A method for preparing a laser in-situ activated liquid metal composite sensor containing Ag flake

Abstract

This invention relates to the field of flexible materials technology and discloses a method for fabricating a liquid metal composite sensor containing Ag microflakes using laser in-situ activation. The method includes ultrasonically treating liquid metal to obtain liquid metal particles, then thoroughly mixing these particles with a solution of the elastic polymer SEBS and silver microflakes to prepare conductive ink. This ink, combined with laser cutting and laser in-situ activation technology, is then used to fabricate a flexible strain sensor pattern. Finally, the sensor is fabricated through transfer packaging. This sensor, based on the self-healing properties of liquid metal and SEBS, combined with the conductivity of silver, forms a highly sensitive and stable composite material. Furthermore, the conductive network is optimized using laser scanning in-situ activation technology, overcoming the problems of complex fabrication processes and insufficient stability in existing flexible sensors. This flexible wearable sensor can be widely used in the field of human-computer interaction, real-time monitoring of finger bending, joint movements, and other actions, converting mechanical deformation into electrical signals for precise motion capture. This invention features a simple fabrication process, excellent performance, and system stability, and has broad application prospects.

Description

Technical Field

[0001] This invention patent belongs to the field of flexible devices, specifically relating to a method for preparing a liquid metal composite material sensor containing Ag microplates by laser in-situ activation. Background Technology

[0002] In recent years, the rapid development of wireless communication technology, low-power electronics technology, the Internet of Things (IoT), and connected health has greatly promoted innovation in flexible electronics technology. Flexible wearable sensor systems have become a research hotspot due to their application potential in medical monitoring, human-computer interaction, and smart electronic skin. However, the development of flexible electronic devices still faces significant challenges, particularly in simultaneously meeting the high electrical performance requirements of traditional electronic devices and the excellent mechanical properties of flexible substrates, where significant technical bottlenecks exist.

[0003] Liquid metal (LM, referring to gallium-based room-temperature liquid alloys) exhibits significant advantages in flexible electronics due to its unique physicochemical properties. However, existing liquid metal application technologies still face several critical technical challenges. First, the high surface tension caused by the oxide layer on the liquid metal surface makes it difficult to achieve precise patterning using conventional printing or lithography processes. Current mainstream microfluidic infusion technology or ultrasonic dispersion-assembly methods are not only complex and costly, but also prone to instability in pattern quality due to variations in the operational process. Second, dispersed liquid metal particles are typically in an insulating state, requiring post-processing such as laser sintering to activate their conductivity. However, activated liquid metal materials are prone to leakage under external forces, thereby compromising the integrity of the circuit structure. Furthermore, the interface between traditional rigid electronic components and liquid metal flexible circuits is prone to failure under high strain conditions, and the potential leakage risk of liquid metal may also damage the elastic substrate material. Summary of the Invention

[0004] The purpose of this invention is to propose a method for preparing a liquid metal composite material sensor containing Ag microflakes by laser in situ activation. The method involves composing a composite material using liquid metal and SEBS, two self-healing materials, adding silver microflakes to the composite material, and using laser scanning to activate the liquid metal composite material in situ. This method achieves the characteristics of patterned molding, enhanced interfacial bonding, and excellent conductivity under high strain conditions.

[0005] Based on the above concept, the technical solution adopted by this invention is as follows: A method for fabricating a liquid metal composite sensor containing Ag microflakes via laser in situ activation includes the following steps: (1) Preparation of liquid metal Molten gallium and indium are mixed in a certain mass ratio and heated in an oil bath to obtain liquid metal LM; (2) Preparation of liquid metal particles Liquid metal LM was placed in a solution of surfactant diluted with anhydrous ethanol and subjected to water bath sonication to obtain a suspension of liquid metal particles LMNPs; after standing, the upper layer of liquid metal particle LMNPs suspension was removed, centrifuged and the liquid was poured out, anhydrous ethanol was added to wash away excess surfactant, and after centrifugation and washing several times, liquid metal particles LMNPs were obtained. (3) Preparation of SEBS solution SEBS and organic solvent are mixed in a certain mass ratio and then ultrasonicated in a water bath until SEBS is completely dissolved to obtain a SEBS solution. (4) Preparation of LM-SEBS-Ag conductive composite material First, LMNPs are added and mixed with SEBS solution, then silver microplates are added and mixed with LM-SEBS solution. The mixed solution is shaken and magnetically stirred to obtain LM-SEBS-Ag conductive composite material solution. (5) In-situ activation of LM ink LMNPs ink is coated onto a polytetrafluoroethylene substrate. After the solvent has completely evaporated, the ink and substrate are transferred to a glass slide. A wire pattern is cut out on the LM ink using a laser. The pattern is then scanned by a laser to induce the Ag micro-flakes to form intermetallic compounds with Ga in the liquid metal, thereby forming a conductive network, reducing the overall resistance, and changing the wire pattern from non-conductive to conductive. (6) Sensor transfer and packaging The wire pattern is transferred onto the SEBS substrate film and then encapsulated with a layer of SEBS film to obtain a wearable sensor based on liquid metal ink.

[0006] Preferably, in step (1), the mass ratio of gallium to indium is 75.5:24.5, the oil bath heating time is 3 hours, and the oil bath heating conditions are as follows: oil bath heating is carried out on a hot plate at 85°C, and magnetic stirring is turned on while heating, with a rotation speed of 600-800 r / min. Nitrogen gas needs to be continuously introduced during heating.

[0007] Preferably, in step (2), the liquid metal is a gallium-indium alloy, and the volume of liquid metal added is 0.5 mL; the surfactant is ethyl 3-mercaptopropionate, the volume of surfactant solution added is 15 mL, and the surfactant solution concentration is 0.1 mM / L; the water bath ultrasonic time is 30 min, the power is 30%, the working time is 3 s, and the working interval is 2 s; the LMNPs suspension solution is 30 mL; the washing volume of anhydrous ethanol added is 25-30 mL; the centrifugation washing speed is 5000 r / min, the centrifugation washing time is 15 min, and the number of centrifugation washing times is 3-5; the particle size of the prepared LM particles is 0.8-1.2 μm.

[0008] Preferably, in step (3), the organic solvent is a mixed solution of toluene and n-hexane; the mass ratio of SEBS particles to organic solvent in the SEBS solution is SEBS:n-hexane:toluene = 1:1:4; and the duration of ultrasonic mixing in the water bath is 3-6 h.

[0009] Preferably, in step (4), the LMNPs, Ag microplates and SEBS solution are mixed in proportion, which, by weight, includes 1-3 parts of LMNPs, 3-5 parts of SEBS solution and 0.5-4.5 parts of Ag microplates. First, LMNPs are added and mixed with SEBS solution, and then Ag microplates are added and mixed with LM-SEBS solution. The shaking time for each addition is 1-3 min, the magnetic stirring time is 30-50 min, and the magnetic stirring speed is 600 r / min.

[0010] Preferably, in step (5), the coating is performed using an adjustable scraper with a scraper height of 500 μm; the volume of the LM-Ag-SEBS ink is 3-5 mL; the glass slide is 14 cm long, 7 cm wide, and 2 mm thick; the solvent has a complete evaporation time of more than 12 h; the laser is an ultraviolet laser; and the cutting parameters are a speed of 500-1000 mm / s, a power of 50-70%, a frequency of 40-60 kHz, and 10 laser cutting revolutions.

[0011] Preferably, in step (5), the range of the laser scan should completely encompass the sensor pattern, and the parameters of the laser scan are a speed of 500-1000 mm / s, a power of 40-60%, a frequency of 40-60 kHz, and a laser scan number of 1.

[0012] Preferably, in step (6), the SEBS substrate film is prepared by spin coating of SEBS solution, the composition of SEBS solution by weight ratio is SEBS:n-hexane:toluene=1:1:2, and the spin coating speed is 300-500 r / min, and the transfer is carried out in a semi-cured state after 10-15 min; the SEBS film for encapsulation is obtained by spin coating of SEBS solution with composition of SEBS:n-hexane:toluene=1:1:3 or 1:1:4 on silicon wafer and then evaporating, and the evaporation time is more than 12 h.

[0013] Preferably, the constraint sensor value ensures that the original value of each sensor is between the user-defined SENSOR_MIN[i] and SENSOR_MAX[i]; the linear mapping is to convert the sensor values ​​into servo angles (SERVO_MIN[i] to SERVO_MAX[i]) using the map() function.

[0014] Preferably, the sensor data is read by directly calling the analogRead() function without filtering, and the voltage divider circuit of the sensor must ensure that the voltage is within the range of 0-5V. The voltage divider resistor used here is 20Ω. The formula for mapping the sensor value to the servo angle is: servo angle = (current sensor value - SENSOR_MIN[i]) / (SENSOR_MAX[i] - SENSOR_MIN[i]) * (SERVO_MAX[i] - SERVO_MIN[i]) + SERVO_MIN[i]. The calculated target angle is written to the corresponding servo by directly setting the angle without a smooth transition. The original sensor value and the mapped servo angle are printed in the following format: Sensors: value1 value2 value3 value4 value5 | Angles: angle1 angle2 angle3 angle4 angle5.

[0015] The beneficial effects of this invention are as follows: 1. The design provided in this invention adds a certain proportion of Ag microplates when mixing LM and SEBS solutions. This reduces the initial resistance of the sensor and significantly improves its sensitivity during stretching. Furthermore, the SEBS in the ink encapsulates the in-situ activated liquid metal, protecting the integrity of the pattern. Compared to sensors prepared with LM-SEBS ink, this invention effectively addresses the issues of low resistance change rate and poor sensitivity during stretching while maintaining high stretchability.

[0016] 2. The design provided by this invention prepares a flexible wearable sensor by mixing liquid metal particles and SEBS solution to form ink, followed by scraping, laser cutting, and laser activation of the ink. The operation process is relatively simple. Scraping ensures uniform ink distribution, while laser cutting enables precise patterning, improving preparation accuracy and ensuring good pattern formation. This avoids the instability in sensor pattern formation caused by differences in operator skill in flexible electronic printing, as well as the instability in the activation effect of the liquid metal within the sensor due to differences in operator skill during press activation.

[0017] 3. The design provided by this invention utilizes the synergistic effect of liquid metal and SEBS dual self-healing materials to enable the activated sensor pattern to exhibit excellent tensile strength and conductivity. The resistance remains stable even under strains up to 100%, allowing it to adapt well to various deformation requirements. Furthermore, the excellent self-healing capability of SEBS facilitates pattern transfer and encapsulation, and provides excellent durability after encapsulation. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the patterning and activation methods for liquid metal ink in this invention; Figure 2 The relationship between resistance and tensile strength of the LM-Ag-SEBS strain sensor in this invention under different ratios of LMPs to Ag microplates; Figure 3 This is a graph showing the resistance change rate of an LM-Ag-SEBS strain sensor printed with ink in a mass ratio of 4:1 of LMPs to Ag in this invention under different tensile strains. Figure 4 This is a schematic diagram of the voltage divider of the flexible sensor in this invention; Figure 5 This is a flowchart of the Arduino NANO program implementation in this invention; Figure 6 This is a graph showing the rate of change of resistance of the strain sensor in Comparative Example 1 of this invention under different tensile strains. Detailed Implementation

[0019] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0020] like Figures 1 to 6As shown, this invention provides a method for preparing a liquid metal composite material sensor containing Ag microsheets by laser in-situ activation. First, liquid metal is ultrasonically treated to obtain liquid metal particles. Then, these particles are thoroughly mixed with a solution of elastic polymer SEBS and Ag flakes to prepare an LM-SEBS-Ag conductive composite material solution. Wearable sensors are then prepared using this ink in combination with laser cutting and laser in-situ activation technology.

[0021] Example 1 In this embodiment, the above method was used to heat 100g of gallium and 32.5g of indium in an oil bath at 85°C, with nitrogen continuously introduced during heating, for 3 hours to obtain gallium-indium liquid metal. 0.5mL of LM was added to 15mL of 0.1mM / L 3... LM particle suspension was obtained by sonicating a solution of ethyl mercaptopropionate in ethanol at 30% power for 20 min. 30 mL of the LM particle suspension was centrifuged at 5000 rpm for 10 min to obtain LM particle precipitate. The LM particle precipitate was mixed with 30 mL of anhydrous ethanol by shaking and allowed to stand for 5 min. The supernatant was then centrifuged and washed three times to obtain LM particles. 5 g of SEBS particles, 5 g of n-hexane, and 20 g of toluene solution were mixed and sonicated in a water bath for 3 h until the SEBS particles were completely dissolved, yielding the SEBS solution. 1g of LM particles, 0.5g of Ag micro-flakes, and 3g of SEBS solution were mixed and shaken for 3 minutes, followed by magnetic stirring for at least 30 minutes to obtain LM ink. The LM ink was then coated onto a polytetrafluoroethylene substrate using a doctor blade coater to a thickness of 500μm. The substrate was placed in a fume hood for at least 12 hours to allow the organic solvents to evaporate. The sensor pattern was then cut using an ultraviolet laser with a speed of 500 mm / s, a power of 50%, and a frequency of 40 kHz. The cut sensor pattern was then scanned and activated using laser scanning parameters of 500 mm / s speed, 40% power, 40 kHz frequency, and 1 laser scan cycle. Finally, the sensor was spin-coated onto a silicon wafer using a SEBS solution with a composition of SEBS:n-hexane:toluene = 1:1:3. After evaporation for at least 12 hours, the wafer was encapsulated to obtain the sensor.

[0022] Based on the packaged sensor, connect one end of the sensor to the power supply and a voltage divider resistor (20Ω), and the other end to GND. Connect the power supply and voltage divider resistor end to the signal input terminal of the Arduino NANO. Connect the output pin of the Arduino NANO to the servo pin of the robotic arm. The Arduino NANO's glove control mechanism includes multiple modules such as user-defined parameter area, hardware pin definition, global variable and object initialization, initialization settings, main loop, and user-defined functions. Initialization settings start serial communication (baud rate 9600) for debugging output, initialize 5 servo objects, bind them to designated pins (D2-D6), and set the initial angle to SERVO_MIN. Wait 1 second to ensure that the servo reset is complete. In the main loop stage, the analog value of the flexible sensor, the constraint sensor value, linear mapping, and driving servo motion are calculated sequentially, and the calculation results are written to the corresponding servo. The serial port debugging output includes printing the original sensor value and the mapped servo angle.

[0023] The changes in resistance of the activated sensor after continuous stretching at 20%, 40%, 60%, 80%, and 100% showed that the resistance change rate reached 180% when stretched to 100%. The incorporation of Ag microplates significantly reduced the initial resistance of the sensor and greatly improved its sensitivity.

[0024] Example 2 Everything else is the same as in Example 1, except that: 1.5g of LM particles, 2.5g of Ag micro-flakes, and 9g of SEBS solution were mixed and shaken for 3 minutes, followed by magnetic stirring for more than 40 minutes to obtain LM ink. The sensor pattern was cut using an ultraviolet laser with a speed of 750 mm / s, a power of 60%, and a frequency of 50 kHz. The cut sensor pattern was then scanned and activated. The laser scanning parameters were a speed of 750 mm / s, a power of 50%, a frequency of 50 kHz, and a laser scanning circle of 1.

[0025] Example 3 Everything else is the same as in Example 1, except that: 3g of LM particles, 4.5g of Ag micro-flakes, and 15g of SEBS solution were mixed and shaken for 3 minutes, followed by magnetic stirring for more than 40 minutes to obtain LM ink. The sensor pattern was cut using an ultraviolet laser with a speed of 1000 mm / s, a power of 70%, and a frequency of 60 kHz. The cut sensor pattern was then scanned and activated. The laser scanning parameters were a speed of 1000 mm / s, a power of 60%, a frequency of 60 kHz, and a laser scanning circle of 1.

[0026] Comparative Example 1 Everything else is the same as in Example 1, except that: In LM-SEBS, no Ag microplates are added. The sensor pattern is cut using an ultraviolet laser with a speed of 500 mm / s, a power of 50%, and a frequency of 40 kHz. The cut sensor pattern is then scanned and activated. The laser scanning parameters are a speed of 500 mm / s, a power of 40%, a frequency of 40 kHz, and a laser scanning circle of 1.

[0027] Figure 2 This invention presents wire samples prepared with LMPs to Ag ratios of 5:1, 4:1, 3:1, 2:1, and without Ag microfibers, and measures the relationship between their resistance and tensile strength. The initial resistances for LMPs to Ag microfiber ratios of 5:1, 4:1, 3:1, 2:1, and without Ag are 500.3, 30.8, 10.4, 6.4, and 3500 ohms, respectively. The samples with ratios of 5:1, 4:1, 3:1, and 2:1 show megaohm-level resistances when stretched to 100%, 200%, 250%, and 300%, respectively. Decreasing the LMPs to Ag microfiber ratio and increasing the number of Ag microfibers results in a lower initial resistance for the LM-Ag-SEBS wire and a lower rate of resistance change (curve slope) within the 100% stretch range. The addition of Ag microfibers effectively improves the sensor's low resistance change rate and poor sensitivity during stretching.

[0028] Figure 6 The changes in resistance of the strain sensor after continuous stretching at 20%, 40%, 60%, 80%, and 100% in Example 1 are compared. When the strain sensor is stretched to 100%, the resistance change rate is less than 7%; while Figure 3 The incorporation of Ag microplates results in a resistance change rate of 180% when stretched to 100%, which greatly improves the sensitivity of the sensor.

[0029] However, as is known from common technical knowledge, the present invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of the present invention or its equivalents are included in the present invention.

Claims

1. A method for preparing a liquid metal composite sensor containing Ag microflakes by laser in-situ activation, characterized in that, The method for preparing the liquid metal composite material includes the following steps: (1) Preparation of liquid metal Molten gallium and indium are mixed in a certain mass ratio and heated in an oil bath to obtain liquid metal LM; (2) Preparation of liquid metal particles Liquid metal LM was placed in a solution of surfactant diluted with anhydrous ethanol and subjected to water bath sonication to obtain a suspension of liquid metal particles LMNPs; after standing, the upper layer of liquid metal particle LMNPs suspension was removed, centrifuged and the liquid was poured out, anhydrous ethanol was added to wash away excess surfactant, and after centrifugation and washing several times, liquid metal particles LMNPs were obtained. (3) Preparation of SEBS solution SEBS and organic solvent are mixed in a certain mass ratio and then ultrasonicated in a water bath until SEBS is completely dissolved to obtain a SEBS solution. (4) Preparation of LM-SEBS-Ag conductive composite material First, LMNPs are added and mixed with SEBS solution, then silver microplates are added and mixed with LM-SEBS solution. The mixed solution is shaken and magnetically stirred to obtain LM-SEBS-Ag conductive composite material solution. (5) In-situ activation of LM ink LMNPs ink is coated onto a polytetrafluoroethylene substrate. After the solvent has completely evaporated, the ink and substrate are transferred to a glass slide. A wire pattern is cut out on the LM ink using a laser. The pattern is then scanned by a laser to induce Ag micro-flakes to form intermetallic compounds with Ga in the liquid metal, forming a conductive network, reducing the overall resistance, and the wire pattern changes from non-conductive to conductive. (6) Sensor transfer and packaging The wire pattern is transferred onto the SEBS substrate film and then encapsulated with a layer of SEBS film to obtain a wearable sensor based on liquid metal ink.

2. The method for preparing a laser-activated liquid metal composite material sensor containing Ag microsheets according to claim 1, characterized in that, In step (1), the mass ratio of gallium to indium is 75.5:24.5; the oil bath heating time is 3 hours.

3. The method for preparing a laser-activated liquid metal composite material sensor containing Ag microsheets according to claim 1, characterized in that, In step (2), the liquid metal is a gallium-indium alloy; the surfactant is ethyl 3-mercaptopropionate, the added volume of the surfactant solution is 15 mL, and the concentration of the surfactant solution is 0.1 mM / L; the water bath ultrasonication time is 20 min; the LM particle suspension solution is 30 mL; the washing volume of anhydrous ethanol is 15-200 mL; the centrifugation washing speed is 5000 r / min, the centrifugation washing time is 10 min, and the number of centrifugation washing cycles is 3-5 times; the particle size of the prepared LM particles is 0.8-1.2 μm.

4. The method for preparing a laser-activated liquid metal composite material sensor containing Ag microsheets according to claim 1, characterized in that, In step (3), the organic solvent is a mixed solution of toluene and n-hexane; the mass ratio of SEBS, n-hexane and toluene in the SEBS solution is SEBS:n-hexane:toluene = 1:1:4 or 1:1:3; the duration of ultrasonic mixing in the water bath is 3-6 h.

5. The method for preparing a laser-activated liquid metal composite material sensor containing Ag microsheets according to claim 1, characterized in that, In step (4), the LMNPs, Ag microplates and SEBS solution, by weight, include 1-3 parts of LMNPs, 3-15 parts of SEBS solution and 0.5-4.5 parts of Ag microplates. The shaking time for each mixing is 1-3 min, the magnetic stirring time is 30-50 min, and the magnetic stirring speed is 600 r / min.

6. The method for preparing a laser-activated liquid metal composite material sensor containing Ag microflakes according to claim 1, characterized in that, In step (5), the coating is performed using an adjustable scraper with a scraper height of 500 μm; the solvent evaporation time is more than 12 h; the laser is an ultraviolet laser; the laser cutting parameters are a speed of 500-1000 mm / s, a power of 50%-70%, a frequency of 40-60 kHz, and 10 laser cutting circles; the laser scanning range should completely include the wire pattern, and the laser scanning parameters are a speed of 500-1000 mm / s, a power of 40-60%, a frequency of 40-60 kHz, and 1 laser scanning circle; the intermetallic compound is Ag3Ga.

7. The method for preparing a laser-activated liquid metal composite material sensor containing Ag microsheets according to claim 1, characterized in that, In step (6), the SEBS substrate film is prepared by spin coating of SEBS solution; the SEBS film for encapsulation is obtained by spin coating of SEBS solution with composition SEBS:n-hexane:toluene = 1:1:3 or 1:1:4 on a silicon wafer and then evaporating the solution, and the evaporation time is more than 12 hours.

8. An application of a method for fabricating a liquid metal composite sensor containing Ag microplates using laser in-situ activation, characterized in that, The liquid metal composite material sensor containing Ag microchips as described in claim 1 is installed in the signal circuit. One end of the sensor is connected to the power supply and the voltage divider resistor, and the other end is connected to GND. The end connected to the power supply and the voltage divider resistor is connected to the signal input terminal of the Arduino NANO. The output pin of the Arduino NANO is connected to the servo pin of the robot arm.

9. The application of the method for preparing a laser-activated liquid metal composite material sensor containing Ag microplates according to claim 8, characterized in that, The application is based on the Arduino Nano glove control robot program. The code integrates core logic such as sensor data processing and servo mapping control, including multiple modules such as user global variables and object initialization, initialization settings, main loop, and user-defined functions.

10. The application of the method for preparing a laser-activated liquid metal composite material sensor containing Ag microsheets according to claim 8, characterized in that, The initialization settings include starting serial communication at a baud rate of 9600, initializing 5 servo objects, binding them to designated pins D2-D6, and setting the initial angle to SERVO_MIN; waiting for 1 second to ensure that the servo reset is complete; The main loop phase includes five parts: reading sensor data, mapping sensor values ​​to servo angles, driving servo motion, serial port debugging output, and loop delay. Reading sensor data includes sequentially reading the analog values ​​of five flexible sensors and storing them in the array sensorValues[]. Mapping sensor values ​​to servo angles includes constraining sensor values ​​and linear mapping. Driving servo motion includes writing the calculated target angle to the corresponding servo using servos[i].write(). Serial port debugging output includes printing the original sensor values ​​and the mapped servo angles.

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