Preparation method of hydrogel flexible sensor based on ultrasonic carbon fiber patterning

Abstract

A method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning involves preparing a hydrogel mixture, adding carbon fibers and dispersing them evenly, pouring the mixture into a mold, and then using an externally mounted ultrasonic signal generator to ultrasonically arrange the carbon fibers within the mold. Finally, the mixture is cured to obtain a hydrogel-based composite material with patterned carbon fibers. This invention utilizes the high material compatibility, non-invasiveness, and label-free nature of ultrasonic manipulation technology. The resulting flexible sensor is defect-free internally, exhibits good electrical properties, stable mechanical properties, and strong fatigue resistance, and can achieve different pattern arrangements under certain boundary conditions.

Description

Technical Field

[0001] This invention relates to a technology in the field of flexible sensors, specifically a method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning. Background Technology

[0002] With the development of wearable electronic devices, smart healthcare, and electronic skin, flexible sensors have become a key technology widely researched and applied. They offer advantages such as wide applicability, high sensitivity, flexible and convenient operation, and strong anti-interference capabilities. Currently, flexible sensors based on conductive particle-hydrogel composite materials are attracting widespread attention due to their large tensile strain range, high flexibility, and relatively stable dynamic characteristics. Among various conductive fillers that enhance the electromechanical properties of reinforcing materials (such as carbon fiber, silver powder, and graphene), carbon fiber is increasingly being used as a conductive reinforcing material to improve the sensing performance of existing polymer composite materials due to its high strength, high modulus, low density, good thermal and electrical conductivity, and low cost. Summary of the Invention

[0003] This invention addresses the problem in existing technologies where the unidirectional ratio of carbon fibers after stretching is not high, and some carbon fibers still maintain different angles from the stretching direction, resulting in insignificant improvement in electrical sensing performance. It proposes a method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning. Utilizing the high material compatibility, non-invasiveness, and label-free characteristics of ultrasonic manipulation technology, the resulting flexible sensor exhibits no internal defects, good electrical performance, stable mechanical properties, strong fatigue resistance, and the ability to achieve different pattern arrangements under certain boundary conditions.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a method for preparing a hydrogel flexible sensor based on ultrasonic carbon fiber patterning. The method involves preparing a hydrogel mixture, adding carbon fibers and dispersing them evenly, pouring the mixture into a mold, and using an external ultrasonic signal generator to ultrasonically arrange the carbon fibers within the mold. Finally, the mixture is cured to obtain a hydrogel-based composite material with patterned carbon fibers.

[0006] The hydrogel mixture is a mixture of N,N-dimethylacrylamide (DMAA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), specifically referring to a mixture of DMAA with a photoinitiator, polyethylene glycol, diacrylate, and an aqueous solution of AMPS. The mass ratio of N,N-dimethylacrylamide (DMAA) to 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) is preferably 1:3-3:1, and more preferably 2:1.

[0007] The carbon fiber is preferably 350 micrometers in length and 50 micrometers in diameter.

[0008] The hydrogel mixture is preferably stored in a sealed, light-proof container after thorough mixing.

[0009] The thorough mixing is achieved by, but is not limited to, ultrasonic dispersion, specifically by ultrasonically vibrating the container in a sealed, light-proof container for more than 30 minutes.

[0010] The mass fraction of the carbon fiber and hydrogel mixture is 0.5%-5%. When the mass fraction is less than 0.5%, the carbon fiber concentration is too low, and the improvement in electrosensing performance is not significant; when the mass fraction is greater than 5%, the carbon fiber concentration is too high, and an effective linear arrangement cannot be formed.

[0011] The uniform dispersion is achieved by, but is not limited to, ultrasonic dispersion, specifically by ultrasonic vibration in a sealed, light-proof container for more than 30 minutes.

[0012] The mold is a cuboid structure with a groove without sidewalls on one side of the top surface. The absence of sidewalls allows the piezoelectric transducer to directly contact the solution, resulting in a more significant excitation effect on the particles and enhancing the arrangement effect.

[0013] The sidewall-free groove is preferably 200-500 micrometers deep, 20 millimeters long, and 5 millimeters wide.

[0014] The mold is preferably printed using a photopolymer 3D printer, and is then rinsed and dried with anhydrous ethanol. The piezoelectric transducer is then adhered to the side without sidewall grooves for demolding, and allowed to air dry.

[0015] The ultrasonic signal generator includes a signal generator and a power amplifier.

[0016] The ultrasonic arrangement is achieved by adjusting the frequency of the signal generator to the optimal frequency of the piezoelectric transducer and the amplitude to within 2Vpp; connecting the signal generator to a power amplifier and setting the amplification factor to 8-10 times; and then connecting the power amplifier to the piezoelectric transducer. When the power amplification exceeds 10 times, the piezoelectric transducer will generate heat, which can easily evaporate the water in the solution within the cavity, affecting the preparation effect. When the power amplification is too low, the piezoelectric transducer cannot generate an effective acoustic field to drive particle arrangement.

[0017] The ultrasonic arrangement process lasts for about 10 seconds. If the arrangement time is too long, it will cause phenomena such as degumming and particle agglomeration.

[0018] The curing process refers to curing the sample using a 405nm wavelength UV lamp. The UV lamp is preferably fixed at a distance of 20cm directly above the surface of the groove containing the carbon fiber hydrogel solution, and the irradiation time is 3-10s, preferably 3s-5s.

[0019] This invention relates to the application of the hydrogel-based composite material prepared by the above method, which is encapsulated together with a conductive medium in a waterproof material to form a resistive sensor.

[0020] Technical Effects

[0021] This invention employs ultrasonic methods to disperse and arrange carbon fibers in a hydrogel solution, ensuring the dispersion of the carbon fibers. Compared with existing technologies, this invention can design high-resolution patterns of particle arrangement in the solution according to actual conditions, constructing complex geometric shapes. It features good ultrasonic penetration, high biocompatibility and material compatibility, requires fewer particle raw materials, and has a simple operation process. Under external force, stress or strain changes occur, resulting in significant changes in the material's resistance. It exhibits high stability; even when stretched to five times its original length, the material can recover its original length in a short time, and the resistance value and its change tend to stabilize. It has strong tensile strength, good flexibility and ductility, and retains basic electrical conductivity even after stretching greater than 600%, without showing obvious damage, cracks, or voids. It also demonstrates strong fatigue resistance and good repeatability; after more than 100 repeated stretching cycles, the resistance value tends to stabilize, the material shape changes little, and the sample shows no permanent deformation. Attached Figure Description

[0022] Figure 1 This is a flowchart of the present invention;

[0023] Figure 2 This is a schematic diagram of the ultrasonic wave arrangement;

[0024] Figure 3 This is a diagram showing the effect of ultrasonic arrangement of carbon fiber reinforced hydrogel.

[0025] Figure 4 Schematic diagram of a carbon fiber reinforced hydrogel flexible sensor;

[0026] In the figure: 1. Pure copper wire; 2. VHB tape; 3. Hydrogel-based composite material prepared in this invention.

[0027] Figure 5 Figure showing the fatigue resistance of carbon fiber reinforced hydrogel;

[0028] Figure 6 This is a diagram showing the electrical performance of a carbon fiber reinforced hydrogel flexible sensor. Detailed Implementation

[0029] like Figure 1 As shown in this embodiment, a method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning is provided, comprising:

[0030] Step a: Weigh 5g of N,N-dimethylacrylamide (DMAA), 0.2g of photoinitiator (TPO-L), and 0.02g of polyethylene glycol (400) diacrylate (PEG400DA), add them to a 50ml sealed light-proof bottle, shake well, and sonicate at room temperature for 30 minutes to ensure uniform mixing of all components, thus obtaining solution A; Weigh 5g of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and 5g of purified water, add them to a 50ml sealed light-proof bottle, shake well, and sonicate at room temperature for 30 minutes to ensure uniform mixing of all components, thus obtaining solution B; Mix the prepared solution A and solution B in a 2:1 ratio, and sonicate at room temperature in the dark for 30 minutes to ensure thorough mixing, thus obtaining hydrogel solution C;

[0031] Step b: Weigh carbon fibers with a length of 350 micrometers and add them to hydrogel solution C at a mass concentration of 0 to 10% to obtain mixture D;

[0032] Step c: Place the mixed solution D in a room temperature, dark environment and sonicate for 1 hour to make the carbon fiber evenly distributed in the solution;

[0033] Step d: Design a mold with a length of 20 mm, a width of 5 mm, and a depth of 200 to 500 micrometers (µm) using CAD software, and fabricate the mold using a photopolymerization 3D printer.

[0034] Step e: Immerse the printed mold in anhydrous ethanol solution for a period of time to ensure that there is no resin residue on its surface;

[0035] Step f: Remove the mold and place it in a hot oven at 50°C for 20 minutes to dry it.

[0036] Step g: Apply solder to the positive and negative terminals of the piezoelectric transducer using an electric welding gun, and then solder the wires to the positive and negative terminals; take out the pre-treated mold, apply ultrasonic coupling agent to the sideless surface, and then attach the piezoelectric transducer to the sideless surface.

[0037] Step h: Place the mold with the piezoelectric transducer attached into a fume hood, spray aerosol release agent evenly at a distance of 20cm from the mold, and let it stand to dry.

[0038] Step i: Turn on the signal generator and adjust the parameters to the optimal frequency of the piezoelectric transducer (1.8MHz) and the optimal amplitude of the arrangement (1.8Vpp). Connect the signal generator to the power amplifier and set the amplification factor to 10x. Take out the mold that has been demolded in step h), connect the positive and negative electrodes to the power amplifier, and place it directly below the observation point of the microscope. Take out the solution from step c) and drop it into the groove using a dropper.

[0039] Step j: Adjust the microscope light and focus to the optimal imaging state, turn on the signal generating device, and observe the movement of particles inside the groove through the microscope;

[0040] Step k: After observing the ideal linear arrangement of particles, use an LED ultraviolet UV curing lamp with a wavelength of 365nm to irradiate the solution at a height of about 20cm directly above the mold for 10 to 30 seconds to solidify the solution into a thin sheet. Take out the solidified sheet from the groove to obtain a composite material formed by carbon fibers arranged in hydrogel.

[0041] like Figure 2 As shown, the ultrasonic arrangement utilizes sound waves to drive uniformly dispersed carbon fiber microparticles in the hydrogel solution within the groove, forming an ultrasonic energy field within the designated groove area. Through the acoustic standing wave, the particles in the hydrogel solution are subjected to acoustic radiation force and move in the direction of propagation of the ultrasonic energy field, ultimately maintaining stability in the valley region of the ultrasonic standing wave.

[0042] like Figure 3 The image shows the actual effect after ultrasonic arrangement in this embodiment. According to the inherent frequency of the piezoelectric transducer, the output signal frequency of the signal generator is adjusted to generate stripe patterns with different spacing. During the experiment, piezoelectric transducers with inherent frequencies of 1MHz, 1.8MHz, and 3MHz were used to form patterned arrangements of lines with different spacing.

[0043] like Figure 4 As shown, this embodiment illustrates the application of the carbon fiber reinforced hydrogel flexible material prepared by the above method. The hydrogel-based composite material 3 and the pure copper wire 1, which serves as the conductive medium, are encapsulated together in VHB tape 2 to form a resistive sensor.

[0044] like Figure 5 The figure shows the resistance response of the resistive sensor in this embodiment at different stages when it is repeatedly stretched 100 times without pre-stretching. In the 100 cycles of driving, the sensor maintains a consistent response resistance value. It can be seen that the sensor size does not change and there is no permanent deformation after repeated stretching.

[0045] like Figure 6 The diagram shown is an electrical performance graph of the resistive sensor in this embodiment. Figure 5 It can be seen that the sensitivity coefficient GF (strain gauge sensitivity coefficient), which is the measured value of resistance change for each strain, of the flexible sensor prepared by ultrasonic arrangement of carbon fibers in the hydrogel solution is significantly better than that of pure hydrogel and carbon powder hydrogel solution.

[0046] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning, characterized in that, After the hydrogel mixture is prepared and carbon fibers are added and dispersed evenly, it is poured into a mold and the carbon fibers in the mold are ultrasonically arranged by an external ultrasonic signal generator. Finally, after curing, a hydrogel-based composite material with patterned carbon fibers is obtained. The hydrogel mixture is a mixture of N,N-dimethylacrylamide (DMAA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS); The uniform dispersion is achieved by ultrasonic dispersion. The hydrogel mixture refers to a mixture of DMAA with a photoinitiator, polyethylene glycol (400) diacrylate and an aqueous solution of AMPS, wherein the mass ratio of N,N-dimethylacrylamide (DMAA) to 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) is 1:3-3:

1.

2. The method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning according to claim 1, characterized in that, The mass ratio of N,N-dimethylacrylamide (DMAA) to 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) is 2:

1.

3. The method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning according to claim 1, characterized in that, The carbon fiber has a length of 350 micrometers and a diameter of 50 micrometers.

4. The method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning according to claim 1, characterized in that, The ultrasonic dispersion specifically involves ultrasonically vibrating the material in a sealed, light-proof container for at least 30 minutes.

5. The method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning according to claim 1, characterized in that, The mass fraction of the carbon fiber and hydrogel mixture is 0.5%-5%.

6. The method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning according to claim 1, characterized in that, The mold is a cuboid structure with a groove without sidewalls on one side of the top surface. The absence of sidewalls allows the piezoelectric transducer to directly contact the solution, resulting in a more significant excitation effect on the particles and enhancing the arrangement effect.

7. The method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning according to claim 1, characterized in that, The ultrasonic arrangement involves adjusting the frequency of the signal generator to the optimal frequency of the piezoelectric transducer and adjusting the amplitude to within 2Vpp; connecting the signal generator to a power amplifier and setting the amplification factor to 8-10 times.

8. The method for fabricating a hydrogel flexible sensor based on ultrasonic carbon fiber patterning according to claim 1, characterized in that, The curing process refers to curing the sample using a 405nm wavelength UV lamp.

9. An application of a hydrogel-based composite material prepared by any one of claims 1-8, characterized in that, It is encapsulated together with the conductive medium in a waterproof material to form a resistive sensor.

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