Polyimide liquid metal microparticle electronic ink, and preparation method and application thereof

Abstract

This invention discloses a polyimide liquid metal microparticle electronic ink, its preparation method, and its applications. The liquid metal ink prepared by this invention can be printed into circuits using a high-temperature sintering method, eliminating the need for time-consuming activation methods such as pressing or scraping. This reduces damage to the circuit pattern, significantly saving preparation time and allowing for the printing of complex patterns, thus saving costs. Furthermore, the circuits prepared by this method exhibit excellent tensile and bending properties, making them suitable for the fabrication of flexible circuits. They can be used as conductive inks in the printing of electronic products in fields such as flexible wearable electronic devices, flexible sensors, and brain-computer interfaces. Various printing methods can be used to create different types of patterning to form conductive pathways.

Description

Technical Field

[0001] This invention relates to a polyimide liquid metal microparticle electronic ink, its preparation method and application, belonging to the field of liquid metal ink technology. Background Technology

[0002] Low-melting-point gallium-based liquid metals (LMs) are metals that remain liquid at room temperature and have recently attracted considerable interest due to their remarkable combination of fluidity, conductivity, stretchability, self-healing properties, and biocompatibility. Furthermore, liquid metals possess the property of being granular; liquid metal particles can be dispersed or suspended in a continuous phase to create "inks" that can be designed to possess desirable properties different from those of bulk liquid metals. For example, this approach makes liquid metals easier to dispense in patterned applications such as screen printing or inkjet printing. Second, liquid metal particles dispersed in a polymer matrix can alter the properties of the final composite material without significantly changing its mechanical properties. Third, smaller particles (less than 100 nanometers) possess plasmonic optical properties that can be used for sensing. However, the ultra-high surface tension of gallium-based liquid metals results in poor wettability with substrates, significantly limiting their widespread application in flexible electronics. Combining liquid metals with polymers offers a structural advantage: the polymer matrix encapsulates the liquid metal, imparting elasticity, providing structural support for electrical components, and preventing leakage. The uncured matrix also provides ideal rheological properties, making liquid metal polymer composites suitable for a variety of patterned applications. Functionally, liquid metals offer high thermal conductivity, high dielectric constant, strain-tunable optical properties, and adjustable stiffness. By selecting specific polymer and liquid metal components, liquid metal polymer composites can be designed to exhibit customizable properties.

[0003] However, gallium-based liquid metals form an oxide film (approximately 3–10 nm) on their surface under atmospheric conditions. This oxide layer forms mechanical and electrical barriers, preventing sufficiently small particles from re-merging, even though these particles are primarily composed of liquid. While this property helps stabilize the particles and their suspension, when liquid metal particles are distributed within a polymer matrix, the polymer forms a thin film between adjacent particles, adding additional barriers to sintering. To obtain conductive pathways, the oxide film must be broken to allow the internal gallium-based liquid metal to flow out and fuse, thereby constructing conductive paths. Currently, researchers mainly use methods such as mechanical sintering (stretching or extrusion), laser sintering, and self-sintering to prepare gallium-based liquid metal ink conductive circuits, thereby breaking down the oxide shell. However, these methods all face many challenges, such as the low operational precision of the mechanical sintering process, the high fluidity of gallium-based liquid metal making it easy to come into contact with other electronic devices, leading to short circuits, the possibility of gallium-based liquid metal leakage due to extrusion of the elastic encapsulation layer, and the difficulty in achieving mechanical sintering on rough and complex surfaces (such as curved or grooved surfaces). While laser sintering can improve the above problems, it is costly and, due to light reflection and scattering, areas such as grooves, corners and pores in complex curved patterns cannot obtain enough energy to achieve conductive paths. Furthermore, the energy from the laser may cause thermal damage to the flexible substrate, thereby deforming and damaging electronic devices. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a conductive ink based on liquid metal particles. After patterning, the liquid metal in this ink automatically breaks down at high temperatures, forming conductive pathways. Circuits manufactured using this ink exhibit excellent flexibility and deformability, allowing for a variety of graphic designs.

[0005] This invention is achieved through the following technical solution:

[0006] The first objective of this invention is to provide a polyimide liquid metal microparticle electronic ink, comprising liquid metal and polyamic acid or polyamic acid salt coated on the surface of the liquid metal.

[0007] In one embodiment of the present invention, the liquid metal is a low-melting-point gallium-based liquid metal.

[0008] In one embodiment of the present invention, the low-melting-point gallium-based liquid metal is one or more of gallium, gallium-indium alloy, and gallium-indium-tin alloy with a melting point below 40°C; more preferably, it is a gallium-indium alloy.

[0009] In one embodiment of the present invention, the polyamic acid is a polymer obtained by polycondensation of a dicarboxylic anhydride and a diamine in an aprotic polar solvent.

[0010] In one embodiment of the present invention, the polyamic acid salt is obtained by reacting polyamic acid and an organic ammonium salt.

[0011] In one embodiment of the present invention, the dicarboxylic acid anhydride is one or more selected from pyromellitic dianhydride (PMDA), 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3'4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-(hexafluoroisopropene)phthalic anhydride (6FDA), 4,4'-diphenyl ether dianhydride (ODPA), bisphenol A type diether dianhydride (BPADA), hydrogenated pyromellitic dianhydride (HPMDA), cyclobutanetetracarboxylic dianhydride (CBDA), and 1,4,5,8-naphthalenetetracarboxylic anhydride (NTDA); more preferably, it is 3,3'4,4'-biphenyltetracarboxylic dianhydride.

[0012] In one embodiment of the present invention, the diamine is 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (p-PDA), m-phenylenediamine (m-PDA), 4,4'-diaminodiphenylmethane (MDA), 9,9-bis(4-aminophenyl)fluorene (FDA), 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine (TFMB), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,4- One or more of bis(4-aminophenoxy)benzene (TPE-Q), 4,4'-diamino-2,2'-dimethylbiphenyl (DMBZ), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ), 2-(4-aminophenyl)-5-aminobenzoxazole (APBOA), 4,4'-diaminobenzoylaniline (DABA), isophthalohydrazide (IPDH), and dihydrazide terephthalate (TPDH); more preferably 4,4'-diaminodiphenyl ether.

[0013] In one embodiment of the present invention, the aprotic polar solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide; more preferably, it is N,N-dimethylacetamide.

[0014] In one embodiment of the present invention, the organic ammonium salt is one or more selected from triethylamine, tributylamine, trihexylamine, trioctylamine, N,N-dimethyl-n-octylamine, and triethanolamine; more preferably, triethylamine.

[0015] A second objective of this invention is to provide a method for preparing the polyimide liquid metal microparticle electronic ink, comprising the following steps:

[0016] S1. Dicarboxylic acid anhydride and diamine are added to an aprotic polar solvent respectively, and the reaction is stirred to prepare a polyamic acid solution;

[0017] S2. Add an organic ammonium salt to a polyamic acid solution and stir to prepare a polyamic acid salt solution.

[0018] S3. Add liquid metal to a polyamic acid solution or a polyamic acid salt solution, and after stirring, mixing and centrifugation, obtain the polyimide liquid metal microparticle electronic ink.

[0019] In one embodiment of the present invention, the total mass of the diacid anhydride and the diamine accounts for 15% to 30% of the total mass of the mixture of the diacid anhydride, the diamine, and the aprotic polar solvent. More preferably, it is 15% to 20%.

[0020] In one embodiment of the present invention, after stirring the reaction, an aprotic polar solvent is added to dilute the polyamic acid solution to a solid content of 1wt% to 10wt%.

[0021] In one embodiment of the present invention, the polyamic acid is obtained by polycondensation at 0-20°C and synthesized under prolonged mechanical stirring; the stirring time is preferably 3-10 hours, more preferably 5-8 hours. In the present invention, to avoid hydrolysis of polyamic acid in the environment, the synthesis environment is preferably a closed, low-humidity environment.

[0022] In one embodiment of the present invention, step S1 specifically involves: first adding the diamine to the aprotic polar solvent to completely dissolve it, then adding the diacid anhydride and polycondensing it at low temperature, and synthesizing a polyamic acid polymer with a high molecular weight under gradual dilution and mechanical stirring conditions.

[0023] In one embodiment of the present invention, the amount of organic ammonium salt added is 100% to 300% of the molar equivalent of diacid anhydride or diamine, more preferably 100%.

[0024] In one embodiment of the present invention, the reaction time of step S2 is preferably 2 to 10 hours, and more preferably 4 to 8 hours.

[0025] In one embodiment of the present invention, step S2 specifically involves adding the organic ammonium salt to the polyamic acid solution prepared in step (1) at a molar equivalent of 100% to 300% of diacid anhydride or diamine, and mechanically stirring at low temperature for 4 to 8 hours to obtain the polyamic acid salt solution.

[0026] In one embodiment of the present invention, the mass ratio of the liquid metal to polyamic acid or polyamic acid salt is preferably 2 to 10:10; more preferably 2 to 5:10.

[0027] In one embodiment of the present invention, a mixture of liquid metal and polyamic acid or polyamate is placed in a container, and liquid metal microparticle electronic ink is prepared under planetary rotation and revolution stirring conditions. The mixing speed is preferably 400-2000 rpm; more preferably 1500-2000 rpm; the mixing time is preferably 20-40 min; more preferably 30-40 min. The degassing speed is preferably 1000-3000 rpm; more preferably 2000-3000 rpm; the degassing time is preferably 5-20 min; more preferably 10-20 min.

[0028] In one embodiment of the present invention, step S3 specifically involves: placing the liquid metal and polyamic acid salt in a container at a mass ratio of 2 to 5:10, mixing them on a planetary mixer at a speed of 1500 to 2000 rpm for 30 to 40 minutes; degassing at a speed of 1000 to 3000 rpm for 10 to 20 minutes; and forming uniform ink particles under the above conditions.

[0029] A third objective of this invention is to provide an application of the polyimide liquid metal microparticle electronic ink in printed flexible electronic circuits.

[0030] The fourth objective of this invention is to provide a method for fabricating flexible electronic circuits using polyimide liquid metal microparticle electronic ink. The method involves printing the liquid metal microparticle electronic ink onto a substrate material and then thermally imidizing it at 100–300°C under nitrogen protection to obtain the flexible electronic circuit.

[0031] In one embodiment of the present invention, the substrate material is polydimethylsiloxane, polyethylene terephthalate, polyimide, white paper, or polyimide aerogel.

[0032] In this invention, the substrate material is preferably polyimide aerogel. Using polyimide aerogel as the substrate allows for stronger intermolecular forces between the ink and the substrate, improving the interfacial bonding ability of the ink on the substrate. This enables it to function better in the field of flexible electronics.

[0033] In one embodiment of the present invention, the printing method is stencil printing, screen printing, or 3D printing.

[0034] In this invention, to reduce costs and facilitate patterning, screen printing or stencil printing is preferred.

[0035] In this invention, liquid metal ink is printed on a substrate to form conductive pathways. By placing the liquid metal ink-printed circuit at a high temperature of 100–300°C, polyamic acid / polyamic acid salt is thermally imidized to form a polyimide film on the surface of the liquid metal, and the film is broken to activate the circuit. The activation is due to the difference in thermal expansion coefficients between the liquid metal and the polymer it covers, as well as gravity and other factors. The liquid metal ink forms conductive pathways inside and a polyimide film on the outside, thereby achieving conductivity of the printed pattern. This pattern can conduct electricity without the need for long activation methods such as pressing or scratching. The printed circuit has excellent tensile and bending properties, making it suitable for the fabrication of flexible circuits.

[0036] The beneficial effects of this invention are:

[0037] The technical solution of this invention prints liquid metal ink into circuits and forms conductive paths through high-temperature sintering, eliminating the need for time-consuming activation methods such as pressing or scraping. This reduces damage to the circuit pattern, significantly saves preparation time, and allows for the printing of complex patterns, thus reducing costs. Furthermore, the circuits prepared by this method exhibit minimal resistance change and good stability during stretching and bending deformation, making them suitable for the fabrication of flexible circuits. They can be used as conductive inks in the printing of electronic products such as flexible wearable electronic devices, flexible sensors, and brain-computer interfaces. Various printing methods can be used to create different types of patterns to form conductive paths. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the preparation process of the polyimide / liquid metal microparticle electronic ink of the present invention;

[0040] Figure 2 These are physical images and SEM characterization images of the polyimide / liquid metal microparticle electronic ink of the present invention;

[0041] Figure 3 This is a particle size distribution diagram of the polyimide / liquid metal microparticle electronic ink of the present invention;

[0042] Figure 4 These are transmission electron microscope (TEM) images and energy dispersive spectroscopy (EDS) results of the polyimide / liquid metal microparticle electronic ink of the present invention.

[0043] Figure 5The present invention relates to circuits printed on different substrates using polyimide / liquid metal microparticle electronic ink;

[0044] Figure 6 This is a schematic diagram of the polyimide / liquid metal microparticle electronic ink of the present invention printed on polyimide aerogel, connected to an LED lamp and emitting light;

[0045] Figure 7 It is a test curve of the resistance change under cyclic stretching conditions of conductive paths formed by printing polyimide / liquid metal microparticle electronic ink on stretchable elastomer.

[0046] Figure 8 It is a curve showing the change in resistance under different deformation conditions after polyimide / liquid metal microparticle electronic ink is printed on polyimide aerogel to form a conductive path;

[0047] Figure 9 The study investigated the effect of different thermal sintering temperatures on the sintering effect by printing polyimide / liquid metal microparticle electronic ink onto a glass slide. Detailed Implementation

[0048] The present invention will be further illustrated below with specific examples. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0049] Test method:

[0050] 1. Liquid metal microparticle ink diluted with anhydrous ethanol was prepared. The morphology of the ink particles was observed using a Hitachi SU8600 field emission scanning electron microscope (SEM) and the elemental composition of the ink particles was detected using a Thermo Fisher Scientific Talos F200X G2 field emission transmission electron microscope (TEM).

[0051] 2. Using a METS microcomputer-controlled electronic universal testing machine, 60% tensile cycle and 60% bending cycle tests were conducted on the stretchable elastomer and polyimide aerogel of printed liquid metal microparticle ink according to GB / T 35465. Resistance data were collected using a Tektronix DMM6500 benchtop digital multimeter data acquisition instrument.

[0052] 3. Prepare polyimide aerogel printed with liquid metal microparticle ink, and calculate its conductivity using a ST2263 dual-electrical-measurement digital four-probe tester from Suzhou Jinglü Electronics Co., Ltd.

[0053] 4. Prepare glass slides printed with liquid metal microparticle ink, and measure the resistance value by changing the hot sintering temperature and using a multimeter.

[0054] Source of raw materials

[0055] Gallium-indium alloy: purchased from Shenyang Jiabei Trading Co., Ltd. (mass ratio of each element: Ga / In = 75:25);

[0056] Dicarboxylic acid anhydrides and diamines were purchased from Tianjin Zhongtai Materials Technology Co., Ltd.; triethylamine and trioctylamine were purchased from Shanghai Titan Technology Co., Ltd.

[0057] Table 1. Structural formulas of diacid anhydrides and diamines

[0058]

[0059]

[0060]

[0061] The technical solution of the present invention will be described in detail below with reference to specific embodiments. In the following embodiments, unless otherwise specified, the reagents, materials and equipment used can be purchased commercially, prepared by conventional methods, or commonly used in the industry.

[0062] Example 1:

[0063] like Figure 1 As shown, a method for preparing polyamic acid salt liquid metal microparticle electronic ink includes the following specific steps:

[0064] 1) Dissolve 10 mmol of 4,4'-diaminodiphenyl ether in 19.776 g of N,N-dimethylacetamide. After mechanical stirring until dissolved, transfer the apparatus to an ice-water bath and add 10 mmol of 3,3',4,4'-biphenyltetracarboxylic dianhydride. Initially, the total mass of 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic dianhydride accounts for 20% of the total mass of the mixture. After dissolution, gradually add N,N-dimethylacetamide to dilute the solution to a solid content of 4 wt% (i.e., the total mass of 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic dianhydride accounts for 4% of the total mass of the mixture). Stir for 8 hours to obtain a polyamic acid solution.

[0065] 2) Slowly add 10 mmol of triethylamine to the polyamic acid solution prepared in step 1) and mechanically stir for 6 h in an ice-water bath to obtain a polyamic acid salt solution.

[0066] 3) Take 4g of the polyamic acid obtained in step 2) into a container, add 1g of gallium indium alloy, mix at 2000rpm for 30min in a planetary mixer, defoam at 2000rpm for 20min, pour off the supernatant to obtain liquid metal microparticle ink.

[0067] Take the ink prepared in step 3) and dilute it 50 times with anhydrous ethanol, then wait for the solvent to evaporate to dryness. Observe it under an electron microscope. Figure 2 , 3 The liquid metal microparticle ink shown has a uniform particle size, with an average diameter of 2 micrometers. For example... Figure 4 As shown, polyamic acid salts are coated on the surface of liquid metal particles.

[0068] The ink prepared in step 3) is used to screen print different patterns onto different substrates. The substrate material can be, but is not limited to, polyimide aerogel or white paper. The conductive patterns of the ink on different substrate materials are as follows: Figure 5 As shown.

[0069] The liquid metal microparticle ink prepared in step 3) is printed onto polyimide and white paper, and heated in a tube furnace at 140°C for 2 hours to form a conductive path, such as... Figure 6 As shown, when the LED light is placed on the line and connected to the circuit, the LED light will light up.

[0070] The liquid metal microparticle ink prepared in step 3) was printed onto a stretchable elastomer and dried in a vacuum oven at 140°C for 2 hours. The sample was then subjected to 1000 cycles of tensile testing with a deformation of 60% using a METS microcomputer-controlled electronic universal testing machine. The resistance change was measured and plotted. The results are as follows: Figure 7 As shown in the figure, the ink exhibits excellent stability.

[0071] The liquid metal microparticle ink prepared in step 3) was printed onto polyimide aerogel and dried under vacuum at 140°C for 2 hours. The sample was then subjected to inward and outward bending tests with deformation ranging from 0% to 60% using a METS microcomputer-controlled electronic universal testing machine. The resistance changes were measured and plotted. The results are as follows: Figure 8 As shown, the change in resistance during deformation is almost negligible.

[0072] Example 2:

[0073] A method for preparing polyamic acid / liquid metal microparticle electronic ink, the specific operation steps are as follows:

[0074] 1) Dissolve 10 mmol of 4,4'-diaminodiphenyl ether in 19.776 g of N,N-dimethylacetamide. Stir mechanically until dissolved. Transfer the apparatus to an ice-water bath and add 10 mmol of 3,3',4,4'-biphenyltetracarboxylic dianhydride. After dissolution, gradually add N,N-dimethylacetamide to dilute the solution to a solid content of 4 wt%. Stir for 8 hours to obtain a polyamic acid solution.

[0075] 2) Take 4g of the polyamic acid obtained in step 1) into a container, add 1g of gallium indium alloy, mix at 2000rpm for 30min in a planetary mixer, defoam at 2000rpm for 20min, pour off the supernatant to obtain liquid metal microparticle ink.

[0076] Compared to liquid metal microparticle inks prepared from polyamates, which are prone to deliquescence when exposed to air, making ink patterning difficult during printing and hindering secondary printing on molds, liquid metal microparticle inks prepared from polyamates exhibit better transmittance during screen printing, resulting in more complete and clearer printed patterns.

[0077] Example 3:

[0078] The amount of polyamic acid salt in step 3) of Example 1 was adjusted to the amount shown in Table 2, while other aspects remained the same as in Example 1, resulting in liquid metal microparticle ink. The liquid metal microparticle ink was then printed onto polyimide aerogel for performance testing. The test results are shown below:

[0079] Table 2

[0080] 1 <![CDATA[8.021×10 4 ]]> 2 <![CDATA[6.402×10 4 ]]> 3 <![CDATA[5.184×10 4 ]]> 4 <![CDATA[8.197×10 5 ]]> 5 <![CDATA[3.812×10 5 ]]>

[0081] Example 4:

[0082] The mixing time in step 3) of Example 1 was adjusted to obtain different liquid metal microparticle inks with liquid metal solid content as shown in Table 3, while other parameters remained consistent with Example 1, resulting in liquid metal microparticle inks. The liquid metal microparticle inks were then printed on polyimide aerogel for performance testing, and the test results are shown below:

[0083] Table 3

[0084]

[0085] Example 5:

[0086] Adjust the amount of gallium-indium alloy in step 3) of Example 1 to the amount in Table 4, while keeping other aspects the same as in Example 1, to obtain liquid metal microparticle ink.

[0087] Furthermore, the liquid metal microparticle ink was printed onto polyimide aerogel for performance testing. The test results are shown below:

[0088] Table 4

[0089] 0.5 <![CDATA[6.711×10 5 ]]> 1 <![CDATA[8.197×10 5 ]]> 1.5 <![CDATA[4.105×10 5 ]]> 2 <![CDATA[3.352×10 5 ]]> 2.5 <![CDATA[1.773×10 5 ]]>

[0090] Example 6:

[0091] The liquid metal microparticle ink prepared in Example 1 was printed onto a glass slide and sintered in a vacuum oven for 2 hours. The sintering temperatures were set to 60℃, 80℃, 100℃, 120℃, 140℃, and 180℃. Performance tests were performed after sintering, and the test results are as follows: Figure 9 As shown, sintering cannot be performed below 120°C. When the sintering temperature exceeds 120°C, the circuit begins to sinter gradually and eventually forms a conductive path.

[0092] Example 7:

[0093] 1) Dissolve 10 mmol of 4,4'-diaminodiphenyl ether in 19.776 g of N,N-dimethylacetamide. Stir mechanically until dissolved. Transfer the apparatus to an ice-water bath and add 10 mmol of 3,3',4,4'-biphenyltetracarboxylic dianhydride. After dissolution, gradually add N,N-dimethylacetamide to dilute the solution to a solid content of 4 wt%. Stir for 8 hours to obtain a polyamic acid solution.

[0094] 2) Slowly add 10 mmol of trioctylamine to the polyamic acid solution prepared in step 1) and mechanically stir for 6 h in an ice-water bath to obtain a polyamic acid salt solution.

[0095] 3) Take 4g of the polyamic acid obtained in step 2) into a container, add 1g of gallium indium alloy, mix at 2000rpm for 30min in a planetary mixer, defoam at 2000rpm for 20min, pour off the supernatant to obtain liquid metal microparticle ink.

[0096] When preparing polyamates using trioctylamine and polyamic acid, it was found that polyamates prepared with the addition of triethylamine at the same solid content of 4 wt% exhibited higher viscosity. This is largely due to the molecular structure of the quaternary ammonium salt; trioctylamine has a longer alkyl chain than triethylamine. Further performance testing was conducted by printing liquid metal microparticle ink onto polyimide aerogel, yielding a conductivity of 7.435 × 10⁻⁶. 4 S / m. Therefore, liquid metal microparticle inks prepared using different quaternary ammonium salts still exhibit good conductivity.

[0097] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing a polyimide liquid metal microparticle electronic ink, characterized by, Includes the following steps: S1. Dicarboxylic acid anhydride and diamine are added to an aprotic polar solvent respectively, and the reaction is stirred to prepare a polyamic acid solution; S2. Add an organic ammonium salt to a polyamic acid solution and stir to prepare a polyamic acid salt solution. S3. Add liquid metal to a polyamic acid solution or a polyamic acid salt solution, and after stirring, mixing and centrifugation, obtain the polyimide liquid metal microparticle electronic ink; The mass ratio of the liquid metal to polyamic acid or polyamic acid salt is 2~10:10; The stirring speed is 1500~2000 rpm; the mixing time is 20~40 min; Polyimide liquid metal microparticle electronic ink is printed on a substrate to form a printed circuit. The printed circuit is placed at a high temperature of 100~300 ℃. Polyamic acid / polyamate is thermally imidized to form a polyimide film on the liquid metal surface and the film is broken to activate the circuit. The liquid metal ink forms a conductive path inside. In step S2, the organic ammonium salt is one or more of triethylamine, tributylamine, trihexylamine, trioctylamine, N,N-dimethyl-n-octylamine, and triethanolamine.

2. The preparation method according to claim 1, characterized in that, The total mass of the diacid anhydride and diamine accounts for 15% to 30% of the total mass of the diacid anhydride, diamine, and aprotic polar solvent mixture; after stirring and reacting, the polyamic acid solution is diluted to a solid content of 1 wt% to 10 wt% by adding the aprotic polar solvent.

3. The preparation method according to claim 1 or 2, characterized in that, The dicarboxylic acid anhydride is one or more of the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-(hexafluoroisopropene)phthalic anhydride, 4,4'-biphenyl ether dianhydride, bisphenol A type diether dianhydride, hydrogenated pyromellitic dianhydride, cyclobutanetetracarboxylic dianhydride, and 1,4,5,8-naphthalenetetracarboxylic anhydride; the diamine is 4,4'-diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 9,9-bis(4-aminophenyl)fluorene, 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine, 2, The solvent is one or more of 2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-diamino-2,2'-dimethylbiphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, 2-(4-aminophenyl)-5-aminobenzimidazole, 2-(4-aminophenyl)-5-aminobenzoxazole, 4,4'-diaminobenzoylaniline, isophthalohydrazide, and dihydrazide terephthalate; the aprotic polar solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

4. The preparation method according to claim 1, characterized in that, The polyamic acid was obtained by polycondensation at 0-20℃ and synthesized under long-term mechanical stirring; the stirring time was 3-10 h.

5. A polyimide liquid metal microparticle electronic ink prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the polyimide liquid metal microparticle electronic ink of claim 5 in printed flexible electronic circuits.

7. A method for fabricating a flexible electronic circuit using the polyimide liquid metal microparticle electronic ink of claim 5, wherein the method involves printing the liquid metal microparticle electronic ink onto a substrate material and thermally imidizing it at 100-300°C under nitrogen protection to obtain the flexible electronic circuit.

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