Liquid metal ink for aerosol jet printing and functional patterning manufacturing method

Abstract

The invention relates to the technical field of high-precision manufacturing, in particular to liquid metal ink for aerosol jet printing and a functional patterning manufacturing method. The liquid metal ink comprises a first solvent, a macromolecular cosolvent, liquid metal and a second solvent, the boiling point of the first solvent is not more than 100 DEG C, the surface tension at 25 DEG C is not more than 75 mN / m, and the viscosity at 25 DEG C is not more than 1.5 mPa.s; the boiling point of the second solvent is 190-250 DEG C, the surface tension at 25 DEG C is less than or equal to 50 mN / m, and the viscosity at 25 DEG C is less than or equal to 40 mPa.s; the macromolecular cosolvent comprises one or more of polyvinylpyrrolidone, polyvinyl alcohol and polymethyl cellulose; and the concentration of the polymer cosolvent is 9.9 mg / ml to 30 mg / ml. The liquid metal printing ink is good in dispersing performance, low in viscosity and surface tension, suitable in volatility, easy to activate and suitable for the aerosol jet printing process of liquid metal.

Description

Technical Field

[0001] The present invention relates to the field of high-precision manufacturing technology, and particularly to a liquid metal ink for aerosol printing and a method for manufacturing functional patterning. Background Art

[0002] Liquid metals, especially room-temperature liquid metals, mainly based on gallium, have broad application prospects in the fields of flexible electronics and stretchable electronics because of their advantages such as room-temperature liquidity, good biocompatibility, and high electrical conductivity. Liquid metals and liquid-metal-based functional materials have been widely explored for constructing flexible sensors, wearable treatment devices, human-machine interfaces, soft actuators, communication, computing, and power supply devices, and are applied to flexible intelligent healthcare and biomedical systems. Different from traditional metal materials (such as gold, silver, copper) and carbon-based materials (such as carbon nanotubes, graphene, conductive carbon black), liquid metals have unique fluidity, which enables them to match well with the elastic interface modulus during deformation and thus retain electrical conductivity, giving them unique advantages in the field of stretchable circuits.

[0003] However, due to the large surface tension of liquid metals (such as EGaIn 25 being 624 mN / m, about 8.7 times that of water) and the unique rheology of shear thinning, it is difficult to achieve high-precision patterning on various substrates, especially flexible polymer substrates for flexible electronics. In recent years, researchers have proposed a series of liquid metal patterning methods, such as injection method, mask printing method, surface modification method, direct writing method, etc. The injection method is based on photolithography technology to prepare microchannels, and can achieve LM patterning with an accuracy of 5 μm, but the microchannel manufacturing process is complex and it is difficult to manufacture complex branched structures. The mask printing method wastes a large amount of materials. The surface modification method has a complex process and limited accuracy. The direct writing method is a simple and effective method, but currently most can only achieve an accuracy of >100 μm.

[0004] Therefore, there is an urgent need to develop a liquid metal patterning technology that can achieve higher precision with a simpler process on more surfaces. Summary of the Invention

[0005] The present invention provides a liquid metal ink for aerosol printing and a method for manufacturing functional patterning to solve the problems such as complex process and limited accuracy existing in the existing functional patterning manufacturing methods.

[0006] According to the first aspect of the present invention, the present invention provides a liquid metal ink for aerosol printing, including a first solvent, a polymer co-solvent, a liquid metal, and a second solvent; The boiling point of the first solvent is ≤100°C, the surface tension at 25°C is ≤75 mN / m, and the viscosity at 25°C is ≤1.5 mPa·s; the boiling point of the second solvent is 190 - 250°C, the surface tension at 25°C is ≤50 mN / m, and the viscosity at 25°C is ≤40 mPa·s; The polymer co-solvent includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, and methylcellulose; based on the amount of the first solvent used, the concentration of the polymer co-solvent is 9.9 mg / ml - 30 mg / ml.

[0007] Furthermore, the liquid metal is a room-temperature liquid metal with a melting point below 25°C; it should be noted that "room temperature" in room-temperature liquid metal generally refers to the temperature range of 20°C to 30°C, specifically depending on the melting point of the metal or alloy. Preferably, the liquid metal is selected from one or more of gallium, indium, tin, or alloys composed of these metals; more preferably, the liquid metal is selected from gallium-indium alloy or gallium-indium-tin alloy.

[0008] Furthermore, the mass concentration of the liquid metal in the liquid metal ink is 0.08 - 0.75 g / ml.

[0009] Furthermore, in the liquid metal ink, the amount of the first solvent used is greater than the amount of the second solvent used.

[0010] Preferably, the volume of the second solvent accounts for 5% - 20% of the total volume of the liquid metal ink.

[0011] Furthermore, the first solvent is selected from water or ethanol, preferably ethanol.

[0012] Furthermore, the second solvent is selected from one or more of diethylene glycol, ethylene glycol, and terpineol, preferably diethylene glycol.

[0013] According to the second aspect of the present invention, the present invention also provides a method for preparing the above liquid metal ink, including the following steps: Add a polymer co-solvent to the first solvent to prepare a mixed solvent; Add liquid metal to the mixed solvent and obtain a nano-micro liquid metal droplet dispersion by ultrasonic fragmentation; Add the second solvent to the nano-micro liquid metal droplet dispersion and mix.

[0014] Furthermore, the power of the ultrasonic fragmentation is 400 - 600 W, the frequency is 10 - 30 kHz, the time is 0.5 - 2 h, and the temperature is 15 - 25°C.

[0015] According to the third aspect of the present invention, the present invention further provides a method for manufacturing a functional pattern, which is to print the above-mentioned liquid metal ink on a substrate by aerosol jet printing to form a liquid metal pattern.

[0016] Further, the aerosol jet printing adopts ultrasonic atomization printing; preferably, the printing conditions of the aerosol jet printing include: the carrier gas flow rate is 10 - 20 sccm, the sheath gas flow rate is 50 - 100 sccm, the printing speed is 2 - 4 mm / s, the printing height is 0.5 - 2 mm, the printing temperature is 50 - 70 °C, and the number of printing times is ≥1 time.

[0017] Further, the accuracy of the aerosol jet printing is 10 - 100 μm.

[0018] Further, the substrate is a flexible substrate or a rigid substrate, preferably a flexible substrate, and more preferably a flexible stretchable substrate.

[0019] According to the fourth aspect of the present invention, the present invention further provides a liquid metal conductive circuit, including liquid metal conductive lines, which are formed by activating the conductivity of the liquid metal pattern after forming the liquid metal pattern on the substrate by using the above-mentioned method for manufacturing a functional pattern.

[0020] Advantages of the present invention: The liquid metal ink for aerosol jet printing provided by the present invention has good dispersion performance, low viscosity, low surface tension, suitable volatilization performance, and is easy to activate, and can be applied to the aerosol jet printing process of liquid metal, achieving a technical breakthrough in aerosol jet printing of liquid metal for the first time.

[0021] By using the aerosol jet printing functional pattern manufacturing method of the present invention, high-precision (10 - 100 μm) printing of liquid metal patterns can be simply achieved on various substrates.

[0022] When the liquid metal ink of the present invention is aerosol jet printed on a flexible substrate and then the conductivity of the pattern is simply mechanically activated, a flexible liquid metal conductive circuit with excellent performance can be prepared, and the flexible liquid metal conductive circuit still retains its conductivity when bent, twisted, and stretched (when using a flexible stretchable substrate). Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 It is a schematic diagram showing the relationship between the general aerosol jet printing process steps and requirements provided by the present invention and the expectations for the ink.

[0025] Figure 2 It is a schematic flow diagram of a method for preparing a liquid metal ink for aerosol jet printing provided by the present invention.

[0026] Figure 3 It is a schematic diagram of an electron microscope image, particle size distribution diagram and stability of the liquid metal ink of Example 1 provided by the present invention (when magnified to 2 microns), where Figure 3 (a) is the electron microscope image of the liquid metal ink of Example 1, Figure 3 (b) is the particle size distribution diagram of the liquid metal ink of Example 1, Figure 3 (c) is the schematic diagram of the stability of the liquid metal ink of Example 1.

[0027] Figure 4 It is a schematic diagram of an electron microscope image, particle size distribution diagram and stability of the liquid metal ink of Comparative Example 1 provided by the present invention (when magnified to 2 microns), where Figure 4 (a) is the electron microscope image of the liquid metal ink of Comparative Example 1, Figure 4 (b) is the particle size distribution diagram of the liquid metal ink of Comparative Example 1, Figure 4 (c) is the schematic diagram of the stability of the liquid metal ink of Comparative Example 1.

[0028] Figure 5 It is a schematic diagram of the rheological properties of the liquid metal inks of Examples 1-4 and Comparative Examples 1-3 provided by the present invention, where Figure 5 (a) is the rheological diagram of the liquid metal inks of Examples 1-4 and Comparative Examples 1-3, Figure 5 (b) is the linear fitting diagram of the concentration of polyvinylpyrrolidone and viscosity in the liquid metal ink.

[0029] Figure 6 It is a schematic diagram of the aerosol jet printing line quality of the liquid metal inks of Example 1, Example 5, Example 6 and Comparative Example 4 provided by the present invention under different second solvent volume ratios (when magnified to 100 microns), where Figure 6 (a) is the schematic diagram of the aerosol jet printing line quality of the liquid metal ink of Comparative Example 4, Figure 6 (b) is the schematic diagram of the aerosol jet printing line quality of the liquid metal ink of Example 5, Figure 6 (c) is the schematic diagram of the aerosol jet printing line quality of the liquid metal ink of Example 1, Figure 6 (d) is the schematic diagram of the aerosol jet printing line quality of the liquid metal ink of Example 6.

[0030] Figure 7Schematic diagrams of the wettability of the liquid metal inks of Example 4, Comparative Example 1, and Comparative Example 3 provided by the present invention on various substrates and the aerosol printing of liquid metal patterns. Among them, Figure 7 (a) is a schematic diagram of the wettability on various substrates, Figure 7 (b) is one of the schematic diagrams of aerosol printing liquid metal patterns on various substrates, Figure 7 (c) is another schematic diagram of aerosol printing liquid metal patterns on various substrates.

[0031] Figure 8 Schematic diagram of the liquid metal line with a precision of up to 10 microns printed by aerosol printing using the liquid metal ink of Example 4 provided by the present invention (when magnified to 100 microns).

[0032] Figure 9 Schematic diagram of the liquid metal after mechanical activation of conductivity shown by the electron microscope of the present invention (when magnified to 2 microns).

[0033] Figure 10 Schematic diagrams of the conductivity of the flexible liquid metal circuit prepared using the liquid metal ink of Example 2 of the present invention under bending, torsion, and different tensile strains. Among them, 10(a) is the schematic diagram of the conductivity of the flexible liquid metal circuit under bending, 10(b) is the schematic diagram of the conductivity of the flexible liquid metal circuit under torsion, and 10(c) is the schematic diagram of the conductivity of the flexible liquid metal circuit under different tensile strains. Detailed implementation manners

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0035] In the first typical mode of the present invention, the present invention provides a liquid metal ink for aerosol printing, including a first solvent, a polymer co-solvent, a liquid metal, and a second solvent; The boiling point of the first solvent ≤ 100°C, the surface tension at 25°C ≤ 75 mN / m, and the viscosity at 25°C ≤ 1.5 mPa·s; the boiling point of the second solvent is 190 - 250°C, the surface tension at 25°C ≤ 50 mN / m, and the viscosity at 25°C ≤ 40 mPa·s; The polymer co-solvent includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, and methylcellulose; based on the amount of the first solvent, the concentration of the polymer co-solvent is 9.9 mg / ml - 30 mg / ml.

[0036] The liquid metal ink of the present invention includes a first solvent, a polymer co-solvent, liquid metal, and a second solvent. The selected first solvent has the characteristics of low surface tension, low boiling point, and low viscosity, and the second solvent has the characteristics of low surface tension, high boiling point, and low viscosity. The low surface tension characteristics of the first solvent and the second solvent can significantly reduce the surface tension of the liquid metal, making it easier to spread and wet on the substrate. The low viscosity of the first solvent, the moderate viscosity of the second solvent, combined with the addition of the polymer co-solvent, can effectively adjust the overall viscosity and rheological properties of the ink. This not only helps the fluidity of the liquid metal during the inkjet printing process but also ensures its smooth ejection from the print head and avoids clogging. Through the rapid evaporation of the first solvent (boiling point ≤ 100°C) and the slower evaporation of the second solvent (boiling point 190 - 250°C), the liquid metal ink can quickly form a stable pattern during the printing process. This evaporation characteristic helps to quickly solidify the ink after printing while avoiding pattern deformation caused by solvent residue. Specific types and amounts of the polymer co-solvent can form a stable coating layer with the liquid metal particles, improving the adhesion of the liquid metal to the substrate. This coating layer can prevent the oxidation of the liquid metal and at the same time enhance its adhesion on flexible or rigid substrates. The addition of the polymer co-solvent not only improves the physical properties of the liquid metal but also maintains the conductivity of the liquid metal through chemical action. For example, certain co-solvents can prevent the oxidation of its surface through interaction with the liquid metal, thus ensuring the stability of the conductive performance. Further, by limiting the concentration range of the polymer co-solvent within a reasonable range value, a stable dispersion system can be formed in the liquid metal ink. This stability not only helps to maintain the performance of the ink during storage and transportation but also ensures the consistency during the printing process.

[0037] Through the synergistic effect of the first solvent, the polymer co-solvent, and the second solvent, the liquid metal ink of the present invention can have good dispersion performance, low viscosity, low surface tension, appropriate evaporation performance, and easy activation characteristics, and thus can be suitable for printing by aerosol inkjet printing technology. Specifically, Figure 1It shows the general aerosol jet printing process steps, requirements, and expectations for the ink. The liquid metal ink of the present invention has good dispersion properties and appropriate low viscosity, and can meet the requirement of stably generating aerosol in the aerosol jet printing process; the liquid metal ink of the present invention has appropriate volatility properties, and can meet the requirement of avoiding overspray phenomenon caused by excessive evaporation of the ink solvent during aerosol focusing and transportation in the aerosol jet printing process; the liquid metal ink of the present invention has appropriate low surface tension and volatility properties, and can meet the requirements of good wettability and effective deposition of aerosol on the substrate in the aerosol jet printing process; the three-step process of aerosol jet printing described above is for the convenience of explanation. When actually carrying out aerosol jet printing, it is only one-step operation, which has simplicity.

[0038] According to some specific embodiments of the present invention, the liquid metal is a room temperature liquid metal with a melting point lower than 25°C; further, the liquid metal does not contain toxic components such as mercury.

[0039] Preferably, the liquid metal is selected from one or more of gallium, indium, tin, or alloys composed of these metals; more preferably, the liquid metal is selected from gallium-indium alloy or gallium-indium-tin alloy, such as gallium-indium alloy GaIn 25 and gallium-indium-tin alloy GaIn 21.5 Sn 10 etc. Further, the preferred liquid metal is gallium-indium alloy GaIn 25 .

[0040] According to some specific embodiments of the present invention, the mass concentration of the liquid metal in the liquid metal ink is 0.08 - 0.75 g / ml. The easy activation and good conductivity of the liquid metal ink pattern are achieved by having a high liquid metal concentration and an appropriate proportion of co-solvent. Limiting the mass concentration of the liquid metal in the liquid metal ink within a reasonable range can comprehensively optimize the conductivity, rheological properties, printing accuracy, cost-effectiveness, and stability of the liquid metal ink, making it more suitable for fields such as flexible electronics and printed circuits.

[0041] According to some specific embodiments of the present invention, in the liquid metal ink, the amount of the first solvent is greater than the amount of the second solvent. The first solvent usually has lower viscosity and higher volatility. When the amount is larger, it can significantly reduce the overall viscosity of the ink, making it more suitable for the jet printing process. This helps to improve the fluidity of the ink in the nozzle, avoid nozzle clogging, and ensure the stability and accuracy of the printing process.

[0042] To balance suitable volatility and viscosity and meet the requirements of aerosol jet printing, the proportion of the second solvent can be adjusted according to the type of the first solvent, ambient temperature and humidity, and substrate temperature. Preferably, the volume of the second solvent accounts for 5%-20% of the total volume of the liquid metal ink, preferably 8%-15%, and more preferably 8%-12%.

[0043] According to some specific embodiments of the present invention, the first solvent is selected from water or ethanol, preferably ethanol.

[0044] According to some specific embodiments of the present invention, the second solvent is selected from one or more of diethylene glycol, ethylene glycol, and terpineol, preferably diethylene glycol.

[0045] In the second typical mode of the present invention, the present invention also provides a method for preparing the above-mentioned liquid metal ink, and its process flow chart is as Figure 2 shown, including the following steps: Add a polymer co-solvent to the first solvent to prepare a mixed solvent.

[0046] Add liquid metal to the mixed solvent and obtain a nano-micron liquid metal droplet dispersion by ultrasonic fragmentation.

[0047] Add the second solvent to the nano-micron liquid metal droplet dispersion and mix.

[0048] The method for preparing the liquid metal ink of the present invention uses the ultrasonic fragmentation method to break the liquid metal into small droplets. The liquid metal small droplets will quickly form an oxide film on the surface of the solution and form stable small droplets under the encapsulation of the polymer co-solvent. Through the synergistic effect of ultrasonic fragmentation and the polymer co-solvent, the nano-dispersion of the liquid metal is realized, significantly improving the stability, conductivity and printing performance of the ink. Then, by adding a second solvent with high boiling point and low surface tension, the volatilization performance of the liquid metal ink is adjusted, so that the prepared liquid metal ink better meets the requirements of the aerosol jet printing process. The preparation method of the present invention is simple and has broad application prospects.

[0049] According to some specific embodiments of the present invention, the power of the ultrasonic fragmentation is 400-600 W, the frequency is 10-30 kHz, the time is 0.5-2 h, and the temperature is 15-25 °C. Limiting the power, frequency, time and temperature of the ultrasonic fragmentation can significantly improve the dispersion uniformity of the liquid metal ink, ensure that the average particle size of the liquid metal is less than 400 nm, and optimize the conductivity and stability of the liquid metal ink.

[0050] In the third typical mode of the present invention, the present invention also provides a method for fabricating a functional pattern, which is to print the above-mentioned liquid metal ink on a substrate by aerosol jet printing to form a liquid metal pattern.

[0051] According to some specific embodiments of the present invention, the aerosol jet printing uses ultrasonic atomization printing. Ultrasonic atomization printing technology has many advantages in aerosol jet printing, such as high precision, wide material compatibility, non-contact printing, efficient deposition, low material waste, and adaptability to complex substrates.

[0052] Preferably, the printing conditions for the aerosol jet printing include: carrier gas flow rate of 10 - 20 sccm, sheath gas flow rate of 50 - 100 sccm, printing speed of 2 - 4 mm / s, printing height of 0.5 - 2 mm, printing temperature of 50 - 70 °C, and number of printing passes ≥ 1. By specifically defining the printing conditions for the aerosol jet printing, the printing precision, stability, and material deposition quality can be significantly improved, while reducing material waste and cost, and broadening its applications in fields such as high-performance electronic devices, flexible electronics, and biomedicine.

[0053] According to some specific embodiments of the present invention, the precision of the aerosol jet printing is 10 - 100 μm.

[0054] The liquid metal ink of the present invention has a low surface tension and can wet a variety of substrates. According to some specific embodiments of the present invention, the substrate is a flexible substrate or a rigid substrate. The rigid substrate can be glass, silicon wafer, etc., and the flexible substrate can be a flexible non-stretchable substrate (paper, polyimide PI, plant leaf, etc.), or a flexible stretchable substrate (nitrile rubber, polydimethylsiloxane PDMS, polyacrylate 3M VHB tape, etc.). The substrate is preferably a flexible substrate, and more preferably a flexible stretchable substrate.

[0055] Before the printing in the method for fabricating a functional pattern of the present invention, it further includes: designing a CAD drawing of the liquid metal pattern; writing G-code according to the drawing and importing it into the printing program.

[0056] In the fourth typical mode of the present invention, the present invention also provides a liquid metal conductive circuit, including liquid metal conductive lines, which are formed by activating the conductive performance of the liquid metal pattern after forming the liquid metal pattern on a substrate by using the above-mentioned method for fabricating a functional pattern.

[0057] The activated liquid metal has good conductive performance, and the prepared liquid metal conductive circuit has excellent conductive performance. In particular, the liquid metal flexible circuit can maintain good conductive performance when bent, twisted, and stretched (when the substrate is a flexible stretchable substrate).

[0058] Specifically, the process for activating the conductive performance of the liquid metal pattern includes: (1) drying the printed liquid metal pattern on a heating table at 100 °C for 1 h; (2) using, but not limited to, rolling a steel roller on the surface of the liquid metal printed sample covered with a polyethylene film to mechanically activate the conductivity of the liquid metal.

[0059] Furthermore, the flexible and stretchable substrate is preferably a polyacrylate 3M VHB tape. When the tensile strain is <620%, the liquid metal conductive circuit with a line width of 1 mm still retains its conductive performance.

[0060] Example 1 This example provides a liquid metal ink for aerosol printing. The liquid metal ink includes a first solvent, absolute ethanol, a polymer co-solvent, polyvinylpyrrolidone (average molecular weight 58000, K30), a liquid metal, gallium-indium alloy GaIn 25 and a second solvent, diethylene glycol.

[0061] Among them, based on the dosage of the first solvent, the concentration of the polymer co-solvent is 10 mg / ml. In the liquid metal ink, the mass concentration of the liquid metal is 0.71 g / ml, and the volume of the second solvent accounts for 10% of the total volume of the liquid metal ink.

[0062] This example also provides a method for preparing the above liquid metal ink, which specifically includes the following steps: (1) Dissolve 100 mg of polyvinylpyrrolidone in 10 ml of absolute ethanol to prepare a mixed solvent.

[0063] (2) Add 9 g of gallium-indium alloy GaIn 25 to the above mixed solvent, and ultrasonically crush it at a power of 500 W and a frequency of 20 kHz for 2 h. During the ultrasonic process, use a cold water bath to keep the sample temperature at about 20 °C to obtain a nano-micro liquid metal droplet dispersion.

[0064] (3) Add diethylene glycol to the obtained nano-micro liquid metal droplet dispersion and mix evenly.

[0065] In Example 1, the ink is named according to the concentration of polyvinylpyrrolidone in step (1). For example, 100 mg of polyvinylpyrrolidone is dissolved in 10 ml of absolute ethanol, and the concentration of polyvinylpyrrolidone is 10 mg / ml. This ink is named LMI@10P.

[0066] Example 2 This example provides a liquid metal ink for aerosol printing, which is only different from Example 1 in that: the concentration of the polymer co-solvent is 15 mg / ml.

[0067] This comparative example also provides the above-mentioned liquid metal ink, the difference from Example 1 being only that: in step (1), 150 mg of polyvinylpyrrolidone was dissolved in 10 ml of absolute ethanol to prepare a mixed solvent. This ink is named LMI@15P.

[0068] Example 3 This example provides a liquid metal ink for aerosol jet printing, the difference from Example 1 being only that: the concentration of the polymer co-solvent is 20 mg / ml.

[0069] This comparative example also provides the above-mentioned liquid metal ink, the difference from Example 1 being only that: in step (1), 200 mg of polyvinylpyrrolidone was dissolved in 10 ml of absolute ethanol to prepare a mixed solvent. This ink is named LMI@20P.

[0070] Example 4 This example provides a liquid metal ink for aerosol jet printing, the difference from Example 1 being only that: the concentration of the polymer co-solvent is 30 mg / ml.

[0071] This example also provides the above-mentioned liquid metal ink, the difference from Example 1 being only that: in step (1), 300 mg of polyvinylpyrrolidone was dissolved in 10 ml of absolute ethanol to prepare a mixed solvent. This ink is named LMI@30P.

[0072] Example 5 This example provides a liquid metal ink for aerosol jet printing, the difference from Example 1 being only that: the volume of the second solvent accounts for 5% of the total volume of the liquid metal ink.

[0073] This example also provides the above-mentioned liquid metal ink, and its preparation method is the same as that of Example 1.

[0074] Example 6 This example provides a liquid metal ink for aerosol jet printing, the difference from Example 1 being only that: the volume of the second solvent accounts for 15% of the total volume of the liquid metal ink.

[0075] This example also provides the above-mentioned liquid metal ink, and its preparation method is the same as that of Example 1.

[0076] Comparative Example 1 This comparative example provides a liquid metal ink, the difference from Example 1 being only that: it does not contain a polymer co-solvent.

[0077] This comparative example also provides the above liquid metal ink, and the difference from Example 1 is only that: in step (1), no polymer co-solvent is added, and anhydrous ethanol is directly used to complete steps (2) and (3) of Example 1 for ink preparation, and the prepared ink is named LMI@0P.

[0078] Comparative Example 2 This comparative example provides a liquid metal ink, and the difference from Example 1 is only that: the concentration of the polymer co-solvent is 5 mg / ml.

[0079] This comparative example also provides the above liquid metal ink, and the difference from Example 1 is only that: in step (1), 50 mg of polyvinylpyrrolidone is dissolved in 10 ml of anhydrous ethanol to prepare a mixed solvent. This ink is named LMI@5P.

[0080] Comparative Example 3 This comparative example provides a liquid metal ink, which is the untreated original gallium-indium alloy GaIn 25 , without the first solvent, polymer co-solvent and second solvent.

[0081] Comparative Example 4 This comparative example provides a liquid metal ink, and the difference from Example 1 is only that: it does not contain the second solvent.

[0082] This comparative example also provides the above liquid metal ink, and the difference from Example 1 is only that: it does not include step (3).

[0083] Example 7 This example provides an activation of the conductivity of an aerosol-printed liquid metal pattern, specifically including the following steps: (1) Using the liquid metal ink in Example 1 on a glass slide, an aerosol inkjet printing device is used to print a 2×6 mm rectangular liquid metal pattern. The printing parameters and conditions are: under the conditions of a carrier gas flow rate of 15 sccm, a sheath gas flow rate of 60 sccm, a printing speed of 3 mm / s, a printing height of 1 mm, and a printing table temperature of 60 °C, print 2 times.

[0084] (2) Dry the printed liquid metal pattern on a 100 °C heating table for 1 h.

[0085] (3) Use an iron roller to roll on the surface of the liquid metal printed sample covered with a polyethylene film to mechanically activate the conductivity of the liquid metal.

[0086] Example 8 This example provides an aerosol-printed liquid metal flexible conductive route, specifically including the following steps: (1) Using the LMI@15P liquid metal ink prepared in Example 2, liquid metal lines with a width of 60 μm and a length of 30 mm were printed on a polyacrylate 3M VHB tape using an aerosol inkjet printing device. The printing parameters and conditions were as follows: carrier gas flow rate of 15 sccm, sheath gas flow rate of 100 sccm, printing speed of 3 mm / s, printing height of 1 mm, and printing table temperature of 60 °C. The printing was performed 9 times.

[0087] (2) Using the method of Example 7, the liquid metal lines were dried on a heating table at 100 °C for 1 h, and a iron roller was used to roll on the surface of the liquid metal printed sample covered with a polyethylene film to mechanically activate the conductivity of the liquid metal.

[0088] (3) Copper wires were led out at both ends of the liquid metal conductive line.

[0089] (4) The polyacrylate 3M VHB tape was used to paste on the surface of the liquid metal conductive circuit obtained in the above steps to achieve circuit encapsulation.

[0090] (5) The above liquid metal wires were connected to a digital source meter (B2912A, Keysight). Under the condition of a constant 0.1 V, a bending, twisting, and stretching test was carried out on the liquid metal circuit using an electronically controlled moving platform.

[0091] Experimental Example Detection of the physical and chemical properties of the liquid metal inks of the examples and comparative examples and analysis of the feasibility of aerosol jet printing: Each link of the aerosol and the expectations of the ink are as Figure 1 shown. Accordingly, the physical and chemical properties of the liquid metal inks were detected, and the feasibility of aerosol jet printing was analyzed. The results of the physical and chemical properties and the feasibility analysis of aerosol jet printing of the liquid metal inks of the examples and comparative examples are shown in Table 1 and Figures 3 - 10 shown below.

[0092] Table 1

[0093] 1. Ink particle size and stable dispersibility The morphologies and particle size distributions of the examples and Comparative Example 1 were observed using a scanning electron microscope (GeminiSEM 300, ZEISS). As shown in Figure 3 and Figure 4 shown, the average particle size of LMI@10P in Example 1 was 291 nm, which was significantly smaller than that of LMI@0P (433 nm) in Comparative Example 1 without adding a polymer co-solvent. In addition, from the corresponding particle size distribution, it can be seen that after adding PVP, the particle size distribution in LMI can be made more concentrated.

[0094] Further, the liquid metal ink was allowed to stand still to observe the time stability of the ink. As Figure 3 shown, the liquid metal ink of Example 1 was gray and could remain stable without stratification within 20 h of standing still (e.g., LMI@10P). Moreover, experiments found that the higher the concentration of polyvinylpyrrolidone, the longer the time it could remain stable. As Figure 4 shown, LMI@0P of Comparative Example 1 was black, started to stratify after 46 min of placement, and after 2.2 h of placement, the liquid metal particles completely settled to the bottom of the bottle, and the supernatant was colorless and transparent. The liquid metal ink of Comparative Example 2 was gray. Due to insufficient addition of the polymer co-solvent in Comparative Example 2, the stability time was longer than that of Comparative Example 1 but shorter than that of Example 1.

[0095] 2. Rheological properties The rheological properties of Examples 1-4 and Comparative Examples 1-3 were measured using a rotational rheometer (MCR302, Anton Paar) respectively. As Figure 5 shown in (a), the liquid metal inks prepared by ultrasonic fragmentation (Examples 1-4, Comparative Examples 1-2) were all Newtonian fluids, and the viscosity was between 1.55 - 4.99 mPa·s.

[0096] Further tests Figure 5 As can be seen from (b), the viscosity of the liquid metal ink increased linearly with the concentration of polyvinylpyrrolidone.

[0097] Comparative Example 3 gallium-indium alloy GaIn 25 showed shear thinning phenomenon, and the viscosity at a shear rate of 14900 s -1 during ultrasonic atomization was 18.99 mPa·s.

[0098] However, the atomization upper limit of the aerosol inkjet printer based on ultrasonic atomization used in the preferred option was 5 mPa·s. Therefore, neither Comparative Example 3 gallium-indium alloy GaIn 25 nor the liquid metal ink using polyethylene as the polymer co-solvent and having a higher content of polyvinylpyrrolidone (>30 mg / ml) could produce aerosols by ultrasonic atomization.

[0099] Considering the ink stability, the liquid metal ink of the embodiments of the present invention can achieve stable ultrasonic atomization, while Comparative Examples 1-3 cannot.

[0100] 3. Volatile properties Using an aerosol inkjet printer, printing experiments were carried out on glass slides using the inks with three different second solvent concentrations of Example 1, Example 5, Example 6 and Comparative Example 4 under the conditions of a sheath gas flow rate of 60 sccm, a carrier gas flow rate of 15 sccm, a printing rate of 3 mm / s, a printing height of 1 mm, and a substrate temperature of 60°C. The results are as Figure 6As shown in Figs. (a) - 6(d). When the concentration of the second solvent is insufficient, the volatilization performance of the ink is too fast, and many scattered dots will appear around the printed lines. This phenomenon is called overspray. As the concentration of the second solvent increases, the overspray phenomenon is inhibited. When the concentration of the second solvent is 10%, that is, LMI@10P in Example 1, the overspray is completely inhibited, and a liquid metal line with smooth edges and good quality can be printed. At this time, the volatilization performance is the best. However, when the concentration of the second solvent is further increased, such as to 15%, the volatilization performance of the ink is too slow, and it cannot be dried in time on the substrate, resulting in excessive spreading, and the printed line is wider than that in Example 1 under the same parameters, that is, the printing accuracy is reduced. Therefore, the volatility of the ink in Example 1 conforms to this printing parameter. In actual implementation, the type and content of the medium - low volatility second solvent in the ink should be adjusted according to the environmental temperature and humidity and printing parameters.

[0101] 4. Surface Tension and Wettability The surface tension and contact angle of Example 4 and Comparative Examples 1 - 3 were measured using a video contact angle tester (OCA - 25302, Dataphysics). After ultrasonic fragmentation into ink (Example 4 and Comparative Examples 1, 2), the surface tension of the ink slightly increased from 22.02 mN / m to 24.16 mN / m with the increase in the concentration of polyvinylpyrrolidone, which was significantly lower than that of the gallium - indium alloy GaIn 25 in Comparative Example 3, which was 624 mN / m, thus improving the wettability of the ink. As Figure 7 shown in Fig. (a), the contact angles of the liquid metal inks of Example 4 and Comparative Example 1 on the glass slide and polydimethylsiloxane (PDMS) were both less than 90°, showing a wetting state, while the gallium - indium alloy GaIn 25 in Comparative Example 3 could not be wetted.

[0102] Furthermore, using LMI@30P of Example 4 for aerosol printing on various substrates, as Figure 7 shown in Figs. (b) and Figure 7 (c), liquid metal patterning was achieved on common rigid substrates (glass slide, silicon wafer), flexible non - stretchable substrates (polyimide, paper, plant leaf), and flexible stretchable substrates (polydimethylsiloxane, polyacrylate 3M VHB tape).

[0103] Furthermore, by optimizing the aerosol printing parameters, high - precision liquid metal lines with a line width of 10 μm were printed on a glass slide using LMI@30P in Example 4, as Figure 8 shown. This is a high - precision solution in the existing liquid metal patterning technology.

[0104] Activation of Liquid Metal Conductivity and Conductivity Test: The liquid metal pattern rolled by an iron cylinder in Example 7 was observed using a scanning electron microscope, asFigure 9 As shown, different from the independent liquid metal spheres in Figure 4 , Figure 5 , the rolled liquid metal forms a continuous sheet. Therefore, the conductivity of the rolled liquid metal pattern is restored. The conductivity of the activated liquid metal is measured using a digital four-probe tester (M3, Suzhou Lattice Electronics Co., Ltd.). After activation by Example 7, the conductivity of LMI@10P-LMI@30P in the examples decreases with the increase in the content of polyvinylpyrrolidone. The conductivity of LMI@10P is the highest, which is 1.1×10 6 S / m; the conductivity of LMI@30P is the lowest, which is 2.2×10 5 S / m.

[0105] Flexible conductivity test of liquid metal conductive lines: The liquid metal ink LMI@15P prepared in Example 2 is selected after comprehensively considering high conductivity and high printing accuracy. The change diagrams of the resistance of the liquid metal wire circuit prepared in Example 2 during bending, twisting, and stretching are shown in Figure 10 Figs. (a)-10(c). When the bending radius gradually decreases and the twisting angle gradually increases, the resistance of the 60-μm-wide liquid metal conductive line remains basically unchanged, verifying that the liquid metal circuit aerosol-printed on the flexible substrate provided by the present invention has good anti-bending and anti-twisting conductive properties and has good prospects for flexible circuit applications. Although the resistance of the liquid metal circuit with a line width of 1 mm prepared in Example 8 increases with the tensile strain, when the tensile strain is less than 620%, the resistance is less than 40 Ω, showing good conductive properties. It is verified that the liquid metal circuit aerosol-printed on the flexible stretchable substrate provided by the present invention has good stretchable conductive properties and has good prospects for flexible stretchable circuit applications.

[0106] In summary, the low-viscosity, low-surface-tension, and easily activated liquid metal ink prepared by the present invention realizes aerosol printing of liquid metal for the first time; using the aerosol printing liquid metal patterning technology of the present invention, liquid metal patterns with high precision (10-100 μm) can be simply printed on various substrates; by printing liquid metal on a flexible substrate using the present invention and preparing a flexible circuit by simply mechanically activating the conductivity of the pattern, the circuit still retains its conductivity during bending, twisting, and stretching (when on a flexible stretchable substrate).

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A liquid metal ink for aerosol jet printing, characterized in that It includes a first solvent, a polymeric cosolvent, a liquid metal, and a second solvent; The boiling point of the first solvent is ≤100 °C, the surface tension at 25 °C is ≤75 mN / m, and the viscosity at 25 °C is ≤1.5 mPa·s; the boiling point of the second solvent is 190 - 250 °C, the surface tension at 25 °C is ≤50 mN / m, and the viscosity at 25 °C is ≤40 mPa·s; The polymeric cosolvent includes one or more of polyvinylpyrrolidone, polyvinyl alcohol, and methylcellulose; based on the amount of the first solvent used, the concentration of the polymeric cosolvent is 9.9 mg / ml - 30 mg / ml.

2. The liquid metal ink according to claim 1, wherein The liquid metal is a room-temperature liquid metal with a melting point below 25 °C; preferably, the liquid metal is selected from one or several of gallium, indium, tin, and their alloys; more preferably, the liquid metal is selected from gallium-indium alloy or gallium-indium-tin alloy; And / or, the mass concentration of the liquid metal in the liquid metal ink is 0.08 - 0.75 g / ml.

3. The liquid metal ink according to claim 1 or 2, characterized in that, In the liquid metal ink, the amount of the first solvent used is greater than that of the second solvent; Preferably, the volume of the second solvent accounts for 5% - 20% of the total volume of the liquid metal ink.

4. The liquid metal ink according to any one of claims 1 to 3, characterized in that, The first solvent is selected from water or ethanol, preferably ethanol; And / or, the second solvent is selected from one or more of diethylene glycol, ethylene glycol, and terpineol, preferably diethylene glycol.

5. The preparation method of the liquid metal ink according to any one of claims 1-4, characterized in that, It includes the following steps: Add a polymeric cosolvent to the first solvent to prepare a mixed solvent; Add a liquid metal to the mixed solvent and obtain a nano-micro liquid metal droplet dispersion by ultrasonic fragmentation; Add a second solvent to the nano-micro liquid metal droplet dispersion and mix.

6. The preparation method according to claim 5, characterized in that, The power of the ultrasonic fragmentation is 400 - 600 W, the frequency is 10 - 30 kHz, the time is 0.5 - 2 h, and the temperature is 15 - 25 °C.

7. A method for manufacturing a functional pattern, characterized in that, The functional patterning manufacturing method is to print the liquid metal ink according to any one of claims 1 - 4 on a substrate by aerosol jet printing to form a liquid metal pattern.

8. The functional patterning manufacturing method according to claim 7, wherein The aerosol jet printing uses ultrasonic atomization printing; preferably, the printing conditions of the aerosol jet printing include: the carrier gas flow rate is 10 - 20 sccm, the sheath gas flow rate is 50 - 100 sccm, the printing speed is 2 - 4 mm / s, the printing height is 0.5 - 2 mm, the printing temperature is 50 - 70 °C, and the printing times ≥ 1 time; And / or, the accuracy of the aerosol jet printing is 10 - 100 μm.

9. The functional patterning manufacturing method according to claim 7 or 8, characterized in that The substrate is a flexible substrate or a rigid substrate, preferably a flexible substrate, more preferably a flexible stretchable substrate.

10. A liquid metal conductive circuit, characterized in that, It includes liquid metal conductive lines, and the liquid metal conductive lines are formed by activating the electrical conductivity of the liquid metal pattern after forming the liquid metal pattern on the substrate by using the functional patterning manufacturing method according to any one of claims 7 - 9.

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