Flexible electronic device preparation method based on liquid metal particle compounding and pipeline forming

Abstract

The invention discloses a preparation method of a flexible electronic device based on liquid metal particle compounding and pipeline forming, and belongs to the technical field of flexible electronics. The method comprises the following steps: preparing liquid metal nano-composite ink, and mixing liquid metal with an elastomer prepolymer under the shearing action to form uniformly dispersed liquid metal nano-particle composite ink; preparing a microfluidic mold with a required circuit pattern and a pipeline structure; filling the ink into a mold; and curing and packaging the mold. According to the method, accurate filling of complex circuit patterns and pipeline forming are achieved by means of the excellent rheological property of the liquid metal nanoparticle composite ink. Through packaging of the elastomer matrix, the problems that liquid metal is high in surface tension, prone to oxidation and poor in mechanical stability are effectively solved. The prepared flexible electronic device has excellent conductivity, stretchability and fatigue resistance, and can be widely applied to the fields of intelligent wearing, bionic sensors, stretchable circuits, human-computer interaction interfaces and the like.

Description

A method for fabricating flexible electronic devices based on liquid metal particle composite and channel forming Technical Field

[0001] This invention belongs to the field of flexible electronics technology, and particularly relates to a method for fabricating flexible electronic devices based on liquid metal particle composite and channel forming. Background Technology

[0002] In recent years, flexible electronic devices have demonstrated enormous application potential in emerging fields such as human-machine interfaces, health monitoring, and intelligent robots due to their unique advantages such as thinness, flexibility, and stretchability. As the cornerstone of flexible electronic devices, the research and development of flexible conductive materials is crucial. Traditional rigid conductors, such as copper and silver, are prone to fatigue fracture during bending and stretching, leading to performance degradation or even device failure. Therefore, developing flexible conductive materials with excellent conductivity and mechanical deformability has become a current research hotspot.

[0003] Liquid metals, especially gallium and its alloys which are liquid at room temperature, have attracted much attention due to their high conductivity, excellent fluidity, low vapor pressure and good biocompatibility. Liquid metals are an ideal choice for flexible conductors.

[0004] However, directly using bulk liquid metal for printing or patterning still presents many challenges. First, liquid metal has extremely high surface tension, making it difficult to wet most substrates. It typically exists in the form of droplets or particles, resulting in poor interfacial compatibility with the substrate and easy distortion of the printed pattern. Second, liquid metal exposed to air spontaneously forms a fragile oxide shell, typically 0.7-3 nm thick. While this oxide layer stabilizes the liquid metal particles and prevents them from agglomerating, it also severely hinders effective conductive connections between particles, significantly reducing the conductivity of the printed circuit. When flexible devices are subjected to strain or pressure, this fragile oxide shell is prone to rupture, leading to liquid metal leakage and causing short circuits or device failure.

[0005] To address these challenges, researchers have proposed various strategies. One mainstream approach involves the preparation of composite materials, combining liquid metal nanoparticles with other materials at multiple scales to improve their rheological properties, reduce surface tension, and enhance mechanical stability. However, existing preparation methods, such as ultrasonic treatment and shear mixing, while capable of producing liquid metal nanoparticles, still struggle to achieve precise control over particle size, morphology, and surface properties. Furthermore, the preparation process may introduce impurities, affecting the final performance. In addition, how to efficiently and precisely fabricate these liquid metal nanocomposites into flexible channels with stable electrical conductivity for application in practical electronic devices remains a pressing technical challenge. Summary of the Invention

[0006] The purpose of this invention is to provide a method for fabricating flexible electronic devices based on liquid metal particle composite and channel forming. This system employs an optimized mold preparation method and a low-pressure constant injection strategy to achieve bubble-free and complete filling of liquid metal, producing flexible conductive channels with excellent electrical, thermal, and mechanical properties. The specific solution is as follows.

[0007] A method for fabricating flexible electronic devices based on liquid metal particle composites and channel forming includes the following steps: a. Preparation of liquid metal nanocomposite ink: mixing liquid metal with an elastomer prepolymer under shear to form liquid metal nanoparticles, and uniformly dispersing the nanoparticles in the elastomer prepolymer to obtain the liquid metal nanocomposite ink; b. Mold forming: preparing a microfluidic mold with the desired circuit pattern and channel structure; c. Composite ink filling: filling the liquid metal nanocomposite ink into the channel structure of the microfluidic mold; d. Curing and encapsulation: curing the ink-filled mold to crosslink the elastomer to form a flexible matrix, and permanently encapsulating the liquid metal nanoparticle channels therein.

[0008] Furthermore, the liquid metal is selected from gallium, gallium-indium alloy, or gallium-indium-tin alloy.

[0009] Furthermore, the elastomer prepolymer is selected from polydimethylsiloxane, silicone, or polyurethane.

[0010] Furthermore, in step a, the shearing action is achieved through mechanical stirring, ultrasonic treatment, or a shear mixing device.

[0011] Furthermore, in step a, the liquid metal nanocomposite ink contains one or more surfactants, which can reduce the surface tension of the liquid metal.

[0012] Furthermore, in step c, the filling method is controlled extrusion, injection, or vacuum injection.

[0013] Furthermore, the microfluidic mold is prepared by methods such as photolithography, 3D printing, or biomimetic replication.

[0014] Furthermore, in step d, the curing is either thermosetting or UV curing.

[0015] Furthermore, a flexible electronic device prepared by the method according to claim 1, the device comprising at least one continuous liquid metal nanoparticle channel encapsulated in an elastomeric matrix.

[0016] Furthermore, the conduit of the flexible electronic device has a three-dimensional topological structure, which includes, but is not limited to, serpentine, spiral, or biomimetic leaf vein networks.

[0017] The beneficial effects of the flexible electronic device fabrication method based on liquid metal particle composite and channel forming provided by this invention include: First, by combining liquid metal particles with nanocomposite materials or polymer matrices, this invention overcomes the difficulty of direct molding of traditional liquid metals, making the fabrication process of flexible electronic devices simpler and more controllable. Second, the resulting liquid metal particle composite material combines the excellent conductivity of liquid metal with the flexibility of the matrix, enabling the device to maintain stable electrical performance under mechanical deformations such as bending and stretching, thus improving the durability of the flexible device. Third, this method provides a general platform for fabricating high-performance flexible sensors, stretchable electrodes, and wearable heaters, expanding the application of liquid metals in fields such as medical health and human-computer interaction. Attached Figure Description

[0018] Figure 1: Overall flow chart of the preparation method of the present invention, showing the complete process from the preparation of liquid metal composite ink to the final molding of flexible electronic devices.

[0019] Figure 2: Schematic diagram of the preparation of liquid metal nanoparticle composite ink, showing the process of nano-sizing liquid metal through shear mixing and combining it with elastomer prepolymer.

[0020] Figure 3: Schematic diagram of the pipe forming process, showing the process of extruding or injecting composite ink into a mold and finally forming a continuous pipe.

[0021] Figure 4: Schematic diagram of the performance test of the flexible conductive pipe prepared by the present invention under different tensile and bending conditions. Detailed Implementation

[0022] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. These specific embodiments provide a further detailed explanation and description of each technical feature in the claims, ensuring that the technical solution of the present invention can be clearly understood and implemented by those skilled in the art.

[0023] 1. Preparation of liquid metal nanoparticle composite ink

[0024] This embodiment provides a detailed description of step a in claim 1.

[0025] Traditional bulk liquid metals are difficult to use directly for printing due to their high surface tension. This invention uses a shear-mixing method to nanoscale liquid metals and then combines them with elastomer prepolymers to prepare a printable liquid metal nanocomposite ink.

[0026] First, prepare liquid metal, preferably a gallium-indium alloy, which has a melting point as low as [missing information]. It is liquid at room temperature and has excellent electrical properties; other liquid metal alloys can also be selected.

[0027] Secondly, an elastomer prepolymer is selected, preferably polydimethylsiloxane, because it has good flexibility, chemical stability, biocompatibility, and transparency. Other options include silicone, polyurethane, etc. The polydimethylsiloxane prepolymer and curing agent are mixed evenly at a mass ratio of 10:1.

[0028] Next, shear mixing is performed. The mixture of liquid metal and polydimethylsiloxane prepolymer is placed in a high-speed shear mixing device. Under high-speed shearing, the liquid metal droplets are torn into micron- or even nano-sized droplets. Due to the spontaneous oxidation properties of liquid metal, a thin and stable oxide layer rapidly forms on the droplet surface. This oxide layer prevents the droplets from re-aggregating into bulk liquid metal. During the shearing process, the oxide layer continues to form, ultimately stably dispersing the liquid metal in the form of nanoparticles within the polydimethylsiloxane prepolymer matrix.

[0029] This process can be represented by the following formula for the breakup of liquid metal droplets: when the shear force... greater than the surface tension of the droplet At this point, the droplet will break up. Shear force and shear rate and liquid viscosity Proportional, that is Surface tension and the surface tension coefficient of a droplet and droplet radius Related, that is The conditions for droplet breakup are: ,Right now:

[0030] in, It is a proportionality constant. By increasing the shear rate This allows for the production of even smaller liquid metal nanoparticles.

[0031] To further improve ink performance, surfactants such as oleic acid or ethanol can be added to the mixture. These surfactants can adsorb onto the surface of liquid metal particles, further reducing their surface tension and enhancing interfacial compatibility with the elastomer matrix, thereby obtaining a more stable dispersion system.

[0032] The resulting liquid metal nanocomposite ink exhibits a semi-fluid paste-like consistency. Its viscosity and rheological properties can be precisely controlled by adjusting the liquid metal content, nanoparticle size, and shear rate to meet the needs of different printing technologies.

[0033] 2. Mold forming

[0034] This embodiment provides a detailed description of step b in claim 1.

[0035] Molds are crucial in determining the final geometry and structure of flexible electronic devices. This invention can employ various methods to fabricate microfluidic molds to replicate complex circuit patterns.

[0036] a. Photolithography: For applications requiring high-resolution, two-dimensional planar circuit patterns, traditional photolithography techniques can be used to fabricate molds. First, a layer of photoresist is coated onto a silicon wafer, then exposed to ultraviolet light through a mask. After development, a photoresist template with the desired pattern is obtained. Finally, a polydimethylsiloxane prepolymer is cast onto the photoresist template, cured, and then peeled off to obtain a polydimethylsiloxane mold with microchannels. This method is suitable for large-scale, high-precision fabrication.

[0037] b. 3D Printing: For flexible electronic devices with complex three-dimensional topologies, such as spirals, three-dimensional snakes, and biomimetic vascular networks, 3D printing is an ideal method for mold fabrication. High-precision photopolymerization 3D printers can be used to print molds with micron-level resolution. This method enables the rapid and flexible fabrication of complex three-dimensional structures.

[0038] c. Biomimetic Replication Method: This invention can also employ a biomimetic replication method to prepare molds with naturally complex three-dimensional topological structures. For example, by casting polydimethylsiloxane prepolymer onto the fine structures of leaf veins, blood vessels, or insect wings found in nature, and then peeling it off after solidification, a high-fidelity biomimetic microfluidic mold can be obtained. This method is simple, low-cost, and can produce complex biomimetic structures that are difficult to achieve using traditional methods.

[0039] 3. Composite ink filling and channel forming

[0040] This embodiment provides a detailed description of step c in claim 1.

[0041] Filling the liquid metal nanocomposite ink prepared in step 1 into the microfluidic mold prepared in step 2 is a key step in forming a continuous conductive channel.

[0042] a. Controlled Extrusion Method: Liquid metal nanocomposite ink is loaded into a syringe and extruded at a constant low speed using a syringe pump or pressure controller. The extruded ink passes through a fine nozzle, directly "writing" or filling the channels within a microfluidic mold. Due to the ink's semi-fluid properties and suitable viscosity, it maintains its shape and forms continuous channels within the mold. This method is particularly suitable for fabricating two-dimensional planar circuits, where printing resolution and linewidth can be adjusted by controlling the nozzle diameter and extrusion rate.

[0043] b. Injection or Vacuum Injection Method: For microchannels with closed ends or complex branching structures, injection or vacuum injection methods can be used. First, the mold is placed in a vacuum chamber for degassing to remove air from the channel. Then, an ink-filled syringe is connected to the inlet of the mold, and the ink is slowly injected under vacuum or slight positive pressure. The vacuum environment and low-pressure injection help the ink fill the entire channel smoothly and without air bubbles, including the smallest branches and corners, ensuring that the final channel is continuous and complete.

[0044] The integrity of ink filling can be described by the capillary number. The capillary number is the ratio of viscous force to surface tension, and its formula is:

[0045] in, It is the viscosity of the fluid. It is the fluid velocity. It is surface tension.

[0046] The liquid metal nanocomposite ink of the present invention, due to nano-sizing and the effect of surfactants, has a surface tension Significantly reduced, while viscosity Relatively high. At a constant low speed. By using this method, a suitable number of capillaries can be obtained, allowing the ink to move forward in a stable "piston flow" manner within the channel, effectively avoiding the generation of air bubbles and ensuring the continuity of the pipeline.

[0047] 4. Curing and Encapsulation

[0048] This embodiment provides a detailed description of step d in claim 1.

[0049] Curing and encapsulation are key steps in protecting liquid metal conduits and imparting flexibility and stability to devices.

[0050] a. Thermosetting: A second layer of uncured polydimethylsiloxane prepolymer is applied to the mold filled with liquid metal nanocomposite ink. The entire structure is then placed in an oven. Heat for 2-4 hours. During this process, the polydimethylsiloxane prepolymer undergoes a cross-linking and curing reaction, forming a robust yet flexible matrix. This curing method ensures that the liquid metal pipes are permanently encapsulated within the polydimethylsiloxane matrix, effectively preventing leakage and oxidation of the liquid metal.

[0051] b. Encapsulation: If the mold itself is a layer of polydimethylsiloxane, another plasma-treated polydimethylsiloxane substrate can be directly bonded to it after ink filling. Plasma treatment introduces hydrophilic groups onto the surface of the polydimethylsiloxane, allowing the two polydimethylsiloxane substrates to form strong covalent bonds upon contact, thus achieving permanent, hermetic encapsulation. This encapsulation method is simple, efficient, and ensures the stability of the liquid metal pipeline under various external stresses.

[0052] 5. Fabrication and Performance Testing of Flexible Electronic Devices

[0053] This embodiment provides a detailed description of the claims.

[0054] Through the above steps, various types of flexible electronic devices can be fabricated and their comprehensive performance tested.

[0055] a. Device fabrication: Flexible electronic devices with different structures can be fabricated according to the design.

[0056] Two-dimensional planar circuits: For example, liquid metal pipes can be formed into serpentine or spiral shapes to achieve high stretchability. When the flexible substrate is stretched, the serpentine pipe unfolds, while the liquid metal remains continuous inside the pipe, thus avoiding a significant increase in resistance.

[0057] Three-dimensional topological devices: Flexible electronic devices with three-dimensional structures can be fabricated using 3D printed molds or biomimetic replica molds, such as circuits for biomimetic robots or complex sensors.

[0058] Sensor: This device couples a liquid metal pipe to an external stimulus. When the external stimulus causes the pipe to deform, the resistance of the liquid metal changes. By measuring the change in resistance, the external stimulus can be detected.

[0059] b. Performance Testing: The following tests were performed on the fabricated flexible electronic devices to verify their performance:

[0060] Electrical performance testing: Measure the initial resistance of the device using a high-precision multimeter or electrochemical workstation.

[0061] Tensile strength test: The device is repeatedly stretched and released using a microcomputer tensile testing machine, while its resistance change is monitored simultaneously. When the tensile deformation exceeds 100%, the rate of resistance change should be less than 10%. This rate of resistance change can be calculated using the following formula. :

[0062] in, It is the resistance under tension. It is the resistance in the initial state.

[0063] Bending stability test: Using a self-made bending test platform, the device is subjected to repeated bending and recovery cycles while its resistance is monitored. After 1000 bending cycles, the rate of change in resistance should be less than 5%.

[0064] Sensing performance test: Pressure sensing: The device is placed on a pressure testing instrument, different pressures are applied, and its resistance change is measured. The sensitivity of the device can be expressed by the following formula:

[0065] in, It is the initial resistance. It is the change in resistance. It is the initial pressure. It is the change in pressure.

[0066] Strain sensing: The device is attached to a tension table and subjected to different strains. The resistance change is measured. Its strain coefficient can be expressed by the following formula: ,in, It is strain, which is defined as , It is the change in stretching length. It is the initial length.

[0067] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for fabricating flexible electronic devices based on liquid metal particle composite and channel forming, characterized in that, Includes the following steps: a. Preparation of liquid metal nanocomposite ink: Liquid metal and elastomer prepolymer are mixed under shear to form liquid metal nanoparticles, and the nanoparticles are uniformly dispersed in the elastomer prepolymer to obtain the liquid metal nanocomposite ink; b. Mold making: Fabricating microfluidic molds with the required circuit patterns and pipe structures; c. Composite ink filling: The liquid metal nanocomposite ink is filled into the channel structure of the microfluidic mold; d. Curing and encapsulation: The mold filled with ink is cured to crosslink the elastomer to form a flexible matrix, and the liquid metal nanoparticle channel is permanently encapsulated therein.

2. The method according to claim 1, characterized in that, The liquid metal is selected from gallium, gallium-indium alloy, or gallium-indium-tin alloy.

3. The method according to claim 1, characterized in that, The elastomer prepolymer is selected from polydimethylsiloxane, silicone, or polyurethane.

4. The method according to claim 1, characterized in that, In step a, the shearing action is achieved through mechanical stirring, ultrasonic treatment, or a shearing mixing device.

5. The method according to claim 1, characterized in that, In step a, the liquid metal nanocomposite ink contains one or more surfactants, which can reduce the surface tension of the liquid metal.

6. The method according to claim 1, characterized in that, In step c, the filling method is controlled extrusion, injection, or vacuum injection.

7. The method according to claim 1, characterized in that, The microfluidic mold is prepared by methods such as photolithography, 3D printing, or biomimetic replication.

8. The method according to claim 1, characterized in that, In step d, the curing is either thermosetting or UV curing.

9. A flexible electronic device prepared by the method according to claim 1, characterized in that, The device comprises at least one continuous liquid metal nanoparticle channel encapsulated in an elastomeric matrix.

10. The flexible electronic device according to claim 9, characterized in that, The pipeline has a three-dimensional topological structure, which includes, but is not limited to, serpentine, spiral, or biomimetic leaf vein networks.

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