Liquid metal nanoparticle-based photoacoustic ultrasonic transducer and preparation method

Abstract

This invention relates to a photoinduced ultrasonic transducer based on liquid metal nanoparticles and its fabrication method. The photoinduced ultrasonic transducer includes a composite thin film layer, or a composite thin film layer and a substrate stacked together. The composite thin film layer is formed by dispersing liquid metal nanoparticles in a polymer. The polymer is formed by curing a polymer substrate precursor solution. The mass ratio of liquid metal nanoparticles to polymer substrate precursor solution is (0.2-0.4):1. This invention uses liquid metal nanoparticles as the basic component for light absorption and heat generation, and uses a polymer as the substrate, which is easily expanded by heat. Using liquid metal as the raw material can avoid unfavorable internal stress concentration. The photoinduced ultrasonic transducer of this invention has good flexibility, high photothermal conversion efficiency, high damage threshold, can excite high sound pressure, and can fully recover after the process, making the device highly durable and extending its service life. The overall fabrication process is simple.

Description

Technical Field

[0001] This invention relates to the field of photo-induced ultrasonic transducers, specifically to a photo-induced ultrasonic transducer based on liquid metal nanoparticles and its fabrication method. Background Technology

[0002] Photoinduced ultrasound transducer technology is an alternative to traditional piezoelectric technology for generating ultrasound, offering advantages such as no electrical connection required, resistance to electromagnetic interference, and miniaturization. Photoinduced ultrasound transducers generate ultrasonic pulses by absorbing short pulses of light, causing a transient temperature increase and elastic thermal expansion. The ultrasound generated by this transducer exhibits high frequency and wide bandwidth, achieving frequencies of hundreds of MHz or even GHz, meeting the demands of high-resolution imaging. Furthermore, the miniaturized structure of photoinduced ultrasound transducers facilitates device miniaturization, enabling applications in space-constrained areas such as nerve stimulation acquisition or imaging research. Moreover, photoinduced ultrasound transducers can generate significant sound pressure levels within a small volume, making them suitable for medical applications requiring high-energy ultrasonic shock waves, such as ultrasonic lithotripsy. Additionally, the resistance to electromagnetic interference makes photoinduced ultrasound transducers easily compatible with magnetic resonance imaging (MRI) systems in clinical settings. These advantages make photoinduced ultrasound transducers a precise and reliable analytical tool in clinical medicine and scientific research.

[0003] The photoacoustic conversion process involves the conversion of light into heat into sound, including light absorption efficiency, photothermal conversion efficiency, and thermoacoustic conversion efficiency. The light absorption efficiency and photothermal conversion efficiency are mainly determined by the light-absorbing material; the higher these efficiencies, the better the generated ultrasonic pulse effect. The thermoacoustic conversion efficiency is mainly determined by the thermal expansion of the composite material consisting of the light-absorbing material and the matrix material; the higher the thermal expansion, the more expansion can occur with the same amount of heat, resulting in greater sound pressure.

[0004] Using a material with a high coefficient of thermal expansion as the matrix material, materials with light absorption and photothermal conversion properties are incorporated into the matrix material and a composite thin film structure is prepared. In actual operation, light energy is absorbed by the light-absorbing material and converted into heat energy. The heat is transferred to the expansion material, causing it to deform and ultimately generate a sound signal, thereby realizing the rapid conversion of light energy to sound energy.

[0005] However, current photo-induced ultrasonic transducers primarily use solid materials as the medium for light absorption and photothermal conversion. Their relatively low coefficient of thermal expansion and high Young's modulus limit the acoustic pressure amplitude and damage threshold of the transducer to some extent. Specifically, reducing the thickness of the composite film is an effective method to balance the center frequency and response bandwidth of the photo-induced ultrasonic transducer. However, reducing the thickness of the composite film affects the utilization rate of the incident light by the light-absorbing medium, thus reducing the generated acoustic pressure. Furthermore, some existing ultrasonic transducers require a focusing structure to generate high acoustic pressure. Although increasing the proportion of light-absorbing material in the composite film can improve its light absorption rate, this method reduces the effective coefficient of thermal expansion and increases the Young's modulus. Moreover, the significant differences in thermally induced deformation among different materials within the composite material can cause irreversible damage to the composite film, reducing its service life. Therefore, finding a material with a large coefficient of thermal expansion, a low Young's modulus, and strong light absorption and photothermal conversion capabilities is crucial. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a photo-induced ultrasonic transducer based on liquid metal nanoparticles and its preparation method, thereby solving the technical problems of existing photo-induced ultrasonic transducers being unable to generate high sound pressure and having a short service life.

[0007] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows:

[0008] In a first aspect, the present invention provides a photo-induced ultrasonic transducer based on liquid metal nanoparticles, the photo-induced ultrasonic transducer comprising a composite thin film layer, or a composite thin film layer and a substrate stacked together; the composite thin film layer is formed by dispersing liquid metal nanoparticles in a polymer; the polymer is formed by curing a polymer substrate precursor liquid; the mass ratio of liquid metal nanoparticles to polymer substrate precursor liquid is (0.2-0.4):1.

[0009] Preferably, the thickness of the photo-induced ultrasonic transducer is 50–200 μm.

[0010] Preferably, the polymer includes polydimethylsiloxane, polymethyl methacrylate, or photoresist.

[0011] Secondly, the present invention provides a method for preparing a photo-induced ultrasonic transducer based on liquid metal nanoparticles, comprising the following steps:

[0012] Liquid metal, surface stabilizer and solvent are mixed, and then ultrasonically treated and concentrated to obtain a dispersion of liquid metal nanoparticles;

[0013] The liquid metal nanoparticle dispersion was then mixed evenly with the polymer substrate precursor solution to obtain a mixed precursor solution; the mass ratio of liquid metal nanoparticles to polymer substrate precursor solution in the mixed precursor solution was (0.2~0.4):1.

[0014] A mixed precursor liquid was coated onto a substrate and then heated to cure, resulting in a photo-induced ultrasonic transducer based on liquid metal nanoparticles.

[0015] Preferably, the liquid metal is EGaIn.

[0016] Preferably, the mass ratio of liquid metal to surface stabilizer is 1:(0.03-0.09), more preferably 1:(0.04-0.06; the surface stabilizer includes one or more of (3-mercaptopropyl)trimethoxysilane (MPTMS) and (3-aminopropyl)trimethoxysilane (APTMS).

[0017] Preferably, the mass-to-volume ratio of liquid metal to solvent is 1 g:(10-30) mL; the solvent includes one or more of n-hexane and toluene.

[0018] Preferably, in ultrasonic treatment, the power is 300-500W and the time is 40-80min.

[0019] Preferably, the concentration step is as follows: the ultrasonically treated mixture is allowed to stand and precipitate, and then more than 75% of the supernatant is removed to obtain a liquid metal nanoparticle dispersion.

[0020] Preferably, the heating curing conditions are 100-130℃ for 30-40 minutes.

[0021] Preferably, the substrate includes, but is not limited to, one or more of glass, quartz, PDMS, PMMA, PI, photoresist, and optical fiber.

[0022] Compared with the prior art, the beneficial effects of the present invention include:

[0023] This invention uses liquid metal nanoparticles as the basic component for light absorption and heat generation, with a polymer as the substrate, which expands easily when heated. The liquid metal nanoparticles are dispersed in the polymer substrate, thus obtaining a photo-induced ultrasonic transducer based on liquid metal nanoparticles. Using liquid metal as the raw material can avoid unfavorable internal stress concentration, and its large coefficient of thermal expansion can reduce the difference in thermal deformation caused by different materials within the photo-induced ultrasonic transducer. After ultrasonic treatment, the liquid metal is broken into nanoparticles. The photo-induced ultrasonic transducer composed of these nanoparticles and the polymer substrate material has good flexibility. The surface plasmon effect of the liquid metal nanoparticles gives it a high light absorption coefficient, while the high loss coefficient of the liquid metal material itself makes the nanomaterials easily convert incident light energy into heat energy. The photothermal conversion efficiency is high, and the damage threshold is high. This photo-induced ultrasonic transducer can generate large deformation and excite high sound pressure through effective absorption of light energy, and can completely recover after the process, making the device highly durable and extending its service life. The overall fabrication process is simple. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a photo-induced ultrasonic transducer based on liquid metal nanoparticles;

[0025] Figure 2 This is a schematic diagram of the optical path of photoinduced ultrasound;

[0026] Figure 3 This is a photograph of liquid metal nanoparticles dispersed in n-hexane.

[0027] Figure 4 This is the optical absorption spectrum of the cured LMNPs / PDMS film in Example 1, which has a high light absorption.

[0028] Figure 5 This is a time-domain waveform diagram of the LMNPs / PDMS thin film obtained in Example 1 of needle hydrophone testing, showing the ultrasonic waves generated after nanosecond pulsed laser excitation.

[0029] Figure 6 These are simulation results of the extinction spectra of liquid metal nanoparticles with different particle sizes. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] Current photo-induced ultrasonic transducers mainly use solid materials as the medium for light absorption and photothermal conversion. Their relatively low coefficient of thermal expansion and high Young's modulus limit the acoustic pressure amplitude and loss threshold of the transducer to some extent. Furthermore, traditional solid nanoparticles do not change with the deformation of the film layer, making it easier for internal stress to concentrate.

[0032] In view of this, the present invention provides a photo-induced ultrasonic transducer structure and preparation method based on liquid metal nanoparticles (LMNPs). The present invention involves mixing liquid metal nanoparticles with a matrix material solution, coating the mixture onto a substrate to form a film, and then curing it to create a photo-induced ultrasonic transducer.

[0033] See Figure 1 The photo-induced ultrasonic transducer of the present invention is a composite film formed by dispersing liquid metal nanoparticles in a matrix material that is easily expanded by heat; specifically, it includes a composite film layer 1 and an optional substrate 2, wherein the composite film layer 1 is formed by dispersing liquid metal nanoparticles 3 in a polymer, and can also be called a vibration layer; the substrate 2 can be selected according to the situation, and can be removed or retained in actual use. If the substrate 2 is retained, the composite film layer 1 and the substrate 2 are stacked.

[0034] Laser excitation of localized surface plasmons in liquid metal nanoparticles in a composite film generates a large amount of heat. This heat is rapidly transferred to the surrounding polymer material. Due to the high coefficient of thermal expansion of the polymer, it undergoes high-frequency vibrations of thermal expansion and cooling contraction under the action of pulsed laser. The vibration of the composite film is radiated outward in the form of ultrasonic waves.

[0035] In practical applications, different sizes, structures, and materials can be selected as substrates for liquid metal nanoparticle-based composite films to support photo-ultrasonic transducers, thereby enabling multifunctional applications of the device. Simultaneously, the size and composition of LMNPs can be adjusted, controlling their concentration in the matrix material and the thickness of the composite film to achieve a thickness of 50–200 μm. This allows for changes in parameters such as sound pressure level and bandwidth of the photo-ultrasonic transducer. Too low a thickness results in insufficient light energy absorption, reducing sound pressure, while too high a thickness leads to longer heat transfer times and greater losses, also affecting the final sound pressure. Compared to traditional piezoelectric ceramic ultrasonic transducers, photo-ultrasonic transducers offer significant advantages such as smaller size and resistance to electromagnetic interference, greatly expanding the device's application scenarios.

[0036] Furthermore, due to the inherent liquid properties of liquid metal, unfavorable internal stress concentration can be avoided. The large coefficient of thermal expansion of liquid metal can reduce the differences in thermally induced deformation within the composite material. By breaking the liquid metal into nanoparticles, the photo-induced ultrasonic transducer formed by these nanoparticles and the matrix material is essentially a composite film with good flexibility. The surface plasmon effect of the liquid metal nanoparticles gives it a high light absorption coefficient, while the high loss coefficient of the liquid metal material itself makes it easy for the nanomaterial to convert incident light energy into heat energy. The composite film can generate significant deformation through effective light absorption, exciting high sound pressure levels, and can fully recover after this process, giving the device high durability and extending its service life. This meets the high sound pressure requirements in some medical fields, avoiding the problem that some existing ultrasonic transducers require a focusing structure to generate high sound pressure, and also solving the problem of excessively low damage threshold of photo-induced ultrasonic transducer films. The overall fabrication process is simple.

[0037] The photo-induced ultrasonic transducer of this invention has a wide range of applications, such as industrial non-destructive testing, medicine, biomedical research, materials science, environmental monitoring, communication engineering, sensing and imaging, and scientific research.

[0038] As a preferred embodiment, the present invention also provides a method for preparing a photo-induced ultrasonic transducer based on liquid metal nanoparticles, comprising the following steps:

[0039] S1, take liquid metal, surface stabilizer and solvent and mix them to obtain liquid metal dispersion A;

[0040] S2, the liquid metal dispersion A is subjected to ultrasonic treatment to obtain liquid metal nanoparticle dispersion B;

[0041] S3, concentrate the liquid metal nanoparticle dispersion B to obtain liquid metal nanoparticle dispersion C;

[0042] S4, a polymer-based precursor solution is prepared using prepolymer and crosslinking agent;

[0043] S5, the liquid metal nanoparticle dispersion C is mixed evenly with the polymer substrate precursor liquid to obtain a mixed precursor liquid; the mass ratio of liquid metal nanoparticles to polymer substrate precursor liquid in liquid metal nanoparticle dispersion C is (0.2~0.4):1; wherein, the loss of liquid metal during the preparation of liquid metal dispersion C can be ignored, and the mass of liquid metal nanoparticles here is calculated according to the mass of liquid metal added in step S1, that is, the mass of liquid metal added in step S1 = the mass of liquid metal nanoparticles in liquid metal dispersion C in step S3;

[0044] S6. The mixed precursor liquid is coated on the substrate and heated to cure, thus obtaining a photo-induced ultrasonic transducer based on liquid metal nanoparticles.

[0045] It is understandable that the numbering of steps S1 to S6 here is only for better differentiation of operations, rather than a limitation on their specific process sequence. For example, steps S1 to S3 can be performed simultaneously with step S4.

[0046] In addition, the mass ratio or volume ratio of liquid metal nanoparticles to thermally expanding materials can be adjusted according to requirements to change the frequency and sound pressure level generated. Under the premise of fixed thickness, within a certain range, by increasing the content of liquid metal in the composite film, the frequency of the resulting photo-ultrasonic transducer will gradually decrease and the sound pressure will increase. This is because liquid metal nanoparticles will reduce the Young's modulus of the film, making it more flexible and with a longer response time, enabling it to make full use of light energy. However, if the content of liquid metal is too high, the sound pressure will gradually decrease.

[0047] Preferably, in step S1, the liquid metal is EGaIn, more preferably EGaIn from Dingguan Metals, with a melting point of 11°C. This invention uses liquid metal nanoparticles as the basic component for light absorption and heat generation; a polymer is used as the substrate, which expands easily when heated; the liquid metal nanoparticles are dispersed in the substrate to form a thin-film photo-ultrasonic transducer, which has a high light absorption coefficient, high photothermal conversion efficiency, can generate high sound pressure, and has a long service life.

[0048] Preferably, in step S1, the mass ratio of liquid metal to surface stabilizer is 1:(0.03-0.09), more preferably 1:(0.04-0.06; the surface stabilizer includes one or more of (3-mercaptopropyl)trimethoxysilane (MPTMS) and (3-aminopropyl)trimethoxysilane (APTMS). Too little surface stabilizer will result in a large number of large-volume liquid metal droplets in the final LMNPs dispersion, while too much will reduce the performance of the photo-induced ultrasonic transducer.

[0049] Preferably, in step S1, the mass-to-volume ratio of liquid metal to solvent is 1 g:(10-30) mL; the solvent includes one or more of n-hexane and toluene.

[0050] Preferably, in step S2, the ultrasonic treatment uses a power of 300–500 W and a time of 40–80 min. This invention uses an ultrasonic probe to sonicate liquid metal in a solvent, thoroughly breaking it down into nanoparticles. Too low a power or too short an ultrasonic time will result in a large number of large-volume liquid metal droplets in the final LMNPs dispersion. Simultaneously, in ordinary air, excessively high ultrasonic power and too long an ultrasonic time will cause the solution temperature to rise rapidly, which is detrimental to the bonding process between the stabilizer and the liquid metal nanoparticles, making the liquid metal nanoparticles more prone to polymerization.

[0051] Preferably, in step S3, concentration involves removing part or all of the supernatant after the liquid metal dispersion B has settled and precipitated, and more preferably, removing more than 75% of the supernatant; the specific concentration ratio can be adjusted according to the required concentration of the mixing precursor solution.

[0052] Preferably, in step S4, the polymer includes polydimethylsiloxane (PDMS), polymethyl methacrylate (PMMA), or photoresist; correspondingly, the polymer substrate precursor liquid is a prepolymer of the above-mentioned polymers and any necessary crosslinking agents to ensure successful curing into a film.

[0053] More preferably, the polymer-based precursor liquid comprises a polydimethylsiloxane (PDMS) prepolymer and a crosslinking agent in a mass ratio of (9-11):1, and the mass ratio is further preferably 10:1; more preferably, both the polydimethylsiloxane (PDMS) prepolymer and the crosslinking agent are Dow Corning DC 184.

[0054] Preferably, the heating curing conditions are 100-130℃ for 30-40 minutes.

[0055] Preferably, the substrate includes, but is not limited to, one or more of glass, quartz, PDMS, PMMA, polyimide (PI), photoresist, and optical fiber. The substrate can be selected in different sizes and shapes according to the application scenario, including, but not limited to, various types of fiber end faces or sides, and square, circular, or irregularly shaped substrate structures.

[0056] Depending on the actual application scenarios and needs, liquid metal nanoparticles and polymer substrates can be used as thermally expanding materials to form composite materials, which can be prepared into thin films or bulk structures of different sizes. The thin film or bulk structure of the composite material can be prepared on a substrate without the support of a substrate structure, or it can be prepared on a substrate according to actual needs.

[0057] The present invention will be further described in detail below through specific embodiments. The liquid metal used is EGaIn from Dingguan Metals, with a melting point of 11°C; the polymer substrate precursor liquid is Dow Corning DC184, which includes PDMS prepolymer (liquid A) and crosslinking agent (liquid B).

[0058] Example 1

[0059] This invention provides a photoinduced ultrasonic transducer, the preparation method of which includes the following steps:

[0060] S1, add 8 ml of n-hexane to a container, weigh 0.5 g of liquid metal (EGaIn) into the n-hexane, and then add 25 mg of surface stabilizer MPTMS ((3-mercaptopropyl)trimethoxysilane, CAS: 4420-74-0) to obtain liquid metal dispersion A;

[0061] S2. Using an ultrasonic probe (Yuanshengte Intelligent Technology, model: LS-1200B), the liquid metal in the liquid metal dispersion A was ultrasonically sonicated for 60 minutes at an ultrasonic power of 360W to fully break it down into nanoparticles (LMNPs) to obtain liquid metal nanoparticle dispersion B.

[0062] S3, let the prepared liquid metal nanoparticle dispersion B stand until all the particles settle to the bottom of the container, then remove 6 mL of the supernatant to increase the concentration of LMNPs in the solution and obtain liquid metal nanoparticle dispersion C.

[0063] S4, PDMS prepolymer and crosslinking agent (Dow Corning DC 184) are mixed at a mass ratio of 10:1. The mass of PDMS prepolymer is 1.2g, and 1.32g of PDMS precursor solution is obtained.

[0064] S5. The liquid metal nanoparticle dispersion C and the PDMS precursor solution are mixed at a mass ratio of 0.3:1. After stirring evenly with a magnetic stirrer, a mixed precursor solution of LMNPs and PDMS is obtained (where the mass ratio of liquid metal nanoparticles to PDMS precursor solution is 0.38:1).

[0065] S6. Take 200 μL of the mixed precursor solution of LMNPs / PDMS and coat it onto a transparent glass substrate (2 cm * 2 cm) by drop coating. Place the glass substrate on a heating stage and heat it at 130 °C for 30 min to solidify the mixed precursor solution, thereby obtaining a PDMS film (LMNPs / PDMS thin film) with dispersed liquid metal nanoparticles. The thickness of the composite film is about 80 μm, which is the photo-induced ultrasonic transducer based on liquid metal nanoparticles.

[0066] The performance of the obtained photo-induced ultrasonic transducer was tested, and the optical path diagram of the photo-induced ultrasonic transducer is shown in the figure below. Figure 2 As shown, a 532nm laser 5 is emitted by laser 4. A photo-induced ultrasonic transducer 6 (including an LMNPs+PDMS composite thin film sample and a substrate, wherein the substrate is transparent glass, which does not affect the test results and only serves to support the composite thin film) is immersed in a water tank 8. The 532nm nanosecond pulsed laser irradiates the photo-induced ultrasonic transducer 6, and the generated ultrasonic signal 9 is received by a standard hydrophone 7 and transmitted to an oscilloscope 10 to obtain the sound pressure signal. The hydrophones involved in this invention are all needle-type hydrophones, model NH0200, from PA Company, UK.

[0067] See Figure 3 The image shows a physical sample of liquid metal dispersion B, in which liquid metal nanoparticles are dispersed in n-hexane and appear blackish-gray.

[0068] See Figure 4Figure 1 shows the optical absorption spectrum of the LMNPs / PDMS thin film in the photo-induced ultrasonic transducer. As can be seen from the figure, the thin film structure has high light absorption.

[0069] See Figure 5 The image shows the time-domain waveform of the LMNPs / PDMS thin film after nanosecond pulsed laser excitation, obtained by a needle hydrophone (PA, UK, model NH0200). Figure 5 The waveform in the image was transformed by FFT, and its center frequency was found to be approximately 1 MHz. Combined with the fact that the sensitivity of the hydrophone at this frequency is 38 mV / MPa, it was calculated that a sound pressure of over 4 MPa was generated (the instability of laser energy will cause the sound pressure to vary, but the overall difference is not significant). Therefore, this thin film structure can generate a large sound pressure under laser excitation.

[0070] Using Mie particle scattering theory and COMSOL simulation software, we conducted simulation experiments on the optical extinction parameters of liquid metal nanoparticles at different particle sizes, setting the average particle sizes to 80 nm, 85 nm, 90 nm, 95 nm, and 100 nm; the simulation results are as follows: Figure 6 As shown.

[0071] Figure 6 The simulation results show that liquid metal nanoparticles of different sizes exhibit localized surface plasmon effects, and that the light absorption of nanoparticles of different diameters is different.

[0072] Since the way metal nanoparticles enhance absorption is by utilizing their LSPR (local surface plasmon resonance) phenomenon, and the size of the nanoparticles affects both the size of their extinction cross section and the position of their SPR absorption peak, simulations are conducted to find the optimal particle size to achieve the best utilization of light energy, thus providing an optimization approach for subsequent devices.

[0073] In summary, nanoparticles of different sizes have different optical properties. Therefore, liquid metal nanoparticles of different sizes have different light absorption effects, resulting in different photothermal conversion efficiencies and different ultrasonic pulse effects. This invention controls the particle size by adjusting the ultrasonic power and time. The preferred ultrasonic power is 300-500W and the time is 40-80min.

[0074] Example 2

[0075] The difference from Example 1 is that the amount of liquid metal nanoparticles was adjusted so that the mass ratio of liquid metal nanoparticles to PDMS precursor solution was 0.2:1.

[0076] The results showed that the acoustic pressure of the obtained photo-induced ultrasonic transducer was approximately 3 MPa.

[0077] Example 3

[0078] The difference from Example 1 is that the amount of liquid metal nanoparticles was adjusted so that the mass ratio of liquid metal nanoparticles to PDMS precursor solution was 0.4:1.

[0079] The results showed that the sound pressure of the obtained photo-induced ultrasonic transducer was approximately 3.5 MPa.

[0080] As can be seen from Examples 1-3, in the photo-induced ultrasonic transducer of the present invention, when the thickness of the composite film is constant, the sound pressure of the resulting photo-induced ultrasonic transducer increases with the increase of the amount of liquid metal nanoparticles, but the increase is not obvious in the later stage. Moreover, it was found through experiments that the sound pressure gradually decreases when the content of liquid metal is too high. Therefore, the preferred mass ratio of liquid metal nanoparticles to polymer substrate precursor liquid in the present invention is (0.2-0.4):1.

[0081] Comparative Example 1

[0082] The difference from Example 1 is that the surface stabilizer is removed, while the other steps and conditions are the same as in Example 1.

[0083] The results showed that the prepared LMNPs-dispersed n-hexane solution (liquid metal dispersion C) was grayish-white in color. During the heating and curing process of the mixed precursor solution with PDMS, many nanoparticles aggregated into large droplets of liquid metal, which caused the reflectivity of the composite film to increase sharply. The absorption rate of the composite film was low, and the generated ultrasonic sound pressure was weak, compared with the sound pressure of about 4 MPa or more in Example 1. The transducer film prepared in Comparative Example 1, after being excited under the same test conditions as in Example 1 and detected by a hydrophone, had an ultrasonic wave pattern that was difficult to distinguish on an oscilloscope, which was about a few kPa.

[0084] Comparative Example 2

[0085] The difference from Example 1 is that a different surface stabilizer is selected, such as PVP or n-octadecyl mercaptan, to replace MPTMS. The other steps and conditions are the same as in Example 1.

[0086] The results showed that although the prepared LMNPs-dispersed n-hexane solution (liquid metal dispersion C) was blackish-gray, during the heating and curing process of the mixed precursor solution with PDMS, the composite film exhibited large-area repolymerization of nanoparticles at 80℃, which increased the film's reflection and reduced its absorption, resulting in a weaker photo-induced ultrasonic effect.

[0087] Comparative Example 3

[0088] The difference from Example 1 is that the mass ratio of surface stabilizer to liquid metal is 0.01:1, while the other steps and conditions are the same as in Example 1.

[0089] The results showed that after the ultrasound was completed, there were still many large liquid metal droplets in the mixture, indicating that the liquid metal could not be dispersed into nanoscale and remain stable in the mixture.

[0090] Comparative Example 4

[0091] The difference from Example 1 is that the ultrasonic power is higher and the time is longer. The observable phenomena are that the solution quickly changes from gray to grayish-black and then from grayish-black back to light gray. The nanoparticle size is significantly larger and the final temperature of the bottle is higher than that of Example 1.

[0092] Compared with existing transducer technologies, the present invention has the following advantages:

[0093] 1. This invention proposes a novel nanomaterial for photo-induced ultrasonic transduction. Due to the localized surface plasmon effect and high loss coefficient of this nanomaterial, it has high absorbance and high photothermal conversion efficiency.

[0094] 2. The film can still maintain high flexibility after being doped with light-absorbing materials, which is expected to generate a large sound pressure and enable the device to have a high laser damage threshold.

[0095] 3. The transducer thin film preparation process is simple and the material cost is extremely low.

[0096] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A photoinduced ultrasonic transducer based on liquid metal nanoparticles, characterized in that, The photo-induced ultrasonic transducer includes a composite thin film layer, or a composite thin film layer and a substrate stacked together; The composite thin film layer is formed by dispersing liquid metal nanoparticles in a polymer; the polymer is formed by curing a polymer substrate precursor liquid; the mass ratio of liquid metal nanoparticles to polymer substrate precursor liquid is (0.2~0.4):

1.

2. The photo-induced ultrasonic transducer based on liquid metal nanoparticles according to claim 1, characterized in that, The thickness of the composite thin film layer is 50–200 μm.

3. The photo-induced ultrasonic transducer based on liquid metal nanoparticles according to claim 1, characterized in that, The polymer includes polydimethylsiloxane, polymethyl methacrylate, or photoresist.

4. The method for fabricating a photo-induced ultrasonic transducer based on liquid metal nanoparticles according to any one of claims 1-3, characterized in that, Includes the following steps: Liquid metal, surface stabilizer and solvent are mixed, and then ultrasonically treated and concentrated to obtain a dispersion of liquid metal nanoparticles; The liquid metal nanoparticle dispersion and the polymer substrate precursor solution were mixed evenly to obtain a mixed precursor solution; the mass ratio of liquid metal nanoparticles to polymer substrate precursor solution was (0.2~0.4):

1. A mixed precursor liquid was coated onto a substrate and then heated to cure, resulting in a photo-induced ultrasonic transducer based on liquid metal nanoparticles.

5. The method for fabricating a photo-induced ultrasonic transducer based on liquid metal nanoparticles according to claim 4, characterized in that, The liquid metal is EGaIn.

6. The method for fabricating a photo-induced ultrasonic transducer based on liquid metal nanoparticles according to claim 4, characterized in that, The mass ratio of liquid metal to surface stabilizer is 1:(0.03-0.09); the surface stabilizer includes one or more of 3-mercaptopropyltrimethoxysilane and 3-aminopropyltrimethoxysilane.

7. The method for fabricating a photo-induced ultrasonic transducer based on liquid metal nanoparticles according to claim 4, characterized in that, The mass-to-volume ratio of liquid metal to solvent is 1 g: (10-30) mL; the solvent includes one or more of n-hexane and toluene.

8. The method for fabricating a photo-induced ultrasonic transducer based on liquid metal nanoparticles according to claim 4, characterized in that, During ultrasonic treatment, the power is 300-500W and the time is 40-80min.

9. The method for fabricating a photo-induced ultrasonic transducer based on liquid metal nanoparticles according to claim 4, characterized in that, The concentration step specifically involves: allowing the ultrasonically treated mixture to settle, then removing more than 75% of the supernatant to obtain a liquid metal nanoparticle dispersion.

10. The method for fabricating a photo-induced ultrasonic transducer based on liquid metal nanoparticles according to claim 4, characterized in that, The curing conditions are 100-130℃ for 30-40 minutes.

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