Method for manipulating liquid drops by means of air tweezers

Abstract

The invention discloses a method for operating liquid drops by means of air tweezers, relates to the technical field of operating the liquid drops by means of the air tweezers, and aims to solve the problem that the liquid drops are affected by wind power in a wind field generated by the air tweezers. The main technology of the application is embodied in that when the position of the liquid drop deviates from the wind tweezers, the liquid drop on the super-hydrophobic platform can be quickly dragged back to the position under the wind tweezers by wind power; therefore, by horizontally moving the air tweezers, the liquid drops can be guided to move along any programmed path; the pair of air tweezers has the advantages of high precision and high flexibility in the aspect of liquid drop operation.

Description

Technical Field

[0001] The invention belongs to the technical field of wind tweezers operating liquid droplets, and in particular relates to a method for manipulating liquid droplets by means of wind tweezers. Background Art

[0002] Since optical tweezers were proposed in 1986 to achieve remote and non-invasive capture and manipulation of particles, various forms of tweezers have been developed. With the continuous expansion of the application scope of tweezer technology, the objects that can be handled are no longer limited to microscale particles, and non-contact operations on larger macroscopic objects such as droplets can also be achieved.

[0003] In particular, contactless droplet manipulation plays a vital role in various practical applications, including microfluidics, biodetection, printing technology, water collection, chemical reactions, energy conversion and thermal management. In recent years, various physical tweezers techniques based on magnetic, optical, electrical, ultrasonic and other external fields have been developed to achieve flexible manipulation of droplets on super-hydrophobic or smooth surfaces. However, magnetic fields and light fields cannot directly exert force on droplets. These methods usually require the addition of responsive materials to the substrate material and indirectly drive the droplets by changing the surface morphology or other physical / chemical properties of the operating surface. Therefore, magnetic field-driven and light-driven methods are limited by the material composition and morphology of the surface microstructures used in the operating platform.

[0004] Although electrostatic tweezers and ultrasonic tweezers can directly apply force to droplets to achieve droplet manipulation, these techniques change the physical or chemical properties of droplets during manipulation, making these techniques invalid or inapplicable in some cases. For example, electrostatic tweezers change the charge distribution inside the droplet and can even charge the droplet, which may affect the results of some chemical reactions or change the activity of some biological fluids. During ultrasonic tweezer droplet manipulation, the droplet usually undergoes a large deformation and may be pressed into an ellipsoidal shape. Although existing physical tweezers have made significant progress in controllable liquid manipulation, flexible and effective droplet manipulation techniques that do not require the material composition or microscale morphology of the operating platform and do not change the physical and chemical properties of the droplet have not yet been developed.

[0005] In nature, the power of wind cannot be ignored. We designed a wind tweezers system that uses the force generated by wind to manipulate droplets; the wind tweezers system consists of a soft air tube, an air pump, a three-dimensional mobile platform, and a superhydrophobic operation platform. The wind tweezers can guide droplets to move along any set path and can move droplets at high speed. The maximum moving speed of a 2μl droplet can reach 160mm / s, and droplets of variable volume and various chemical compositions can be manipulated, with the advantages of high precision and flexibility. In addition, the wind tweezers can move multiple droplets at the same time and move Leidenfrost droplets on a hot smooth substrate. The proposed wind tweezers-based droplet manipulation technology has been shown to realize various applications, including chemical reactions, circuit repair, and cell transport in bioactive liquids. In addition, the wind tweezers can also improve the detection performance of surface-enhanced Raman scattering. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art;

[0007] To this end, the present invention proposes a method for manipulating droplets by means of wind tweezers, the method specifically comprising the following steps:

[0008] A super-hydrophobic surface or a super-slippery surface filled with lubricating fluid is used as an operating platform, and the operating platform is used to place droplets;

[0009] A wind tweezers system is constructed to generate a gradient wind field by suction and drive droplets to move on an operating platform.

[0010] Furthermore, the super hydrophobic surface is a PDMS surface processed by femtosecond laser.

[0011] Furthermore, the specific method of processing the PDMS surface by femtosecond laser processing technology is as follows:

[0012] The PDMS surface was burned using a line-by-line laser scanning method;

[0013] Then, ultrasonic cleaning was performed using alcohol and deionized water.

[0014] Furthermore, during the femtosecond laser processing technology:

[0015] The laser power was maintained at 500 mW, the laser scanning speed was 15 mm / s, and the scanning interval was controlled at 20 μm.

[0016] Furthermore, the wind tweezers system comprises:

[0017] The soft air duct connected to the air pump is used to extract air.

[0018] Furthermore, the wind tweezers system also includes a three-dimensional moving device for clamping the soft air duct and controlling its movement, thereby driving the droplets to move accordingly on the super-hydrophobic platform.

[0019] Furthermore, the soft air duct is a plastic tube with a hardness of 30A.

[0020] Furthermore, the soft air duct is a polytetrafluoroethylene tube.

[0021] Furthermore, a flow meter and a flow valve are inserted in the middle of the flexible air duct for real-time detection and adjustment of the gas flow rate.

[0022] Furthermore, the three-dimensional mobile device comprises a fixed platform, and a moving block 1 slidably arranged on the fixed platform, the moving block 1 is slidably connected to the moving block 2, the moving block 2 is fixedly connected to the vertical plate, the moving block 3 is slidably connected to the vertical plate, the moving block 3 is fixedly connected to one side of the clamping plate, and the clamping plate is provided with a through hole for clamping the soft air duct;

[0023] Moving block 1, moving block 2 and moving block 3 are used to drive the flexible air duct to move along the X, Y and Z axes respectively.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] In the wind field generated by the wind tweezers, the wind force acting on the droplets is mainly caused by the Bernoulli effect. When the position of the droplets deviates from the wind tweezers, the wind force can quickly pull the droplets on the superhydrophobic platform back to just below the wind tweezers. Therefore, by moving the wind tweezers horizontally, the droplets can be guided to move along any programmed path. The wind tweezers have the advantages of high precision and flexibility in droplet manipulation, and do not require the addition of any responsive materials to the droplets or substrates.

[0026] These features enable wind tweezers to manipulate various volumes from 100nL to 3mL or chemical compositions such as strongly acidic / alkaline / salt solutions, liquid metals, and organic alcohol droplets with surface tensions as low as 22.3mN / m; in addition, the application of wind tweezers can improve the detection performance of SERS sensors. The wind tweezers droplet manipulation technology we developed can be widely used in microfluidics, electronic information, biomedicine, chemical detection and analysis, and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of a droplet manipulation system of wind tweezers of the present invention;

[0028] Figure 2 A schematic diagram of the wind field around the wind tweezers of the present invention;

[0029] Figure 3 It is a superimposed image of the liquid droplet of the present invention moving along the programmed path under the guidance of the wind tweezers;

[0030] Figure 4 Schematic diagram of the structure and superhydrophobicity of the PDMS surface after laser etching;

[0031] Figure 5 This is a schematic diagram of a femtosecond laser processing system;

[0032] Figure 6 The process of capturing horizontally deviated droplets by wind tweezers;

[0033] Figure 7 Define a schematic diagram for the constraint radius BR;

[0034] Figure 8 Schematic diagram of three different states of a droplet being manipulated by wind tweezers;

[0035] Fig. 9 Schematic diagram for guiding the liquid metal robot to weld the circuit. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only 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 ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] See also Figure 1-Figure 9 The present application provides a method for manipulating droplets by means of wind tweezers, the method specifically comprising the following steps:

[0038] The PDMS surface is made super-hydrophobic by using femtosecond laser processing technology, thereby obtaining super-hydrophobic PDMS as an operating platform;

[0039] The specific method is: Figure 5 As shown in the figure, the PDMS surface is made super-hydrophobic by femtosecond laser processing technology, and the PDMS surface is ablated by a typical line-by-line laser scanning method. After ultrasonic cleaning with alcohol and deionized water, the ablated surface is super-hydrophobic, and the super-hydrophobic PDMS is used as the operating platform. In this process, the laser power is 500mW, the laser scanning speed is 15mm / s, and the scanning spacing is controlled at 20μm; Figure 4 As shown, a and b are low-magnification and high-magnification scanning electron microscope images of the laser-induced PDMS surface microstructure; c is a schematic diagram of the rolling process of a water droplet on the superhydrophobic PDMS surface;

[0040] Construct a wind tweezers system, which includes a soft air duct, an air pump, a flow meter, a flow valve, a 3D mobile platform and an operating platform;

[0041] A polytetrafluoroethylene plastic tube is vertically mounted on a three-dimensional mobile device; an air pump VN-60V is connected to the upper end of the air pipe; a flow meter and a flow valve are inserted in the middle of the pipe to detect and adjust the flow rate, and the flow meter model is AFM0750-50L; a laser-prepared super-hydrophobic PDMS surface is used as an operating platform, and droplets are placed on its surface in advance; the bottom of the air pipe is above the droplet and is at an appropriate height; during the droplet operation process, the three-dimensional mobile device allows the wind tweezers to move horizontally, so that the droplet moves accordingly on the super-hydrophobic platform; the three-dimensional mobile device includes a fixed table 1, and a moving block 1 2 slidably arranged on the fixed table, a moving block 2 3 is slidably connected to the moving block 1 2, a vertical plate 4 is fixedly connected to the moving block 2 3, a moving block 3 5 is slidably connected to the vertical plate 4, a clamping plate 6 is fixedly connected to one side of the moving block 3 5, and a through hole 7 for clamping the soft air duct is opened on the clamping plate 6; the moving blocks 1 2, 2 3, and 3 5 are used to drive the soft air duct to move along the X, Y, and Z axes respectively.

[0042] like Figure 6 As shown in the figure, for a droplet that deviates horizontally from the wind tweezers, if the system starts to pump air, the droplet can be quickly pulled back by the wind tweezers. After a rapid damped oscillation process, due to the inertia of the droplet, the droplet on the operating platform finally stops at the center position directly below the wind tweezers. This is the basis for the wind tweezers to manipulate the droplet. And the droplet will only be recaptured by the wind tweezers within a certain distance. The certain distance refers to the constraint radius, such as Figure 7 as shown; otherwise, the droplets cannot be controlled.

[0043] By moving the wind tweezers horizontally, the droplets can be guided to move on the super-hydrophobic platform. The wind speed V and height H of the wind tweezers significantly affect the operation process of the droplets; Figure 8 As shown in the figure, there are generally three states of droplet manipulation based on wind tweezers: droplets cannot be moved, droplets can be moved, and droplets are sucked up. Droplets can only be effectively manipulated under appropriate conditions, that is, appropriate wind speed and wind tweezer height. Figure 2 As shown, the arrows indicate the direction and speed of the airflow;

[0044] Wind tweezers can manipulate acid, alkali, and salt droplets on super-hydrophobic surfaces, as well as on super-hydrophobic surfaces of different material substrates such as glass, silicon, and aluminum. They can also manipulate low surface energy droplets such as alcohol on super-slippery surfaces.

[0045] like Fig. 9 As shown in the figure, liquid metal with excellent conductivity can be manipulated by wind tweezers, so liquid metal droplets can be manipulated to weld or repair circuits. We use wind tweezers to transport liquid metal droplets to the broken part of the circuit, so that the liquid metal contacts the two broken parts of the circuit. After the liquid metal droplets repair and connect the circuit, the light bulb in the circuit can be lit.

[0046] The above embodiments are only used to illustrate the technical method of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical method of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical method of the present invention.

Claims

1. A method for manipulating a droplet by means of wind tweezers, characterized in that: The method specifically comprises the following steps: A super-hydrophobic surface or a super-slippery surface filled with lubricating fluid is used as an operating platform, and the operating platform is used to place droplets; Construct a wind tweezers system, which is used to generate a gradient wind field by suction and drive droplets to move on the operating platform.

2. A method for manipulating droplets by means of wind tweezers according to claim 1, characterized in that: The super-hydrophobic surface is a PDMS surface processed by femtosecond laser.

3. A method for manipulating droplets by means of wind tweezers according to claim 2, characterized in that: The specific method of femtosecond laser processing technology to process the PDMS surface is: The PDMS surface was burned using a line-by-line laser scanning method; Then, ultrasonic cleaning was performed using alcohol and deionized water.

4. A method for manipulating droplets by means of wind tweezers according to claim 3, characterized in that: During femtosecond laser processing technology: The laser power was maintained at 500 mW, the laser scanning speed was 15 mm / s, and the scanning interval was controlled at 20 μm.

5. The method for manipulating droplets by means of wind tweezers according to claim 1, characterized in that: The wind tweezers system includes: The soft air duct connected to the air pump is used to extract air.

6. A method for manipulating droplets by means of wind tweezers according to claim 5, characterized in that: The wind tweezers system also includes a three-dimensional moving device for clamping the soft air tube and controlling its movement, thereby driving the droplets to move accordingly on the super-hydrophobic platform.

7. A method for manipulating droplets by means of wind tweezers according to claim 5 or 6, characterized in that: The soft air duct is a plastic pipe with a hardness of 30A.

8. The method for manipulating droplets by means of wind tweezers according to claim 7, characterized in that: The soft air duct is a polytetrafluoroethylene tube.

9. The method for manipulating droplets by means of wind tweezers according to claim 5, characterized in that: A flow meter and a flow valve are also inserted in the middle of the soft air duct to detect and adjust the gas flow rate in real time.

10. The method for manipulating droplets by means of wind tweezers according to claim 6, characterized in that: The three-dimensional mobile device comprises a fixed platform, and a moving block 1 slidably arranged on the fixed platform, the moving block 1 is slidably connected to the moving block 2, the moving block 2 is fixedly connected to the vertical plate, the moving block 3 is slidably connected to the vertical plate, the moving block 3 is fixedly connected to one side of the clamping plate, and the clamping plate is provided with a through hole for clamping the soft air duct; The moving block 1, the moving block 2 and the moving block 3 are used to drive the flexible air duct to move along the X, Y and Z axes respectively.

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