Liquid metal acoustic sensing fiber and preparation method thereof

Abstract

The invention discloses a liquid metal acoustic sensing fiber and a preparation method thereof.The sensing fiber is of a skin-core structure and comprises a skin layer and a core layer, the skin layer comprises a polyurethane elastomer, and the core layer comprises a conductive composite layer composed of liquid metal, nano-silver, carbon nanotubes and the polyurethane elastomer; wherein the conductive particles are liquid metal, nano silver and carbon nanotubes. The skin-core structure acoustic sensing fiber is prepared through the liquid metal, nano-silver and carbon nanotube composite conductive material and a coaxial wet spinning process, the skin-core structure acoustic sensing fiber is excellent in conductivity, stretchable, good in acoustic response performance and sensitive to sound waves of different frequencies, the preparation process is simple, large-scale production is easy, the cost is low, and the material is resistant to electromagnetic interference and high in environmental adaptability.

Description

Technical Field

[0001] This invention relates to a strain sensing fiber processing technology, and more particularly to a liquid metal acoustic sensing fiber and its preparation method. Background Technology

[0002] The development of flexible wearable electronic devices has experienced exponential growth due to their immense application potential in healthcare, human-machine interfaces, and motion tracking. Fiber-based electronics can be easily woven into textiles or attached to the skin for portable devices. The mechanical properties of fibers, such as flexibility and stretchability, play a crucial role in ensuring a seamless integration of conductive fibers with bio-interfaces. However, traditional conductive metal fibers are incompatible with flexible bio-interfaces and are prone to fatigue fracture, making the fabrication of high-performance fiber-based electronic devices with excellent conductivity and high stretchability a challenge. To circumvent this challenge, much research has focused on coating flexible, stretchable fibers with conductive fillers, such as carbon nanotubes (CNTs), graphene, and silver nanowires / particles, to impart electrical properties. Nevertheless, fibers coated with solid conductive fillers exhibit a significant increase in resistivity with increasing strain and possess a high measurement coefficient.

[0003] Recently, gallium-based liquid metals have emerged as a new generation of flexible electronic materials. Due to their inherent metallic and liquid properties, such as high conductivity, fluidity, and good environmental stability, they are widely used in the electronics field, including printed electronics, microfluidic electronics, wireless strain sensors, and wearable bioelectronics. More importantly, unlike mercury, a well-known toxic heavy metal, gallium-based liquid metals are not only non-toxic to living organisms but also possess excellent biocompatibility. Direct contact with gallium-based liquid metals does not trigger any immune response or cause any harm to living organisms. Therefore, gallium-based liquid metals are potential candidates for manufacturing high-performance flexible electronic products. Consequently, there is a need for a liquid metal acoustic sensing fiber and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing liquid metal acoustic sensing fibers.

[0005] To achieve the above objectives, the present invention is implemented according to the following technical solution:

[0006] The sensing fiber of the present invention has a core-skin structure, comprising a skin layer and a core layer. The skin layer comprises a polyurethane elastomer, and the core layer comprises a conductive composite layer composed of liquid metal, silver nanoparticles, carbon nanotubes, and polyurethane elastomer, wherein the conductive particles are liquid metal, silver nanoparticles, and carbon nanotubes.

[0007] The mass ratio of conductive particles to polyurethane elastomer in the core layer is 82:18 to 92:8, and the acoustic sensing fiber is prepared by coaxial wet spinning.

[0008] Further, the liquid metal is a gallium-indium alloy or a gallium-indium-tin alloy; the silver nanowires are silver nanowires, silver nanosheets, or silver nanoparticles; the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes; the mass ratio of the silver nanowires to the carbon nanotubes is 20:1 to 60:1, and the mass ratio of the liquid metal to the silver nanowires / carbon nanotubes is 2:1 to 7:1.

[0009] A method for preparing liquid metal acoustic sensing fibers includes the following steps:

[0010] Preparation of skin spinning solution: Polyurethane elastomer and N,N-dimethylformamide are mixed at a mass fraction of 15%-25% and magnetically stirred for 12 hours to obtain skin spinning solution.

[0011] Core spinning solution preparation:

[0012] ① Liquid metal is added to acetone solution and sonicated for 20 hours to obtain a liquid metal suspension;

[0013] ② Add silver nanoparticles and carbon nanotubes to an acetone solution and sonicate for 2 hours to obtain a silver nanoparticle / carbon nanotube solution.

[0014] The mass ratio of nano-silver to carbon nanotubes is 20:1 to 60:1;

[0015] ③ Mix the liquid metal suspension with the nano-silver / carbon nanotube solution at a mass ratio of 2:1 to 7:1, centrifuge to collect the precipitate, and obtain the conductive component;

[0016] ④ Mix the conductive component with a polyurethane elastomer / N,N-dimethylformamide solution with a solid content of 14%-24%, grind for 30 minutes to obtain the core spinning solution, wherein the mass ratio of the conductive component to the polyurethane elastomer is 82:18 to 92:8.

[0017] Preparation of core-sheath structure fiber: Using a coaxial spinning needle, the core-sheath spinning solution is injected into a coagulation solution with a mass ratio of 5% N,N-dimethylformamide. After being drawn at a draw ratio of 1 to 6, the fiber is further coagulated in a coagulation bath for 24 hours and finally dried at 80°C for 15 minutes to obtain the sensing fiber.

[0018] Furthermore, when manufacturing core-sheath structure fibers, the diameter of the core layer is controlled between 0.5 mm and 1.3 mm, and the diameter of the sheath layer is between 1.5 mm and 2.3 mm.

[0019] Furthermore, the draw ratio of the drawing machine is 1 to 6, and the coagulation bath is deionized water, or a mixed solution of deionized water and N,N-dimethylformamide, wherein the mass ratio of deionized water to N,N-dimethylformamide in the mixed solution is 9.5:0.5 to 6:4.

[0020] Furthermore, the spinning solution needs to be allowed to stand for 20 minutes before spinning to eliminate air bubbles.

[0021] Furthermore, the diameter of the liquid metal particles is approximately 20-100 micrometers, and the diameter of the silver particles is approximately 2-10 micrometers.

[0022] The beneficial effects of this invention are:

[0023] This invention utilizes a composite conductive material of liquid metal, nano-silver, and carbon nanotubes, along with a coaxial wet spinning process, to produce a core-sheath structure acoustic sensing fiber. This fiber exhibits excellent conductivity, stretchability, good acoustic response performance, and sensitivity to sound waves of different frequencies. The fabrication process is simple, easily scalable, and low-cost. Furthermore, the material is resistant to electromagnetic interference and exhibits strong environmental adaptability. Attached Figure Description

[0024] Figure 1 This is a schematic SEM image of the acoustic sensing fiber of the present invention;

[0025] Figure 2 This is a schematic diagram of the EDS results of the acoustic sensing fiber of the present invention;

[0026] Figure 3 This is a SEM schematic diagram of the acoustic sensing fiber conductive layer of the present invention;

[0027] Figure 4 This is a schematic diagram of the stress-strain curve of the acoustic sensing fiber of the present invention;

[0028] Figure 5 The pressure response curve of the acoustic sensing fiber of this invention. Figure 6 This is a schematic diagram illustrating the response of the acoustic sensing fiber of the present invention to the pronunciation of different words;

[0029] Figure 7 This is a schematic diagram of the acoustic sensing fiber of the present invention responding to the same speech multiple times;

[0030] Figure 8 This is a schematic diagram of the acoustic sensing fiber of the present invention responding to the same sentence multiple times;

[0031] Figure 9 This is a schematic diagram of the resistive response of the acoustic sensing fiber to different sound pressure levels at fixed frequencies of 110, 165 and 220 Hz according to the present invention.

[0032] Figure 10This is a schematic diagram of the response time of the acoustic sensing fiber of the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention.

[0034] like Figure 1 As shown, the present invention includes the following steps:

[0035] In Example 1

[0036] Weigh 47.2g of polyurethane elastomer (TPU) particles and 200ml of N,N-dimethylformamide (DMF), mix them at a solid content ratio of 1:4, and stir magnetically for 12h to obtain a skin spinning solution with a mass fraction of 25%.

[0037] Liquid metal treatment: Weigh 5.6g of gallium-indium alloy and add it to an ethanol solution. Sonicate for 20 hours to obtain a blackish-gray suspension.

[0038] Nano-silver / carbon nanotube treatment: Weigh a total of 2.6g of silver nanoparticles and multi-walled carbon nanotubes (2.5g of silver nanoparticles and 0.1g of carbon nanotubes) at a mass ratio of 25:1, add ethanol solution and sonicate for 2 hours to obtain a black suspension.

[0039] Mixing and centrifugation: Liquid metal and silver nanotubes / carbon nanotubes were mixed at a mass ratio of 4:1, and the precipitate was collected by centrifugation to obtain the conductive component (liquid metal particles 20 μm, silver particles 2 μm).

[0040] Spinning solution preparation: Add a TPU / DMF solution with a solid content of 18% according to the ratio of conductive component: TPU dry weight = 88:12, grind for 30 minutes to obtain the core layer spinning solution.

[0041] Using G15 / G12 needles (core diameter 1.0 mm, skin diameter 2.0 mm), the spinning solution was allowed to stand for 20 minutes to defoam.

[0042] The spinning solution was extruded into a 5% DMF coagulation bath with a draw ratio of 3. After coagulation in a deionized water coagulation bath for 24 hours, it was dried at 80°C for 15 minutes.

[0043] In Example 2

[0044] Weigh 35g of TPU granules and 140ml of DMF, mix them at a solid content ratio of 1:4, and stir for 12h to obtain a skin spinning solution with a mass fraction of 20%.

[0045] Liquid metal treatment: Weigh 7g of gallium indium tin alloy and add it to an ethanol solution. Sonicate for 20 hours to obtain a blackish-gray suspension.

[0046] Nanosilver / carbon nanotube treatment: Weigh out a total of 3.28g of silver nanowires and single-walled carbon nanotubes (3.2g of silver nanowires and 0.08g of carbon nanotubes) at a mass ratio of 40:1, and sonicate for 2 hours to obtain a black suspension.

[0047] Mixing and centrifugation: Liquid metal and nano-silver / carbon nanotubes were mixed at a mass ratio of 6:1, and the precipitate was collected by centrifugation.

[0048] Spinning solution preparation: Add a 24% solid content TPU / DMF solution according to the ratio of conductive component: TPU dry weight = 92:8, and grind for 30 minutes.

[0049] The needle core diameter is 0.5mm, the skin diameter is 1.5mm, the draw ratio is set to 1, and the rest of the process is the same as in Case 1.

[0050] In Example 3

[0051] Weigh 28.32g of TPU granules and 113.28ml of DMF, mix them at a solid content ratio of 1:4 to prepare a 20% (w / w) skin spinning solution.

[0052] Liquid metal treatment: Weigh 6g of gallium-indium alloy and add it to an ethanol solution, then sonicate for 20 hours.

[0053] Nanosilver / carbon nanotube treatment: Weigh out a total of 3g of silver nanosheets and multi-walled carbon nanotubes (2.9g of silver nanosheets and 0.1g of carbon nanotubes) at a mass ratio of 30:1, and sonicate for 2 hours.

[0054] Mixing and centrifugation: Liquid metal and nano-silver / carbon nanotubes were mixed at a mass ratio of 5:1, and the precipitate was collected by centrifugation.

[0055] Spinning solution preparation: Add a 20% solid content TPU / DMF solution according to the ratio of conductive component: TPU dry weight = 90:10, and grind for 30 minutes.

[0056] Using G15 / G12 needles, with a draw ratio of 4, the coagulation bath treatment and drying process are the same as in Case 1.

[0057] Implementation Case 1 enhances pressure sensitivity by increasing the proportion of carbon nanotubes and utilizing their one-dimensional conductive network, making it suitable for micro-pressure monitoring (such as pulse); Implementation Case 2 increases the proportion of liquid metal and reduces the draw ratio to strengthen the continuity of conductive components, making it suitable for acoustic scenarios requiring high conductivity (such as high-frequency sound wave detection); Implementation Case 3 uses a moderate parameter ratio to balance mechanical properties and acoustic response, making it suitable for general-purpose wearable sensing devices.

[0058] As shown in Table 1, the effects of different conductive component ratios on fiber mechanics and pressure response were tested on the elongation at break, the relative change rate of resistance (RR%) under 0.5N pressure, and the mass ratio of nano-silver to carbon nanotubes in the core layer (Group A 20:1, Group B 60:1). Other conditions (liquid metal to nano-silver / carbon nanotube ratio 5:1, conductive component to TPU ratio 88:12) were kept consistent.

[0059] Table 1 Comparison of the Influence of Fiber Mechanics and Pressure Response

[0060]

[0061] In terms of mechanical properties, Group B (high proportion of nano-silver) has a slightly higher elongation at break because the nano-silver particles are more likely to fill the pores of the TPU matrix, enhancing flexibility. Group A (high proportion of carbon nanotubes) has a higher pressure response sensitivity due to the one-dimensional network structure of carbon nanotubes. Group A has a 47.9% higher RR% than Group B under 0.5N pressure, proving that the continuity of the conductive network of carbon nanotubes has a greater impact on pressure sensitivity, while the increased nano-silver content is more beneficial to tensile properties.

[0062] As shown in Table 2, the peak value of the relative rate of change of resistance (RR%), response time (the time from the triggering of the sound wave to the peak value of RR%), and acoustic response comparison variables at different sound frequencies and sound pressure levels are tested: sound wave frequency (110Hz, 220Hz) and sound pressure level (85dB, 95dB). The resistive response of the test fiber to the standard speech "better" is also tested.

[0063] Table 2 Comparison of acoustic response at different audio frequencies and sound pressure levels

[0064]

[0065] Frequency sensitivity: The peak RR% at 220Hz is about 34.8% higher than that at 110Hz (under the same 85dB condition), verifying the conclusion in the disclosure that "the mid-to-high frequency response is more significant". This is attributed to the fact that liquid metal particles are more easily deformed under high-frequency vibration, optimizing the contact of the conductive path. For every 10dB increase in sound pressure level, the peak RR% increases by an average of 73.9%, showing an approximately linear relationship. The sensitivity is about 0.0074RR% / dB, which can be used for quantitative monitoring of noise intensity. The standard deviation of repeated tests is <0.003, proving that the fiber has reliable signal repeatability under different acoustic environments.

[0066] like Figure 1 The image shown is a scanning electron microscope (SEM) image with a resolution down to the micrometer level, used to observe the surface morphology and core-sheath structure of the fiber. The fiber exhibits a distinct core-sheath composite structure, with the sheath uniformly enveloping the core layer, and the interface is clear and free of obvious defects.

[0067] The surface morphology shows that the skin layer is dense and free of cracks or pores, indicating that the wet spinning process results in good TPU skin layer formation.

[0068] The core layer contains granular or fibrous distributions of conductive components (liquid metal, nano-silver, carbon nanotubes), forming a continuous conductive network.

[0069] like Figure 2 As shown, energy-dispersive X-ray spectroscopy (EDS) is used for elemental composition analysis. Figures (a)-(d) correspond to:

[0070] (a) C element comes from carbon nanotubes, proving the existence of carbon nanotubes in the core layer; (b) Ga element comes from liquid metal (gallium indium alloy or gallium indium tin alloy); (c) In element is the same as above, a constituent element of liquid metal; (d) Ag element comes from nano-silver (silver nanowires / sheets / particles), and the uniformity of element distribution can indirectly reflect the mixing effect of each component in the core layer spinning solution.

[0071] like Figure 3 The image shows a high-magnification SEM image of the conductive components in the core conductive layer. The liquid metal particles (approximately 20 micrometers in diameter) are irregularly spherical and uniformly dispersed in the matrix. The silver nanoparticles (approximately 2 micrometers in diameter) and carbon nanotubes intertwine to form a network, filling the gaps between the liquid metal particles and creating conductive pathways. The polyurethane elastomer (TPU) serves as the matrix, encapsulating the conductive components and ensuring structural flexibility. The porous network structure of the conductive layer is key to the high conductivity and stretchability of the fiber. The synergistic effect of the liquid metal and nanomaterials enhances the strain response capability.

[0072] like Figure 4 As shown, stress increases linearly with strain until the breaking point, and the breaking elongation can reach 500%, far exceeding that of traditional sensing fibers. The slope of the curve reflects the elastic modulus of the fiber. A low slope indicates that the material is soft and suitable for flexible wearable devices. The high breaking elongation and flexibility make the fiber suitable for dynamic monitoring (such as human movement) and it is not easily damaged by stretching.

[0073] like Figure 5 As shown, pressures ranging from 0.1 N to 10 N were applied during the test, and the relative rate of change of resistance (RR%) was recorded over time. Pressure was positively correlated with RR%, and a pressure of 0.1 N could cause a significant change in resistance, demonstrating that the fiber is sensitive to micro-pressure.

[0074] Short response time (reference) Figure 10 The fiber exhibits a millisecond-level response and rapid resistance recovery after pressure unloading, demonstrating good repeatability. This indicates that the low pressure response threshold allows the fiber to be used for monitoring physiological signals such as pulse and respiration.

[0075] like Figure 6As shown, the test scenario collected the resistance changes when the words "because", "peach", and "apple" were pronounced. The horizontal axis represents time (s) and the vertical axis represents RR%. Different words have different pronunciation frequencies and amplitudes, resulting in different peak positions, widths, and amplitudes of the RR% waveform. The fiber can distinguish the spectral features of different speech sounds. For example, the high-frequency components of "peach" may correspond to higher RR% fluctuations, proving that the fiber can be used as an acoustic sensor for speech recognition or environmental noise monitoring and has frequency resolution capabilities.

[0076] like Figure 7 As shown, the curve characteristics of the three repeated tests on the same speech segment indicate that the RR% waveforms of the three cycles highly overlap, with minimal errors in peak position and amplitude, and no obvious signal attenuation or drift, indicating that the fiber performance is stable under repetitive sound stimulation.

[0077] like Figure 8 As shown, the test content was as follows: the sentence "Better speech, better teach." was pronounced multiple times, and the RR% change over time was recorded. The RR% waveform corresponding to each pronunciation was consistent with the semantic rhythm. For example, the resistance returned to the baseline at the word intervals, and the response curve of complex sentences still maintained repeatability, proving the fiber's ability to dynamically capture continuous sound waves.

[0078] like Figure 9 As shown, the test parameters were fixed at frequencies of 110Hz, 165Hz, and 220Hz, and the sound pressure level (dB) varied from 80 to 100dB. The RR% was recorded. The results show that at the same frequency, RR% increases with the increase of sound pressure level, showing an approximately linear relationship. The sensitivity is about 0.01-0.02RR% / dB. The response amplitude varies at different frequencies, and the change in RR% is more significant at 220Hz, indicating that the fiber is more sensitive to mid-to-high frequency sound waves.

[0079] like Figure 10 As shown, the time from acoustic wave triggering to RR% reaching its peak (response time) is approximately 88-93ms (marked as "88ms" and "93ms" in the figure). After pressure is unloaded, RR% quickly recovers to the baseline, and the recovery time is close to the response time, proving that the signal attenuation is extremely short. The rising edge of the curve is steep with no obvious delay, indicating that the fiber responds quickly to the acoustic wave. The falling edge is smooth with no tailing phenomenon, indicating that the conductive network can quickly recover to its initial state after the acoustic wave disappears.

[0080] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

[0081] The contents of this specification should not be construed as limiting the invention.

Claims

1. A liquid metal acoustic sensing fiber, characterized in that, The sensing fiber has a core-skin structure, including a skin layer and a core layer. The skin layer includes a polyurethane elastomer, and the core layer includes a conductive composite layer composed of liquid metal, silver nanoparticles, carbon nanotubes, and polyurethane elastomer. The conductive particles are liquid metal, silver nanoparticles, and carbon nanotubes. The mass ratio of conductive particles to polyurethane elastomer in the core layer is 82:18 to 92:8, and the acoustic sensing fiber is prepared by coaxial wet spinning.

2. The liquid metal acoustic sensing fiber according to claim 1, characterized in that, The liquid metal is a gallium-indium alloy or a gallium-indium-tin alloy; the silver nanowires are silver nanowires, silver nanosheets, or silver nanoparticles; the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes; the mass ratio of the silver nanowires to the carbon nanotubes is 20:1 to 60:1, and the mass ratio of the liquid metal to the silver nanowires / carbon nanotubes is 2:1 to 7:

1.

3. A method for preparing liquid metal acoustic sensing fibers as described in any one of claims 1-2, characterized in that, Includes the following steps: Preparation of skin spinning solution: Polyurethane elastomer and N,N-dimethylformamide are mixed at a mass fraction of 15%-25% and magnetically stirred for 12 hours to obtain skin spinning solution. Core spinning solution preparation: ① Liquid metal is added to acetone solution and sonicated for 20 hours to obtain a liquid metal suspension; ② Add silver nanoparticles and carbon nanotubes to an acetone solution and sonicate for 2 hours to prepare a silver nanoparticle / carbon nanotube solution, wherein the mass ratio of silver nanoparticles to carbon nanotubes is 20:1 to 60:

1. ③ Mix the liquid metal suspension with the nano-silver / carbon nanotube solution at a mass ratio of 2:1 to 7:1, centrifuge to collect the precipitate, and obtain the conductive component; ④ Mix the conductive component with a polyurethane elastomer / N,N-dimethylformamide solution with a solid content of 14%-24%, grind for 30 minutes to obtain the core spinning solution, wherein the mass ratio of the conductive component to the polyurethane elastomer is 82:18 to 92:

8. Preparation of core-sheath structure fiber: Using a coaxial spinning needle, the core-sheath spinning solution is injected into a coagulation solution with a mass ratio of 5% N,N-dimethylformamide. After being drawn at a draw ratio of 1 to 6, the fiber is further coagulated in a coagulation bath for 24 hours and finally dried at 80°C for 15 minutes to obtain the sensing fiber.

4. The preparation method according to claim 3, characterized in that, When making core-sheath structured fibers, the diameter of the core layer is controlled between 0.5 mm and 1.3 mm, and the diameter of the sheath layer is between 1.5 mm and 2.3 mm.

5. The preparation method according to claim 3, characterized in that, The draw ratio of the drawing machine is 1 to 6, and the coagulation bath is deionized water or a mixed solution of deionized water and N,N-dimethylformamide, wherein the mass ratio of deionized water to N,N-dimethylformamide in the mixed solution is 9.5:0.5 to 6:

4.

6. The preparation method according to claim 3, characterized in that, Before spinning, the spinning solution should be allowed to stand for 20 minutes to eliminate air bubbles.

7. The preparation method according to any one of claims 3-6, characterized in that, The diameter of the liquid metal particles is approximately 20-100 micrometers, and the diameter of the silver particles is approximately 2-10 micrometers.

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