Method for controlling the direction of motion of a microsuspension droplet by laser-droplet interaction

Abstract

The application provides a method for controlling micron suspension droplet movement by laser-droplet reaction, which comprises the following steps: uniformly mixing graphene oxide with solvent water by ultrasonic; atomizing the mixed solution by ultrasonic to obtain microdroplets containing graphene oxide sheet layers; blowing the graphene oxide micron suspension droplets atomized by ultrasonic into a laser beam; the laser and the droplets generate optical effect, ionization decomposition reaction and phase change evaporation reaction to generate optical pressure, ionization reaction thrust and evaporation thrust, and the resultant force drives the droplets to move; the cooperation force direction and size change with the droplet size, and the large-sized droplets are driven to form back light movement, and the small-sized droplets are driven to move towards light. The application can control the back light movement of large-sized droplets and the movement towards light of small-sized droplets, has simple process, obvious effect and simple device, and does not need to rely on complex components or systems.

Description

Technical Field

[0001] This invention belongs to the field of optical-fluid dynamics and relates to a method for controlling the motion of micron-sized suspended droplets, specifically a method for controlling the suspended motion of micron-sized droplets by laser-droplet reaction. Background Technology

[0002] Droplets are a common form of matter in the natural environment, daily life, and industrial production. Controlling droplet motion has always been a hot research topic across various industries and academia. In the microscopic world, due to the small size of micrometer-sized droplets (typically less than 10 micrometers), they experience significant viscous drag during motion, causing them to typically suspend in a medium and move relatively slowly relative to the surrounding medium (the relative speed of a 5-micrometer water droplet falling in air is approximately 0.2 μm / s). Therefore, micrometer-sized suspended droplets usually move with the surrounding medium, and their direction of motion is primarily influenced by the surrounding medium, making directional motion difficult. In fields such as chemistry, chemical engineering, fluid mechanics, and surface science, the direction and behavior of droplet motion are key factors in applications such as reaction synthesis, liquid collection, evaporation, and condensation. Controlling the direction of motion of micrometer-sized suspended droplets has a wide-ranging impact across these fields.

[0003] Currently, optical tweezers are a technology for capturing and controlling the motion of suspended droplets. This technology uses a highly focused laser beam to create an optical trap, thereby capturing the droplet and controlling its spatial position by moving the focal point. It is non-contact and non-destructive. However, traditional optical tweezers technology has the following characteristics when controlling micron-sized droplets: 1. After the laser beam is generated, it needs to be focused by a complex optical system before irradiating the droplet surface to form the necessary optical trap; 2. The focal point of the laser beam needs to be moved to control the droplet's motion, and the movement speed is relatively slow (less than 0.1 mm / s); 3. The optical trap formed by a single optical tweezer (a region with x, y, and z all less than 10 μm) can only control a specific droplet at a specific location in space (CN101149449A+ A dual-core single-fiber optical tweezer for capturing microparticles and its fabrication method). As can be seen from the above characteristics, in the field of micron suspended droplet motion control, optical tweezers technology has problems such as large system size, complex structure, high operation requirements and small operation range, making it difficult to achieve low cost, simple system, simple operation and large-scale control in the field of micron suspended droplet motion control. Summary of the Invention

[0004] To address the aforementioned technical problems in the prior art, this invention provides a method for controlling the motion of micron-sized suspended droplets through laser-droplet reaction. The method aims to utilize the interaction between a laser and a micron-sized suspended droplet, and to generate forces through ionization, optical diffraction, and phase transition reactions during the process. By using the combined force, the motion of the micron-sized suspended droplet can be controlled, enabling large-sized suspended droplets to move against the light and small-sized suspended droplets to move towards the light (backward motion).

[0005] The technical solution adopted in this invention is as follows: A method for controlling the movement of micron-sized suspended droplets by laser-droplet reaction, comprising the following steps:

[0006] Step (1): Ultrasonically mix graphene oxide and solvent to obtain graphene oxide solution, and then atomize the graphene oxide solution by ultrasonication to obtain micron-sized suspended droplets of graphene oxide.

[0007] Step (2): Blow graphene oxide micron suspension droplets into the laser beam so that the graphene oxide micron suspension droplets interact with the laser. After the laser beam is emitted, it does not need to go through an additional optical system for processing and directly irradiates the droplets, thus interacting with the suspension droplets.

[0008] Step (3): After the graphene oxide micron suspended droplets interact with the laser, they generate interaction forces, including light pressure, ionization reaction thrust and evaporation thrust. The light pressure of the laser propagating from top to bottom is in the same direction as the laser propagation (downward), while the ionization reaction thrust and evaporation thrust are in the opposite direction to the laser propagation (upward).

[0009] In step (4), the graphene oxide micron suspended droplets are subjected to the combined effects of light pressure, ionization reaction thrust, and evaporation thrust. The direction and magnitude of the combined forces are affected by the size of the suspended droplets. Larger suspended droplets move away from the light, while smaller suspended droplets move towards the light.

[0010] Furthermore, the ratio of graphene oxide, ultrasonic atomization parameters, and laser parameters need to be matched to achieve laser-droplet reaction control of the movement direction of micron-sized suspended droplets.

[0011] Furthermore, in step (1), the solvent is water, the concentration of the graphene oxide solution is any one of 0.01 g / L–1 g / L, the ultrasonic atomization frequency is 10-30 MHz, the ultrasonic atomization power is 40-60 W, and the diameter of the graphene oxide micron suspended droplets is less than 10 μm.

[0012] Furthermore, in step (2), the wavelength of the laser is 1064 nm, the pulse length is 10-1000 ns, and the power density is 0.1-10 GW / cm². 2 .

[0013] The parameters included: graphene oxide concentration of 0.1 g / L, ultrasonic atomization frequency of 17 MHz, ultrasonic atomization power of 50 W, laser pulse length of 133 ns, and power density of 2.5 GW / cm². 2 The optimal time to achieve laser-droplet reaction control of micron-sized suspended droplets is when the laser can achieve this. The generated graphene oxide droplets are mainly 3 μm in size, with a main range of 0–10 μm. The concentration of the graphene oxide solution affects the amount of graphene oxide inside the droplets; too low or too high a concentration will result in an excessively weak or strong subsequent laser-droplet reaction. Excessively high or low ultrasonic atomization power and frequency will result in droplet size distribution and main size that are too large or too small. Excessively high or low laser pulse length and power density will lead to an overly strong or weak laser-droplet reaction, resulting in a single upward or downward motion.

[0014] Furthermore, in step (3), the absolute value of the interaction force is related to the size of the suspended droplet, and the absolute value of the interaction force increases with the increase of the size of the suspended droplet; the light pressure is the light pressure of the suspended droplet affecting the spatial propagation of the laser; the ionization reaction thrust is the reaction thrust of the suspended droplet induced by the laser to produce ionization decomposition; the evaporation thrust is the laser heating of graphene oxide, which causes rapid evaporation on its surface and generates thrust on the suspended droplet.

[0015] Furthermore, in step (4), the direction and magnitude of the combined force of light pressure, ionization reaction thrust, and evaporation thrust on the suspended droplet change with the size of the suspended droplet. By adjusting the size of the suspended droplet, the direction and magnitude of the combined force driving the movement of the suspended droplet are controlled, thereby achieving the control of the movement direction of the micron-sized suspended droplet. Large droplets (diameter > 3 μm) move against the light (controlling the large droplet and the laser to move in the same direction). The downward light pressure generated by the interaction between the laser and the large droplet (diameter > 3 μm) is greater than the sum of the upward ionization reaction thrust and the upward evaporation thrust, causing the large droplet to move downward (against the light). Small droplets (diameter < 3 μm) move towards the light (controlling the small droplet and the laser to move in opposite directions). The downward light pressure generated by the interaction between the laser and the small suspended droplet (diameter < 3 μm) is less than the sum of the upward ionization reaction thrust and the upward evaporation thrust, causing the small droplet to move upward (towards the light). Based on the laser-droplet reaction energy, the movement direction of multiple suspended droplets within a large range can be controlled simultaneously, which can drive the droplets to move at high speed in space in a short time to achieve spatial displacement.

[0016] Furthermore, the laser beam irradiation range x, y > 10 μm, and the spatial range of at least 0.1 mm above and below the inherent focal plane of the laser (z > 100 μm); the simultaneous control of the motion direction of multiple suspended droplets is achieved within 0.25 ms to 1 ms, for at least 2-5 micrometer suspended droplets within the above-mentioned large area.

[0017] The beneficial effects of this invention are: it utilizes the combined force generated by the interaction between laser and micron-sized droplets to control the motion of micron-sized suspended droplets, and induces the optical effect, ionization reaction and phase transition reaction of the laser-droplet interaction, and adjusts the direction and orientation of the combined force by controlling the droplet size, thereby achieving optical motion of large droplets and optical motion of small droplets. The process is simple, the effect is obvious, the device is simple, and it does not rely on complex components or systems.

[0018] Compared to traditional optical tweezers, the method in this invention has the following advantages: 1. After the laser beam is generated, before it irradiates the droplet surface, no additional optical system is needed to focus it, and no optical trap needs to be formed to control the droplet; 2. The up-and-down movement of the droplet is controlled by controlling the droplet, without needing to move the focal point of the laser up and down; 3. Since there is no need to focus the laser beam to form an optical trap, droplets within the laser beam irradiation range (x, y>10μm, z>100μm) can be controlled, achieving spatial up-and-down movement.

[0019] This invention uses a high-energy-density laser beam to irradiate ultrasonically atomized graphene oxide microdroplets. By utilizing the combined force generated by the optical effects, ionization reactions, and phase transition reactions of the laser and the microdroplets, the movement direction of the micrometer-sized suspended droplets is controlled and powered.

[0020] The laser-droplet reaction of this invention generates a force sufficient to overcome the air resistance of micron-sized droplets moving at high speed, propelling the droplets to move at high speed in space for a short period of time. The sum of the forces generated by the laser-droplet reaction is about 1-100 nN, which can propel micron-sized droplets (diameter 1-10 μm) to overcome air resistance and move at high speed. The speed of the propelled suspended droplets is higher than 1 mm / s, enabling the micron-sized droplets to achieve spatial movement of 1 μm-50 μm within 0.25-1 ms. Attached Figure Description

[0021] Figure 1 The particle size distribution diagram of the ultrasonically atomized graphene oxide micron-sized suspended droplets in the example is shown.

[0022] Figure 2 This is a schematic diagram illustrating the forces involved in the optical interaction, ionization reaction, and phase transition reaction between the laser and the droplet in the embodiment.

[0023] Figure 3 This is a graph showing the relationship between the direction and magnitude of the laser-droplet reaction-generated photopressure, ionization reaction thrust, and evaporation thrust as a function of droplet size in the embodiment.

[0024] Figure 4 This is a graph showing the relationship between the direction and magnitude of the combined forces of photopressure, ionization reaction thrust, and evaporation thrust as a function of droplet size in the embodiment.

[0025] Figure 5This is a photograph of the laser-droplet reaction controlling the motion of a micron-sized suspended droplet in the example.

[0026] Figure 6 The example shows the simultaneous imaging of the motion direction of multiple micron-sized suspended droplets over a large spatial area using laser-droplet reaction.

[0027] Figure 7 This is a schematic diagram illustrating the atomization results of a previous study on a graphene oxide concentration of 0.33 g / L, at 25 MHz and 4 W.

[0028] Figure 8 This is a schematic diagram based on previous work on laser power density of 2GW / cm2, pulse length of 8ns, and droplet size >0.1mm.

[0029] Figure 9 This is a schematic diagram based on previous work using 25μm droplets, with laser energy densities of 600–4000 GW / cm², and the laser propagation direction from bottom to top.

[0030] Figure 10 This is a schematic diagram of traditional optical tweezers technology. Detailed Implementation

[0031] To facilitate understanding of the technical means, creative features, objectives, and effects of this invention, the following embodiments, in conjunction with the accompanying drawings, provide a detailed description of a laser-droplet reaction method for controlling droplet motion. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0032] A method for controlling the motion of micron-sized suspended droplets by laser-droplet reaction includes the following steps:

[0033] (1) Weigh 1g of graphene oxide and mix it with 1L of water using ultrasonication to obtain a graphene oxide solution with a concentration of 1g / L; take 100mL of the 1g / L graphene oxide solution and atomize it using ultrasonication at a frequency of 17MHz and a power of 50W to obtain micron-sized suspended droplets of graphene oxide. The particle size distribution is as follows: Figure 1 As shown, the horizontal axis represents the diameter of the micrometer-sized suspended droplets, and the vertical axis represents the statistical number of micrometer-sized suspended droplets;

[0034] (2) Micron-sized droplets of graphene oxide were blown into a laser beam by blowing air. The laser wavelength was 1064 nm, the laser pulse length was 100 ns, and the power density was 2.50 GW / cm². 2 The focal spot diameter is 20 μm; under the irradiation of the laser beam, the graphene oxide microdroplets will undergo optical effects, ionization reactions, and evaporation reactions.

[0035] (3) The laser-droplet reaction generates photopressure, ionization reaction thrust, and evaporation thrust. The directions of each force are as follows: Figure 2 As shown; the magnitudes of each force change with the droplet size, and as the droplet size increases, the absolute values ​​of each force tend to increase accordingly, such as... Figure 3 As shown (the laser propagation direction is negative, the force is negative if it is in the same direction as the laser propagation, and positive if it is in the opposite direction to the laser propagation);

[0036] (4) The graphene oxide suspension droplets are subjected to the combined effects of light pressure, ionization reaction thrust, and evaporation thrust. The direction and magnitude of these combined forces are influenced by the size of the droplets. Figure 4 As shown: The light pressure on small droplets is less than the sum of the ionization reaction thrust and the evaporation thrust. The ionization reaction thrust and the evaporation thrust overcome the light pressure and propel the droplets toward the light. The light pressure on large droplets is greater than the sum of the ionization reaction thrust and the evaporation thrust. The light pressure overcomes the ionization reaction thrust and the evaporation thrust and propels the droplets toward the back of the light.

[0037] (5) Large droplets move away from the light, while small droplets move towards the light, such as... Figure 5 As shown, the speed of the droplet is approximately 10 mm / s.

[0038] This method uses a high-energy-density laser beam to irradiate ultrasonically atomized micron-sized suspended droplets of graphene oxide. The combined force of the light pressure, ionization reaction thrust, and evaporation thrust generated by the reaction between the laser and the micron-sized droplets is used to control the movement of the micron-sized suspended droplets, thereby enabling large-sized droplets to move away from the light and small-sized droplets to move towards the light.

[0039] This method achieves motion control of micron-sized suspended droplets through laser-droplet interaction. It can simultaneously control the motion direction of a large number of droplets, with simple process, obvious effect, and simple device, without relying on complex components or systems.

[0040] Table 1 shows the results of previous studies (Kooij S, Astefanei A, Corthals GL, Bonn D. Sized distributions of droplets produced by ultrasonic nebulizers. Sci Rep. 2019 Apr 16; 9(1): 6128. doi: 10.1038 / s41598-019-42599-8. PMID: 30992484; PMCID: PMC6468117.) on the relationship between atomization power and ultrasonic frequency and the size of pure water droplets. High-frequency, high-power ultrasound easily atomizes small droplets, while low-frequency, low-power ultrasound atomizes larger droplets. This study provides a general relationship between the size of atomized droplets and ultrasonic power and frequency, providing a general rule for selecting ultrasonic power and frequency to prepare 3μm droplets in this invention.

[0041] Table 1 shows the general relationship between ultrasonic frequency, power, and the main diameter of the generated droplets. High frequency and high power produce small droplets, while low frequency and low power produce large droplets.

[0042] Ultrasonic frequency and power Main droplet size (micrometers) 9.6MHz, 100W 1.1 High frequency, high power 1700±50kHz, 30W 5.6 Medium frequency, medium power 105±5kHz, 2W 9.5 Low frequency, low power

[0043] Figure 7 The results from previous researchers (SMBalashov et al. 2012ECS Trans.49 445) on atomization at a graphene concentration of 0.33 g / L, 25 MHz, and 4 W showed that the main droplet size was 100 μm. To reduce the droplet size to 3 μm, the frequency was slightly increased while the power was significantly increased, and the solution concentration was slightly decreased (to reduce viscosity and facilitate atomization), according to the pattern in the table above. Based on the relationship between power, frequency, and atomized droplet size, this invention adjusts the concentration to 0.1 g / L combined with 50 W and 25 MHz as one of the better methods to generate 3 μm droplets.

[0044] Figure 8 Previous researchers (ALKlein, W. Bouwhuis, CW Visser, H. Lhuissier, C. Sun, J. H. S. Noeijer, E. Villermaux, D. Lohse, and H. Gelderblom, Phys. Rev. Appl. 3 (2015)) have reported a laser power density of 2 GW / cm², a pulse length of 8 ns, and a droplet size >0.1 mm (where the droplet moves in the same direction as the laser; if the droplet size is too large, the laser-microdroplet reaction in the formulation of this invention cannot be achieved). Therefore, this invention aims to control the droplet movement direction by adjusting the droplet size to 1-10 μm.

[0045] Figure 9 Previous researchers (S. Efimenko, YAMalkov, AAMurzanev, and AN Stepanov, PlasmaSources Sci Technol 31 (2014)) used 25μm droplets with laser energy densities of 600–4000 GW / cm², propagating the laser from bottom to top (excessive laser power resulted in a single, opposite direction of droplet motion). Therefore, this patent aims to control the droplet's motion direction by adjusting the laser power to 0.1–10 GW / cm². 2 .

[0046] Figure 10Traditional optical tweezers techniques, as used by predecessors (A. Ashkin, Phys. Rev. Lett. 24, 156 (1970)), can only control one or two droplets at a time, and the controlled droplet movement speed is relatively low (far less than 1 mm / s). This is because optical tweezers manipulate droplets using optical pressure, resulting in a small and singular force with a limited range of action, making it unable to efficiently control a large number of droplets. The embodiment of this patent acts on the droplets through optical pressure, evaporation thrust, and ionization reaction thrust, resulting in a larger force and the ability to control multiple droplets simultaneously, thus achieving greater efficiency.

[0047] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the motion of micron-sized suspended droplets via laser-droplet reaction, characterized in that: Includes the following steps: Step (1): Ultrasonically mix graphene oxide and solvent to obtain graphene oxide solution, and then atomize the graphene oxide solution by ultrasonication to obtain micron-sized suspended droplets of graphene oxide. Step (2): Blow graphene oxide micron suspension droplets into the laser beam so that the graphene oxide micron suspension droplets interact with the laser. After the laser beam is emitted, it does not need to go through an additional optical system to process the droplets directly and interact with the suspension droplets. Step (3): After the graphene oxide micron suspended droplets interact with the laser, they generate interaction forces, including light pressure, ionization reaction thrust and evaporation thrust. The light pressure of the laser propagating from top to bottom is in the same direction as the laser propagation, while the ionization reaction thrust and evaporation thrust are in the opposite direction to the laser propagation. In step (4), the graphene oxide micron suspended droplets are subjected to the combined effects of light pressure, ionization reaction thrust, and evaporation thrust. The direction and magnitude of the combined forces are affected by the size of the suspended droplets. Larger suspended droplets move away from the light, while smaller suspended droplets move towards the light. In step (1), the solvent is water, the concentration of the graphene oxide solution is any one of 0.01 g / L–1 g / L, the ultrasonic atomization frequency is 10-30 MHz, the ultrasonic atomization power is 40-60 W, and the diameter of the graphene oxide micron suspended droplets is less than 10 μm. In step (2), the laser wavelength is 1064 nm, the pulse length is 10-1000 ns, and the power density is 0.1-10 GW / cm². 2 .

2. The method for controlling the motion of micron-sized suspended droplets by laser-droplet reaction according to claim 1, characterized in that: The graphene oxide concentration was 0.1 g / L, the ultrasonic atomization frequency was 17 MHz, the ultrasonic atomization power was 50 W, the laser pulse length was 133 ns, and the power density was 2.5 GW / cm². 2 It can achieve laser-droplet reaction control of micron-sized suspended droplets.

3. The method for controlling the motion of micron-sized suspended droplets by laser-droplet reaction according to claim 2, characterized in that: In step (3), the absolute value of the interaction force is related to the size of the suspended droplet. The light pressure is the light pressure of the suspended droplet affecting the spatial propagation of the laser. The ionization reaction thrust is the reaction thrust of the suspended droplet induced by the laser to produce ionization decomposition. The evaporation thrust is the laser heating of graphene oxide, which causes rapid evaporation on its surface and generates thrust on the suspended droplet.

4. The method for controlling the motion of micron-sized suspended droplets by laser-droplet reaction according to claim 3, characterized in that: In step (4), the direction and magnitude of the combined forces of light pressure, ionization reaction thrust, and evaporation thrust on the suspended droplet change with the size of the suspended droplet. By adjusting the size of the suspended droplet, the direction and magnitude of the combined forces that drive the movement of the suspended droplet can be controlled, thereby achieving the control of the movement direction of the micron suspended droplet, with large droplets moving away from the light and small droplets moving towards the light.

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