Intrinsic graphene dynamic crosslinking ink for micro-droplet printing three-dimensional structure as well as preparation method and application of intrinsic graphene dynamic crosslinking ink

Abstract

The invention discloses intrinsic graphene dynamic crosslinking ink for a micro-droplet printing three-dimensional structure as well as a preparation method and application, and particularly relates to the field of graphene ink. Raw materials of the graphene composite material comprise the following components in percentage by mass: 0.5-2.5% of intrinsic graphene, 2-10% of water-soluble polyamide acid, 0.05-1% of a rheology modifier and the balance of deionized water. Preparing the organic solution of the water-soluble polyamide acid into water-soluble polyamide acid salt powder; preparing an intrinsic graphene dispersion liquid by utilizing intrinsic graphene; adding water-soluble polyamide acid salt powder into the intrinsic graphene dispersion liquid, and carrying out stepped ultrasonic treatment to obtain a mixed dispersion liquid; and adding a rheology modifier into the mixed dispersion liquid to obtain the ink. Based on the method, the intrinsic characteristics of graphene can be reserved, and stable connection and structural support of the lamellae can be realized.

Description

Technical Field

[0001] This application relates to the field of graphene ink preparation, and particularly to an intrinsic graphene dynamic cross-linking ink for microdrop printing three-dimensional structures, a preparation method and an application thereof. Background Art

[0002] As a two-dimensional nanomaterial with high strength, high electrical conductivity and high thermal conductivity, graphene exhibits great application potential in the field of metal matrix composites. Graphene-reinforced magnesium matrix composites have the characteristics of light weight, high strength, high thermal conductivity and excellent electrical conductivity, and show broad application prospects in the fields of aerospace, automotive industry and electronic equipment. As an ideal composite reinforcement phase, the introduction of graphene significantly improves the mechanical properties, thermal conductivity, electrical conductivity and corrosion resistance of the composites. The dispersion, distribution and configuration design of graphene have a significant impact on the mechanical properties, thermoelectric conductivity and corrosion resistance of magnesium matrix composites. Assembling two-dimensional graphene sheets into a three-dimensional connected structure not only inherits the excellent properties of graphene, but also has the characteristics of low density, high electrical conductivity, compressibility, high porosity and large specific surface area. Compared with the deficiencies of traditional graphene three-dimensional structure manufacturing methods (such as template method and self-assembly method) in terms of complex structure designability and unified macro / microstructure regulation, the uniform microdrop printing technology avoids the agglomeration of graphene sheets by controlling droplet freezing, and uses directional freezing to guide the sheets to align along the ice crystal growth direction, realizing more refined macro / microstructure regulation.

[0003] In the existing preparation methods of graphene dispersions, although the use of common physical dispersants (surfactants) can temporarily inhibit aggregation, the interfacial binding force between them and graphene is weak, and it cannot provide stable connection support during freeze-drying or subsequent heat treatment processes, resulting in slippage between lamellae or even structural collapse. During the freeze-drying stage, the growth of ice crystals will squeeze the graphene lamellae, and traditional additives (such as polyvinyl alcohol PVA) only form a physical cross-linking network through hydrogen bonds, and its mechanical strength is insufficient to resist the capillary force generated by ice sublimation, resulting in the collapse of the porous structure after drying. The porosity of the collapsed graphene preform is significantly reduced, and the contact area between lamellae decreases, severely weakening its load-bearing capacity and functional properties (such as electrical / thermal conductivity) as a reinforcing phase of the composite material. In addition, the interfacial compatibility between these additives and graphene is limited, and it is difficult to establish a strong and tough connection between lamellae, resulting in easy interfacial peeling during the subsequent composite material forming process. Additionally, there are methods that utilize the activation of a large number of carboxyl functional groups on graphene oxide (GO), react the activated carboxyl groups with chitosan, and cross-link to generate amide bonds, thereby endowing the material with strong interfacial bonding and improving the mechanical properties of the cross-linked structure. However, the PG surface has fewer oxygen-containing functional groups and cannot be cross-linked using functional groups. Covalently connecting graphene lamellae by grafting functional groups on the surface of intrinsic graphene or performing complex chemical modifications on it will introduce structural defects, destroy the intrinsic excellent properties of graphene (such as electrical conductivity), and the process flow is cumbersome and costly. Summary of the Invention

[0004] The main purpose of this application is to provide an intrinsic graphene dynamic cross-linking ink for microdroplet printing three-dimensional structures, its preparation method and application, aiming to solve the problem in the existing methods that it is impossible to provide stable connection support while retaining the intrinsic characteristics of graphene.

[0005] To achieve the above purpose, this application provides an intrinsic graphene dynamic cross-linking ink for microdroplet printing three-dimensional structures, and its raw materials include the following components according to mass fraction: 0.5 - 2.5% intrinsic graphene, 2 - 10% water-soluble polyamic acid, 0.05 - 1% rheology regulator, and the balance is deionized water.

[0006] Optionally, the rheology regulator includes a composition of one or two of sodium carboxymethylcellulose and xanthan gum.

[0007] Optionally, the viscosity of the ink is 3 - 10 mPa·s, the absolute value of the Zeta potential is less than or equal to 40 mV, and the surface tension is 28 - 50 mN / m; the ink includes graphene lamellae, and the lateral size of the graphene lamellae is 2 - 10 μm, and the thickness is less than or equal to 5 layers.

[0008] To achieve the above object, the present application also provides a method for preparing the intrinsic graphene dynamic crosslinking ink for microdroplet printing three-dimensional structures, which is characterized by including: preparing a water-soluble polyamic acid salt powder from an organic solution of water-soluble polyamic acid; preparing an intrinsic graphene dispersion using intrinsic graphene; adding the water-soluble polyamic acid salt powder into the intrinsic graphene dispersion, and performing stepped ultrasonic treatment to obtain a mixed dispersion; adding a rheology regulator into the mixed dispersion to obtain the ink.

[0009] Optionally, the method for preparing the water-soluble polyamic acid salt powder is: precipitating the water-soluble polyamic acid organic solution into deionized water, drying and crushing the precipitated water-soluble polyamic acid precipitate to obtain a water-soluble polyamic acid powder; dissolving the water-soluble polyamic acid powder in triethylamine, and performing freeze-drying to obtain the water-soluble polyamic acid salt powder.

[0010] Optionally, during the drying process, the drying temperature is 40 - 70 °C, and the drying duration is 3 - 10 h.

[0011] Optionally, the molar ratio of the water-soluble polyamic acid powder to triethylamine is 2:0.5 - 1.

[0012] Optionally, the method for preparing the intrinsic graphene dispersion is: ultrasonically dispersing the intrinsic graphene in deionized water to obtain an intrinsic graphene dispersion with a concentration of 2 - 10 mg / ml.

[0013] Optionally, during the stepped ultrasonic treatment, the powers are successively 100 - 300 W, 200 - 400 W, 300 - 500 W, and the corresponding ultrasonic durations are 0.5 - 1 h, 1 - 2 h, 0.2 - 1 h.

[0014] To achieve the above object, the present application also provides the application of the above-mentioned intrinsic graphene dynamic crosslinking ink for microdroplet printing three-dimensional structures in the field of microdroplet printing.

[0015] Compared with the prior art, the beneficial effects of the present application are as follows: The intrinsic graphene dynamic crosslinking ink for microdroplet printing three-dimensional structures of the present invention uses water-soluble polyamic acid as a surfactant, and utilizes its amphiphilic molecular structure to adsorb at the gas-liquid interface, significantly reducing the surface tension of the ink; during the freeze-drying process, PAAs serves as a support framework for intrinsic graphene, and maintains the stability of the three-dimensional structure through the crosslinking of its molecular chains, ensuring the integrity and mechanical properties of the preform after printing, providing a reliable basis for the preparation of high-performance composite materials, and solving the problem of collapse of the printed preform caused by the lack of structural support in the intrinsic graphene ink; the π-π conjugation of the amide bond and the hydrogen bond of the carboxylic acid group in the PAAs molecular chain are used to anchor the PG sheets, realizing the stable dispersion of the ink. While retaining the intrinsic properties of graphene, the covalent modification of the graphene structure is avoided.

[0016] The preparation method of the intrinsic graphene dynamic cross-linking ink for microdroplet printing three-dimensional structures of the present invention obtains PG ink with physical and chemical properties meeting the requirements of microdroplet printing through the synergistic regulation of the PAAs concentration and the rheology regulator. Its surface tension is precisely adapted within the range of 28-50 mN / m, so that the intrinsic graphene ink with stable PAAs has high compatibility and practicability, and is especially suitable for the microdroplet printing process requiring high resolution and stability; the raw material components are simple, and the preparation process is green and environmentally friendly.

[0017] The application of the intrinsic graphene dynamic cross-linking ink for microdroplet printing three-dimensional structures of the present invention in the field of microdroplet printing can print a three-dimensional structure of an intrinsic graphene preform. After freeze-drying, the preform does not shrink or deform and still maintains a three-dimensional support structure. Description of the Drawings

[0018] Figure 1 is a flow chart of a preparation method of an intrinsic graphene dynamic cross-linking ink for microdroplet printing three-dimensional structures of the present application; Figure 2 is a mechanism diagram of an intrinsic graphene dynamic cross-linking ink for microdroplet printing three-dimensional structures of the present application; Figure 3 is an optical photograph of the ink obtained in Example 1 without precipitation after standing for 14 days; Figure 4 is an optical photograph of the three-dimensional structure microdroplet printed with the ink obtained in Example 1; Figure 5 is a stress-strain curve of the three-dimensional structure microdroplet printed with the ink obtained in Example 1; Figure 6 is a sheet scanning electron micrograph of the ink obtained in Example 3.

[0019] The realization, functional features and advantages of the purpose of the present application will be further described with reference to the embodiments and the accompanying drawings. Detailed Embodiments

[0020] To make the purpose, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below with reference to the drawings in the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0021] The first embodiment of the present invention provides an intrinsic graphene dynamic cross-linking ink for micro-droplet printing three-dimensional structures, and its raw materials include the following components according to mass fraction: 0.5-2.5% intrinsic graphene, 2-10% water-soluble polyamic acid, 0.05-1% rheology regulator, and the balance is deionized water.

[0022] The rheology regulator includes a composition of one or two of sodium carboxymethylcellulose and xanthan gum.

[0023] The viscosity of the ink is 3-10 mPa·s, the absolute value of the Zeta potential is less than or equal to 40 mV, and the surface tension is 28-50 mN / m; the ink includes graphene sheets, and the lateral size of the graphene sheets is 2-10 μm, and the thickness is less than or equal to 5 layers.

[0024] The second embodiment of the present invention provides a preparation method of an intrinsic graphene dynamic cross-linking ink for micro-droplet printing three-dimensional structures, as Figure 1 shown, based on the raw material component content of the first embodiment, specifically including the following steps: Step S1, prepare a water-soluble polyamic acid salt powder from an organic solution of water-soluble polyamic acid; Specifically, in step S11, precipitate the organic solution of water-soluble polyamic acid into deionized water, dry and crush the precipitated water-soluble polyamic acid to obtain water-soluble polyamic acid powder; wherein, during the drying process, the drying temperature is 40-70 °C, and the drying duration is 3-10 h; Step S12, dissolve the water-soluble polyamic acid powder in triethylamine according to a molar ratio of 2:0.5-1, and perform freeze-drying to obtain a water-soluble polyamic acid salt powder. Further, the addition method of triethylamine is to dropwise add triethylamine to the water-soluble polyamic acid powder until it is completely dissolved.

[0025] Step S2, prepare an intrinsic graphene dispersion using intrinsic graphene; It can be understood that the intrinsic graphene is a nanosheet of intrinsic graphene prepared by a liquid-phase exfoliation method using flake graphite and a surfactant as raw materials. Specifically, the method for preparing the intrinsic graphene dispersion is: ultrasonically disperse the intrinsic graphene in deionized water to obtain an intrinsic graphene dispersion with a concentration of 2-10 mg / ml, wherein the power of the ultrasonic wave is 100-300 W.

[0026] Step S3, add the water-soluble polyamic acid salt powder to the intrinsic graphene dispersion, and perform stepwise ultrasonic treatment to obtain a mixed dispersion; wherein, during the stepwise ultrasonic treatment process, the power is sequentially 100-300 W, 200-400 W, 300-500 W, and the corresponding ultrasonic durations are 0.5-1 h, 1-2 h, 0.2-1 h.

[0027] The mechanism diagram of the dispersion of water-soluble polyamic acid (PAAs) in pristine graphene in this embodiment is shown in Figure 2 As shown in the figure, the aromatic rings in the PAAs molecules are combined with the conjugated six-membered ring structure of graphene through π-π stacking, enabling the PAAs to be tightly adsorbed on the surface of graphene and form a uniform coating layer. At the same time, the carboxylic acid groups (-COOH) of PAAs form hydrogen bonds with the oxygen-containing functional groups (such as hydroxyl groups and epoxy groups) on the surface of graphene, enhancing the adsorption strength. The hydrophobic segments in the PAA molecules tend to bind to the hydrophobic surface of graphene, while the hydrophilic groups face outward and contact with water, forming an "anchoring-stretching" structure. The coated PAA molecular chains stretch outward, forming a physical barrier on the surface of graphene to prevent adjacent sheets from re-aggregating due to van der Waals forces. The carboxylic acid groups of PAAs are ionized into negative charges, making the surface of the coated graphene negatively charged, and enhancing the dispersion stability through the repulsion of like charges.

[0028] Step S4: Add a rheology regulator to the mixed dispersion and stir magnetically for 1 - 3 h to obtain the ink.

[0029] In this embodiment, water-soluble polyamic acid is used as a surfactant, and its amphiphilic molecular structure adsorbs at the gas-liquid interface, significantly reducing the surface tension of the ink. Through the synergistic regulation of the PAAs concentration and the ratio of the rheology regulator, the surface tension of the ink is precisely adapted within the range of 28 - 50 mN / m. The surface tension in this range enables the PAAs-stabilized pristine graphene ink to have high compatibility and practicability, especially suitable for the microdroplet printing process requiring high resolution and stability.

[0030] After printing is completed, it is necessary to first perform freeze-drying on the printed product to form a stable preform at room temperature, and then perform low-temperature heat treatment for reinforcement. During the freeze-drying process, the expulsion effect of ice crystal growth localizes and enriches the PAA molecular chains in the ice-liquid interface region, and its restricted movement induces dynamic hydrogen bond cross-linking of the carboxylic acid groups, realizing the spontaneous construction of a three-dimensional stable structure in the printed preform during freezing. Moreover, the molecular structure of PAAs contains aromatic rings and hydrophilic chain segments, and through the synergistic action of non-covalent interactions (such as π-π conjugation, hydrogen bonds) and steric hindrance effects, the efficient and stable dispersion of pristine graphene is achieved. This method retains the intrinsic properties of graphene while avoiding the damage to the graphene structure caused by covalent modification.

[0031] During the low-temperature heat treatment process, water-soluble PAAs can be dehydrated and cyclized to form polyimide (PI), forming a graphene / PI composite structure; the high mechanical strength and high temperature resistance of polyimide not only enhance the durability of the printed structure but also maintain the integrity of the graphene conductive network.

[0032] Example 1 Step S1: Slowly precipitate 10 g of an organic solution of water-soluble polyamic acid (the solvent is N-methylpyrrolidone, NMP) into 300 g of deionized water. After stirring for 30 min, let it stand. After complete precipitation, filter and wash twice with deionized water. Place the washed water-soluble polyamic acid precipitate in a vacuum drying oven and dry at 50 °C for 8 h until constant weight. Crush the dried polyamic acid precipitate into powder in a mortar to obtain water-soluble polyamic acid powder. Drop 0.5 g of triethylamine into 2 g of polyamic acid powder, continuously stir magnetically for 2 h until it is completely dissolved, and then perform freeze-drying to obtain water-soluble polyamic acid salt powder.

[0033] Step S2: Disperse 100 mg of intrinsic graphene in 10 ml of deionized water and ultrasonically treat it at a power of 200 W for 1 h to obtain an intrinsic graphene dispersion with a concentration of 10 mg / ml. Step S3: Add 300 mg of water-soluble polyamic acid salt powder to the intrinsic graphene dispersion obtained in Step S2 in batches and stir magnetically for 30 min. And perform stepped ultrasonic treatment. The first stage: power is 100 W, ultrasonic treatment for 0.5 h; the second stage: power is 200 W, ultrasonic treatment for 1 h; the third stage: power is 300 W, ultrasonic treatment for 0.5 h to obtain a mixed dispersion. Step S4: Add 0.05 g of sodium carboxymethylcellulose to the mixed dispersion and stir magnetically for 1 h to obtain ink.

[0034] Test the ink obtained in this example. The measured viscosity of the ink is 6 mPa·s (25 °C, shear rate 1000 s⁻¹), and the surface tension is 28 mN / m. The optical photo after standing for 14 d is as Figure 3 shown. It can be seen from the figure that there is no obvious precipitation in the ink after standing for 14 d, which proves that the prepared ink can maintain long-term uniformity and stability. According to the viscosity and surface tension of the ink, the Ohnesorge number Oh≈0.113, which is between 0.1 and 1, meeting the requirements of microdroplet printing. Thus, it can be known that the ink obtained in this example can be stably used in microdroplet printing technology and is suitable for manufacturing high-precision three-dimensional structures. The absolute value of the Zeta potential of the tested ink is 30 mV, indicating that the ink has high stability, ensuring the uniform dispersion of graphene and excellent electrical conductivity. Using the ink obtained in this example as the ink for microdroplet printing, the three-dimensional supportable structure printed is as Figure 4 shown. With the assistance of PAAs, the graphene droplets overlap, and the preform structure formed by droplet printing is complete. As Figure 5 shown, the compressive strength of the preform formed by microdroplet printing of the graphene ink configured according to this example is about 30 Kpa, overcoming the problem of easy collapse of the preform structure.

[0035] Example 2 Step S1: Slowly precipitate 15 g of the organic solution of water-soluble polyamic acid (with N-methylpyrrolidone as the solvent) into 600 g of deionized water. After stirring for 30 min, let it stand. After complete precipitation, filter and wash it 3 times with deionized water. Place the washed water-soluble polyamic acid precipitate in a vacuum drying oven and dry it at 60 °C for 8 h until constant weight. Grind the dried polyamic acid precipitate into a powder in a mortar to obtain water-soluble polyamic acid powder. Drop 1 g of triethylamine into 3 g of polyamic acid powder, continuously stir magnetically for 2 h until it is completely dissolved, and perform freeze-drying to obtain water-soluble polyamic acid salt powder.

[0036] Step S2: Disperse 150 mg of intrinsic graphene in 10 ml of deionized water and ultrasonically treat it at a power of 250 W for 1.5 h to obtain an intrinsic graphene dispersion with a concentration of 15 mg / ml. Step S3: Add 200 mg of water-soluble polyamic acid salt powder to the intrinsic graphene dispersion obtained in Step S2 in batches and stir magnetically for 30 min. And perform stepwise ultrasonic treatment. The first stage: power is 200 W, ultrasonic treatment for 1 h; the second stage: power is 300 W, ultrasonic treatment for 1.5 h; the third stage: power is 400 W, ultrasonic treatment for 0.5 h to obtain a mixed dispersion. Step S4: Add 0.1 g of xanthan gum to the mixed dispersion and stir magnetically for 1 h to obtain ink.

[0037] Test the ink obtained in this example. The measured viscosity of the ink is 8 mPa·s (25 °C, shear rate 1000 s⁻¹), and the surface tension is 35 mN / m. According to the viscosity and surface tension of the ink, the Ohnesorge number Oh≈0.135, which is between 0.1 and 1. This result shows that the viscosity and surface tension of this ink are in the ideal range and are suitable for forming stable droplets and achieving high-precision printing.

[0038] Example 3 Step S1: Slowly precipitate 20 g of the organic solution of water-soluble polyamic acid (with N-methylpyrrolidone as the solvent) into 800 g of deionized water. After stirring for 30 min, let it stand. After complete precipitation, filter and wash it 3 times with deionized water. Place the washed water-soluble polyamic acid precipitate in a vacuum drying oven and dry it at 60 °C for 5 h until constant weight. Grind the dried polyamic acid precipitate into a powder in a mortar to obtain water-soluble polyamic acid powder. Drop 1.5 g of triethylamine into 4 g of polyamic acid powder, continuously stir magnetically for 2 h until it is completely dissolved, and perform freeze-drying to obtain water-soluble polyamic acid salt powder.

[0039] Step S2: Disperse 50 mg of intrinsic graphene in 10 ml of deionized water, and ultrasonically treat it for 2 h at a power of 150 W to obtain an intrinsic graphene dispersion with a concentration of 5 mg / ml. Step S3: Add 100 g of water-soluble polyamic acid salt powder in batches to the intrinsic graphene dispersion obtained in Step S2, and magnetically stir for 30 min; and perform stepped ultrasonic treatment. The first stage: power is 100 W, ultrasonic treatment for 1 h; the second stage: power is 200 W, ultrasonic treatment for 2 h; the third stage: power is 300 W, ultrasonic treatment for 1 h to obtain a mixed dispersion. Step S4: Add 0.1 g of a rheology modifier (a mixture of sodium carboxymethyl cellulose and xanthan gum with a mass ratio of 1:1) to the mixed dispersion, and magnetically stir for 1 h to obtain the ink.

[0040] The ink obtained in this example was tested. The viscosity of the ink was measured to be 10 mPa·s (25 °C, shear rate 1000 s⁻¹), and the surface tension was 40 mN / m. Calculated from the viscosity and surface tension of the ink, the Ohnesorge number Oh≈0.158, which is between 0.1 and 1. This result indicates that the viscosity and surface tension of the ink are within the ideal range, suitable for forming stable droplets and achieving high-precision printing.

[0041] Comparative Example 1 Step S1: Slowly precipitate 10 g of an organic solution of water-soluble polyamic acid (the solvent is N-methylpyrrolidone, NMP) into 300 g of deionized water, stir for 30 min and then let it stand. After complete precipitation, filter and wash twice with deionized water; place the washed water-soluble polyamic acid precipitate in a vacuum drying oven and dry it at 50 °C for 8 h until constant weight; crush the dried polyamic acid precipitate into powder in a mortar to obtain water-soluble polyamic acid powder; add 0.5 g of triethylamine dropwise to 2 g of polyamic acid powder, continuously magnetically stir for 2 h to completely dissolve it, and perform freeze-drying to obtain water-soluble polyamic acid salt powder.

[0042] Step S2: Disperse 100 mg of intrinsic graphene in 10 ml of deionized water, and ultrasonically treat it for 1 h at a power of 200 W to obtain an intrinsic graphene dispersion with a concentration of 10 mg / ml. Step S3: Add 300 mg of water-soluble polyamic acid salt powder in batches to the intrinsic graphene dispersion obtained in Step S2, and magnetically stir for 30 min; and perform stepped ultrasonic treatment. The first stage: power is 100 W, ultrasonic treatment for 0.5 h; the second stage: power is 200 W, ultrasonic treatment for 1 h; the third stage: power is 300 W, ultrasonic treatment for 0.5 h to obtain a mixed dispersion. Step S4: Magnetically stir the mixed dispersion for 1 h to obtain the ink.

[0043] The ink obtained in this comparative example was tested, and the viscosity of the ink was measured to be 2 mPa·s (25 °C, shear rate 1000 s⁻¹), and the surface tension was 35 mN / m. Calculated from the viscosity and surface tension of the ink, the Ohnesorge number Oh≈0.034, which is not between 0.1 and 1. When printing, satellite droplets appeared due to too low viscosity, and the physical and chemical properties of the ink with this formulation did not meet the requirements of high-resolution stable printing.

[0044] Comparative Example 2 Step S1: Slowly precipitate 10 g of an organic solution of water-soluble polyamic acid (the solvent is N-methylpyrrolidone, NMP) into 300 g of deionized water. After stirring for 30 min, let it stand. After complete precipitation, filter it, and wash it twice with deionized water; Place the washed water-soluble polyamic acid precipitate in a vacuum drying oven and dry it at 50 °C for 8 h until constant weight; Crush the dried polyamic acid precipitate into powder in a mortar to obtain water-soluble polyamic acid powder; Add 0.5 g of triethylamine dropwise to 2 g of polyamic acid powder, and continuously stir magnetically for 2 h until it is completely dissolved, and then perform freeze-drying to obtain water-soluble polyamic acid salt powder.

[0045] Step S2: Disperse 100 mg of pristine graphene in 10 ml of deionized water, and ultrasonically treat it at a power of 200 W for 1 h to obtain a pristine graphene dispersion with a concentration of 10 mg / ml; Step S3: Add 300 mg of water-soluble polyamic acid salt powder in batches to the pristine graphene dispersion obtained in Step S2, and stir magnetically for 30 min; And perform stepped ultrasonic treatment. The first stage: power is 100 W, ultrasonic treatment for 0.5 h; The second stage: power is 200 W, ultrasonic treatment for 1 h; The third stage: power is 300 W, ultrasonic treatment for 0.5 h to obtain a mixed dispersion; Step S4: Add 0.5 g of sodium carboxymethylcellulose to the mixed dispersion and stir magnetically for 1 h to obtain ink.

[0046] The ink obtained in this comparative example was tested, and the viscosity of the ink was measured to be 50 mPa·s (25 °C, shear rate 1000 s⁻¹), and the surface tension was 32 mN / m. Calculated from the viscosity and surface tension of the ink, the Ohnesorge number Oh≈1.04, which is greater than 1. When printing, due to too high viscosity, the droplets could not break away from the nozzle, resulting in jetting failure or severe tailing. Fibrous structures were observed when the droplets broke by high-speed photography. The measured clogging frequency exceeded 40 times per hour, and the physical and chemical properties of the ink with this formulation did not meet the requirements of high-resolution stable printing.

[0047] Comparative Example 3 Step S1: Slowly precipitate 10 g of an organic solution of water-soluble polyamic acid (the solvent is N-methylpyrrolidone, NMP) into 300 g of deionized water. After stirring for 30 min, let it stand. After complete precipitation, filter it and wash it twice with deionized water. Place the washed water-soluble polyamic acid precipitate in a vacuum drying oven and dry it at 50 °C for 8 h until constant weight. Grind the dried polyamic acid precipitate into powder in a mortar to obtain water-soluble polyamic acid powder. Drop 0.5 g of triethylamine into 2 g of polyamic acid powder and continuously stir magnetically for 2 h until it is completely dissolved, and then perform freeze-drying to obtain water-soluble polyamic acid salt powder.

[0048] Step S2: Disperse 100 mg of intrinsic graphene in 10 ml of deionized water and ultrasonically treat it at a power of 200 W for 1 h to obtain an intrinsic graphene dispersion with a concentration of 10 mg / ml. Step S3: Add 50 mg of water-soluble polyamic acid salt powder to the intrinsic graphene dispersion obtained in Step S2 in batches and stir magnetically for 30 min. And perform stepped ultrasonic treatment. The first stage: the power is 100 W and the ultrasonic treatment is 0.5 h; the second stage: the power is 200 W and the ultrasonic treatment is 1 h; the third stage: the power is 300 W and the ultrasonic treatment is 0.5 h to obtain a mixed dispersion. Step S4: Add 0.05 g of sodium carboxymethylcellulose to the mixed dispersion and stir magnetically for 1 h to obtain ink.

[0049] Test the ink obtained in this comparative example. The viscosity of the ink is measured to be 5 mPa·s (25 °C, shear rate 1000 s⁻¹), and the surface tension is 60 mN / m. PAAs belong to polymer surfactants, and their concentration directly affects the surface tension of the solution. When the concentration of the dispersant is lower than the critical micelle concentration, the molecules are mainly adsorbed on the surface of graphene and the gas-liquid interface in the form of monomers, and the ability to reduce the surface tension is limited. The dispersant molecules adsorbed on the liquid-gas interface are insufficient to effectively reduce the surface tension, resulting in the surface tension of the dispersion approaching the level of pure water (about 72 mN / m). Due to the large surface tension and viscosity, this ink cannot form stable droplets during the printing process and is ejected in the form of a jet.

[0050] Comparative Example 4 Step S1: Slowly precipitate 15 g of an organic solution of water-soluble polyamic acid (with N-methylpyrrolidone as the solvent) into 600 g of deionized water. After stirring for 30 min, let it stand. After complete precipitation, filter and wash three times with deionized water. Place the washed water-soluble polyamic acid precipitate in a vacuum drying oven and dry at 60 °C for 8 h until constant weight. Crush the dried polyamic acid precipitate into powder in a mortar to obtain water-soluble polyamic acid powder. Drop 1 g of triethylamine into 3 g of polyamic acid powder, continuously stir magnetically for 2 h until completely dissolved, and then perform freeze-drying to obtain water-soluble polyamic acid salt powder.

[0051] Step S2: Disperse 150 mg of intrinsic graphene in 10 ml of deionized water and ultrasonically treat it at a power of 250 W for 1.5 h to obtain an intrinsic graphene dispersion with a concentration of 15 mg / ml. Step S3: Add 200 mg of water-soluble polyamic acid salt powder to the intrinsic graphene dispersion obtained in Step S2 in batches and stir magnetically for 30 min to obtain a mixed dispersion. Step S4: Add 0.1 g of xanthan gum to the mixed dispersion and stir magnetically for 1 h to obtain the ink.

[0052] Test the ink obtained in this comparative example. Since it is only mixed by magnetic stirring without stepwise ultrasonic treatment, large agglomerations of graphene occur, blocking the nozzle during the printing process and preventing the droplets from being ejected smoothly.

[0053] The third embodiment of the present invention provides an application of an intrinsic graphene dynamic cross-linking ink for microdrop printing three-dimensional structures in the field of microdrop printing.

[0054] The above are only the preferred embodiments of this application, and do not limit the patent scope of this application accordingly. Any equivalent structural or equivalent process transformation made by using the content of the specification and drawings of this application, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of this application.

Claims

1. An intrinsic graphene dynamic cross-linking ink for microdrop printing three-dimensional structures, characterized in that, Its raw materials include the following components by mass fraction: 0.5 - 2.5% of intrinsic graphene, 2 - 10% of water-soluble polyamic acid, 0.05 - 1% of rheology regulator, and the balance being deionized water.

2. The intrinsic graphene dynamic cross-linking ink for microdrop printing three-dimensional structures according to claim 1, wherein The rheology regulator includes a composition of one or both of sodium carboxymethyl cellulose and xanthan gum.

3. The intrinsic graphene dynamic crosslinking ink for microdrop printing three-dimensional structures according to claim 1, wherein The viscosity of the ink is 3 - 10 mPa·s, the absolute value of the Zeta potential is greater than or equal to 25 mV, and the surface tension is 28 - 50 mN / m; The ink includes graphene sheets, and the lateral size of the graphene sheets is 2 - 10 μm, and the thickness is less than or equal to 5 layers.

4. A preparation method of an intrinsic graphene dynamically cross-linked ink for microdroplet printing three-dimensional structures as described in claim 1, characterized in that, It includes: Preparing a water-soluble polyamic acid salt powder from an organic solution of water-soluble polyamic acid; Preparing an intrinsic graphene dispersion using intrinsic graphene; Adding the water-soluble polyamic acid salt powder to the intrinsic graphene dispersion and performing stepped ultrasonic treatment to obtain a mixed dispersion; Adding a rheology regulator to the mixed dispersion to obtain an ink.

5. The preparation method of the intrinsic graphene dynamic cross-linking ink for microdroplet printing three-dimensional structures according to claim 4, characterized in that, The preparation method of the water-soluble polyamic acid salt powder is: Precipitating the water-soluble polyamic acid organic solution into deionized water, drying and crushing the precipitated water-soluble polyamic acid precipitate to obtain a water-soluble polyamic acid powder; Dissolving the water-soluble polyamic acid powder in triethylamine and performing freeze-drying to obtain a water-soluble polyamic acid salt powder.

6. According to the preparation method of the intrinsic graphene dynamic cross-linking ink for micro-drop printing three-dimensional structures as claimed in claim 5, during the drying process, the drying temperature is 40 - 70°C, and the drying duration is 3 - 10 h.

7. According to the preparation method of the intrinsic graphene dynamic cross-linking ink for micro-drop printing three-dimensional structures as claimed in claim 5, the molar ratio of the water-soluble polyamic acid powder to triethylamine is 2:0.5 - 1.

8. According to the preparation method of the intrinsic graphene dynamic cross-linking ink for micro-drop printing three-dimensional structures as claimed in claim 4, the preparation method of the intrinsic graphene dispersion is: Ultrasonically dispersing the intrinsic graphene in deionized water to obtain an intrinsic graphene dispersion with a concentration of 2 - 10 mg / ml.

9. According to the preparation method of the intrinsic graphene dynamic cross-linking ink for micro-drop printing three-dimensional structures as claimed in claim 4, during the stepped ultrasonic treatment process, the powers are 100 - 300 W, 200 - 400 W, and 300 - 500 W in sequence, and the corresponding ultrasonic durations are 0.5 - 1 h, 1 - 2 h, and 0.2 - 1 h.

10. An application of the intrinsic graphene dynamic cross-linking ink for micro-drop printing three-dimensional structures as claimed in claim 1 in the field of micro-drop printing.

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