Liquid metal magnetic rotor preparation device based on surface acoustic waves

Abstract

The invention discloses a liquid metal magnetic rotor preparation device based on surface acoustic waves. The liquid metal magnetic rotor preparation device comprises a surface acoustic wave device and a low-aspect-ratio section flow focusing type liquid drop generation micro-channel. The surface acoustic wave device comprises a focusing interdigital transducer and a 128-degree Y-X lithium niobate piezoelectric substrate. The flow focusing type droplet generation micro-channel comprises a dispersed phase inlet, two continuous phase inlets, a two-phase intersection channel, a tapered channel, a contraction zone channel, a divergent channel and an outlet channel. The interface of the liquid metal mixed with ferroferric oxide is unstable and fractured under the action of a continuous phase, and micron-sized aspheric micro-droplets with a large length-diameter ratio are generated, namely the liquid metal magnetic micro-droplet rotor. Under the common influence of the oxidizability of the liquid metal and the wrapping property of the PVA material, the liquid metal magnetic microdroplet rotor can keep the original form. The prepared liquid metal magnetic microdroplet rotor can be embedded into a microchannel of a circular structure, and two-phase fluid can be rapidly mixed under the action of a rotating magnetic field.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid micro-mixing in biochips and micro-total analysis systems, and the technology involves the fields of magnetic materials, liquid metals, surface acoustic waves and microfluidics, and in particular provides a device and method for preparing a micron-level liquid metal magnetic droplet rotor. Background Art

[0002] Liquid metal magnetic materials are composed of magnetic substances and liquid metals. Magnetic particles evenly distributed in liquid metal materials can give them unique liquid properties and magnetic response characteristics. In the field of microfluidics, liquid metal magnetic materials can be used as intelligent fluids to achieve precise control and rapid response through external magnetic fields. They can be applied to the processing of complex fluids such as micro-mixing, micro-pumping, and micro-separation. They have wide applications in chemical analysis and drug development. By discretizing liquid metal magnetic materials into micron-sized droplets with different aspect ratios, they can be used as magnetic rotors under magnetic field regulation to break the stratified flow state of traditional microscale fluids, promote chaotic convection, increase the fluid contact area, and achieve precise control of the degree of fluid mixing, effectively improving the mixing efficiency of the two-component materials. Traditional macroscopic magnetic rotors usually rotate 360 ​​degrees, while the micron-sized liquid metal magnetic rotors currently proposed are mostly spherical, and only the horizontal movement of droplets induced by magnetic fields accelerates fluid mixing, and the mixing efficiency needs to be improved. Therefore, it is necessary to further explore the stable preparation method of multi-morphological liquid metal magnetic droplets with different aspect ratios to achieve multi-angle rotation of magnetic droplets and improve mixing efficiency.

[0003] At present, the common methods for preparing liquid metal magnetic droplets include titration, mold method, ultrasonic treatment, mechanical stirring and microfluidics. Among them, the titration method directly uses a syringe to squeeze liquid metal to achieve material discretization, which can realize the preparation of millimeter-level droplet metal, but the pressure control accuracy is low and the uniformity of droplet size is difficult to control. The mold method can improve the uniformity of the droplet size of the metal droplet by injecting liquid metal into a prefabricated mold, but the adhesion effect between the metal and the mold will cause the droplet to be difficult to demold. The ultrasonic treatment method and mechanical stirring method induce the dispersion of liquid metal materials by applying pressure or shear force. However, the problem of uneven distribution of macroscopic ultrasonic energy and shear force along space will make it difficult to control the size of the gold droplet. When the microfluidics method is applied to the preparation of liquid metal droplets, due to the problem that the liquid metal is not hydrophilic or lipophilic and has a high interfacial tension coefficient, the liquid metal will have a large-scale interface jitter and retraction phenomenon in the micron-level channel by only changing the fluid properties or flow conditions, resulting in uneven droplet size.

[0004] At present, the generation method of liquid metal magnetic droplets has the disadvantages of low efficiency, poor generation repeatability, and uncontrollable shape. In order to achieve efficient preparation of micron-sized liquid metal magnetic droplets with different aspect ratios, it is necessary to further introduce micron-wavelength surface acoustic waves into droplet microfluidics technology, apply acoustic radiation force to the liquid metal interface as additional pressure, and achieve controllable adjustment of droplet size and generation stability, so as to prepare various types of magnetic micron-sized rotors and accelerate fluid mixing efficiency. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a micron-sized liquid metal magnetic droplet rotor with high efficiency, controllable shape and high generation repeatability. The liquid metal magnetic droplet rotor can rotate on a fixed axis under the induction of a magnetic field, thereby increasing the contact area between fluids in a micron-sized channel and improving the mixing efficiency.

[0006] The technical solution adopted by the present invention is a liquid metal magnetic droplet rotor preparation device based on surface acoustic wave, including a surface acoustic wave device and a low aspect ratio cross-section flow focusing type droplet generation microchannel. The surface acoustic wave device includes a focusing interdigital transducer and a 128°YX lithium niobate piezoelectric substrate. The flow focusing type droplet generation microchannel has a cross-section height to width ratio between 0.08 and 0.2, and includes a dispersed phase inlet, two continuous phase inlets, a two-phase intersection channel, a gradually contracting channel, a contraction zone channel, a gradually expanding channel and an outlet channel.

[0007] like Figure 1 As shown, the dispersed phase inlet channel, the continuous phase inlet channel, the two-phase intersection channel and the outlet channel have the same width. The width of the contraction zone channel is 40% of the width of the two-phase intersection channel. The gradually contracting channel is responsible for connecting the two-phase intersection channel and the contraction zone channel, and the gradually expanding channel is responsible for connecting the contraction zone channel and the downstream outlet. The channel wall is inclined at a 15° angle to the two-phase intersection channel. The first continuous phase inlet and the second continuous phase inlet are respectively at an angle of 45° to the dispersed phase inlet. The axial central axes of the dispersed phase inlet channel, the two-phase intersection channel, the gradually contracting channel, the contraction zone channel, the gradually expanding channel, the outlet channel and the dispersed phase inlet are consistent, and the two continuous phase inlets are symmetrical about the central axis.

[0008] Liquid metal mixed with ferroferric oxide powder flows in from the dispersed phase inlet channel as a dispersed phase fluid, and 10wt% PVA aqueous solution flows in from the first continuous phase inlet and the second continuous phase inlet as a continuous phase fluid at a flow rate lower than that of the dispersed phase. The continuous phase and the dispersed phase fluid meet at the channel where the two phases meet, and flow through the contraction zone channel. The dispersed phase fluid is unstable and fractured at the interface under the combined action of the viscous shearing action, extrusion action and acoustic radiation force of the continuous phase.

[0009] Liquid metal is subject to non-uniform wall shear in a low aspect ratio channel, and is prone to form a non-spherical ellipsoidal shape with an adjustable aspect ratio, namely, a liquid metal magnetic droplet rotor. This special-shaped droplet shape is jointly affected by the oxidizability of the liquid metal and the wrapping of the PVA material on the liquid metal surface. When it flows out of the outlet and in the actual application process, it will always maintain its original shape when it is generated.

[0010] The present invention has the following advantages after adopting the above technical solution:

[0011] 1. The present invention adopts a low aspect ratio microchannel and utilizes its isotropic non-uniform wall extrusion effect to induce the formation of magnetic liquid metal droplets with a large aspect ratio, which is beneficial to increasing the influence range of the magnetic liquid metal rotor on the fluid during rotation.

[0012] 2. The dispersed phase flow rate used in the present invention is greater than the continuous phase flow rate, ensuring that the liquid metal is stretched downstream under the action of a higher inertial force, effectively improving the problem of unstable flow caused by the back-and-forth interface fluctuations in the microchannel due to the combined influence of the liquid metal being non-hydrophilic, non-lipophilic and having a high interface coefficient.

[0013] 3. The present invention utilizes surface acoustic wave technology to apply acoustic radiation force as additional pressure to the liquid metal interface, thereby solving the problem of high randomness of liquid metal interface fracture under the drive of high inertial force and significantly reducing the problem of uneven size of liquid metal magnetic droplets.

[0014] 4. The present invention achieves precise control of the size of liquid metal magnetic droplets by changing the input power of the acoustic field, thereby realizing efficient preparation of micron-sized liquid metal magnetic droplets with different aspect ratios.

[0015] 5. The present invention utilizes the oxidizability of the dispersed phase liquid metal material and the wrapping property of the continuous phase material PVA on the liquid metal surface to maintain the droplet morphology, avoid the liquid metal magnetic droplets being affected by fluidity, and restore the spherical shape at the channel outlet and during use.

[0016] 6. The liquid metal magnetic droplet rotor prepared by the present invention can be embedded in a circular structure microchannel and rotated on a fixed axis under the action of a rotating magnetic field to achieve rapid mixing of two-phase fluids. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the planar structure of a device for preparing a micron-sized liquid metal magnetic droplet rotor mentioned in the invention;

[0018] Figure 2 It is a schematic diagram of the three-dimensional structure of the magnetic stirring device;

[0019] Figure 3 Schematic diagram of the planar structure of the liquid metal magnetic droplet rotor micromixer.

[0020] In the figure: 1. first continuous phase inlet, 2. dispersed phase inlet, 3. second continuous phase inlet, 4. two-phase intersection channel, 5. gradually contracting channel, 6. contraction zone channel, 7. gradually expanding channel, 8. outlet channel, 9. focused interdigital transducer, 10. YX lithium niobate piezoelectric substrate, 11. tachometer, 12. speed regulator, 13. transformer, 14. motor, 15. magnet, 16. liquid metal magnetic droplet rotor micromixer, 17. first component inlet, 18. second component inlet, 19. mixing zone, 20. liquid metal magnetic droplet rotor, 21. mixing outlet. DETAILED DESCRIPTION

[0021] A low aspect ratio cross-sectional flow focusing type droplet generation microchannel is made of polydimethylsiloxane silicone. The channel structure pattern transfer and polydimethylsiloxane curing are first achieved on a single crystal silicon wafer by injection molding, and then the cured polydimethylsiloxane is separated from the silicon wafer. Holes are punched on the cured polydimethylsiloxane according to the relative channel inlet and outlet positions, and irreversible bonding is performed with the cured polydimethylsiloxane film by a corona machine to completely close the droplet generation microchannel. The focusing interdigital transducer is made of 100nm gold deposited on a 128°YX lithium niobate piezoelectric substrate by an evaporator. The closed microfluidic chip is pressed on the 128°YX lithium niobate piezoelectric substrate according to the relative position of the focusing interdigital transducer. Finally, the three inlet holes and one outlet hole reserved on the cured polydimethylsiloxane are installed with a connecting plastic catheter to complete the packaging preparation of the experimental piece.

[0022] like Figure 1 The liquid metal magnetic droplet rotor preparation device based on surface acoustic wave shown in the figure is composed of a surface acoustic wave device and a low aspect ratio cross-section flow focusing type droplet generation microchannel. Among them, the surface acoustic wave device includes a focusing interdigital transducer and a 128°YX lithium niobate piezoelectric substrate. The flow focusing type droplet generation microchannel includes a dispersed phase inlet, two continuous phase inlets, a two-phase intersection channel, a gradually contracting channel, a contraction zone channel, a gradually expanding channel and an outlet channel. The dispersed phase inlet channel, the first continuous phase inlet channel, and the second continuous phase inlet channel converge at one point and are connected to the two-phase intersection channel. The subsequent gradually contracting channel, the contraction zone channel, the gradually expanding channel, and the outlet channel are connected in series in sequence, and the cross-sections of all channels are rectangular.

[0023] The width of the dispersed phase inlet channel, the first continuous phase inlet channel, the second continuous phase inlet channel, the two-phase intersection channel and the outlet channel of the flow focusing droplet generation microchannel are all 500μm, the width of the contraction zone channel is 200μm, and the length of all channels except the gradually contracting channel and the gradually expanding channel is 5000μm, and the height of each channel is 40μm. The gradually contracting channel is responsible for connecting the two-phase intersection channel and the contraction zone channel, and the gradually expanding channel is responsible for connecting the contraction zone channel and the downstream outlet. The channel wall is inclined at a 15° angle to the two-phase intersection channel. The first continuous phase inlet and the second continuous phase inlet are at an angle of 45° to the dispersed phase inlet, respectively. The axial central axes of the dispersed phase inlet channel, the two-phase intersection channel, the gradually contracting channel, the contraction zone channel, the gradually expanding channel, the outlet channel and the dispersed phase inlet are consistent, and the two continuous phase inlets are symmetrical about the central axis.

[0024] When the present invention is working, Figure 1 As shown, liquid metal mixed with ferroferric oxide powder flows in from the dispersed phase inlet channel as a dispersed phase fluid, and 10wt% PVA aqueous solution flows in from the first continuous phase inlet and the second continuous phase inlet at a constant speed as a continuous phase fluid. The continuous phase and the dispersed phase fluid meet in the channel at the intersection of the two phases, flow through the contraction zone channel, and the dispersed phase fluid is unstable and fractured at the interface under the combined action of the viscous shearing action, extrusion action and acoustic radiation force of the continuous phase.

[0025] Liquid metal is subject to non-uniform wall shearing in a low aspect ratio channel, and is prone to forming a non-spherical ellipsoidal shape with an adjustable aspect ratio, namely a liquid metal magnetic droplet rotor. This special-shaped droplet morphology is affected by the oxidizability of the liquid metal and the wrapping property of the PVA material on the surface of the liquid metal. Therefore, after the generated liquid metal magnetic droplet rotor flows out of the outlet and during the actual application process, it will always maintain its original shape when it was generated. The liquid metal magnetic droplet rotor prepared by the present invention can be embedded in a circular structure microchannel, and rotate on a fixed axis under the action of a rotating magnetic field to achieve rapid mixing of the two-phase fluid.

Claims

1. A liquid metal magnetic rotor preparation device based on surface acoustic wave, characterized in that: The invention comprises a surface wave device and a low aspect ratio cross-section flow focusing type droplet generation microchannel. The surface acoustic wave device is composed of a focusing interdigital transducer and a 128°YX lithium niobate piezoelectric substrate. The ratio of the cross-section height to the width of the flow focusing type droplet generation microchannel is between 0.08 and 0.2, and the microchannel comprises a dispersed phase inlet, two continuous phase inlets, a two-phase intersection channel, a gradually contracting channel, a contraction zone channel, a gradually expanding channel and an outlet channel. The dispersed phase inlet channel, the first continuous phase inlet channel and the second continuous phase inlet channel converge at one point and are connected to the two-phase intersection channel. The subsequent gradually contracting channel, the contraction zone channel, the gradually expanding channel and the outlet channel are connected in series in sequence, and the cross sections of all channels are rectangular.

2. The liquid metal magnetic rotor manufacturing device based on surface acoustic wave according to claim 1, characterized in that: The aspect ratio of the microchannel cross section is between 0.08 and 0.

2. The interface between the two phases is restricted by the uneven wall surface in the microchannel, and the droplets are in a non-spherical state with a large aspect ratio.

3. The liquid metal magnetic rotor manufacturing device based on surface acoustic wave according to claim 1, characterized in that: A contraction zone channel is set downstream of the channel where the two phases meet. By reducing the cross-sectional size of the microchannel, the flow rate of the two-phase fluid is increased, the shear force and extrusion force on the interface of the continuous phase and the dispersed phase are increased, and the liquid metal interface is induced to break.

4. The liquid metal magnetic rotor manufacturing device based on surface acoustic wave according to claim 1, characterized in that: A surface acoustic wave device is set on one side of the microchannel contraction area, and the acoustic radiation force applied by the surface acoustic wave on the two-phase interface is used to squeeze the interface fracture and realize the precise control of the droplet size. At the same time, the problem of uneven droplet size when liquid metal is driven by high inertial force and randomly fractured by Rayleigh Prandtl instability is improved.

5. The liquid metal magnetic rotor manufacturing device based on surface acoustic wave according to claim 1, characterized in that: Liquid metal mixed with ferroferric oxide powder is used as the dispersed phase fluid, and 10wt% PVA aqueous solution is used as the continuous phase. The engulfing property of liquid metal on other metals enables the liquid metal and ferroferric oxide powder to quickly fuse at room temperature to form a magnetic alloy. The easy oxidation of liquid metal forms a solid thin shell on the surface of liquid metal droplets, which facilitates the heterogeneous liquid metal magnetic rotor to maintain a high aspect ratio morphology. At the same time, PVA forms a coating layer on the surface of the liquid metal to prevent deformation and fusion of liquid metal droplets after collision.

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