Device and method for regulating three-dimensional motion of microdroplets by electric field

Abstract

The present invention discloses a device and method for controlling the three-dimensional motion of microdroplets using an electric field. The device comprises a support, a high-speed camera, an XY-directional electric translation stage, a sample cell, an ITO glass substrate coated with PDMS, a magnet, an illumination light source, a Z-direction lifting platform, and a needle-tip electrode. The support is respectively fixed with the high-speed camera, the XY-directional electric translation stage, the illumination light source, and the Z-direction electric translation stage. The sample cell is fixed above the XY-direction electric translation stage. An iron sheet is fixed to the bottom surface of the sample cell, on which the ITO glass substrate coated with PDMS is placed, and magnets are placed at the corners of the ITO glass substrate coated with PDMS. The needle-tip electrode is fixed to the Z-direction electric translation stage. The needle-tip electrode controls the three-dimensional motion of the microdroplet, including changing the contact angle of the microdroplet, the vertical vibration of the microdroplet, and the two-dimensional planar motion of the microdroplet. The device can also be used as a general contact angle meter to study the morphology and contact angle of droplets in a liquid environment.

Description

Technical Field

[0001] The present invention belongs to the fields of biomedical engineering and surface and interface physics, and particularly relates to a device and method for regulating the three-dimensional motion of microdroplets by an electric field. Background Art

[0002] In 1875, Lippmann experimentally observed that the height of mercury in a capillary tube changes under the influence of an electric field, thus initiating the study of electrowetting. In 1993, Berge separated a droplet from an underlying electrode using an insulating dielectric layer and observed changes in the droplet's contact angle, a phenomenon known as dielectric wetting. He combined the Young equation describing the contact angle at a three-phase interface with Lippmann's electrowetting equation to propose the Young-Lippmann equation for dielectric wetting. The surface tension coefficient is a crucial physical parameter in surface and interface physics, linked to various physical phenomena of dielectric wetting. Currently, there is no experimental method for measuring the surface tension coefficient between a microdroplet and its surrounding environment (gas or liquid phase) using dielectric wetting. A Chinese patent (CN 114023773 A) discloses a digital microfluidic chip, in which microdroplets are restricted to one-dimensional motion along a fixed track on the chip, and chip fabrication is relatively complex. Different from dielectric wetting control methods, another method for controlling microdroplets is electrostatic induction. When the high-potential needle-tip electrode approaches (without contact) the grounded micro-droplet, under the electrostatic induction effect of the electric field near the needle-tip electrode, the grounded micro-droplet as a whole is negatively charged, and the negatively charged droplet moves toward the needle-tip electrode under the action of the electric field force. At present, the electrostatic induction method for regulating the movement of micro-droplets requires an extremely high driving voltage, and it is still impossible to achieve the free movement of micro-droplets in a two-dimensional plane. For the vibration of micro-droplets, a Chinese patent (CN 104655832A) discloses a droplet vibration device and a droplet vibration method, which utilizes electrostatic induction to drive the vertical vibration of the droplet under an alternating voltage. However, this regulation also has the following disadvantages: first, an alternating voltage of 4kV is required to achieve effective attraction of the droplet, and the actual operability is poor; second, only vertical vibration can be achieved.

[0003] Existing microdroplet devices are limited by a single control method, making it impossible to achieve three-dimensional motion of microdroplets. Currently, microdroplet devices typically control microdroplet motion in air or silicone oil environments. In air, the friction between the microdroplets and the substrate is high, requiring a very high drive voltage. In silicone oil, the viscosity of the oil also requires a very high drive voltage, and the microdroplets respond slowly to changes in the electric field, preventing the generation of diverse motion patterns. Summary of the Invention

[0004] In response to the shortcomings of existing micro-droplet devices such as "single control method" and "large resistance to micro-droplet movement", the present invention discloses a device and method for electric field control of micro-droplet three-dimensional movement. Its main purpose is to realize the control of the three-dimensional movement of micro-droplets by needle-tip electrodes, including changing the contact angle of micro-droplets, the vertical vibration of micro-droplets, the two-dimensional planar movement of micro-droplets, etc. It can also be used as a general contact angle meter to study the morphology and contact angle of droplets in a liquid environment.

[0005] This application adopts the following technical solutions:

[0006] A device for regulating the three-dimensional motion of micro-droplets by electric field, comprising a bracket, a high-speed camera, an XY-direction electric displacement stage, a sample pool, an ITO glass substrate spin-coated with PDMS, a magnet, an illumination light source, a Z-direction lifting stage and a needle tip electrode (11);

[0007] The high-speed camera, XY direction electric translation stage, lighting source and Z direction electric lifting stage are fixed on the bracket respectively;

[0008] Fix the sample pool above the XY direction electric translation stage;

[0009] An iron sheet is fixed on the bottom of the sample cell, on which an ITO glass substrate with PDMS spin-coated is placed, and magnets are placed at the corners of the ITO glass substrate with PDMS spin-coated;

[0010] The needle tip electrode is fixed on the Z-direction electric lifting platform.

[0011] Furthermore, the sample pool has a liquid inlet pipe and a liquid outlet pipe.

[0012] Furthermore, the device also includes a syringe; the syringe is located next to the needle tip electrode, the head of the needle tip electrode is lower than the syringe mouth, and the heights of the needle tip electrode and the syringe are adjustable.

[0013] Furthermore, the device also includes electrode connecting wires and ITO glass substrate connecting wires; a U-shaped wiring clamp is fixed on the magnet and connected to the power supply through the ITO glass substrate connecting wires; and the needle tip electrode is connected to the power supply through the electrode connecting wires.

[0014] Furthermore, on the ITO glass substrate on which the PDMS is spin-coated, the thickness of the PDMS dielectric layer is 4-5 μm.

[0015] The method for using the device as described in any of the above items is used to measure the surface tension coefficient of microdroplets, regulate the horizontal movement of microdroplets based on dielectric wetting, regulate the vibration of microdroplets based on dielectric wetting, or regulate the horizontal movement of microdroplets based on electrostatic induction.

[0016] Furthermore, the measuring of the surface tension coefficient of the micro-droplet comprises:

[0017] Tetrapropoxysilane was injected into the sample cell to immerse the surface of the ITO glass substrate coated with PDMS. Water was added to the surface of the ITO glass substrate coated with PMDS using a syringe to form water microdroplets. A needle tip electrode was inserted into the above microdroplets, with a distance of 0.5 mm between the needle tip electrode and the ITO glass substrate coated with PDMS. The DC driving voltage was between 0 and 50 V. A high-speed camera was used to capture the shape of the water microdroplets under different driving voltages, and the driving voltage (U 2 ) and the contact angle (cosθ).

[0018] Furthermore, the dielectric wetting-based control of the horizontal motion of micro-droplets includes: injecting tetrapropoxysilane into a sample pool to immerse the ITO glass substrate spun on PDMS, and adding propylene carbonate droplets onto the surface of the ITO glass substrate spun on PDMS using a syringe to form propylene carbonate micro-droplets; inserting a needle tip electrode into the above-mentioned micro-droplets without contacting the ITO glass substrate spun on PDMS, an AC driving voltage between 0-500V, and horizontal movement of the XY direction electric translation stage, so that the needle tip electrode can control the free movement of the propylene carbonate liquid droplets on the surface of the ITO glass substrate spun on PDMS, and using a high-speed camera to record the motion state of the propylene carbonate micro-droplets.

[0019] Furthermore, the control of micro-droplet vibration based on dielectric wetting includes:

[0020] Tetrapropoxysilane is injected into a sample cell to immerse the PDMS-coated ITO glass substrate, and propylene carbonate is added dropwise onto the surface of the PDMS-coated ITO glass substrate using a syringe to form propylene carbonate microdroplets. The first vibration is a large-amplitude vibration in the vertical direction: a needle tip electrode is touched to the top of the above-mentioned microdroplet, a DC or AC driving voltage is between 100-500V, and the needle tip electrode is used to control the vertical vibration of the propylene carbonate microdroplet on the surface of the PDMS-coated ITO glass substrate, and a high-speed camera is used to record the large-amplitude vibration state of the propylene carbonate microdroplet under different driving voltages; or the second vibration is a deformation at the same frequency as the alternating current: a needle tip electrode is inserted into the above-mentioned microdroplet, an AC driving voltage is between 100-500V and a frequency of 50Hz, and the needle tip electrode is used to control the propylene carbonate microdroplet to produce a deformation at the same frequency as the alternating current on the surface of the PDMS-coated ITO glass substrate, and the vibration state of the propylene carbonate microdroplet under different driving voltages is recorded using a high-speed camera.

[0021] Furthermore, the electrostatic induction-based control of the horizontal motion of microdroplets includes: injecting tetrapropoxysilane into a sample pool to immerse the ITO glass substrate spun on PDMS, and using a syringe to drop propylene carbonate onto the surface of the ITO glass substrate spun on PMDS to form propylene carbonate microdroplets; placing a needle tip electrode close to the above-mentioned microdroplets, 0.55 mm away from the top of the microdroplets, with an AC drive voltage between 200-500V, and moving the needle tip electrode horizontally through an XY direction electric translation stage, so that the propylene carbonate microdroplets can be controlled to move freely on the surface of the ITO glass substrate spun on PDMS; and using a high-speed camera to record the motion state of the propylene carbonate microdroplets.

[0022] Specifically, the structure of the device for regulating the three-dimensional motion of micro-droplets by electric field of the present invention is as follows: Figure 1 As shown, the device mainly consists of a bracket 1, a high-speed camera 2, an XY-direction electric translation stage 3, a sample cell 4, an ITO glass substrate 5 with PDMS spin-coated on it, a liquid inlet pipe 6, a liquid outlet pipe 7, a magnet 8, an illumination light source 9, a Z-direction electric lifting platform 10, a needle-tip electrode 11, a syringe 12, a connecting wire 13 for the electrode, and a connecting wire 14 for the ITO glass substrate. The specific connection method of the device is as follows: First, the high-speed camera 2, the XY-direction electric translation stage 3, the illumination light source 9, and the Z-direction electric lifting platform 10 are fixed to the bracket 1. Secondly, the sample cell 4 is fixed above the XY-direction electric translation stage 3. An iron sheet is fixed to the bottom surface of the sample cell 4, on which the ITO glass substrate 5 is placed. Cylindrical magnets 8 are placed at the corners of the ITO glass substrate. U-shaped wiring clamps are fixed to the magnets 8, which are connected to the power supply via the ITO glass substrate connecting wire 14. The sample cell 4 has a liquid inlet pipe 6 and a liquid outlet pipe 7. The needle-tip electrode 11 is fixed to the Z-direction electric lifting platform 10, and the needle-tip electrode 11 is connected to the power supply via the connecting wire 13 for the electrode. The syringe 12 is located beside the needle tip electrode 11 , the head of the needle tip electrode 11 is lower than the mouth of the syringe 12 , and the heights of the needle tip electrode 11 and the syringe 12 are adjustable.

[0023] The present invention proposes a method for preparing an ITO substrate for spin-coating PDMS. First, a polydimethylsiloxane prepolymer (PDMS) is prepared using Dow Corning Sylgard 184 polydimethylsiloxane reagent (containing a base and a curing agent) in a mass ratio of base: curing agent: cyclohexane = 10:1:2. The prepared PDMS prepolymer is then placed in a vacuum drying oven and dried for 15 minutes to remove any small bubbles in the PDMS. Next, a corner of a clean ITO glass is covered with Capton tape for connecting wires. The ITO glass is then placed on the suction cup of a spin coater and secured with an air pump. Approximately 0.5 mL of PDMS prepolymer is pipetted and evenly coated on the ITO glass. The spin coater is turned on for spin coating, and the speed is set sequentially as follows: increasing to 3000 rpm in 35 seconds, increasing to 7500 rpm in 50 seconds, maintaining 7500 rpm for 60 seconds, decelerating to 3000 rpm in 45 seconds, and stopping the rotation for 30 seconds. The coated ITO glass is baked at 70° C. for 15 minutes to coat a PDMS dielectric layer with a thickness of about 5 μm on the ITO glass.

[0024] The advantages and positive effects of the present invention are as follows:

[0025] Existing micro-droplet control devices have limitations and shortcomings. The device of the present invention has the following advantages:

[0026] (1) The existing device has a large resistance to the movement of micro-droplets. The present invention uses tetrapropoxysilane as the environment for the micro-droplets, and its viscosity is about 1.7 mPa·s, which makes the resistance to the movement of the micro-droplets extremely small, thereby greatly reducing the required driving voltage to tens of volts.

[0027] (2) The electrodes of the existing devices are complicated to process, and the droplets can only move along a specific route. The present invention realizes direct attraction of the needle tip to the micro-droplets, thereby realizing the arbitrary movement of the micro-droplets in a two-dimensional plane. The needle tip direct attraction method provided by the present invention is divided into two types: one is a contact attraction method, based on the principle of dielectric wetting, inserting the energized needle tip (AC or DC) into the micro-droplet, under a driving voltage of about 70V, the moving needle tip can effectively regulate the synchronous movement of 6μL micro-droplets; the other is a non-contact attraction method, suspending the needle tip electrode above the micro-droplet without contacting the micro-droplet, applying AC or DC to the needle tip electrode, and using the electrostatic induction effect to induce charge in the micro-droplet. Under a driving voltage of about 180V, the moving needle tip can effectively regulate the synchronous movement of 2μL micro-droplets.

[0028] (3) The existing devices have a single function and a limited number of phenomena. The present invention can observe four physical phenomena of dielectric wetting. First, when the needle tip electrode is inserted into the micro-droplet, direct current can significantly change the contact angle of the micro-droplet and can also measure the surface tension coefficient of the micro-droplet. Second, when the needle tip electrode is inserted into the micro-droplet, alternating current can drive the micro-droplet to vibrate at the same frequency. Third, when the needle tip electrode contacts the micro-droplet, alternating current or direct current can drive the droplet to vibrate greatly in the vertical direction. Fourth, when the needle tip electrode is inserted into the micro-droplet, under alternating current or direct current, the needle tip electrode attracts the droplet to move arbitrarily in the horizontal plane. Among them, the above three and four forms of movement are novel physical phenomena. Therefore, the device of the present invention can produce a variety of physical phenomena.

[0029] (4) The sample cell provided by the present invention is cleverly designed, allowing for easy replacement of the liquid environment and substrate, and strong experimental scalability. It can also be used to study the contact angle of microdroplets in different environments. Therefore, the device of the present invention is highly versatile. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the structure of the device of the present invention;

[0031] Figure 2 The relationship between driving voltage and microdroplet contact angle;

[0032] Figure 3 The relationship between the droplet limiting velocity and the driving voltage;

[0033] Figure 4 Relationship between the droplet's terminal velocity and the tip electrode height (dielectric wetting);

[0034] Figure 5 Large amplitude vibration period of propylene carbonate microdroplets in vertical direction (dielectric wetting);

[0035] Figure 6 The deformation cycle of propylene carbonate microdroplets at the same frequency as alternating current;

[0036] Figure 7 The relationship between the ultimate droplet motion velocity and the driving voltage (electrostatic induction). DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are intended only to explain the present invention, and the scope of protection of the present invention should include the entire contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement the entire contents of the claims of the present invention.

[0038] In response to the shortcomings of existing micro-droplet devices such as "single control method" and "large resistance to micro-droplet movement", the present invention discloses a device and method for controlling the three-dimensional movement of micro-droplets based on electric fields. Its main purpose is to realize the control of the three-dimensional movement of micro-droplets by needle-tip electrodes, including changing the contact angle of micro-droplets, the vertical vibration of micro-droplets, the two-dimensional planar movement of micro-droplets, etc. It can also be used as a general contact angle meter to study the morphology and contact angle of droplets in a liquid environment.

[0039] The structure of the device for controlling the three-dimensional motion of micro-droplets by electric field of the present invention is as follows: Figure 1 As shown, the device mainly consists of a bracket 1, a high-speed camera 2, an XY-direction electric translation stage 3, a sample cell 4, an ITO glass substrate 5 with PDMS spin-coated, a liquid inlet pipe 6, a liquid outlet pipe 7, a magnet 8, an illumination light source 9, a Z-direction electric lifting platform 10, a needle-tip electrode 11, a syringe 12, a connecting wire 13 for the electrode, and a connecting wire 14 for the ITO glass substrate. The specific connection method of the device is as follows: First, the high-speed camera 2, the XY-direction electric translation stage 3, the illumination light source 9, and the Z-direction electric lifting platform 10 are fixed on the bracket 1. Secondly, the sample cell 4 is fixed above the XY-direction electric translation stage 3. An iron sheet is fixed to the bottom surface of the sample cell 4, on which the ITO glass substrate 5 is placed. Cylindrical magnets 8 are placed at the corners of the ITO glass substrate. U-shaped wiring clips are fixed on the magnets 8, which are connected to the power supply via the ITO glass substrate connecting wire 14. The sample cell 4 has a liquid inlet pipe 6 and a liquid outlet pipe 7. The needle-tip electrode 11 is fixed on the Z-direction electric lifting platform, and the needle-tip electrode 11 is connected to the power supply via the connecting wire 13 for the electrode. The syringe 12 is located beside the needle tip electrode 11 , the head of the needle tip electrode 11 is lower than the mouth of the syringe 12 , and the heights of the needle tip electrode 11 and the syringe 12 are adjustable.

[0040] The present invention provides a method for preparing an ITO glass substrate for spin-coating PDMS. First, a polydimethylsiloxane prepolymer (PDMS) is prepared using Dow Corning Sylgard 184 polydimethylsiloxane reagent (containing a base and a curing agent) in a mass ratio of base: curing agent: cyclohexane = 10:1:2. The prepared PDMS prepolymer is then placed in a vacuum drying oven for 15 minutes to remove any small bubbles in the PDMS. Next, a corner of the clean ITO glass is covered with Capton tape for connecting wires. The ITO glass is then placed on the suction cup of a spin coater and secured with an air pump. Approximately 0.5 mL of PDMS prepolymer is pipetted and evenly coated on the ITO glass. The spin coater is turned on for spin coating, and the speed is set sequentially as follows: increasing to 3000 rpm in 35 seconds, increasing to 7500 rpm in 50 seconds, maintaining 7500 rpm for 60 seconds, decelerating to 3000 rpm in 45 seconds, and stopping the rotation for 30 seconds. The coated ITO glass is baked at 70° C. for 15 minutes to coat a PDMS dielectric layer with a thickness of about 5 μm on the ITO glass.

[0041] Example 1: Measuring the surface tension coefficient between a microdroplet and its surroundings

[0042] Using the liquid inlet tube 6, tetrapropoxysilane was injected into the sample cell 4 to submerge the surface 5 of the PDMS-coated ITO glass substrate. Using a syringe 12, water (~6 μL) was dripped onto the surface 5 of the PMDS-coated PDMS-coated ITO glass substrate to form water droplets. A needle tip electrode 11 was inserted into the droplets, with a distance of 0.5 mm between the needle tip electrode 11 and the PDMS-coated ITO glass substrate 5. The DC drive voltage was between 0 and 50 V. A high-speed camera 2 was used to capture the shape of the water droplets at different drive voltages, and the drive voltage (U 2 ) and the contact angle (cosθ). The contact angle of the water droplet changes with the driving voltage, such as Figure 2 When the needle tip electrode 11 is inserted into the water droplet, the DC driving voltage between the needle tip electrode 11 and the ITO glass substrate 5 with PDMS spin-coated thereon changes in the range of 0-45V, and the contact angle of the water droplet changes in the range of 160-75°.

[0043] Figure 2 Indicates the relationship between the contact angle (cosθ) and the square of the driving voltage (U 2 ) is approximately linearly related, according to the Young-Lippmann equation:

[0044]

[0045] Among them, the dielectric constant of PDMS ε d With thickness d being 25.14 pF / m and 5 μm respectively, the linear fitting U 2 -cosθ relationship, the surface tension coefficient γ between the water droplet and the liquid environment is obtained LL' It is 4.33mN / m.

[0046] Example 2: Controlling the horizontal motion of microdroplets based on dielectric wetting

[0047] Tetrapropoxysilane was injected into the sample cell 4 via a liquid inlet tube 6 to submerge the PDMS-coated ITO glass substrate 5. Propylene carbonate (~6 μL) was then dripped onto the surface of the PMDS-coated PDMS-coated ITO glass substrate 5 using a syringe 12 to form propylene carbonate microdroplets. A needle-tip electrode 11 was inserted into the microdroplets (without contacting the ITO glass). An AC drive voltage between 0 and 500 V (at a frequency of 50 Hz) was applied. The needle-tip electrode 11 was horizontally moved by an XY motorized translation stage 3, allowing the propylene carbonate liquid microdroplets to freely move on the PDMS-coated ITO glass substrate 5. The motion of the propylene carbonate microdroplets was recorded using a high-speed camera 2.

[0048] The limiting migration velocity of propylene carbonate microdroplets changes with the driving voltage, e.g. Figure 3 When the distance between the needle tip electrode 11 and the surface of the ITO glass substrate 5 coated with PDMS is 0.6 mm and the driving voltage is 100V, 120V, 140V, 160V, 180V, and 200V respectively, the limit movement rate of the propylene carbonate microdroplet is shown in FIG. Figure 3 It can be seen that the limiting movement velocity of the propylene carbonate microdroplets is linearly positively correlated with the driving voltage, that is, the greater the driving voltage, the stronger the attraction of the needle tip electrode 11 to the droplets.

[0049] When the driving voltage is 160 V, and the distances between the tip electrode 11 and the surface of the ITO glass substrate 5 coated with PDMS are 0.64 mm, 0.69 mm, 0.75 mm, 0.83 mm, 1.04 mm, 1.14 mm, 1.31 mm, and 1.43 mm, respectively, the limiting movement rate of the propylene carbonate microdroplet is as follows: Figure 4 As shown. Figure 4 It can be seen that the limiting movement rate of the propylene carbonate microdroplets decreases as the distance between the needle tip electrode 11 and the surface 5 of the ITO glass substrate on which PDMS is spin-coated increases. That is, the smaller the distance between the needle tip electrode 11 and the surface 5 of the ITO glass substrate on which PDMS is spin-coated, the stronger the attraction of the needle tip electrode 11 to the droplets.

[0050] Example 3: Controlling microdroplet vibration based on dielectric wetting

[0051] Using the liquid inlet tube 6, tetrapropoxysilane is injected into the sample pool 4 to immerse the ITO glass substrate 5 coated with PDMS, and propylene carbonate (~6μL) is added to the surface of the ITO glass substrate 5 coated with PMDS by using a syringe 12 to form propylene carbonate microdroplets. The first vibration is a large-amplitude vibration in the vertical direction: the needle tip electrode 11 is just touching the top of the above-mentioned microdroplet, and the DC or AC (frequency 50Hz) driving voltage is between 100-500V. The needle tip electrode 11 is used to control the propylene carbonate droplet to vibrate in a large amplitude in the vertical direction on the surface of the ITO glass substrate 5 coated with PDMS, and the high-speed camera 2 is used to record the large-amplitude vibration state of the propylene carbonate microdroplet under different driving voltages. Under a driving voltage of 100V, the vibration state of the propylene carbonate microdroplet within one cycle is as follows: Figure 5As shown. Starting from the time when the needle tip electrode 11 does not touch the micro-droplet, as time goes by, the needle tip electrode 11 contacts the micro-droplet, and the contact angle of the micro-droplet changes; when the needle tip electrode 11 leaves the micro-droplet, the contact angle of the micro-droplet instantly recovers; under the action of surface tension, the micro-droplet rebounds. The second vibration is deformation at the same frequency as the alternating current: the needle tip electrode 11 is inserted into the above-mentioned micro-droplet, the AC driving voltage is between 100-500V, and the frequency is 50Hz. The needle tip electrode 11 is used to control the propylene carbonate micro-droplet to produce deformation at the same frequency as the alternating current on the surface 5 of the ITO glass substrate spun on PDMS, and the high-speed camera 2 is used to record the vibration state of the propylene carbonate micro-droplet under different driving voltages. Under a driving voltage of 120V, the vibration state of the propylene carbonate micro-droplet within one cycle is as follows. Figure 6 As shown, the needle tip electrode 11 is inserted into the micro-droplet. As time goes by, the morphology of the micro-droplet undergoes a series of changes. The frequency of the micro-droplet vibration is the same as the frequency of the AC driving voltage.

[0052] Example 4: Controlling the horizontal motion of microdroplets based on electrostatic induction

[0053] Using the liquid inlet tube 6, tetrapropoxysilane is injected into the sample pool 4 to immerse the ITO glass substrate 5 coated with PDMS, and a syringe 12 is used to drop propylene carbonate (~2μL) onto the surface of the ITO glass substrate 5 coated with PMDS to form propylene carbonate microdroplets. The needle tip electrode 11 is brought close to the above-mentioned microdroplets, about 0.55mm away from the top of the microdroplets, the AC driving voltage is between 200-500V, the frequency is 50Hz, and the needle tip electrode 11 is moved horizontally by the XY direction electric translation stage 3. The needle tip electrode 11 can control the free movement of the propylene carbonate microdroplets on the surface of the ITO glass substrate 5 coated with PDMS, and the movement state of the propylene carbonate microdroplets is recorded by the high-speed camera 2. The limiting movement rate of the propylene carbonate microdroplets changes with the driving voltage, as shown in FIG. Figure 7 When the driving voltage increases from 210V to 470V, the limiting migration velocity of the propylene carbonate microdroplets is linearly positively correlated with the driving voltage, that is, the greater the driving voltage, the stronger the attraction of the needle tip electrode 11 to the microdroplets.

[0054] The present invention does not describe in detail parts that belong to the common knowledge of those skilled in the art. The above-described embodiments are merely descriptions of preferred embodiments of the present invention. The preferred embodiments do not describe all details in detail, nor do they limit the invention to the specific embodiments described. Without departing from the spirit of the present invention, various modifications and improvements made by those skilled in the art to the technical solution of the present invention should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A device for regulating the three-dimensional motion of micro-droplets by an electric field, characterized in that: It includes a bracket (1), a high-speed camera (2), an XY-direction electric translation stage (3), a sample pool (4), an ITO glass substrate (5) spin-coated with PDMS, a magnet (8), an illumination light source (9), a Z-direction electric lifting stage (10), and a needle tip electrode (11); A high-speed camera (2), an XY-direction electric translation stage (3), an illumination light source (9), and a Z-direction electric lifting stage (10) are fixed on the bracket (1). A sample pool (4) is fixed above the XY direction electric translation stage (3); An iron sheet is fixed to the inner bottom surface of the sample pool (4), on which an ITO glass substrate (5) coated with PDMS is placed, and cylindrical magnets (8) are placed at the corners of the ITO glass substrate (5) coated with PDMS; A needle tip electrode (11) is fixed on a Z-direction electric lifting platform (10); The sample pool (4) has a liquid inlet pipe (6) and a liquid outlet pipe (7); The device further comprises a syringe (12); the syringe (12) is located next to the needle tip electrode (11), the head of the needle tip electrode (11) is lower than the nozzle of the syringe (12), and the heights of the needle tip electrode (11) and the syringe (12) are adjustable; The device further comprises an electrode connecting wire (13) and an ITO glass substrate connecting wire (14); a U-shaped connecting clamp is fixed on the magnet (8), and is connected to a power supply via the ITO glass substrate connecting wire (14); and the needle tip electrode (11) is connected to a power supply via the electrode connecting wire (13); On the ITO glass substrate on which the PDMS is spin-coated, the thickness of the PDMS dielectric layer is 4-5 μm.

2. The method for using the device according to claim 1, characterized in that: The device is used for measuring the surface tension coefficient of micro-droplets, regulating the horizontal movement of micro-droplets based on dielectric wetting, regulating the vibration of micro-droplets based on dielectric wetting, or regulating the horizontal movement of micro-droplets based on electrostatic induction.

3. The method according to claim 2, characterized in that The surface tension coefficient of the micro-droplet is measured as follows: Tetrapropoxysilane is injected into the sample pool (4) to immerse the surface of the ITO glass substrate (5) spin-coated with PDMS, and water is added to the surface of the ITO glass substrate (5) spin-coated with PMDS using a syringe (12) to form water microdroplets; a needle tip electrode (11) is inserted into the above microdroplets, and the distance between the needle tip electrode (11) and the ITO glass substrate (5) spin-coated with PDMS is 0.5 mm, and the DC driving voltage is between 0-50 V; a high-speed camera (2) is used to capture the shape of the water microdroplets under different driving voltages, and the dependence of the driving voltage on the contact angle is obtained.

4. The method according to claim 2, characterized in that The method for regulating the horizontal movement of micro-droplets based on dielectric wetting comprises: injecting tetrapropoxysilane into a sample pool (4) to immerse the ITO glass substrate (5) coated with PDMS, and using a syringe (12) to drop propylene carbonate onto the surface of the ITO glass substrate (5) coated with PDMS to form propylene carbonate micro-droplets; inserting a needle tip electrode (11) into the above-mentioned micro-droplets without contacting the ITO glass substrate (5) coated with PDMS, and moving the needle tip electrode (11) in the horizontal direction by an XY direction electric translation stage (3) with an AC driving voltage between 0 and 500 V. The needle tip electrode (11) can regulate the free movement of the propylene carbonate liquid micro-droplets on the surface of the ITO glass substrate (5) coated with PDMS, and using a high-speed camera (2) to record the movement state of the propylene carbonate micro-droplets.

5. The method according to claim 2, characterized in that The method of regulating micro-droplet vibration based on dielectric wetting includes: Tetrapropoxysilane is injected into the sample pool (4) to immerse the spin-coated PDMS ITO glass substrate (5), and propylene carbonate is added to the surface of the spin-coated PDMS ITO glass substrate (5) using a syringe (12) to form propylene carbonate microdroplets; the first vibration is a large-amplitude vibration in the vertical direction: the needle tip electrode (11) is touched to the top of the above-mentioned microdroplet, the DC or AC driving voltage is between 100-500 V, and the propylene carbonate droplet is regulated by the needle tip electrode (11) to vibrate in the vertical direction on the surface of the spin-coated PDMS ITO glass substrate (5), and the large-amplitude vibration state of the propylene carbonate microdroplet under different driving voltages is recorded using a high-speed camera (2); or the second vibration is a deformation at the same frequency as the alternating current: the needle tip electrode (11) is inserted into the above-mentioned microdroplet, the AC driving voltage is between 100-500 V, and the frequency is 50 Hz, a needle-tip electrode (11) is used to control the deformation of propylene carbonate microdroplets on the surface of the ITO glass substrate (5) spin-coated with PDMS to produce the same frequency as the alternating current, and a high-speed camera (2) is used to record the vibration state of the propylene carbonate microdroplets under different driving voltages.

6. The method according to claim 2, characterized in that The electrostatic induction-based control of the horizontal motion of microdroplets includes: injecting tetrapropoxysilane into a sample pool (4) to immerse the ITO glass substrate (5) spin-coated with PDMS, and using a syringe (12) to drop propylene carbonate onto the surface of the ITO glass substrate (5) spin-coated with PMDS to form propylene carbonate microdroplets; placing a needle tip electrode (11) close to the above-mentioned microdroplets, 0.55 mm away from the top of the microdroplets, with an AC driving voltage between 200-500 V, and moving the needle tip electrode (11) horizontally through an XY direction electric translation stage (3), so that the propylene carbonate microdroplets can be controlled to move freely on the surface of the ITO glass substrate (5) spin-coated with PDMS; and using a high-speed camera (2) to record the motion state of the propylene carbonate microdroplets.

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