A method for preparing a carbon nanofiber-based photoacoustic ultrasonic transducer

Abstract

The present application relates to the technical field of ultrasonic, in particular to a preparation method of carbon nanofiber-based photo-induced ultrasonic transducer.The preparation method of the carbon nanofiber-based photo-induced ultrasonic transducer comprises the following steps: 1) spinning polyacrylonitrile (PAN) film by electrospinning method, and controlling the thickness of the PAN film by spinning time and solution amount; 2) carbonizing the PAN fiber film in inert gas at high temperature to obtain carbon nanofiber film; 3) growing metal nanoparticles on the surface of the carbon nanofiber film by physical vapor deposition method to obtain metal nanoparticle-carbon nanofiber composite film; 4) preparing metal nanoparticle-carbon nanofiber-PDMS composite layer on a quartz glass sheet; and 5) placing the quartz glass sheet together with the metal nanoparticle-carbon nanofiber-PDMS composite layer into a vacuum drying oven, and vacuum heating and curing to obtain the photo-induced ultrasonic transducer.The method is simple in process, and the ultrasonic generated by the photo-induced ultrasonic transducer has the advantages of high intensity, high frequency and wide frequency band.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of ultrasonic technology, in particular to a preparation method of a carbon nanofiber-based photo-induced ultrasonic transducer. BACKGROUND

[0002] Laser ultrasonic transducers have a wide range of applications in the field of ultrasonic diagnosis and medical imaging. Traditional ultrasonic sound sources are piezoelectric ultrasonic transducers, which have the disadvantages of large volume, low frequency, high driving voltage, susceptibility to electromagnetic interference, and large volume of acoustic focusing points. With the continuous development of science and technology, researchers have proposed the concept of photo-induced ultrasonic, which has the characteristics of high intensity, high frequency and wide frequency band, and is not affected by electromagnetic interference and has the advantage of miniaturization. The ultrasonic emitter prepared by using the photo-induced ultrasonic effect can be used in the medical field such as ultrasonic minimally invasive surgery, thrombus dissolution, targeted drug delivery and micro-injection.

[0003] A laser ultrasonic transducer is usually composed of a light-absorbing material and a thermal expansion material. Commonly used absorbing materials include carbon-based materials such as carbon black, carbon nanotubes and candle soot particles, and the thermal expansion material is polydimethylsiloxane (PDMS). The incident light is absorbed by the absorbing material, and the generated heat is conducted to the PDMS to produce ultrasonic waves by using the thermal elastic effect. However, in most laser ultrasonic transducer devices, the thickness of the light-absorbing material cannot be accurately controlled, resulting in ultrasonic attenuation; and the light-absorbing material and the thermal expansion material cannot be in full contact, resulting in low acoustic pressure. Therefore, it is a technical problem to be solved to prepare a new structure of laser ultrasonic transducer to improve the ultrasonic intensity, bandwidth and photo-thermal conversion efficiency.

[0004] At present, most photo-induced ultrasonic transducers use carbon nanotubes and carbon nanofibers, etc. For example, Chinese Patent Application No. CN201910570950.0 provides a photo-induced ultrasonic transducer and a preparation method thereof. The manufacturing process uses a high-temperature chemical vapor deposition method in a mixture of C2H4, H2 and / or He to prepare a carbon nanotube array film. The manufacturing process is relatively complex, and the thickness of the carbon nanotube array film cannot be accurately controlled.

[0005] The master's thesis of Wu Yue from Huazhong University of Science and Technology, entitled "Research on Photo-induced Ultrasonic Transducer Based on CNT Yarn-PDMS Composite Material", discloses a preparation process of carbon nanotube yarn (CNT yarn) in the light-absorbing layer. The preparation process is to introduce hydrogen gas mixed with ethanol and propanol into the chemical vapor deposition chamber. These gas molecules drive the CNT to the outer periphery of the gas flow to produce mechanical interaction. Since the CNT concentration in the gas flow is very high, a multi-layer carbon nanotube sock-like object is formed. Ethanol and hydrogen gas in this preparation process are flammable and explosive, especially ethanol can reach an extremely flammable state after being added to hydrogen gas, which is dangerous.

[0006] Hsieh B-Y, Kim J, Zhu J, et al. A laser ultrasound transducer using carbon nanofibers-polydimethylsiloxane composite thin film [J]. Appl Phys Lett, 2015, 106(2). Polyacrylonitrile (PAN) fiber film is prepared by electrospinning method, and the PAN fiber film is carbonized at high temperature in inert gas to obtain carbon nanofiber film. The thickness of the fiber film can be controlled by the spinning time. The preparation process is relatively safe and simple. However, the performance of the ultrasonic transducer prepared by this method is relatively poor, and the-6dB bandwidth is only 7.84MHz. SUMMARY

[0007] In order to overcome the shortcomings of the prior art, the present application provides a preparation method of a carbon nanofiber-based photo-induced ultrasonic transducer.

[0008] The inventors improved the method in "Hsieh B-Y, Kim J, Zhu J, et al. A laser ultrasound transducer using carbon nanofibers-polydimethylsiloxane composite thin film [J]. Appl Phys Lett, 2015, 106(2)". Metal nanoparticles are self-assembled and deposited on the surface and internal voids of the carbon nanofiber film obtained by carbonization. First, a (PAN) fiber film is obtained by electrospinning method. The obtained (PAN) fiber film is carbonized at a high temperature of 900℃ for 120min in inert argon gas to obtain a porous carbon nanofiber film. Then, metal nanoparticles are self-assembled and deposited on the surface and internal pores of the carbon nanofiber film, thereby forming a metal nanoparticle-carbon nanofiber composite layer. The metal nanoparticle-carbon nanofiber composite film constitutes a light absorber, which serves as a light absorbing element of the ultrasonic transducer. The light absorbing coefficient is higher, and the-6dB bandwidth is 10MHz, which is 2.16MHz higher than the original.

[0009] The preparation method of the carbon nanofiber-based photo-induced ultrasonic transducer of the present application is a metal nanoparticle-carbon nanofiber-PDMS photo-induced ultrasonic transducer, wherein the metal nanoparticles and the carbon nanofiber film serve as the light absorbing part, and the PDMS serves as the thermal expansion part.

[0010] The preparation method comprises the following steps:

[0011] 1) first spin polyacrylonitrile PAN film by electrospinning method, control the thickness of PAN film by spinning time and solution amount;

[0012] 2) carbonize PAN fiber film in inert gas at high temperature to obtain carbon nanofiber film;

[0013] 3) grow metal nanoparticles on the surface of carbon nanofiber film by physical vapor deposition method to obtain metal nanoparticle-carbon nanofiber composite film, the physical vapor deposition method includes vacuum evaporation, sputtering, ion plating; the application mainly adopts sputtering. By controlling the deposition rate and time of magnetron sputtering, the depth, quantity and diameter of metal nanoparticles deposited in the gap of carbon nanofiber are controlled;

[0014] 4) prepare metal nanoparticle-carbon nanofiber-PDMS composite layer on a quartz glass sheet, the specific process can be as follows: mix and stir PDMS and curing agent with a mass ratio of 10:1, and then stand in vacuum until the bubbles in the PDMS mixture completely dissipate; spin the stirred PDMS mixed solution on the quartz glass substrate first, with a thickness of about 5 μm, then adhere the metal nanoparticle-carbon nanofiber composite film, ensuring that there is no gap between the metal nanoparticle-carbon nanofiber composite film and the quartz glass substrate; spin the PDMS mixed solution evenly on the metal nanoparticle-carbon nanofiber composite film again, with a thickness of about 100 μm, so that the thermal expansion material PDMS and the metal nanoparticle-carbon nanofiber composite film can fully contact, to obtain the metal nanoparticle-carbon nanofiber-PDMS composite layer;

[0015] 5) place the quartz glass sheet together with the metal nanoparticle-carbon nanofiber-PDMS composite layer in a vacuum drying oven, and vacuum heat and cure to obtain a photo-induced ultrasonic transducer.

[0016] Further, in step 1), the voltage of electrospinning is controlled at 16KV-20KV; the distance from the needle to the receiving plate is 15-20 cm; the feeding speed of the electrospinning liquid is 0.8ml / h; the ambient temperature is 25-28℃, and the ambient humidity is 30-40%.

[0017] Further, in step 1), the spinning time is 40-230 min; and the spinning solution amount is 1-3 ml.

[0018] Further, in step 2), the carbonization temperature is 700-900℃.

[0019] Further, in step 2), the high-temperature carbonization process is as follows: heat to 700-900℃ at a heating rate of 5℃ / min in nitrogen or argon or other inert gas, and the carbonization time is 60-120 min.

[0020] Further, in the step 2), the thickness of the carbon nanofiber film is 1-50 μm.

[0021] Further, in the step 3), the thickness of the metal nanoparticles is 8-20 nm.

[0022] Further, in the step 3), the deposition rate of the magnetron sputtering is 0.1 nm / s-0.2 nm / s.

[0023] Further, in the step 3), the time of the magnetron sputtering is 1 min-2 min.

[0024] Further, in the step 4), the stirring time is 1-30 min.

[0025] Further, in the step 5), the time of the vacuum heating is 20-200 min.

[0026] Further, in the step 5), the heating temperature is 80-120 ℃.

[0027] The principle of the present application is explained as follows: the present application discloses a carbon nanofiber-based photo-induced ultrasonic transducer and a preparation method thereof. The device is composed of a metal nanoparticle-carbon nanofiber-polydimethylsiloxane (PDMS) composite layer, the metal nanoparticle-carbon nanofiber composite layer is used for absorbing incident light and converting it into heat. The thermal expansion material PDMS is filled in the pores of the carbon nanofiber film, used for absorbing heat energy and emitting ultrasonic waves through the thermoelastic effect. The substrate is a quartz glass substrate. The device utilizes the photo-induced ultrasonic principle to generate ultrasonic signals under the action of pulsed laser. The light absorption layer of the device is a polyacrylonitrile (PAN) film spun out by the electrospinning method, the PAN fiber film is carbonized at high temperature in an inert gas to obtain a carbon nanofiber film, and metal nanoparticles are prepared on the surface of the carbon nanofiber film by physical vapor deposition, including vacuum evaporation, sputtering, and ion plating; the present application mainly adopts sputtering. Then PDMS and a curing agent (the ratio is 10:1) are uniformly mixed, a layer of PDMS with a thickness of about 5 μm is first spin-coated on the glass substrate, the metal nanoparticle-carbon nanofiber film is closely attached to avoid the generation of bubbles; then a layer of PDMS with a thickness of about 100 μm is spin-coated on the carbon nanofiber film, and a metal nanoparticle-carbon nanofiber-PDMS composite layer-based photo-induced ultrasonic transducer is obtained through vacuum drying and curing. The method of the present application has simple manufacturing process, and the ultrasonic waves generated by the photo-induced ultrasonic transducer have the advantages of high intensity, high frequency, and wide frequency band.

[0028] The beneficial effects of the present application are as follows:

[0029] 1、In the present application, the thickness of the carbon nanofiber film can be controlled by controlling the time and solution volume of electrospinning, the smaller the film thickness, the smaller the ultrasonic attenuation. In addition, the film formed by electrospinning will have a fiber pore structure even after carbonization, so that the metal particles deposited by physical vapor deposition method can be better deposited into the gap between the carbon nanofibers, so that the prepared metal nanoparticle-carbon nanofiber composite film has high light absorption coefficient.

[0030] 2、The metal nanoparticle-carbon nanofiber composite film constitutes a light absorber, which is used as a light absorbing element of an ultrasonic transducer, and because it is prepared by an electrospinning method, the fibers are filled with pores, which can greatly promote the penetration of the elastomer PDMS and improve the intensity of the ultrasonic waves generated by the ultrasonic transducer.

[0031] 3、The metal nanoparticle-carbon nanofiber composite film in the device can be cut into a size similar to the diameter of a multimode optical fiber, so that it can be used in an optical fiber-based ultrasonic transmitter, and has the potential for further miniaturization. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is a structure diagram of metal nanoparticle-carbon nanofiber and a structure diagram of a laser ultrasonic transducer in the embodiment of the present application. Among them, a: structure diagram of metal nanoparticle-carbon nanofiber; b: structure diagram of laser ultrasonic transducer.

[0033] Figure 2 It is a SEM microstructure diagram of the metal nanoparticle-carbon nanofiber film in the present application.

[0034] Figure 3 It is an ultrasonic pressure signal diagram obtained by testing the embodiment of the present application.

[0035] Figure 4 It is a frequency spectrum diagram of the ultrasonic signal obtained by testing the embodiment of the present application.

[0036] Figure 5 It is an ultrasonic pressure signal diagram obtained by testing different carbon fiber film thicknesses in the present application.

[0037] Figure 6 It is a light absorption degree diagram obtained by testing the embodiment of the present application.

[0038] Among them, 1 is a carbon nanofiber film, 2 is a gold nanoparticle, 3 is PDMS, 4 is a gold nanoparticle-carbon nanofiber composite film, 5 is a gold nanoparticle, and 6 is a quartz glass plate. DETAILED DESCRIPTION

[0039] The technical solutions of the present application will be further described in detail below in combination with the drawings:

[0040] Example 1

[0041] The invention discloses a carbon nanofiber-based photo-ultrasonic transducer and a preparation method thereof, which has the advantages of small size and simple structure, and the ultrasound generated by the transducer has low attenuation, high frequency and wide bandwidth.

[0042] The carbon nanofiber-based photoacoustic transducer is divided into a light absorption part and a thermal expansion part. Figure 1 As shown, the light absorption part of the device is gold nanoparticle-carbon nanofiber, which includes a carbon nanofiber membrane (1) and gold nanoparticles (2), and the thermal expansion part includes PDMS (3).

[0043] The preparation steps of the carbon nanofiber-based photoultrasonic transducer are as follows:

[0044] Polyacrylonitrile (PAN) films were first electrospun. 2.4 g of PAN (Mw = 150,000) was added to 30 g of N,N-dimethylformamide (DMF). The mixture was stirred continuously at 50°C for 12 hours, producing a viscous, homogeneous solution. This solution was then transferred to a plastic syringe with a sharp needle. The syringe pump system used a 15 cm distance between the needle and the collector, and a feed rate of 0.8 ml / h. Under a high-voltage electric field of 16 kV, the solution in the syringe was electrospun, forming a polyacrylonitrile (PAN) film on the surface of the collector plate. The PAN film was then carbonized at 900°C under an inert atmosphere of nitrogen or argon to produce a porous carbon nanofiber membrane. Gold nanoparticles were then grown within the pores by physical vapor deposition.

[0045] in,

[0046] The volume of electrospinning solution was 1 ml;

[0047] The electrospinning time was 75 min;

[0048] The carbonization temperature is 900°C and the carbonization time is 120 min.

[0049] The thickness of carbon nanofibers is 25 μm, and the diameter of a single carbon fiber filament is 100-200 nm.

[0050] The growth rate of gold nanoparticles is 0.14 nm / s.

[0051] The thickness of the gold nanoparticles is 10 nm.

[0052] The deposition rate of magnetron sputtering was 0.136 nm / s.

[0053] The magnetron sputtering time was 1 min 13 s.

[0054] 2. The thermal expansion material is obtained by mixing PDMS and curing agent in a ratio of 10:1. The preparation steps are as follows:

[0055] Take 4g PDMS and 0.4g curing agent mixed, added into beaker; by magnetic stirring 5 min makes both fully mixed; put into vacuum box, and vacuumize, and stand by its bubble to dissipate.

[0056] 3, preparation of ultrasonic transmitter device, cross section structure schematic diagram as Figure 1 Shown, including PDMS (3), gold nanoparticles-carbon nanofiber membrane (4), gold nanoparticles (5) and quartz glass plate (6). Its preparation steps are as follows:

[0057] 1) the PDMS mixed solution of stirring is first spin-coated on quartz glass substrate, and the thickness is about 5 μm.

[0058] 2) the gold nanoparticles-carbon nanofiber membrane is adhered, so that the gold nanoparticles-carbon nanofiber membrane and quartz glass are free of bubbles.

[0059] 3) again the PDMS mixed solution is uniformly spin-coated on gold nanoparticles-carbon nanofiber composite membrane, and the thickness is about 100 μm;

[0060] 4) the gold nanoparticles-carbon nanofiber membrane-PDMS composite layer prepared is placed in 80 ℃ vacuum drying environment and heated for 3 h.

[0061] The microstructure of gold nanoparticles-carbon nanofiber membrane is measured by SEM, as shown in Figure 2 The diameter of single carbon fiber is about 100-200 nm.

[0062] Example 2

[0063] The difference from example 1 is only that the solution amount of electrospinning is 2 ml.

[0064] Example 3

[0065] The difference from example 1 is only that the solution amount of electrospinning is 3 ml.

[0066] Performance detection:

[0067] 1) the laser ultrasonic transducer prepared in example 1 is placed in a quartz water tank filled with water, and a nanosecond pulse laser (532 nm, pulse width 10 nanoseconds, repetition frequency 100 Hz) is used for irradiation, and an underwater microphone is used to record the sound pressure signal at a distance of 1 mm from the sample. As shown in Figures 3-4 At 25 mJ / cm 2Under the irradiation of laser energy density, the carbon nanofiber-PDMS composite layer obtains an acoustic intensity of 4.5 MPa and a frequency bandwidth (-6dB) of 5 MHz; the gold nanoparticle-carbon nanofiber-PDMS composite layer obtains an acoustic intensity of 6.5 MPa and a frequency bandwidth (-6dB) of 10 MHz; thus, it is concluded that the acoustic intensity of the gold nanoparticle-carbon nanofiber film-PDMS composite layer prepared by the physical vapor deposition method on the surface of the carbon nanofiber and the spin coating of PDMS is 1.5 times that of the carbon nanofiber film-PDMS composite layer; the frequency bandwidth (-6dB) is 2 times that of the carbon nanofiber film-PDMS composite layer.

[0068] 2) Different amounts of spinning solution can affect the thickness of carbon nanofiber, so different amounts of spinning solution, 1ml, 2ml and 3ml, i.e. Examples 1-3, are electrospun, and different thicknesses of carbon nanofiber films are prepared by high-temperature carbonization of the spinning solutions in inert gas; gold nanoparticles with a thickness of 10 nm are grown on the surfaces of the three kinds of carbon nanofiber films with different thicknesses by the physical vapor deposition method; then, PDMS and a curing agent (the ratio is 10:1) are uniformly mixed, a glass substrate is first uniformly spin coated with a layer of PDMS with a thickness of about 5μm, the gold nanoparticle-carbon nanofiber film is closely attached to the glass substrate to avoid the generation of bubbles; then, the carbon nanofiber film is spin coated with a layer of PDMS with a thickness of about 100μm on the carbon nanofiber film, and a gold nanoparticle-carbon nanofiber-PDMS composite layer photo-induced ultrasonic transducer of three different thicknesses of carbon nanofiber is obtained by vacuum drying and curing. As shown in Figure 5 Under the irradiation of laser energy density of 25mJ / cm 2 Under the irradiation of laser energy density, the acoustic intensity obtained by the spinning solution with an amount of 1ml and 2ml is about 5MPa, and the acoustic intensity obtained by the spinning solution with an amount of 3ml is about 7MPa, so it can be concluded that the acoustic intensity is the largest when the amount of the spinning solution is 3ml.

[0069] 3) The absorbance of the laser ultrasonic transducer prepared in Example 3 at a wavelength of 400-800nm is measured by a spectrophotometer. As shown in Figure 6 As shown in the figure, the absorbance of the gold nanoparticle-carbon nanofiber film-PDMS composite layer is higher than that of the carbon nanofiber film-PDMS composite layer at a wavelength of 400-800nm.

[0070] In summary, the present application provides a preparation process of a laser ultrasonic transducer, and the preparation process is simple. A new type of laser ultrasonic transducer structure is provided by using the photo-induced ultrasonic effect, and the laser ultrasonic transducer has smaller ultrasonic attenuation and higher ultrasonic wave conversion; when pulsed laser acts on the ultrasonic transducer, a high-intensity ultrasonic signal is generated.

[0071] The above merely illustrates the embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent transformation or direct or indirect application in other related technical fields based on the content of the present application is also included in the patent protection scope of the present application.

Claims

1. A method for preparing a carbon nanofiber-based photoacoustic transducer, characterized in that: The photoacoustic transducer is a metal nanoparticle-carbon nanofiber-PDMS photoacoustic transducer, wherein the metal nanoparticles and carbon nanofiber membrane serve as light absorption parts, and PDMS serves as thermal expansion part; The preparation method comprises the following steps: 1) Use electrospinning to spin polyacrylonitrile (PAN) membrane, and control the thickness of the PAN membrane by adjusting the spinning time and solution volume; 2) Carbonizing the PAN fiber membrane at high temperature in an inert gas to obtain a carbon nanofiber membrane; 3) Using physical vapor deposition to grow metal nanoparticles on the surface of the carbon nanofiber membrane to obtain a metal nanoparticle-carbon nanofiber composite membrane. The physical vapor deposition method is selected as magnetron sputtering. By controlling the deposition rate and time of magnetron sputtering, the depth, number and diameter of the metal nanoparticles deposited in the gaps of the carbon nanofiber are controlled; 4) Preparation of a metal nanoparticle-carbon nanofiber-PDMS composite layer on a quartz glass sheet; 5) placing the quartz glass sheet together with the metal nanoparticle-carbon nanofiber-PDMS composite layer in a vacuum drying oven and heating and curing them in a vacuum to obtain a photoinduced ultrasonic transducer; In step 1), the electrospinning voltage is controlled at 16 kV to 20 kV; the distance from the needle to the receiving plate is 15 cm to 20 cm; the feed rate of the electrospinning liquid is 0.8 ml / h; the ambient temperature is 25°C to 28°C, and the ambient humidity is 30% to 40%; In the step 1), the spinning time is 40 min-230 min; and the amount of the spinning solution is 1 ml-3 ml.

2. The preparation method according to claim 1, characterized in that In the step 2), the carbonization temperature is 700-900°C. The specific process of high-temperature carbonization is as follows: heating to 700-900°C at a heating rate of 5°C / min in nitrogen or argon, and the carbonization time is 60-120 min.

3. The preparation method according to claim 1, characterized in that In the step 2), the thickness of the carbon nanofiber membrane is 1-50 mm.

4. The preparation method according to claim 1, characterized in that In the step 3), the deposition rate of magnetron sputtering is 0.1 nm / s-0.2 nm / s, and the time of magnetron sputtering is 1 min-2 min.

5. The preparation method according to claim 1, characterized in that In the step 3), the metal material is gold or silver, and the thickness of the metal nanoparticles is 8-20 nm.

6. The preparation method according to claim 1, characterized in that The specific process of step 4) is as follows: PDMS and a curing agent are mixed and stirred at a mass ratio of 10:1, and then allowed to stand in a vacuum until the bubbles in the PDMS mixture are completely dissipated; the stirred PDMS mixed solution is first spin-coated on a quartz glass substrate to a thickness of 5 mm, and the metal nanoparticle-carbon nanofiber composite film is adhered thereto, ensuring that there is no gap between the metal nanoparticle-carbon nanofiber composite film and the quartz glass substrate; the PDMS mixed solution is then evenly spin-coated on the metal nanoparticle-carbon nanofiber composite film to a thickness of 100 mm, so that the thermal expansion material PDMS and the metal nanoparticle-carbon nanofiber composite film can fully contact each other, thereby obtaining a metal nanoparticle-carbon nanofiber-PDMS composite layer.

7. The preparation method according to claim 6, characterized in that In the step 4), the stirring time is 1-30 min.

8. The preparation method according to claim 1, characterized in that In the step 5), the vacuum heating time is 20-200 min, and the heating temperature is 80-120°C.

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