Normal-temperature leidenfrost droplet suspension device and droplet manipulation method

Abstract

A room-temperature Leiden Frost-like droplet suspension device and droplet manipulation method are disclosed, comprising a porous airflow substrate platform and electrostatic tweezers. An array of micropores is formed on the surface of the porous airflow substrate platform, and an air inlet chamber is provided at the bottom of the platform. Pressurized gas is introduced into the air inlet chamber and then ejected upwards through the array of micropores, forming an air cushion layer on the surface of the porous airflow substrate platform, thus suspending the droplet. The electrodes of the electrostatic tweezers are mounted on a three-dimensional precision-moving insulating support, and an electrostatic generator is connected externally to the electrodes. The electrostatic generator supplies a controllable electrostatic potential to complete the electrostatic capture and traction drive of the droplet. This invention utilizes the airflow ejected from the array of micropores to form a stable air cushion layer between the droplet and the substrate, constructing a room-temperature Leiden Frost-like droplet suspension state. Combined with electrostatic capture and traction drive technology, it achieves precise programmable manipulation of suspended droplets under conditions without solid-liquid contact.

Description

Technical Field

[0001] This invention relates to the field of droplet manipulation technology, specifically to a room-temperature Leiden Frost-type droplet suspension device and droplet manipulation method. Background Technology

[0002] Droplet manipulation technology is now widely used in many basic research and industrial fields, including biological detection, microfluidics, water collection, printing, energy conversion, chemical engineering, and thermal management. Currently, mainstream non-contact droplet manipulation technologies mostly rely on external fields such as magnetic fields, electric fields, and ultrasound to drive droplets on superhydrophobic or oil-lubricated modified substrates. A typical approach is traditional electrostatic tweezers (PNAS, 2022), which mainly relies on electrostatic induction to apply a driving force to the droplet. However, the droplet remains in direct contact with the solid substrate during its movement, achieving only nominal non-contact manipulation between the driving component and the droplet. This method struggles to avoid problems such as droplet residue, sample contamination, and charge exchange. Furthermore, the substrate material and its surface modification layer may alter the physicochemical properties or biological activity of the droplet, and this method typically depends on customized superhydrophobic or oil-lubricated special wetting substrates, limiting its applicability.

[0003] While ultrasonic levitation (Study on the dynamic behavior of droplets under suspension conditions [D]. Xi'an: Northwestern Polytechnical University, 2008.) can suspend droplets, the acoustic field is sensitive to the node position, and airflow and slight vibrations can easily cause droplets to detach, making it difficult to achieve high-precision directional transport. The natural Leidenfrost effect usually relies on high-temperature substrates to induce vaporization at the bottom of the droplet, forming a vapor cushion between the droplet and the substrate, thereby achieving non-contact levitation of the droplet. However, this process requires high temperatures, making it difficult to apply to heat-sensitive droplets and biological sample droplets; in addition, the direction and trajectory of suspended droplets are random under the condition of no external constraints, making it difficult to achieve precise positioning and programmable control. Summary of the Invention

[0004] To overcome the aforementioned shortcomings, the present invention aims to provide a room-temperature Leidenfrost-like droplet suspension device and droplet manipulation method. By artificially constructing a room-temperature Leidenfrost-like suspension state through external airflow, and combining electrostatic capture and traction drive technology, the suspended droplets can be precisely and programmably manipulated under conditions without solid-liquid contact.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A room-temperature Leiden Frost-like droplet suspension device includes a porous airflow substrate platform and electrostatic tweezers. An array of micropores is formed on the surface of the porous airflow substrate platform, and an air inlet chamber is located at the bottom of the platform. Pressurized gas is introduced into the air inlet chamber and then ejected upwards through the array of micropores, forming an air cushion layer on the surface of the porous airflow substrate platform, thus suspending the droplets. The electrodes of the electrostatic tweezers are mounted on a three-dimensional precision-moving insulating support, and an electrostatic generator is connected externally to the electrodes. A controllable electrostatic potential is supplied through the electrostatic generator to complete the electrostatic capture and traction drive of the droplets.

[0006] The porous airflow substrate platform is made of a thin metal plate, and a uniformly distributed through-array of micropores is processed on the thin metal plate using a femtosecond laser.

[0007] The metal sheet is 0.3 mm thick, and the array of micropores has a pore size of 50 μm.

[0008] The electrostatic tweezers use copper rods as electrodes with a diameter of 5 mm.

[0009] A method for manipulating droplets using a room-temperature Leiden Frost-like droplet suspending device includes the following steps: 1) Under normal temperature and pressure, a porous airflow substrate platform with 50μm array micropores and a thickness of 0.3mm, which has been processed by femtosecond laser, is horizontally fixed. The lower end of the porous airflow substrate platform is sealed and connected to the air inlet chamber and the pressurized air source. 2) After the pressurized air source is turned on, compressed air enters the air intake chamber and is sprayed upward through the array of micropores of the porous airflow base platform. A stable air cushion layer is formed on the surface of the porous airflow base platform. After the droplet is placed above the micropore area, the droplet is separated from the base and kept suspended under the support of the air cushion layer, thus forming a room temperature Leidenfrost-like suspension state. 3) Adjust the position of the insulating support so that the electrostatic tweezers electrode is vertically positioned directly above the droplet, and the electrode axis is vertically coaxial with the center of the droplet; 4) Turn on the electrostatic generator and apply a DC electrostatic potential to the electrostatic tweezers. A stable electrostatic field is formed around the electrodes, and the droplets are charged and polarized by electrostatic induction. 5) The droplet is subjected to the combined effects of electrostatic attraction, gravity, and the upward lifting force of the air cushion layer, and reaches a dynamic equilibrium, so that the droplet is stably located directly below the electrostatic tweezers electrode. 6) The insulating support moves at a constant speed in the horizontal direction by a preset program. The droplets move synchronously with the electrostatic tweezers under the traction of the horizontal component of the electrostatic force, realizing non-contact directional transport of droplets at room temperature. 7) During the entire operation, fine-tune the output voltage of the electrostatic generator, the vertical height of the electrode, and the air supply pressure as needed to ensure that the droplets are always within the effective control range.

[0010] The electrostatic generator applies a 3.5 kV DC electrostatic potential to the electrostatic tweezers.

[0011] Compared with the prior art, the present invention has the following technical effects: (A) Because the present invention uses a 0.3 mm metal plate with 50 μm array micropores and a bottom pressurized air supply structure, and uses the Bernoulli effect to replace the high temperature vapor layer with an air cushion layer, it achieves the replication of the Leiden Frost suspension effect under normal temperature conditions, gets rid of the high temperature use limitation, and is suitable for testing temperature-sensitive reagents, biological fluids and other droplets that are not resistant to temperature.

[0012] (B) Because the present invention isolates the droplets from the solid surface through an air cushion layer, it achieves no solid-liquid contact throughout the entire process, eliminating the drawbacks such as droplet residue, sample contamination, charge migration, and substrate modification from the root, thereby improving the reliability of micro-droplet detection.

[0013] (C) Since the substrate of this invention is made of ordinary metal sheet, it can be formed by femtosecond laser drilling only, without the need for superhydrophobic and lubricating coating modification, thus realizing the universalization of substrate and effectively reducing the platform processing cost.

[0014] (D) This invention uses the coordinated control of electrostatic tweezers electrodes and a three-dimensional programmable support to capture and stably constrain suspended droplets by polarized electrostatic force, thereby achieving precise programmable movement of suspended droplets along a preset trajectory. This overcomes the problems of disordered drift, difficulty in precise positioning and trajectory control of natural Leidenfrost droplets.

[0015] (E) This invention achieves dynamic adaptation of the force state of suspended droplets by linking and controlling electrostatic parameters, electrode height and air inlet pressure, thereby widening the stable suspension and control range and improving the operational stability and control reliability of the device. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the device structure in an embodiment of the present invention.

[0017] Figure 2 This is a schematic diagram of femtosecond laser fabrication of porous stainless steel sheet in an embodiment of the present invention.

[0018] Figure 3 This is a magnified photograph of a portion of the suspended droplet in an embodiment of the present invention.

[0019] Figure 4 This is a time-series image of a suspended droplet moving along a preset direction under the traction of electrostatic tweezers in an embodiment of the present invention.

[0020] In the figure: 1—Porous airflow substrate platform, 2—Electrostatic tweezers, 3—Air inlet chamber, 4—Air cushion layer, 5—Femtosecond laser, 6—Droplet, 7—Stainless steel sheet. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the embodiments and accompanying drawings.

[0022] Reference Figure 1 A room-temperature Leiden Frost-like droplet suspension device includes a porous airflow substrate platform 1 and electrostatic tweezers 2. The porous airflow substrate platform 1 is made of a stainless steel sheet with an array of micropores. An air inlet chamber 3 is provided at the bottom of the sheet. After pressurized gas is introduced into the air inlet chamber 3, it is sprayed upward through the array of micropores and forms an air cushion layer 4 on the upper surface of the stainless steel sheet, thus suspending the droplets. The electrostatic tweezers 2 uses a 5 mm diameter copper rod as an electrode. The electrode is mounted on an insulating support that can move in three dimensions with precision, allowing for flexible adjustment of its spatial position. An electrostatic generator is connected to the electrode, which supplies a controllable electrostatic potential to complete the electrostatic capture and traction drive of the droplets.

[0023] Reference Figure 1 , Figure 2 The porous airflow substrate platform 1 is made of a 0.3 mm thick stainless steel sheet 7. A femtosecond laser 5 is used to process uniformly distributed, through-array micropores with a diameter of approximately 50 μm on the stainless steel sheet 7. The micropore area in the illustration is shown on a scale of 200 μm. Pressurized gas is introduced into the cavity through the lower air inlet 3 and then ejected upwards through the array micropores on the stainless steel sheet 7, forming a continuous and stable air cushion layer 4 above the stainless steel sheet 7. The air cushion layer 4 provides upward air film support for the droplets, causing the droplets to separate from the surface of the stainless steel sheet 7, thereby achieving suspension.

[0024] Reference Figure 3 There is a light-transmitting air cushion layer 4 between the droplet 6 and the porous airflow substrate platform 1. The size scale in the figure is 500μm. The droplet 6 is isolated from the solid substrate by the air cushion layer 4 to avoid direct solid-liquid contact. Under the support of the air film, it exhibits a non-contact suspension characteristic similar to that of high-temperature natural Leiden Frost droplets, thus forming a room-temperature Leiden Frost-like droplet suspension state.

[0025] A method for manipulating droplets using a room-temperature Leiden Frost-like droplet suspending device includes the following steps: 1) Under normal temperature and pressure, a porous airflow substrate platform 1 with 50μm array micropores and a thickness of 0.3mm, which has been processed by femtosecond laser, is horizontally fixed. The lower end of the porous airflow substrate platform 1 is sealed and connected to the air inlet chamber 3 and the pressurized air source. 2) Turn on the pressurized air source, and compressed air enters the air intake chamber 3 and is sprayed upward through the array of micropores of the porous airflow base platform 1, forming a stable air cushion layer 4 on the upper surface of the porous airflow base platform 1. After the droplet 6 is placed above the micropore area, the droplet 6 is suspended in the air under the support of the air cushion layer 4, forming a room temperature Leiden Frost-like suspension state. 3) Adjust the position of the insulating support so that the electrostatic tweezers electrode is vertically positioned directly above the droplet 6, and the electrode axis is vertically coaxial with the center of the droplet 6; 4) Turn on the electrostatic generator and apply a DC electrostatic potential of 3.5kV to the electrostatic tweezers 2. A stable electrostatic field is formed around the electrode, and the droplet 6 is charged and polarized by electrostatic induction. 5) The electrostatic attraction of droplet 6, its own gravity, and the upward lifting force of air cushion layer 4 work together and reach a dynamic equilibrium, so that droplet 6 is stably located directly below the electrode of electrostatic tweezers 2. 6) Control the insulating bracket to move horizontally to the right at a uniform speed through a preset program, referring to... Figure 4 The position of droplet 6 was collected at 0s, 10.3s and 18.5s respectively. Under the traction of the horizontal component of electrostatic force, droplet 6 has no solid friction resistance and moves synchronously to the right with electrostatic tweezers 2, realizing non-contact directional transport of droplet 6 at room temperature. The scale size in the figure is 2 mm. 7) During the entire operation, fine-tune the output voltage of the electrostatic generator, the vertical height of the electrode, and the gas supply pressure as needed to ensure that the droplet 6 is always within the effective control range.

Claims

1. A room-temperature Leiden Frost-like droplet suspension device, characterized in that: It includes a porous airflow substrate platform and electrostatic tweezers; the porous airflow substrate platform has an array of micropores on its surface and an air inlet chamber at its lower part. After pressurized gas is introduced into the air inlet chamber, it is ejected upward through the array of micropores and forms an air cushion layer on the surface of the porous airflow substrate platform, which suspends the droplets; the electrodes of the electrostatic tweezers are mounted on a three-dimensional precision moving insulating support, and the electrodes are connected to an electrostatic generator. The electrostatic generator supplies a controllable electrostatic potential to complete the electrostatic capture and traction drive of the droplets.

2. The apparatus according to claim 1, characterized in that: The porous airflow substrate platform is made of a thin metal plate, and a uniformly distributed through-array of micropores is processed on the thin metal plate using a femtosecond laser.

3. The apparatus according to claim 2, characterized in that: The metal sheet is 0.3 mm thick and the array of micropores has a pore size of 50 μm.

4. The apparatus according to claim 1, characterized in that: The electrostatic tweezers use copper rods as electrodes with a diameter of 5 mm.

5. A method for manipulating droplets using a room-temperature Leiden Frost-like droplet suspending device according to any one of claims 1-4, characterized in that, Includes the following steps: 1) Under normal temperature and pressure, a porous airflow substrate platform with 50μm array micropores and a thickness of 0.3mm, which has been processed by femtosecond laser, is horizontally fixed. The lower end of the porous airflow substrate platform is sealed and connected to the air inlet chamber and the pressurized air source. 2) After the pressurized air source is turned on, compressed air enters the air intake chamber and is sprayed upward through the array of micropores of the porous airflow base platform. A stable air cushion layer is formed on the surface of the porous airflow base platform. After the droplet is placed above the micropore area, the droplet is separated from the base and kept suspended under the support of the air cushion layer, thus forming a room temperature Leidenfrost-like suspension state. 3) Adjust the position of the insulating support so that the electrostatic tweezers electrode is vertically positioned directly above the droplet, and the electrode axis is vertically coaxial with the center of the droplet; 4) Turn on the electrostatic generator and apply a DC electrostatic potential to the electrostatic tweezers. A stable electrostatic field is formed around the electrodes, and the droplet undergoes charge polarization due to electrostatic induction. 5) The droplet is subjected to the combined effects of electrostatic attraction, gravity, and the upward lifting force of the air cushion layer, and reaches a dynamic equilibrium, so that the droplet is stably located directly below the electrostatic tweezers electrode. 6) The insulating support moves at a constant speed in the horizontal direction by a preset program, and the droplets move synchronously with the electrostatic tweezers under the traction of the horizontal component of electrostatic force, so as to realize non-contact directional transport of droplets at room temperature. 7) During the entire operation, fine-tune the output voltage of the electrostatic generator, the vertical height of the electrode, and the gas supply pressure as needed to ensure that the droplet is always within the effective control range.

6. The droplet manipulation method according to claim 5, characterized in that: The electrostatic generator applies a 3.5 kV DC electrostatic potential to the electrostatic tweezers.

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