Electrokinetic circulating pump based on gallium-indium liquid metal droplets and methods of use

Abstract

The application relates to an electric circulating pump based on gallium-indium liquid metal droplets and a use method thereof, and relates to the technical field of microfluidics.The application is to solve the problems that the existing liquid metal pump adopts a direct current electric field, liquid metal droplets are prone to strong oxidation, and the pumping direction cannot be changed after the electric field direction is fixed.The mainboard is provided with two flow channels, a droplet cavity and two electrode grooves, the two flow channels are communicated through the droplet cavity, the two electrode grooves are located on the two sides of the droplet cavity and are communicated with the two flow channels respectively, the gallium-indium metal droplets are located in the droplet cavity, the two electrodes are located in the two electrode grooves respectively, the two flow channels are used for bearing the driven fluid, and alternating current and direct current pulse signals can be simultaneously applied to the two electrodes.

Description

Technical Field

[0001] This invention belongs to the field of microfluidics technology, and particularly relates to fluid circulation drive devices. Background Technology

[0002] Actuators are systems that convert different types of energy into mechanical motion and can be used in various micro-systems, including microreactors, microactuators, and micro heat exchangers in lab-on-a-chip applications. One crucial component of actuator systems is the drive pump, especially the circulation pump, which is widely used for fluid cooling, particle flow circulation filtration and collection at the microscale. At the millimeter scale, drive pumps can be mainly divided into mechanical and non-mechanical types. For mechanical pumps, the driving force is generated by driving moving parts through piezoelectric, electrostatic, thermal, pneumatic, electromagnetic effects, or by electrowetting deformation. This system has several significant drawbacks: first, energy loss due to frictional heat generation from moving parts and its rather complex manufacturing process; second, the presence of moving parts increases the likelihood of mechanical failure, which becomes particularly severe in complex systems. Non-mechanical pumps, without moving parts, can generate driving force through ions in an electrolyte solution caused by electroosmosis or electrochemical effects. However, ion pumps are generally only suitable for liquids with low conductivity, produce relatively low flow rates, and require very high voltages (on the order of kilovolts) to operate. Most importantly, both methods are difficult to use for circulating fluid pumping. Therefore, pumping systems with no moving parts, high flow rates, low power consumption, and the ability to achieve fluid circulation pumping are ideal for many current and emerging applications in microfluidics systems.

[0003] In recent years, room-temperature liquid metals, represented by gallium-based alloys, have gradually become a new hot material attracting widespread international attention. These alloys, due to their melting point below room temperature, can exist in a liquid state at room temperature, thus possessing properties of both "metal" and "liquid." More importantly, they can modulate surface tension in response to external stimuli, with electric fields being one of the most effective and flexible physical stimuli for regulating surface tension, as their amplitude, phase, and frequency can be easily adjusted. In 2014, the article "Liquid metal enabled pump," published in the journal *Proceedings of the National Academy of Sciences*, first proposed a liquid metal pump for pumping liquids. This research showed that when liquid metal droplets immersed in a high-concentration NaOH solution are exposed to a square-wave electric field with DC bias, the liquid metal droplets will pump fluid.

[0004] However, liquid metals are easily oxidized, forming an oxide layer on their surface. This not only reduces the surface tension to almost zero but also significantly weakens the controllability of the electric field. Current liquid metal pumps typically use a DC electric field, but this introduces three problems:

[0005] First, a direct current electric field can cause liquid metal droplets to undergo strong oxidation, resulting in an excessive oxide layer on their surface that makes them uncontrollable. To address this issue, current research primarily uses high-concentration NaOH (sodium hydroxide) solutions (2 mol / L), which significantly limits its further applications.

[0006] Secondly, once the direction of the electric field is fixed, the pumping direction cannot be changed.

[0007] Third, the structure with an opening at the top makes it difficult to modularize liquid metal pumps.

[0008] Regarding the first two issues, current theoretical understanding holds that liquid metal pumps can only be controlled by a direct current (DC) electric field. Since alternating current (AC) electric fields, due to their periodic changes in direction, cannot generate unidirectional fluid transport, the main focus is on how to reduce dependence on high-concentration alkaline solutions while utilizing DC control. Methods employed include reducing the voltage amplitude and using AC with DC bias. However, introducing AC only suppresses oxide layer formation; it cannot achieve fluid transport. As for the third issue, no relevant research has been conducted yet. Summary of the Invention

[0009] This invention addresses the problems of existing liquid metal pumps using a DC electric field, which makes liquid metal droplets highly susceptible to strong oxidation; and the inability to change the pumping direction once the electric field direction is fixed. The invention provides an electric circulating pump based on gallium-indium liquid metal droplets and its usage method.

[0010] An electric circulating pump based on gallium-indium liquid metal droplets includes: a main board 1, a gallium-indium metal droplet 5, and two electrodes 12. The main board 1 has two flow channels 3, a droplet cavity 4, and two electrode slots 2. The two flow channels 3 are connected through the droplet cavity 4. The two electrode slots 2 are located on both sides of the droplet cavity 4 and are respectively connected to the two flow channels 3. The gallium-indium metal droplet 5 is located in the droplet cavity 4. The two electrodes 12 are located in the two electrode slots 2 respectively. The two flow channels 3 are used to carry the driven fluid. Alternating current and direct current pulse signals can be applied to the two electrodes 12 simultaneously.

[0011] Furthermore, the free ends of the two flow channels 3 are respectively connected to the outside world via two connecting pipes 6.

[0012] Furthermore, the aforementioned flow channel 3 and its connected pipe 6 are sealed together by a sealing element 7.

[0013] Furthermore, the aforementioned electric circulating pump based on gallium indium liquid metal droplets also includes two cover plates 8, which are respectively attached to the upper and lower sides of the main board 1.

[0014] Furthermore, the two cover plates 8 and the main board 1 are connected by bolts 9.

[0015] The specific method for using the electric circulating pump based on gallium-indium liquid metal droplets described above is as follows:

[0016] When the conductivity of the driven fluid is less than 1.6 S / m, an alternating current with a frequency greater than 50 Hz is applied to the two electrodes 12, causing the driven fluid to flow toward the flow channel 3 that is closer to the gallium indium metal droplet 5. When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes 12 on the basis of the alternating current, causing the gallium indium metal droplet 5 to move closer to the other flow channel 3, and the driven fluid to flow in the opposite direction.

[0017] When the conductivity of the driven fluid is greater than or equal to 1.6 S / m, an alternating current with a frequency greater than 50 Hz and less than or equal to 100 Hz is applied to the two electrodes 12, causing the driven fluid to flow toward the flow channel 3 that is closer to the gallium indium metal droplet 5. When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes 12 on the basis of the alternating current, causing the gallium indium metal droplet 5 to move closer to the other flow channel 3, and the driven fluid to flow in the opposite direction.

[0018] When the conductivity of the driven fluid is greater than or equal to 1.6 S / m, an alternating current with a frequency greater than 100 Hz and a voltage amplitude less than 5 V is applied to the two electrodes 12, causing the driven fluid to flow toward the flow channel 3 closest to the gallium indium metal droplet 5. When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes 12 on the basis of the alternating current, causing the gallium indium metal droplet 5 to move closer to the other flow channel 3 and the driven fluid to flow in the opposite direction, or the voltage amplitude of the alternating current is adjusted to be greater than or equal to 5 V, so that the gallium indium metal droplet 5 remains stationary and the driven fluid flows in the opposite direction.

[0019] When the conductivity of the driven fluid is greater than or equal to 1.6 S / m, an alternating current with a frequency greater than 100 Hz and a voltage amplitude greater than or equal to 5 V is applied to the two electrodes 12, causing the driven fluid to flow in the direction of the flow channel 3 that is far from the gallium indium metal droplet 5. When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes 12 on the basis of the alternating current, so that the gallium indium metal droplet 5 moves closer to the other flow channel 3 and the driven fluid flows in the opposite direction, or the voltage amplitude of the alternating current is adjusted to be less than 5 V, so that the gallium indium metal droplet 5 remains stationary and the driven fluid flows in the opposite direction.

[0020] Furthermore, the voltage amplitude of the aforementioned DC pulse signal is 2V, and the superposition time is 0.1s.

[0021] Furthermore, when the conductivity of the driven fluid is less than 1.6 S / m, the driven fluid is a 0.1 mol / L NaOH solution; when the conductivity of the driven fluid is greater than or equal to 1.6 S / m, the driven fluid is a 0.25 mol / L NaOH solution.

[0022] The present invention has the following advantages:

[0023] 1. The alternating current electric field itself can suppress the formation of oxide layers on the surface of liquid metal droplets, enabling the pumping of low-concentration NaOH solutions (as low as 0.1 mol / L), PBS biological buffer solutions, NaCl solutions, etc., thus expanding the application range of the pump;

[0024] 2. The direction of the pump can be changed by adjusting the voltage amplitude, frequency and position of the liquid metal droplets, which gives great convenience to the adjustment of the pumping direction, and the position of the liquid metal droplets in the chamber can be adjusted by the DC pulse electric field.

[0025] 3. The bolted connection structure has the advantages of simple structure and easy disassembly and assembly, which makes the pump a single module that can be used in various occasions. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of an electric circulating pump based on gallium-indium liquid metal droplets;

[0027] Figure 2 for Figure 1 The main view;

[0028] Figure 3 A schematic diagram of an electric circulating pump with a cover plate;

[0029] Figure 4 for Figure 3 A schematic diagram of the discrete structure;

[0030] Figure 5 This is a schematic diagram showing the flow direction of the metal droplets;

[0031] Figure 6 This is a schematic diagram showing the flow direction of the driven liquid.

[0032] Main board 1, electrode groove 2, flow channel 3, droplet cavity 4, metal droplet 5, connecting pipe 6, seal 7, cover plate 8, bolt 9, nut 10, gasket 11, electrode 12. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0034] Specific implementation method one: Refer to Figures 1 to 4 This embodiment describes an electric circulating pump based on gallium-indium liquid metal droplets, comprising: a main board 1, gallium-indium metal droplets 5, two cover plates 8, and two electrodes 12.

[0035] The mainboard 1 has two flow channels 3, a droplet cavity 4, and two electrode slots 2.

[0036] The two flow channels 3 are connected through the droplet cavity 4. The free ends of the two flow channels 3 are respectively connected to the outside through two connecting pipes 6. The flow channels 3 and their connected connecting pipes 6 are sealed together by a sealing element 7.

[0037] The two electrode slots 2 are located on both sides of the droplet cavity 4 and are respectively connected to the two flow channels 3.

[0038] The gallium-indium metal droplet 5 is located inside the droplet cavity 4, the two electrodes 12 are located in the two electrode slots 2 respectively, and the two flow channels 3 are used to carry the driven fluid.

[0039] Alternating current and direct current pulse signals can be applied simultaneously to the two electrodes 12.

[0040] The two cover plates 8 are respectively attached to the upper and lower sides of the main board 1. The two cover plates 8 and the main board 1 are connected by bolts 9, which are threadedly connected to nuts 10 to secure each other. A washer 11 is also provided between the nut 10 and its adjacent cover plate 8. In this embodiment, the cover plates 8 prevent the driven fluid and gallium indium metal droplets 5 from flowing out, making the electric circulation pump modular. At the same time, the bolted connection structure has the advantage of simple assembly and disassembly.

[0041] The fabrication process of the electric circulating pump based on gallium-indium liquid metal droplets described in this embodiment is as follows:

[0042] The cover plate 8 and the main plate 1 are obtained by cutting a 3mm thick plexiglass plate using a laser engraving machine;

[0043] Insert two Teflon pipes into the inlets on both sides of the flow channel 3 about 5mm in, and then seal them with the sealing piece 7.

[0044] The two cover plates 8 and the main plate 1 are connected using bolts 9, and an aqueous solution is introduced to test the sealing performance of the connection.

[0045] Two graphite electrodes are fixed in two electrode slots 2 by interference fit.

[0046] Specific Implementation Method Two: Both traditional DC and AC electric fields can cause liquid metal droplets to move. A DC electric field can further enable the directional transport of fluid around the liquid metal droplet, i.e., a liquid metal pump. However, it is not believed that an AC electric field can achieve fluid transport. The movement of liquid metal droplets originates from the surface gradient of interfacial tension. When the gradient is not zero, it causes the flow of fluid around the liquid metal droplet, i.e., Marangoni flow. This flow reacts on the liquid metal droplet, ultimately propelling it to move, analogous to electrophoresis.

[0047] Based on the above traditional theories, this embodiment provides a method for using the electric circulating pump based on gallium-indium liquid metal droplets as described in Embodiment 1, specifically as follows:

[0048] When the conductivity of the driven fluid is less than 1.6 S / m, an alternating current with a frequency greater than 50 Hz is applied to the two electrodes 12, causing the driven fluid to flow toward the flow channel 3 that is closer to the gallium indium metal droplet 5. When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes 12 on the basis of the alternating current, causing the gallium indium metal droplet 5 to move closer to the other flow channel 3, and the driven fluid to flow in the opposite direction.

[0049] When the conductivity of the driven fluid is greater than or equal to 1.6 S / m, an alternating current with a frequency greater than 50 Hz and less than or equal to 100 Hz is applied to the two electrodes 12, causing the driven fluid to flow toward the flow channel 3 that is closer to the gallium indium metal droplet 5. When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes 12 on the basis of the alternating current, causing the gallium indium metal droplet 5 to move closer to the other flow channel 3, and the driven fluid to flow in the opposite direction.

[0050] When the conductivity of the driven fluid is greater than or equal to 1.6 S / m, an alternating current with a frequency greater than 100 Hz and a voltage amplitude less than 5 V is applied to the two electrodes 12, causing the driven fluid to flow toward the flow channel 3 closest to the gallium indium metal droplet 5. When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes 12 on the basis of the alternating current, causing the gallium indium metal droplet 5 to move closer to the other flow channel 3 and the driven fluid to flow in the opposite direction, or the voltage amplitude of the alternating current is adjusted to be greater than or equal to 5 V, so that the gallium indium metal droplet 5 remains stationary and the driven fluid flows in the opposite direction.

[0051] When the conductivity of the driven fluid is greater than or equal to 1.6 S / m, an alternating current with a frequency greater than 100 Hz and a voltage amplitude greater than or equal to 5 V is applied to the two electrodes 12, causing the driven fluid to flow in the direction of the flow channel 3 that is far from the gallium indium metal droplet 5. When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes 12 on the basis of the alternating current, so that the gallium indium metal droplet 5 moves closer to the other flow channel 3 and the driven fluid flows in the opposite direction, or the voltage amplitude of the alternating current is adjusted to be less than 5 V, so that the gallium indium metal droplet 5 remains stationary and the driven fluid flows in the opposite direction.

[0052] Preferably, the amplitude of the DC pulse signal is 2V and the superposition time is 0.1s.

[0053] When the conductivity of the driven fluid is less than 1.6 S / m, the driven fluid is a 0.1 mol / L NaOH solution; when the conductivity of the driven fluid is greater than or equal to 1.6 S / m, the driven fluid is a 0.25 mol / L NaOH solution.

[0054] Liquid metal droplets are manipulated using a pure alternating current (AC) electric field. The droplets are placed within a cylindrical cavity, with rectangular channels connected to both sides. When the droplet approaches one side of the cavity, the electric field distribution becomes uneven, resulting in different fluid flow intensities on either side of the droplet. This ultimately achieves directional fluid transport, i.e., an AC-controlled liquid metal pump. The direction of fluid pumping is directly related to the droplet's position within the cavity. When AC is applied, the droplet remains stationary; changing its position requires external force. Therefore, this embodiment introduces a DC pulse signal. When the droplet's position needs to be changed, a DC pulse signal is superimposed on the two electrodes 12 on top of the AC current. This allows for flexible changes in the droplet's position within the cavity, thus changing the direction of fluid pumping.

[0055] Working principle:

[0056] The principle of electric field-controlled liquid metal droplet fluid pumping is Marangoni flow driven by electrocapillary effect: According to the Lippmann equation, the non-uniform charge distribution on the surface of the liquid metal droplet causes the interfacial tension gradient to be non-zero. The shear stress caused by the interfacial tension gradient causes the fluid to flow along the droplet surface. When the electric field distribution around the droplet is uniform, the flow field is also symmetrical, and the time-averaged net flow is zero. When the left and right sides of the droplet are asymmetrical, the fluid begins to flow in one direction.

[0057] In a direction perpendicular to the two electrodes 12, the liquid metal droplet can be divided into an upper half and a lower half, such as... Figure 6As shown. The state of a liquid metal droplet in an electric field can be divided into two states: the presence or absence of an oxide layer on the surface. However, it must be emphasized that unlike the strong oxidation of liquid metal droplets in a DC electric field, the surface of the droplet in an AC electric field exhibits weak oxidation, with a relatively thin oxide layer. Electrically, this layer can be analogous to a capacitor, allowing the AC electric field to penetrate. When there is no oxide layer on the droplet surface, the upper part causes the fluid to flow downwards, while the lower part causes it to flow upwards. When the droplet approaches the lower side, the electric field is stronger there, causing the fluid in the lower part to flow faster, resulting in an overall upward flow. The presence or absence of an oxide layer on the droplet surface is related to factors such as the characteristics of the pumped solution, the amplitude of the electric field, and its frequency. Conversely, when an oxide layer forms on the droplet surface, the upper part causes the fluid to flow upwards, while the lower part flows downwards. When the droplet approaches the lower side of the chamber, the fluid in the lower part flows faster, ultimately causing the fluid to flow downwards. Changing the droplet's position alters the direction of fluid movement.

[0058] With an output waveform of cosine wave, an output frequency of 50 to 500 Hz, and an AC voltage amplitude of 0 to 10 V, the fluid flow rate can be adjusted within the range of -15 to 20 mm / s.

[0059] This invention utilizes an alternating current electric field to manipulate liquid metal droplets for fluid transport, while a direct current pulse signal is used to change the droplet's position within a chamber. Theoretical analysis and experimental verification ultimately demonstrate that when the alternating current electric field frequency exceeds 50Hz, and the electric field distribution on both sides of the liquid metal droplet is uniform, the flow on the left and right sides is symmetrical and opposite, preventing unidirectional flow. However, when the electric field is asymmetrical, the flow intensity on both sides is different, ultimately resulting in unidirectional flow.

[0060] Compared to conventional DC electric field manipulation of liquid metal droplets, the AC electric field used in this invention can suppress oxide layer formation. This allows it to manipulate low-concentration NaOH solutions and extends to PBS buffer solutions, NaCl electrolyte solutions, and more. Furthermore, unlike DC electric fields, liquid metal droplets can easily change position in AC electric fields. Therefore, the pumping direction can be changed by altering the droplet's position. The pumping direction can also be changed by adjusting the amplitude and frequency of the electric field to alter the oxidation state of the liquid metal droplets.

[0061] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A method for using an electric circulating pump based on gallium-indium liquid metal droplets, characterized in that, An electric circulating pump based on gallium-indium liquid metal droplets includes: a main board (1), gallium-indium metal droplets (5), and two electrodes (12). The main board (1) has two flow channels (3), a droplet cavity (4), and two electrode slots (2). The two flow channels (3) are connected through the droplet cavity (4). The two electrode slots (2) are located on both sides of the droplet cavity (4) and are connected to the two flow channels (3). The gallium-indium metal droplet (5) is located in the droplet cavity (4). The two electrodes (12) are located in the two electrode slots (2). The two flow channels (3) are used to carry the driven fluid. Alternating current and direct current pulse signals can be applied simultaneously to the two electrodes (12); When the conductivity of the driven fluid is less than 1.6 S / m, an alternating current with a frequency greater than 50 Hz is applied to the two electrodes (12) to make the driven fluid flow toward the flow channel (3) that is closer to the gallium indium metal droplet (5). When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes (12) on the basis of the alternating current to make the gallium indium metal droplet (5) move closer to the other flow channel (3) and the driven fluid flows in the opposite direction. When the conductivity of the driven fluid is greater than or equal to 1.6 S / m, an alternating current with a frequency greater than 50 Hz and less than or equal to 100 Hz is applied to the two electrodes (12) to make the driven fluid flow toward the flow channel (3) closer to the gallium indium metal droplet (5). When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes (12) on the basis of the alternating current to make the gallium indium metal droplet (5) move closer to the other flow channel (3) and the driven fluid flows in the opposite direction. When the conductivity of the driven fluid is greater than or equal to 1.6 S / m, an alternating current with a frequency greater than 100 Hz and a voltage amplitude less than 5 V is applied to the two electrodes (12) to make the driven fluid flow toward the flow channel (3) closer to the gallium indium metal droplet (5). When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes (12) on the basis of the alternating current to make the gallium indium metal droplet (5) move closer to the other flow channel (3) and the driven fluid flow in the opposite direction. Alternatively, the voltage amplitude of the alternating current is adjusted to be greater than or equal to 5 V so that the gallium indium metal droplet (5) remains stationary and the driven fluid flows in the opposite direction. When the conductivity of the driven fluid is greater than or equal to 1.6 S / m, an alternating current with a frequency greater than 100 Hz and a voltage amplitude greater than or equal to 5 V is applied to the two electrodes (12) to make the driven fluid flow toward the flow channel (3) that is far from the gallium indium metal droplet (5). When it is necessary to change the flow direction of the driven fluid, a DC pulse signal is superimposed on the two electrodes (12) on the basis of the alternating current to make the gallium indium metal droplet (5) move closer to the other flow channel (3) and the driven fluid flow in the opposite direction. Alternatively, the voltage amplitude of the alternating current is adjusted to be less than 5 V so that the gallium indium metal droplet (5) remains stationary and the driven fluid flows in the opposite direction.

2. The method of using the electric circulating pump based on gallium-indium liquid metal droplets according to claim 1, characterized in that, The free ends of the two flow channels (3) are respectively connected to the outside through two connecting pipes (6).

3. The method of using the electric circulating pump based on gallium-indium liquid metal droplets according to claim 2, characterized in that, The flow channel (3) and its connected pipe (6) are sealed together by a seal (7).

4. The method of using the electric circulating pump based on gallium-indium liquid metal droplets according to claim 1, 2, or 3, characterized in that, It also includes two cover plates (8), which are respectively attached to the upper and lower sides of the main board (1).

5. The method of using the electric circulating pump based on gallium-indium liquid metal droplets according to claim 4, characterized in that, The two cover plates (8) and the main board (1) are connected by bolts (9).

6. The method of using the electric circulating pump based on gallium-indium liquid metal droplets according to claim 1, characterized in that, The amplitude of the DC pulse signal is 2V, and the superposition time is 0.1s.

7. The method of using the electric circulating pump based on gallium-indium liquid metal droplets according to claim 1, characterized in that, When the conductivity of the driven fluid is less than 1.6 S / m, the driven fluid is a 0.1 mol / L NaOH solution. When the conductivity of the driven fluid is greater than or equal to 1.6 S / m, the driven fluid is a 0.25 mol / L NaOH solution.

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