graphene foam film precursor. (4) The dried graphene foam film precursor was placed in a tube furnace under argon protection for high-temperature heat treatment. The heat treatment temperature was 3000℃, the heating rate was 5℃ / min, and the temperature was held for 2 hours before natural cooling to obtain a vertically oriented graphene foam film.

[0034] The density of the obtained vertically oriented graphene foam film is 90 mg / cm³. 3 The inter-surface thermal conductivity is 21.7 W / (m·K).

[0035] When the spinning solution enters the expansion channel through the spinning head, in addition to the axial shearing action, a shearing action is also formed in the thickness expansion direction, forming a bidirectional flow field in the axial and thickness directions. This causes the GO sheet at the thickness center to tilt or even flip, producing a parabolic structure with curvature. Due to strong axial shearing, parallel GO sheets are formed on the upper and lower surfaces.

[0036] Therefore, the graphene oxide sheets are in curvature contact with the surface. During the drying process, the sheets always bend uniformly in one direction, making it difficult for internal fracture stress to form. Furthermore, the graphene oxide sheet structure has a certain curvature connection at the contact points of the upper and lower surfaces, ensuring the integrity of the upper and lower surfaces and the overall film. After direct room temperature drying, despite the significant deformation in the thickness direction, the parabolic structure with curvature and the curvature connection of the upper and lower surfaces ensure that the vertical thermal conduction channels within the film material remain intact. After high-temperature heat treatment and roll densification, a smooth graphene film with biaxial high thermal conductivity (both in-plane and inter-plane) is obtained. Due to the interconnected vertical graphene sheet structure, the peel strength of the graphene film is greatly increased.

[0037] Example 2 (1) Prepare a GO solution into a spinnable GO aqueous dispersion (concentration 15 mg / mL), place it in a vacuum homogenizer, and perform homogenization and degassing treatment at a speed of 1200 r / min for 6 min to remove bubbles in the solution and ensure the system is uniform. (2) After the prepared GO solution is extruded through the extrusion port, it is introduced into an expansion channel to form a continuous gel film. The extrusion speed is adjusted to 18 mL / min, and the solution is extruded onto a PET substrate that moves continuously at a speed of 12 cm / min. The expansion flow field effect of the nozzle is used to guide the GO crystals to align vertically, forming a continuous vertically oriented GO gel film on the substrate. The width of both the extrusion port and the expansion channel is 6 cm, the thickness of the extrusion port is 2 mm, and the thickness of the expansion channel is 5 mm.

[0038] (3) The above vertically oriented GO gel film was peeled off from the PET substrate, immersed in a 4 wt% sodium ascorbate reducing solution, and reduced at room temperature for 4 h. After the reduction of GO was completed, it was taken out and freeze-dried (-50 ℃, vacuum degree 10 Pa, drying for 24 h) to obtain the vertically oriented graphene foam film precursor. (4) The dried graphene foam film precursor was placed in a tube furnace under argon protection for high-temperature heat treatment. The heat treatment temperature was 3000℃, the heating rate was 5℃ / min, and the temperature was held for 2 hours before natural cooling to obtain a vertically oriented graphene foam film.

[0039] The density of the obtained vertically oriented graphene foam film is 550 mg / cm³. 3 It has an inter-plane thermal conductivity of 334.6 W / (m·K), an in-plane thermal conductivity of 281.4 W / (m·K) in the width direction, and an in-plane thermal conductivity of 18.1 W / (m·K) in the length direction, exhibiting excellent directional heat transfer performance.

[0040] Example 3 (1) Prepare a GO solution into a spinnable GO aqueous dispersion (concentration 15 mg / mL), place it in a vacuum homogenizer, and perform homogenization and degassing treatment at a speed of 1200 r / min for 6 min to remove bubbles in the solution and ensure the system is uniform. (2) After the prepared GO solution is extruded through the extrusion port, it is introduced into an expansion channel to form a continuous gel film. The extrusion speed is adjusted to 18 mL / min, and the solution is extruded onto a PET substrate that moves continuously at a speed of 12 cm / min. The expansion flow field effect of the nozzle is used to guide the GO flakes to align vertically, forming a continuous vertically oriented GO gel film on the substrate. The width of both the extrusion port and the expansion channel is 5 cm, the thickness of the extrusion port is 1 mm, and the thickness of the expansion channel is 2 mm.

[0041] (3) The above vertically oriented GO gel film was peeled directly from the PET substrate without chemical reduction and placed in an 80°C forced-air drying oven to dry at room temperature for 12 h to remove moisture, thus obtaining a continuous vertically oriented GO dense film precursor. (4) The dried GO dense film precursor was placed in a tube furnace under argon protection for high-temperature heat treatment at a temperature of 3000 ℃ and a heating rate of 8 ℃ / min. After holding at the temperature for 2 h, it was naturally cooled to obtain a vertically oriented graphene dense film.

[0042] The density of the obtained vertically oriented graphene dense film was 2.09 g / cm³. 3 It has an inter-plane thermal conductivity of 24.7 W / (m·K) and an in-plane thermal conductivity of 1042.7 W / (m·K), making it a graphene thermal conductive film with excellent in-plane and inter-plane thermal conductivity.

[0043] Comparative Example 1 The difference from Example 1 is that the thickness of the expanded flow channel is the same as that of the extrusion orifice, and the width is twice that of the extrusion orifice.

[0044] The density of the obtained graphene dried film was 1.24 g / cm³. 3 The inter-plane thermal conductivity is 1.7 W / (m·K), and the in-plane thermal conductivity is 361.4 W / (m·K).

[0045] The expansion direction of the channel apertures is in the width direction, forming a dual flow field in the width direction. Therefore, a parabolic curvature structure is generated in the width direction, while the graphene sheet structure in the thickness direction is completely vertical, with rigid, non-curvature connections to the upper and lower surfaces. Although the vertically oriented graphene framework can be maintained during freeze-drying, the film thickness shrinks significantly during drying and densification. The completely vertical graphene oxide sheets have a high modulus during deformation, and the deformation direction is inconsistent, causing a spatial crushing effect. This generates huge internal stress between the internal sheets, ultimately leading to structural instability and easy fracture during the process of becoming a dense film, and the thermal conductivity pathway is destroyed.

[0046] The above embodiments detail the structure, features, and effects of the present invention. The above descriptions are merely preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent variations, that do not exceed the scope covered by the specification, should be within the protection scope of the present invention.

Claims

1. A method for preparing a vertically oriented continuous graphene film material, characterized in that, An aqueous solution of graphene oxide is extruded through an extruder and then introduced into an expanded flow channel to form a continuous gel film. Subsequently, it is dried and heat-treated to graphitize it to obtain an oriented graphene film. The thickness of the expanded flow channel is not less than twice the thickness of the extruder, and the width of the expanded flow channel is the same as that of the extruder.

2. The method according to claim 1, characterized in that, The width of the extrusion port is not less than 5cm and the thickness is not greater than 2mm.

3. The method according to claim 1, characterized in that, The concentration of the aqueous solution of graphene oxide is not less than 10 mg / g.

4. The method according to claim 1, characterized in that, The drying process is performed at room temperature.

5. The method according to claim 1, characterized in that, The heat treatment temperature is 2600-3000℃.

6. The method according to claim 1, characterized in that, The aqueous solution of graphene oxide includes one or more of PAN, PAA, PVA, PVP, carbon nanotubes, and nanocellulose.

7. The method according to claim 1, characterized in that, The continuous gel membrane is immersed in a reducing agent, which is sodium ascorbate, hydroiodic acid, hydrobromic acid, tin dichloride solution or hydrazine hydrate.

8. An oriented graphene film prepared by the method described in claim 1.

9. The oriented graphene film according to claim 8, characterized in that, The graphene sheets in the graphene film are oriented perpendicular to the film surface, and at least some of the graphene sheets are arched along their length. The two ends of the arched graphene sheet overlap with the upper and lower surfaces of the adjacent graphene sheet or the graphene film.

10. An application of the oriented graphene film as described in claim 8.

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