An imprintable-activated breathable and stretchable circuit, its preparation method and application

Abstract

The present invention relates to a stamp-activatable breathable and stretchable circuit, its preparation method and application, belonging to the field of flexible electronic technology. The preparation method of the stamp-activatable breathable and stretchable circuit of the present invention comprises the following steps: dissolving a thermoplastic polymer in a solvent, adding liquid metal particles and mixing and dispersing them to obtain a mixed solution; electrospinning the obtained mixed solution to prepare a nanofiber membrane; stamping the obtained nanofiber membrane with a stamping mold having a circuit pattern to obtain a stamp-activatable breathable and stretchable circuit. The present invention ensures breathability and stretchability through the use of the nanofiber membrane. Since the liquid metal particles match the fiber diameter, the liquid metal inside the nanofibers can overflow through stamping to form a conductive path, realizing the high-precision preparation of the circuit.

Description

Technical Field

[0001] The present invention relates to the field of flexible electronics, and in particular to a breathable and stretchable circuit that can be imprint-activated, and a preparation method and application thereof. Background Art

[0002] Stretchable electronic products and systems have attracted great interest due to their applications in wearable electronics, soft robotics, human-machine interfaces, and bioelectronic devices. A key aspect of stretchable electronics is the development of stretchable conductors. Many studies have focused on incorporating rigid conductors such as metal nanowires or conductive polymers into elastic substrates through methods such as bending, wrinkling design, or spray dispersion to create macroscopically deformable conductors. However, the inherent rigidity of conductive materials often impairs the stability of stretchable conductors during long-term deformation. Problems such as the segregation of metal nanowires under repeated external forces and the cracking of conductive polymers result in an irreversible decrease in the conductivity of stretchable conductors. In contrast, gallium-based liquid metals (LMs) have also received extensive attention due to their excellent deformation ability and extremely high conductivity at room temperature.

[0003] To circumvent the challenges posed by the low viscosity and high surface tension of liquid metals and the spontaneous formation of the non-conductive Ga2O3 oxide layer, liquid metal-based wires typically require complex manufacturing processes such as sintering, transfer printing, or doping treatments. These complexities limit the scalability and flexibility of stretchable electronic device designs. In addition, the elastic substrates commonly used for stretchable conductors are impermeable films with poor adhesion and compatibility with human skin. This makes them less suitable for long-term applications such as healthcare monitoring and may even have inflammatory or allergic effects on health. Nanofiber meshes capable of loading liquid metals have recently received attention because liquid metals can infiltrate the gaps between nanofibers through coating or spraying to form a grid-like conductive path during stretching. The resulting materials have high conductivity and extensibility while maintaining good breathability. However, existing studies usually rely on methods such as coating or spraying. Due to the high surface tension of liquid metals and poor interfacial compatibility with polymer fiber networks, on a macroscopic level, liquid metals and polymer networks usually appear as two layers, namely a liquid metal conductive layer and a polymer support layer. The adhesion between these two layers is poor, easily leading to liquid metal leakage, resulting in low precision of the prepared circuit and difficulty in achieving good cyclic stretching stability, which has become a problem in the industry. That is to say, the disadvantages of the existing technologies are as follows: 1. Existing stretchable circuits lack breathability; 2. The circuit line widths of existing stretchable circuits are large and the precision is low; 3. The activation of conductive paths is difficult and it is difficult to prepare quickly.

[0004] Therefore, how to fabricate a stable and precise conductive circuit and how to alleviate the serious interfacial problems between liquid metals and the elastic network of the substrate have become urgent problems to be solved. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a stamping-activatable breathable and stretchable circuit, its preparation method and application. The present invention ensures breathability and stretchability through the use of a nanofiber membrane. Since the liquid metal particles match the fiber diameter, the liquid metal inside the nanofibers can overflow through stamping to form a conductive path, realizing the high-precision preparation of the circuit.

[0006] The present invention is realized through the following technical solutions:

[0007] The first object of the present invention is to provide a preparation method of a stamping-activatable breathable and stretchable circuit, comprising the following steps:

[0008] Dissolve a thermoplastic polymer in a solvent, add liquid metal particles and mix and disperse them to obtain a mixed solution;

[0009] Perform electrospinning on the obtained mixed solution to prepare a nanofiber membrane;

[0010] Use a stamping mold with a circuit pattern to stamp the obtained nanofiber membrane to obtain a stamping-activatable breathable and stretchable circuit.

[0011] In an embodiment of the present invention, the thermoplastic polymer is selected from one or more of polyurethane, PVDF, PVDF-HFP, PVA, SBS, and SEBS.

[0012] In an embodiment of the present invention, the solvent is selected from one or more of hexafluoroisopropanol, tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, water, and dichloromethane.

[0013] In an embodiment of the present invention, the metal in the liquid metal particles is selected from one or more of gallium, gallium-indium alloy, gallium-indium-tin alloy, and indium-tin-bismuth alloy.

[0014] In an embodiment of the present invention, the liquid metal particles are prepared by the following method:

[0015] Place the metal in alcohol and perform ultrasonic treatment to obtain the liquid metal particles.

[0016] In an embodiment of the present invention, the mass ratio of the liquid metal particles to the thermoplastic polymer in the thermoplastic polymer solution is 4-10:1.

[0017] In an embodiment of the present invention, the ratio of the particle size of the liquid metal particles in the nanofiber membrane to the fiber diameter is 1:0.35-2.

[0018] In one embodiment of the present invention, the electrospinning satisfies one or more of the following conditions:

[0019] The needle size is 20G - 24G;

[0020] The applied voltage is 6 kV - 15 kV;

[0021] The solution feeding rate is 0.5 mL h -1 -1.2 mL h -1 ;

[0022] The fiber collection distance is 8 cm - 16 cm;

[0023] The rotation speed of the metal roller for collecting the fiber membrane is 120 rpm - 200 rpm;

[0024] The humidity of the electrospinning is 40%.

[0025] In one embodiment of the present invention, the conditions for stamping are: the pressure applied to the contact surface of the nanofiber membrane is 100 kPa - 1 MPa.

[0026] The second object of the present invention is to provide a stampable and activatable breathable and stretchable circuit prepared by the preparation method.

[0027] The third object of the present invention is to provide the application of the stampable and activatable breathable and stretchable circuit in wearable electronic products, soft robots, human - machine interfaces or bio - electronic devices.

[0028] The above - mentioned technical solutions of the present invention have the following advantages compared with the prior art:

[0029] The present invention provides a breathable and stretchable circuit, which uses stamping technology and nanofiber membranes containing liquid metal (LMNM) to create flexible and personalized circuit designs. Through the adaptable selection of liquid metal microparticles and electrospun fibers, the stretchable nanofiber membrane exhibits excellent properties under a high liquid metal content load, such as super elasticity (up to 400%) and moisture permeability (2941 g m -2 d -1) Initially, the liquid metal particles are semi-embedded and unconnected in the polymer nanofibers, and at this time, the stretchable nanofiber membrane is electrically insulating. The stamping process causes the external liquid metal particles to break and penetrate the nano-network gaps, thereby forming conductive regions within the stretchable nanofiber membrane. The liquid metal particles inside the fibers become fixed anchor points, while the overflowing liquid metal tightly binds to the nanofibers on the same plane, which greatly improves the interfacial compatibility between the liquid metal and the polymer fibers. This process facilitates the subsequent fabrication of patterned circuits and provides greater flexibility for personalized circuit design. After being integrated with various electronic components, these circuits can achieve multiple functions, such as outputting square wave signals, lighting circuits, and wireless charging. In addition, the fabricated flexible electronic components have high precision, with a minimum line width of 50 microns, good cycle stability, and can be recycled more than 30,000 times. Their excellent biocompatibility and permeability make them suitable for collecting bioelectric signals, such as electrocardiogram (ECG) and electromyogram (EMG), and have broad application prospects in the field of flexible electronics. This technology is also considered environmentally friendly because after use, both the polymer components and the liquid metal particles can be easily separated and recycled. In addition, experimental studies have been carried out on various common polymers for preparing stretchable nanofiber membranes, demonstrating the great potential of this technology in the field of flexible electronics. Brief Description of the Drawings

[0030] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in combination with the drawings, where

[0031] Figure 1 is a schematic diagram of the preparation process of the stamping-activated breathable and stretchable circuit of the present invention;

[0032] Figure 2 is the circuit schematic diagram in Embodiment 1 of the present invention;

[0033] Figure 3 is a schematic diagram of the stretchable light-emitting circuit in Embodiment 1 of the present invention;

[0034] Figure 4 is the diameter distribution of liquid metal particles of different sizes in the test example of the present invention;

[0035] Figure 5 is the resistance and conductivity of the nanofiber membrane containing liquid metal particles with different particle sizes after stamping in the test example of the present invention;

[0036] Figure 6 is the fiber diameter diagram corresponding to different liquid metal contents in the test example of the present invention;

[0037] Figure 7 is the stress-strain curve of the circuit under different liquid metal loadings in the test example of the present invention;

[0038] Figure 8 It is the strain-impedance curve of the circuit under different liquid metal loadings in the test examples of the present invention;

[0039] Figure 9 It is the impedance stability of the circuit under cyclic stretching in the test examples of the present invention;

[0040] Figure 10 It is the air permeability of the circuit under different pressure differences in the test examples of the present invention;

[0041] Figure 11 It is the scanning electron microscope photos of different wire widths of the conductive wires (50 microns, 100 microns, 500 microns, and 1 mm) in the test examples of the present invention;

[0042] Figure 12 It is the template used for imprinting and the circuit prepared after imprinting in the test examples of the present invention;

[0043] Figure 13 It is the test diagram of the circuit conductivity of the nanofiber membrane in the test examples of the present invention. Detailed implementation manners

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited are not intended to limit the present invention.

[0045] Embodiment 1

[0046] This embodiment provides a preparation method of a stamp-activatable breathable stretchable circuit, and the specific steps are as follows:

[0047] (1) Preparation of the composite spinning solution

[0048] Dissolve 1 g of thermoplastic polyurethane in 19 g of hexafluoroisopropanol and stir at room temperature for 12 h to prepare a polymer solution. Put 1 g of eutectic alloy of EGaIn into 5 g of absolute ethanol and ultrasonically treat it in a 10 mL centrifuge tube to prepare liquid metal particles. Ultrasonically treat it at a power of 50% for 5 min in an ultrasonic cell disruptor, and the centrifuge tube is always placed in an ice-water bath during the ultrasonic treatment. The obtained liquid metal slurry is centrifuged at a speed of 100 rpm for 60 s by a centrifuge; retain the supernatant, and then continue to centrifuge at a speed of 500 rpm for 90 s and then remove the supernatant. The remaining slurry is vacuum dried at room temperature for 6 h, and then liquid metal particles are added to the polymer solution according to a certain mass ratio (mass of liquid metal particles: mass of polymer solution = 8:1), and stirred at room temperature for two hours to ensure that the particles are evenly dispersed in the solution.

[0049] (2) Preparation of the nanofiber membrane by electrospinning

[0050] A mixed solution containing a polymer solution and liquid metal particles was loaded into a 10 mL syringe and electrospun using an electrospinning machine. During the electrospinning process, the needle size, applied voltage, solution feeding rate, and fiber collection distance were set to 23G, 12 kV, 1 mL h -1 and 12 cm, respectively. The fiber membrane was collected by a metal roller rotating at 110 rpm. The entire process was carried out at room temperature with the humidity controlled at 40%, and the syringe was rotated every 2 h to prevent the settlement of liquid metal particles in the solution. Finally, the fiber membrane prepared by electrospinning was placed in an oven at 40 °C for 6 h to remove the residual solvent.

[0051] (3) Activating the conductive network by pressure stamping

[0052] Using a stamping mold with the desired circuit pattern, a pressure of 500 kPa was applied to the nanofiber membrane to stamp out a stretchable circuit board with a patterned circuit; the liquid metal loading of the obtained stretchable circuit board was 40 wt%, and the ratio of the particle size of the liquid metal particles in the nanofiber membrane to the fiber diameter was 1:0.5 - 2.

[0053] Example 2

[0054] This example provides a method for preparing a breathable and stretchable circuit that can be activated by imprinting, and the specific steps are as follows:

[0055] (1) Preparation of the composite spinning solution

[0056] 1 g of PVDF-HFP was dissolved in 9 g of DMF and stirred at room temperature for 12 h to prepare a polymer solution. 1 g of the eutectic alloy EGaIn was placed in 5 g of absolute ethanol and ultrasonically treated in a 10 mL centrifuge tube to prepare liquid metal particles. Ultrasonic treatment was carried out at 50% power for 5 min in an ultrasonic cell disruptor, and the centrifuge tube was always placed in an ice-water bath during the ultrasonic process. The obtained liquid metal slurry was centrifuged at a speed of 100 rpm for 60 s by a centrifuge; the supernatant was retained, and then centrifuged at a speed of 500 rpm for 90 s to remove the supernatant. The remaining slurry was vacuum dried at room temperature for 6 h, and then liquid metal particles were added to the polymer solution according to a certain mass ratio (liquid metal particle mass: polymer solution mass = 3:1), and stirred at room temperature for two hours to ensure that the particles were uniformly dispersed in the solution.

[0057] (2) Preparation of the nanofiber membrane by electrospinning

[0058] A mixed solution containing a polymer solution and liquid metal particles was loaded into a 10 mL syringe and electrospun using an electrospinning machine. During the electrospinning process, the needle size, applied voltage, solution feeding rate, and fiber collection distance were set to 22G, 14 kV, 1 mL h-1 and 15 cm. The fiber membrane was collected by a metal roller with a rotation speed of 110 rpm. The entire process at 110 rpm was carried out at room temperature, the humidity was controlled at 40%, and the syringe was rotated every 2 hours to prevent the settlement of liquid metal particles in the solution. Finally, the electrospun fiber membrane was placed in an oven at 40 °C for 6 h to remove the residual solvent.

[0059] (3) Activate the conductive network by pressure stamping

[0060] Using a stamping mold with the required circuit pattern, a pressure of 300 kPa was applied to stamp on the nanofiber membrane to obtain a stretchable circuit board with a patterned circuit; the liquid metal loading of the obtained stretchable circuit board was 30 wt%, and the ratio of the particle size of the liquid metal particles in the nanofiber membrane to the diameter of the fiber was 1:0.35 - 1.5.

[0061] Test examples

[0062] (1) The liquid metal slurry obtained by the ultrasonic cell disruption system can be separated into liquid metal particles of different particle sizes by centrifugation at different speeds and vacuum drying at room temperature; the average particle sizes obtained by Gaussian fitting are 0.36 μm, 0.99 μm, and 3.95 μm respectively. Nanofiber membranes with different liquid metal particle sizes were prepared by the method of Example 1.

[0063] After stamping, the resistance and conductivity of the nanofiber membranes containing liquid metal particles with different particle sizes were detected, and the results are as Figure 5 shown. Among them, the nanofiber membrane of a can be activated by the stamping process, and the average particle size of the liquid metal particles it contains is 0.99 μm (Example 1), and the size matches that of the nanofibers; while b is the nanofiber membrane with a liquid metal particle size of 0.36 μm, which does not match the nanofiber size and cannot be activated by the stamping process. The liquid metal particles with an average particle size of 3.95 μm are too large to be stably coated by the fibers, resulting in misconnection before stamping, so they are not used.

[0064] (2) Nanofiber membranes with different liquid metal loadings (20 wt%, 30 wt%, 40 wt%, and 50 wt%) were prepared by the method of Example 1, and stretchable circuit boards with patterned circuits were obtained after stamping. The diameters of the nanofibers in the nanofiber membranes were detected, and the results are as Figure 6 shown. It can be seen from Figure 6 that the liquid metal loading has little effect on the diameter of the nanofibers.

[0065] The mechanical properties of strip-shaped samples with a morphology of 50 mm × 10 mm were evaluated using a tensile testing machine (Instron), as specifically shown in Figure 7 shown.Figure 7 It is confirmed that the overall circuit with different liquid metal loadings is stretchable, and the lower the metal loading, the stronger the stretchability.

[0066] The resistance changes of the embossable-activated breathable stretchable circuits with different liquid metal loadings (20 wt%, 30 wt%, 40 wt%, and 50 wt%) during stretching were measured using a Keithley DMM6500 connected to a computer. The 4-terminal method was used to accurately measure the resistance changes of the samples and avoid interference. The results are as Figure 8 , and it can be seen from Figure 8 that the higher the metal loading, the higher the electrical conductivity of the circuit. The stretchable circuit with a 40 wt% metal loading was subjected to cyclic stretching. The results are as Figure 9 shown, and it is confirmed from Figure 9 that the circuit has high impedance stability under cyclic stretching at a 40 wt% metal loading.

[0067] (3) The moisture permeability of the samples was determined by the water method according to the ASTM E96 / E96M-2012 textile standard. The test was carried out at 32 °C and 50% relative humidity for 24 h. The sample with a 40 wt% liquid metal loading was sealed on the mouth of a cup filled with water and then placed in the test environment. The weight loss of water during this period was measured to determine the mass of the exuded water vapor. According to the ASTM D737-75 standard test method, the air permeability was measured using a fully automatic air permeability instrument (YG461G, Ningbo Dahe Instrument Co., Ltd., China) at different pressure drops. The output air flow rate (unit: mm / s) represents the air permeability of the sample. The results are as Figure 10 shown. It can be seen from Figure 10 that the stretchable circuit prepared by the present invention has overall moisture and air permeability.

[0068] (4) The embossable-activated breathable stretchable circuits with different conductive wire widths (50 μm, 100 μm, 500 μm, and 1000 μm) were prepared according to the method of Example 1. The conductive line widths were characterized by a scanning electron microscope (Regulus 8230) as Figure 11 shown. It is confirmed from Figure 11 that the circuit has high precision in the minimum line width.

[0069] (5) The circuit design was carried out using Altium Designer software, and the corresponding 3D model was made using SolidWorks software. A stamping model with the required pattern was made using a 3D printer (Zortrax Inkspire), and then it was stamped on the nanofiber membrane prepared in Example 1 using a pneumatic press (LNA001-63). The results are as Figure 12 shown, which confirms that different circuit preparations can be achieved through the embossing technique.

[0070] (6) Power the nanofiber membrane prepared in Example 2 using a constant voltage power supply, and use the on / off of a light-emitting diode as a test for circuit conductivity. The results are as Figure 13 shown, confirming that the imprinting technique can achieve the transformation of the nanofiber membrane from non-conductive to conductive circuit.

[0071] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A preparation method of a stamping-activated breathable and stretchable circuit, characterized in that, It includes the following steps: Dissolve the thermoplastic polymer in a solvent, add liquid metal particles and mix them for dispersion to obtain a mixed solution; Electrospun the obtained mixed solution to prepare a nanofiber membrane; Stamp the obtained nanofiber membrane with a stamping mold having a circuit pattern to obtain a stamping-activated breathable and stretchable circuit; The ratio of the particle size of the liquid metal particles to the fiber diameter in the nanofiber membrane is 1:0.35 - 2.

2. The preparation method according to claim 1, wherein The thermoplastic polymer is selected from one or more of polyurethane, PVDF, PVDF-HFP, PVA, SBS, and SEBS.

3. The preparation method according to claim 1, characterized in that, The solvent is selected from one or more of hexafluoroisopropanol, tetrahydrofuran, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, water, and dichloromethane.

4. The preparation method according to claim 1, characterized in that, The metal in the liquid metal particles is selected from one or more of gallium, gallium-indium alloy, gallium-indium-tin alloy, and indium-tin-bismuth alloy.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the liquid metal particles to the thermoplastic polymer is 4 - 10:

1.

6. The preparation method according to claim 1, characterized in that, The electrospinning satisfies one or more of the following conditions: The needle size is 20 G - 24 G; The applied voltage is 6 kV - 15 kV; The solution feeding rate is 0.5 mL h -1 -1.2 mL h -1 ; The fiber collection distance is 8 cm - 16 cm; The rotation speed of the metal roller for collecting the fiber membrane is 120 rpm - 200 rpm.

7. The preparation method according to claim 1, wherein The conditions for the stamping are: the pressure on the contact surface of the nanofiber membrane is 100 kPa - 1 MPa.

8. A stamping-activated breathable and stretchable circuit prepared by the preparation method according to any one of claims 1 - 7.

9. Application of the stamping-activated breathable and stretchable circuit according to claim 8 in wearable electronic products, soft robots, human-machine interfaces, or bioelectronic devices.

Images