A method for periodic generation of cavitation bubbles based on laser plasmon effect

Abstract

The present application relates to the field of micro-nano fluid, in particular to a cavitation bubble periodic generation method based on laser plasmon effect. The method uses continuous wave laser in plasmon resonance wave band, which is focused by a microscope objective and irradiated to the surface of a fused quartz sample covered with noble metal nanoparticles placed in liquid water environment; the laser spot is positioned near the solid object on the sample surface in advance, and the laser is turned on, the laser with power exceeding the threshold value will induce micron-scale cavitation bubble nucleation, growth and collapse at the laser spot position; the solid object near the laser spot as the flow field boundary will make the bubble produce movement towards the solid object during the collapse process, so that the bubble nucleus after collapse is pinned out of the laser spot area; the laser spot area is covered by liquid again, and under the condition of continuous laser energy input, cavitation bubble nucleation can be induced again at the laser spot position, thus forming a high-frequency, periodic cavitation bubble nucleation, growth and collapse process. The operation of the present application to realize the periodic generation of cavitation bubbles is very simple and easy to realize, can produce strong disturbance to the local fluid, and can realize the control of the generation frequency, size, periodic generation area range size of cavitation bubbles.

Description

Technical Field

[0001] This invention relates to the field of micro- and nanofluids, specifically to a method and technique for the periodic and cyclical generation of micron-sized cavitation bubbles near a solid object based on the laser plasmon effect. Background Technology

[0002] With the widespread application of microfluidic chips in important fields such as point-of-care diagnostics, blood testing, micro-reaction containers, and drug development, they have received considerable attention in the past two decades. However, the pursuit of miniaturization, efficiency, portability, and environmental friendliness has intensified the contradiction between the low Reynolds number flow dominated by laminar flow within microfluidic devices and more efficient and precise micro- and nano-fluidic motion. Therefore, finding more efficient active perturbation methods for microfluidics is of paramount importance.

[0003] Currently, commonly used methods for microfluidic disturbance include surface acoustic wave (SAW) vibration, centrifugation, and the hot Marangoni method. SAW vibration relies on pre-designed microstructures within the microchannel to generate vibrations under ultrasonic action, thus disturbing the fluid within a localized area. This includes using air bubbles trapped at designed apertures within the microchannel as the liquid flows, and pre-designed and fabricated microstructures within the microchannel. Centrifugation requires the pre-design of multiple annular flow channels within the microchannel, utilizing the centripetal acceleration generated by the liquid flow to mix and disturb the inner and outer fluids. The hot Marangoni method is based on bubbles generated during laser irradiation. A second laser beam heats the gas-liquid interface, inducing localized hot Marangoni convection, achieving large-scale disturbance of the fluid within a localized area.

[0004] In summary, both surface acoustic wave (SAW) vibration and centrifugation methods require specific design of the microchannels in advance, inevitably leading to complex electrical connections, limited applicability to various scenarios, and complex implementation processes. The hot Marangoni method requires simultaneous control of multiple beams, making operation difficult. Therefore, novel microfluidic perturbation methods that are simple, easy to use, and highly applicable are particularly important. Cavitation bubbles based on the laser plasmon resonance effect, with an expansion velocity of ~20 m / s, can induce strong micron-level local perturbations. By utilizing the channel walls or colloidal microspheres in the microchannel to induce flow field asymmetry, cavitation bubbles can be periodically generated in the local fluid, resulting in strong local flow field perturbations. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing microfluidic perturbation technologies by proposing a technical method for the periodic and cyclic generation of micron-sized cavitation bubbles near solid objects based on the laser plasmon effect, thereby achieving localized fluid perturbation that is simple to operate, low in cost, and highly efficient.

[0006] To achieve the above objectives, the present invention includes: providing a method for periodic generation of cavitation bubbles based on the laser plasmon effect. This method uses a continuous-wave laser located in the plasmon resonance band, which, after being focused by a microscope objective, irradiates the surface of a fused silica sample covered with noble metal nanoparticles placed in a liquid water environment; the laser spot is pre-adjusted to be positioned near a solid object on the sample surface; the laser is then turned on, and laser power exceeding a threshold will induce the nucleation, growth, and collapse of micron-sized cavitation bubbles at the spot location; the solid object near the spot acts as a flow field boundary, causing the bubbles to move towards the solid object during collapse, thereby causing the collapsed bubble nuclei to detach from the spot area and become pinned; the spot area is then re-covered by liquid, and under continuous laser energy input, the spot location can induce another round of cavitation bubble nucleation, thus forming a high-frequency, periodic process of cavitation bubble nucleation, growth, and collapse.

[0007] Furthermore, the noble metal nanoparticles are gold nanoparticles.

[0008] Furthermore, the solid object is a flat cuboid or spherical object, existing on the sample surface as a flow field boundary.

[0009] Furthermore, the distance L between the laser spot and the solid object is less than 500 μm.

[0010] Furthermore, this invention uses a laser located in the plasmonic resonance band to irradiate noble metal nanoparticles, rapidly converting light energy into heat, causing the surrounding liquid to vaporize and generate cavitation bubbles.

[0011] Furthermore, by adjusting the laser spot to the vicinity of a solid object, the present invention can break the symmetry of the fluid environment around the cavitation bubble, causing the bubble to move under asymmetrical pressure, break free from the pinning of the spot area, and allow the liquid to re-cover the spot area.

[0012] Furthermore, by changing the power of the input laser, the frequency and size of the periodic generation of cavitation bubbles can be controlled.

[0013] Furthermore, by changing the power of the input laser, the size of the region containing the periodic cavitation bubble can be controlled.

[0014] Furthermore, by modulating the pulse width of the input laser, the frequency of periodic generation of cavitation bubbles can be controlled.

[0015] The effects of the invention

[0016] Compared with previous methods, this invention can achieve the periodic generation of cavitation bubbles based on the laser plasmon effect simply by adjusting the laser spot to the vicinity of the solid object; and by adjusting the laser intensity and pulse width modulation, the generation frequency, size, and periodic generation area of ​​the cavitation bubbles can be controlled. It is simple to operate and easy to implement. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the operation of generating periodic cavitation bubbles according to the present invention.

[0018] Figure 2 This is a time series diagram of a 100kHz periodic cavitation bubble example implemented in this invention.

[0019] Figure 3 This is a time series diagram of an example of periodic cavitation bubbles at approximately 10 kHz, as implemented in this invention.

[0020] Figure 4 This is a time series diagram of an example of periodic cavitation bubbles at 12.5 kHz implemented in this invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below with reference to the accompanying drawings.

[0022] This invention, based on the relative position control between the solid object on the surface of a fused silica sample and the laser spot, breaks the symmetry of the flow field boundary conditions, causing cavitation bubbles to collapse and move asymmetrically. The spot area is then re-covered by liquid, preventing the continued growth of bubble nuclei in the spot area. This achieves simple and efficient high-frequency periodic generation of surface cavitation bubbles, providing a powerful tool for precise local fluid perturbation. The entire implementation process is as follows: Figure 1 As shown, the sample includes a fused silica sample 1 covered with noble metal nanoparticles, a solid object 2, a continuous wave laser 3, and cavitation bubbles 4. The distance L between the laser spot and the solid object is L.

[0023] Before implementation, the laser spot is positioned near a solid object on the sample surface, and the laser power is adjusted to exceed the threshold power. During implementation, the laser is turned on and kept in a normally open state or pulse width modulation is performed according to a preset duty cycle. The plasmon effect rapidly converts light energy into heat, causing the surrounding liquid to vaporize and periodically generate cavitation bubbles.

[0024] The inventors of this invention have conducted experiments, and the data results are given in the following embodiments.

[0025] Example 1

[0026] The laser power was set to 135mW, the distance L between the center of the laser spot and the solid object was 15μm, and a high-speed camera was used to acquire real-time images of the generated cavitation bubbles.

[0027] like Figure 2 As shown in the figure, the experiment shows that when the laser is turned on and the sample surface is irradiated, cavitation bubbles are generated at the spot position. When the bubbles undergo the collapse process, they move toward the solid object. The spot area is covered by liquid again, which prevents the bubble nucleus from continuing to grow in the spot area, and realizes the periodic generation of cavitation bubbles on the sample surface at 100Khz.

[0028] Example 2

[0029] The laser power was set to 74mW, the distance L between the center of the laser spot and the solid object was 40μm, and a high-speed camera was used to acquire real-time images of the generated cavitation bubbles.

[0030] like Figure 3 As shown, the experiment shows that when the laser is turned on and the sample surface is irradiated, cavitation bubbles are generated at the spot position, and the bubble size is larger than that in Example 1. When the bubble undergoes the collapse process, it moves towards the solid object, and the spot area is covered by liquid again, which prevents the bubble nucleus from continuing to grow in the spot area, and achieves the periodic generation of cavitation bubbles on the sample surface at about 10 kHz.

[0031] Example 3

[0032] The laser power was set to 135mW, the distance L between the center of the laser spot and the solid object was 15μm, and the laser was pulse width modulated with a 35% duty cycle (i.e., the laser on time was 28μs and the laser off time was 52μs in each laser cycle). A high-speed camera was used to acquire real-time images of the generated cavitation bubbles.

[0033] like Figure 4 As shown, the experiment shows that when the laser is turned on and irradiates the sample surface, cavitation bubbles are generated at the spot position. The bubble size is similar to that in Example 1. When the bubble undergoes the collapse process, it moves towards the solid object. The spot area is covered by liquid again, which prevents the bubble nucleus from continuing to grow in the spot area, and achieves the periodic generation of cavitation bubbles on the sample surface at about 12.5 kHz.

[0034] The experimental comparison between Example 1 and Example 2 shows that by adjusting the laser power, the frequency and size of the periodic generation of cavitation bubbles can be controlled, and the size of the area where the laser spot is located can be controlled to achieve the periodic generation of cavitation bubbles.

[0035] The experimental comparison between Example 1 and Example 3 shows that by modulating the pulse width of the input laser, the frequency of periodic generation of cavitation bubbles can be controlled.

Claims

1. A method for periodically generating cavitation bubbles based on the laser plasmon effect, characterized in that: This method uses a continuous-wave laser located in the plasmon resonance band, which is focused by a microscope objective and irradiated onto the surface of a fused silica sample covered with noble metal nanoparticles placed in a liquid water environment. The laser spot is pre-positioned near a solid object on the sample surface. When the laser is turned on, the laser power exceeding the threshold will induce the nucleation, growth, and collapse of micron-sized cavitation bubbles at the spot location. The solid object near the spot acts as a flow field boundary, causing the bubbles to move towards the solid object during the collapse process, thereby causing the collapsed bubble nuclei to detach from the spot area and become pinned. The spot area is then re-covered by liquid, and with continuous laser energy input, another cavitation bubble nucleation can be induced at the spot location, thus forming a high-frequency, periodic cavitation bubble nucleation, growth, and collapse process.

2. The method for periodically generating cavitation bubbles based on laser plasmon resonance effect according to claim 1, characterized in that: The precious metal nanoparticles are gold nanoparticles.

3. The method for periodically generating cavitation bubbles based on laser plasmon resonance effect according to claim 1, characterized in that: The solid object is a flat rectangular or spherical object that exists on the sample surface as a flow field boundary.

4. The method for periodically generating cavitation bubbles based on laser plasmon resonance effect according to claim 1, characterized in that: The distance L between the laser spot and the solid object is less than 500 μm.

5. The method for periodically generating cavitation bubbles based on laser plasmon resonance effect according to claim 1, characterized in that: Using a laser located in the plasmonic resonance band to irradiate noble metal nanoparticles, the light energy is rapidly converted into heat, causing the surrounding liquid to vaporize and generate cavitation bubbles.

6. The method for periodically generating cavitation bubbles based on laser plasmon resonance effect according to claim 1, characterized in that: The presence of solid objects disrupts the symmetry of the fluid environment surrounding cavitation bubbles, causing the bubbles to move under asymmetrical pressure, break free from the pinning of the light spot area, and allow the liquid to re-cover the light spot area.

7. The method for periodically generating cavitation bubbles based on laser plasmon resonance effect according to claim 1, characterized in that: By changing the power of the input laser, the frequency and size of the periodic generation of cavitation bubbles can be controlled.

8. The method for periodically generating cavitation bubbles based on laser plasmon resonance effect according to claim 1, characterized in that: By changing the power of the input laser, the size of the region containing the periodic cavitation bubble can be controlled.

9. The method for periodically generating cavitation bubbles based on laser plasmon resonance effect according to claim 1, characterized in that: By modulating the pulse width of the input laser, the frequency of periodic generation of cavitation bubbles can be controlled.

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