Method for driving liquid circulation through laser

Abstract

The invention provides a method for driving liquid circulation through laser, and belongs to the field of light-controlled flow, and the method comprises the following steps: selecting a rectangular vessel; selecting an iron sheet, and polishing the iron sheet; the polished iron sheet is attached to the inner side of the side face of a rectangular vessel, deionized water is added into the rectangular vessel, and a part of the iron sheet is soaked in liquid; a laser and a convex lens are arranged on the outer side, away from the iron sheet, of the rectangular vessel, and the convex lens is arranged between the rectangular vessel and the laser; a laser is used for emitting laser, the emitted laser is focused by a convex lens and then enters an iron sheet, an incidence point after focusing is located on the iron sheet 2-3 mm above deionized water, and it is guaranteed that the incidence point is not located on the center line of the iron sheet in the vertical direction; and the energy of the laser only drives the liquid surface to move and promotes the liquid on the surface to form large circulation in a limited whole container. According to the invention, long-range and stable liquid circulation driven by laser is realized, the control source is single, and the control precision is high.

Description

Technical Field

[0001] The present invention belongs to the field of light-controlled flow, and particularly relates to a method for laser-driven liquid circulation. Background Art

[0002] Light-controlled flow technology has a large number of applications in microfluidic systems, biological and chemical basic research, and medical devices. Driving fluids with light has excellent characteristics such as no energy loss, no contact and no pollution, and easy precise control in time and space. Since photons have linear momentum and mechanical kinetic energy, and laser has been widely used in this field due to its significant advantages of high intensity, high directivity and monochromaticity. Transferring the momentum of laser to fluids and efficiently and precisely controlling fluids has been a research hotspot in recent decades. Currently, there are mainly the following four methods to achieve light-controlled flow:

[0003] Optical momentum drive. Deformation is generated through optical momentum to control fluids. A laser beam irradiates on the interface between two immiscible liquids with different refractive indices, and optical radiation pressure is generated to cause surface distortion between the two liquid surfaces, that is, the interface distorts towards the side with the lower refractive index in the two liquids. Optical tweezers technology is also one of them.

[0004] Photothermal drive. The surface tension of the liquid surface is locally changed through the photothermal effect to control fluids. When a laser irradiates at the interface between two liquids, the temperature of the irradiated part increases. After the temperature increases, the density of liquid molecules decreases, resulting in an obvious difference in the surface tension of the two liquid surfaces, and then forming a surface tension difference gradient, causing the liquid to flow from the place with high surface tension to the place with low surface tension, forming the Marangoni effect.

[0005] Light-modulated voltage drives fluids. It is realized by integrating a photoconductive material under an electrowetting electrode, that is, a charged micro-droplet is attached to an electrode covered with an optically conductive medium. By changing the irradiation of the laser, the conductivity of the medium itself changes, and then the potential difference changes, so that the attachment angle of the micro-droplet becomes smaller, and the droplet can be driven to move.

[0006] Optical ultrasonic-driven fluid motion. In 2017, Wang et al. irradiated a cuvette filled with gold nanoparticle solution with a pulsed laser of 527 nm. After focusing the laser on the front surface of the cuvette, after a processing time of several minutes or ten minutes, a strong linear jet could be observed on the surface of the cuvette where the laser was incident through a CCD camera. The maximum jet speed could reach 4 cm / s. Injecting gold nanoparticles into the four walls of the cuvette or attaching a glass substrate coated with a gold nanolayer to the four walls of the cuvette could also generate a strong linear jet at the laser incidence point. This is because gold has an absorption peak near 527 nm. When a laser with a wavelength near the absorption peak in the metal spectrum irradiates the metal, the metal undergoes a surface plasmon resonance effect, absorbs a large amount of laser light and partially converts it into ultrasonic waves. The ultrasonic waves have kinetic energy and then drive the fluid to perform a directional movement perpendicular to the surface of the cuvette. An ultrasonic signal detector placed in the solution also successfully detected the ultrasonic signal.

[0007] When further studying the factors affecting the jet intensity, it was found that ordinary metals such as iron and tungsten could also achieve the same jet effect because the absorption peaks of iron and tungsten in the visible light range were also in the green light band (459 - 570 nm). However, since the laser could not penetrate the metal iron and metal tungsten layers, the generated laser was reflected at the metal layer, so the direction of the jet was completely opposite, that is, opposite to the laser incidence direction, and a linear return flow occurred. However, since the jet was completely in the liquid at this time, the driving force generated by the laser was consumed by the liquid in all directions, and the generated jet could not maintain a long path (about 3 - 5 cm). Summary of the Invention

[0008] The object of the present invention is to provide a method for laser-driven liquid circulation to solve the technical problem in the prior art that laser-driven fluid motion can only achieve linear motion and cannot achieve circulation.

[0009] To solve the above technical problem, the method for laser-driven liquid circulation of the present invention includes the following steps:

[0010] Step S1: Select a rectangular container, the selected rectangular container is lidless and transparent, and has the characteristic of high temperature resistance;

[0011] Step S2: Select an iron sheet, and polish the iron sheet with 800 - 1200 mesh sandpaper to remove the iron oxide on the surface of the iron sheet;

[0012] Step S3: Attach the polished iron sheet to the inner side of the side where the width and height of the rectangular container are located, and add deionized water to the rectangular container. The height of the added deionized water is 2 / 3 of the height of the rectangular container, so that a part of the iron sheet is immersed in the liquid;

[0013] Step S4: Place the laser and the convex lens outside the rectangular container, away from the iron sheet, with the convex lens positioned between the rectangular container and the laser.

[0014] Step S5: Use the laser to emit laser light. The emitted laser light is focused by the convex lens and then incident on the iron sheet. The focused incident point is on the iron sheet 2 - 3 mm above the deionized water, and it is ensured that the incident point is not on the vertical center line of the iron sheet to form a non - equilibrium liquid surface state, breaking the equilibrium state of the liquid surface tension, so that the energy of the laser only drives the movement of the liquid surface and promotes the formation of a large circulation of the surface liquid in the rectangular container.

[0015] Further, the length of the iron sheet is equal to the inner width of the rectangular container, the width of the iron sheet is equal to the inner height of the rectangular container, and the thickness of the iron sheet is 1 mm.

[0016] Further, the length of the rectangular container is less than the focal length of the convex lens.

[0017] Further, the laser is a 532 - nm pulsed laser or a semiconductor laser.

[0018] Further, the laser parameters are 1 KHz and 300 mW.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] 1) The present invention realizes long - range and stable liquid circulation driven by laser. The way of only pushing the liquid surface makes the energy generated by the laser dissipated only in a two - dimensional plane, enhancing the utilization efficiency of the laser as a power source compared with underwater. At the same time, it can promote the research on acoustic non - reciprocal propagation in the circulation medium.

[0021] 2) The control source of the present invention is single and the control precision is relatively high. Except for the laser as the control source, no other physical fields need to be added, and the requirement for setting up the experimental environment is low. The fewer control sources also result in the fact that the results are not affected by other redundant conditions, only strictly related to the laser power, and the controllability is strong.

[0022] 3) The present invention is non - contact. It does not require any external rotating shafts, wires, etc. for connection, and the laser source can also be remotely controlled without direct contact with the equipment. It has higher flexibility.

[0023] 4) The equipment used in the present invention is simple, the cost is relatively low, and the results are easy to reproduce. Description of the Drawings

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 Schematic diagram of the laser-driven fluid circulation device of the present invention.

[0026] Figure 2 Schematic diagram of the laser driving liquid circulation in the top view direction at the center of the present invention.

[0027] Figure 3 Schematic diagram of the laser driving liquid circulation in the top view direction at a non-center of the present invention.

[0028] Reference numerals in the figure: 1 - rectangular vessel, 2 - iron sheet, 3 - laser, 4 - convex lens. Specific embodiments

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0030] As Figure 1 shown, a laser-driven liquid circulation device proposed by the present invention is shown. The device includes a rectangular vessel 1, an iron sheet 2, a laser 3, and a convex lens 4. The iron sheet 1 is vertically attached to the inside of one side of the rectangular vessel 2, and the laser 3 and the convex lens 4 are arranged outside the rectangular vessel away from the iron sheet 2, and the convex lens 4 is arranged between the rectangular vessel 1 and the laser 3.

[0031] The laser beam emitted by the laser 3 is refracted through the upper half of the convex lens 4 and the beam is focused on the iron sheet 2 at a position 2 - 3 mm above the liquid surface on one side of the rectangular vessel 1. The iron atoms at the laser incident point convert the energy of the laser into ultrasonic waves through the surface plasmon resonance effect and act on the water surface, breaking the equilibrium state of the water surface tension, and using this as the power to promote the generation of the jet.

[0032] Based on the above laser-driven liquid circulation device, the present invention proposes a method for laser-driven liquid circulation, and the method includes the following steps:

[0033] Step S1: Select a rectangular vessel, and the selected rectangular vessel is lidless and transparent and has the characteristic of being heat-resistant.

[0034] Further, the rectangular vessel is made of one of glass, quartz, and borosilicate glass.

[0035] Step S2: Select an iron sheet and polish it with 800 - 1200 - mesh sandpaper to remove the iron oxide on the surface of the iron sheet.

[0036] Further, the length of the iron sheet is equal to the width of the inner wall of the rectangular vessel, the width of the iron sheet is equal to the height inside the rectangular vessel, and the thickness of the iron sheet is 1 mm.

[0037] Step S3: Attach the polished iron sheet to the inner side of the side where the width and height of the rectangular vessel are located, and add deionized water to the rectangular vessel. The height of the added deionized water is about 2 / 3 of the height of the rectangular vessel, so that a part of the iron sheet is immersed in the liquid.

[0038] Step S4: Set the laser and the convex lens on the outer side of the rectangular vessel away from the iron sheet, and place the convex lens between the rectangular vessel and the laser.

[0039] Further, the laser can be a 532 - nm pulsed laser or a semiconductor laser with laser parameters of 1 KHz and 300 mW, or other green lasers with wavelengths near 524 nm can also be selected.

[0040] Further, the length of the rectangular vessel is slightly less than the focal length of the convex lens to ensure low dissipation of light in the air; a large difference between the length of the rectangular vessel and the focal length of the convex lens will result in a long propagation distance of the laser in the air and cause large dissipation. During use, the length of the rectangular vessel can be determined according to the focal length of the convex lens, or a convex lens with a suitable focal length can be selected according to the length of the rectangular vessel.

[0041] Step S5: Use the laser to emit laser light. The emitted laser light is focused by the convex lens and then incident on the iron sheet. The focal point of the incident light is on the iron sheet 2 - 3 mm above the deionized water. The iron atoms at the laser - incident position absorb the energy of the laser and generate a surface plasmon resonance effect, converting light energy into sound energy as the driving force for the liquid flow on the liquid surface. And ensure that the incident point is not on the vertical center line of the iron sheet to form a non - equilibrium liquid surface state, breaking the equilibrium state of the liquid surface tension, so that the energy of the laser only drives the movement of the liquid surface and promotes the surface liquid to form a large - scale circulation in the entire limited container.

[0042] In the present invention, the focused laser beam irradiates the iron sheet at the liquid surface. The iron sheet converts the energy of the laser to break the surface tension of the liquid, promoting the generation of a jet flow and circulating in the container. The present invention only promotes the movement of the liquid surface, so that the energy generated by the laser is only dissipated in a two - dimensional plane, enhancing the utilization efficiency of the laser as a power source and enabling the laser - driven circulation phenomenon to exist stably for a long time.

[0043] Figure 2It shows the linear flow of the liquid when the laser is incident on the exact center of the metal iron sheet (which is also the center of the container) from an overlooking perspective. In this two-dimensional plane at the water-air interface, when the laser power is 300 mW, the jet is linear with a speed of about 5 cm / s. The jet path is much longer than the side length of the container, which is 8 cm. When the jet reaches the opposite side, due to the obstruction and reflection of the container wall, the jet starts to return. Since the spaces on both sides are the same, the water flows back the same amount to both sides and forms two circulation loops in opposite directions with the same size. The dynamic forces on both sides cancel each other out, making the direct flow in the middle dominant. This state continues until the opposite side of the container, being long-range and stable.

[0044] Figure 3 It shows the ideal circulation situation of the present invention, that is, the liquid circulation state when the laser is incident on a non-center position of the metal iron sheet from an overlooking perspective. The generation of the jet at a non-center position results in different spaces for the liquid to flow back on both sides in the two-dimensional plane. The side with a smaller return space requires a larger return speed, causing the overall liquid flow to move towards the side with a larger return space, thus forming a biased circulation as a whole. As the jet intensity increases, the circulation loop becomes larger and larger, forming a complete circulation in the entire container, achieving the effect of laser-driven liquid rotation and circulation.

[0045] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and embodiments. Additionally, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A method for laser-driven liquid circulation, characterized in that: The method comprises the following steps: Step S1: Select a rectangular container, the selected rectangular container is transparent without a cover and has high temperature resistance; Step S2: Select an iron sheet and polish it with 800-1200 mesh sandpaper to remove iron oxide on the surface of the iron sheet; Step S3: stick the polished iron sheet to the inner side of the side where the width and height of the rectangular container are located, and add deionized water into the rectangular container. The height of the added deionized water is 2 / 3 of the height of the rectangular container, so that a part of the iron sheet is immersed in the liquid; Step S4: placing the laser and the convex lens on the outer side of the rectangular container away from the iron sheet, and placing the convex lens between the rectangular container and the laser; Step S5: Use a laser to emit laser, and the emitted laser is focused by a convex lens and incident on the iron sheet. The incident point after focusing is located on the iron sheet 2-3 mm above the deionized water, and it is ensured that the incident point is not on the center line of the vertical direction of the iron sheet to form an unbalanced liquid surface state, breaking the equilibrium state of the liquid surface tension, so that the energy of the laser only drives the movement of the liquid surface and causes the surface liquid to form a large circulation in the rectangular container.

2. The method for laser-driven liquid circulation according to claim 1, characterized in that: The length of the iron sheet is equal to the width of the inner wall of the rectangular container, the width of the iron sheet is equal to the height inside the rectangular container, and the thickness of the iron sheet is 1 mm.

3. The method for laser-driven liquid circulation according to claim 1, characterized in that: The length of the rectangular vessel is less than the focal length of the convex lens.

4. The method for laser-driven liquid circulation according to claim 1, characterized in that: The laser is a 532nm pulse laser or a semiconductor laser.

5. The method for laser-driven liquid circulation according to claim 1, characterized in that: The laser parameters are 1KHz, 300mW.

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