Coaxial co-polymerization microfluidic droplet generation device and method with adjustable focusing distance

Abstract

This invention belongs to the field of microfluidic control technology and discloses a coaxial copolymer microfluidic droplet generation device and method with adjustable focusing distance. The device includes a focusing distance adjustment mechanism, a coaxial premixing module, and a flow focusing module. The coaxial premixing module achieves stable premixing of the inner and middle phase fluids through coaxial arrangement of inner and outer capillaries and a turbulence support structure within the annular gap, forming a core-shell structured preemulsion. The flow focusing module receives the outer phase input and performs hydraulic focusing and shearing on the preemulsion to generate uniform droplets. By precisely adjusting the distance between the two modules through the focusing distance adjustment mechanism, the focusing distance can be continuously changed within the range of 0.0-10.0 mm, achieving fine control over droplet size (260-650 μm) and shell thickness. This invention features a stable structure, precise adjustment, and high pressure resistance, and is suitable for W / O / W multiphase systems, solving the problems of limited adjustment parameters and invariable structure in traditional devices for emulsion droplet control.

Description

Technical Field

[0001] This invention belongs to the field of microfluidic control technology, and in particular relates to a coaxial copolymer microfluidic droplet generation device and method with adjustable focusing distance. Background Technology

[0002] Droplet microfluidics is one of the important research directions in the fields of precision chemistry, biomedicine and materials science. By controlling the interface morphology of multiphase fluids in microchannels, the controllable generation of monodisperse droplets can be achieved. However, traditional droplet generation devices mainly rely on fixed geometric channel structures to achieve fluid focusing. The size and shape of the droplets are mainly controlled by the flow ratio, viscosity and surface tension, with limited adjustment range. Moreover, the structure is immutable and easily affected by flow field disturbances and interface contamination. Currently, two types of devices are widely used: (1) microfluidic chip droplet generators, whose channels are usually formed by polydimethylsiloxane (PDMS) or glass micro-etching, which have good optical transparency, but are prone to channel deformation or blockage under high pressure or high viscosity systems, resulting in poor durability; (2) coaxial capillary droplet generators, which form a flow focusing structure by coaxially inserting two glass or metal capillaries. Although such devices are easy to observe and control, the relative positions between the inner and outer capillaries are usually fixed, making it impossible to achieve a precisely adjustable focusing distance during the experiment, resulting in the droplet size being limited by the flow ratio control. Furthermore, such devices are prone to problems such as loose joints, alignment misalignment, and liquid residue blockage after long-term use. In summary, existing technologies lack a droplet generation device that is structurally stable, has a variable focusing distance, is repeatedly adjustable, and can withstand high pressure. Therefore, it is necessary to develop a structurally adjustable, modular, and mechanically stable coaxial metal microfluidic droplet generation device to meet the precise control requirements for droplet preparation in complex systems. Summary of the Invention

[0003] The purpose of this invention is to provide a coaxial copolymer microfluidic droplet generation device and method with adjustable focusing distance to solve the above-mentioned technical problems.

[0004] To solve the above-mentioned technical problems, the specific technical solution of the coaxial copolymer microfluidic droplet generation device and method with adjustable focusing distance of the present invention is as follows:

[0005] An adjustable focusing distance coaxial copolymer microfluidic droplet generation device includes: a focusing distance adjustment mechanism, a coaxial premixing module, and a flow focusing module. The coaxial premixing module and the flow focusing module are mounted on the focusing distance adjustment mechanism and are dynamically sealed together. The coaxial premixing module is used to coaxially and stably pre-form an inner phase droplet uniformly dispersed in the mesophase preemulsion flow by the inner phase and the mesophase fluid. The flow focusing module is used to introduce an outer phase, and under the hydraulic focusing and shearing action of the outer phase fluid, shear the preemulsion flow into target droplets. The focusing distance adjustment mechanism is used to adjust the distance between the coaxial premixing module and the flow focusing module, thereby adjusting the focusing distance of the droplets and achieving precise control over the size and shell thickness of the target droplets.

[0006] Furthermore, the coaxial premixing module is provided with a pre-emulsion flow output port for outputting the pre-emulsion flow, and the pre-emulsion flow output port is connected to the fluid cavity inlet of the flow focusing module through a dynamic sealing structure.

[0007] Furthermore, the focusing distance adjustment mechanism includes a base, a slide rail, a lead screw slider, a lead screw, a transmission input source, a moving slider, and a stationary slider. The slide rail is vertically fixed on the base. Both the moving slider and the stationary slider are mounted on the slide rail. The lead screw slider is threadedly connected to the lead screw. The transmission input source is mounted on one side of the upper end of the slide rail, and its output end is fixedly connected to the lead screw for driving the lead screw to rotate. The moving slider is fixedly connected to the lead screw slider. The coaxial premixing module is mounted on the moving slider, and the flow focusing module is mounted on the stationary slider.

[0008] Furthermore, the moving slider and the stationary slider are respectively provided with a sliding resistance adjustment knob one and a sliding resistance adjustment knob two, which are used to adjust the resistance between the moving slider and the stationary slider and the slide rail.

[0009] Furthermore, the transmission input source is a stepper motor, which drives the lead screw to rotate, causing the lead screw slider to slide along the slide rail, thereby driving the moving slider to move the coaxial premixing module closer to or away from the flow focusing module on the stationary slider, so as to achieve precise adjustment of the focusing distance.

[0010] Furthermore, the coaxial premixing module also includes: a hexahedral nut, an inner capillary tube and an outer capillary tube, a turbulence-supporting alloy winding, an inner tube input connection port, and an intermediate phase input port. The hexahedral nut has three sets of through holes Aa, Bb, and Cc. The inner and outer capillary tubes are coaxially arranged and connected to holes a and A of the hexahedral nut, respectively. The turbulence-supporting alloy winding is disposed in the annular gap between the inner and outer capillary tubes. The inner tube input connection port is connected to the inner capillary tube. The intermediate phase input port and the pre-emulsion output port are connected to holes b and A of the hexahedral nut, respectively, through threaded joints. The hexahedral nut is fixedly connected to the movable slider through hole B. Holes C and c of the hexahedral nut are sealed with transparent material to form observation windows.

[0011] Furthermore, the flow focusing module includes a hexahedral nut II, a perforated silicone plug, a collection tube, an external phase inlet, an outlet tube, and a transparent glass tube. The hexahedral nut II has three sets of through holes Aa, Bb, and Cc. The transparent glass tube is connected to hole a, and the pre-emulsion outlet is dynamically sealed to the transparent glass tube through the perforated silicone plug. The external phase inlet and outlet tube are connected to holes b and A of the hexahedral nut II, respectively, through threaded joints. The hexahedral nut II is fixedly connected to the static slider through hole B. The collection tube and outlet tube are integrally formed, with the upper end extending into the transparent glass tube, and the upper end of the collection tube gradually narrows.

[0012] Furthermore, the C-hole and c-hole of the hexahedral nut II are sealed with a transparent material to form an observation window.

[0013] Furthermore, the focusing distance adjustment mechanism can drive the focusing distance D to be continuously adjusted within the range of 0.0mm to 10.0mm, and when the focusing distance D increases from 0.0mm to 10.0mm, the equivalent diameter of the target droplet continuously increases from 260μm to 650μm.

[0014] The present invention also discloses a method for preparing droplets using the aforementioned device, comprising the following steps:

[0015] Step 1: Input the inner phase, intermediate phase, and outer phase into the device through independent flow paths. The inner and intermediate phases enter the coaxial premixing module to form a pre-emulsion flow, while the outer phase enters the flow focusing module.

[0016] Step 2: Activate the focusing distance adjustment mechanism to drive the coaxial premixing module to move relative to the flow focusing module and adjust the droplet focusing distance to the target value;

[0017] Step 3: Maintain a stable focusing distance. The external phase fluid generates hydraulic shear on the pre-emulsion flow through the collecting pipe, forming the target droplet.

[0018] Step 4: If it is necessary to adjust the droplet size or shell thickness, repeat step 2 and adjust the size by changing the focusing distance: when the focusing distance increases, the droplet size increases and the shell thickness increases; when the focusing distance decreases, the droplet size decreases and the shell thickness decreases.

[0019] The coaxial copolymer microfluidic droplet generation device and method with adjustable focusing distance of the present invention has the following advantages:

[0020] Adjustable focusing distance: The coaxial capillary spacing is continuously adjustable through a slider-lead screw-drive input source linkage structure, breaking the limitations of traditional fixed geometry. High structural strength: Constructed primarily of hexahedral metal bolts, the system is resistant to high pressure, solvents, and mechanical fatigue, making it suitable for complex or corrosive systems. Flow field optimization: The module incorporates an alloy wire winding structure, effectively agitating laminar flow, reducing the risk of gelation and clogging, and maintaining stable flow. Modular design: Each module can be independently disassembled and replaced, reducing maintenance costs and improving experimental flexibility. Visual operation: A glass observation window and transparent glass tube are provided through the through-hole, allowing real-time monitoring of liquid level and focusing status for precise control. Precise electronic adjustment: The motor-driven pitch fine-tuning mechanism achieves micron-level pitch resolution, enabling precise control of droplet size over a wide range. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the device of the present invention;

[0022] Figure 2 This is a schematic diagram of the internal structure of the device of the present invention;

[0023] Figure 3 Schematic diagram of droplet structures formed at different focusing distances;

[0024] The markings in the diagram are as follows: 100, Distance adjustment mechanism; 41, Base; 42, Slide rail; 43, Lead screw slider; 44, Lead screw; 45, Transmission input source; 31, Moving slider; 32, Sliding resistance adjustment knob one; 33, Static slider; 34, Sliding resistance adjustment knob two; 1, Coaxial premixing module; 11, Inner tube input connection port; 121, Capillary inner tube; 122, Capillary outer tube; 13, Hexahedral nut one; 14, Intermediate phase input threaded connector; 15, Intermediate phase input port; 16, Intermediate phase output threaded connector; 17, Turbulence support alloy winding wire; 18, Pre-emulsion flow output port; 2, Flow focusing module; 21, Perforated silicone plug; 22, Liquid collection tube; 23, External phase input port; 24, External phase input threaded connector; 25, Hexahedral nut two; 26, Outlet pipe threaded connector; 27, Outlet pipe; 28, Transparent glass tube. Detailed Implementation

[0025] To better understand the purpose, structure, and function of this invention, the following detailed description, in conjunction with the accompanying drawings, provides an adjustable focusing distance coaxial copolymer microfluidic droplet generation device and method of this invention.

[0026] like Figure 1 Figure 2 As shown, the present invention discloses a coaxial copolymer microfluidic droplet generation device with adjustable focusing distance, comprising a focusing distance adjustment mechanism 100, a coaxial premixing module 1, and a flow focusing module 2. The coaxial premixing module 1 and the flow focusing module 2 are mounted on the focusing distance adjustment mechanism 100 and are dynamically sealed together. The coaxial premixing module 1 is used to coaxially and stably pre-assemble the inner phase and intermediate phase fluids into a core-shell structured preemulsion flow. The flow focusing module 2 is used to introduce an outer phase, hydraulically focusing and shearing the preemulsion flow to ultimately generate uniformly sized target droplets. The focusing distance adjustment mechanism 100 is used to adjust the distance between the coaxial premixing module 1 and the flow focusing module 2, thereby adjusting the focusing distance D of the droplets and achieving precise control over the droplet morphology.

[0027] The focusing distance adjustment mechanism 100 includes a base 41, a slide rail 42, a lead screw and slider 43, a lead screw 44, a transmission input source 45, a moving slider 31, a sliding resistance adjustment knob 1 32, a stationary slider 33, and a sliding resistance adjustment knob 2 34. The slide rail 42 is vertically fixed on the base 41. The moving slider 31 and the stationary slider 33 are mounted on the slide rail 42. The moving slider 31 has a sliding resistance adjustment knob 1 32 on one side, which can adjust the resistance between the moving slider 31 and the slide rail 42. The stationary slider 33 has a sliding resistance adjustment knob 2 34 on one side, which can adjust the resistance between the stationary slider 33 and the slide rail 42. The transmission input source 45 is fixedly installed on one side of the upper end of the slide rail 42. The transmission input source 45 is a power drive mechanism such as a stepper motor. The output end of the transmission input source 45 is fixedly connected to the lead screw 44, which can drive the lead screw 44 to rotate. The lead screw slider 43 is threadedly connected to the lead screw 44. The moving slider 31 is fixedly connected to the lead screw slider 43. The coaxial premixing module 1 is fixedly installed on the moving slider 31. The flow focusing module 2 is fixedly installed on the stationary slider 33. In use, the stationary slider 33 is adjusted to the maximum resistance by the sliding resistance adjustment knob 2 34 and is fixedly installed on the slide rail 42. The moving slider 31 is adjusted to a smaller resistance by the sliding resistance adjustment knob 1 32, so that it can slide along the slide rail 42. The transmission input source 45 drives the lead screw 44 to rotate, which drives the lead screw slider 43 to slide along the slide rail 42, thereby driving the moving slider 31 to move the coaxial premixing module 1 closer to or away from the flow focusing module 2 on the stationary slider 33, thereby realizing the precise and continuous adjustment of the focusing distance D between the coaxial premixing module 1 and the flow focusing module 2.

[0028] The coaxial premixing module 1 includes an inner tube input connection port 11, a capillary inner tube 121, a capillary outer tube 122, a hexahedral nut 13, an intermediate phase input threaded connector 14, an intermediate phase input port 15, an intermediate phase output threaded connector 16, a turbulence support alloy winding 17, and a pre-emulsion flow output port 18. The hexahedral nut 13 has three sets of through holes Aa, Bb, and Cc on its six sides. Through hole Aa is parallel to the slide rail and perpendicular to the base, representing the vertical direction in the front view of the device; the upper end is hole a, and the lower end is hole A, with holes a and A connected. Through hole Bb is perpendicular to the sliding surface of the moving slider, representing the front-back direction in the front view; the front is hole b, and the back is hole B, with holes b and B connected. Through hole Cc is parallel to the sliding surface of the moving slider and perpendicular to the slide rail, representing the left-right direction in the front view; the left side is hole c, and the right side is hole C, with holes c connected. Two metal capillaries (inner capillary tube 121 and outer capillary tube 122) are connected to each other via hole A and hole a to form a coaxial structure. The outer capillary tube 122 is fixed to hole A, and the inner capillary tube 121 passes through hole a and is placed on the central axis. A flow-turbing support alloy wire 17 is provided between the outer wall of the inner capillary tube 121 and the inner wall of the outer capillary tube 122. This wire serves as a support and liquid premixing structure, while also changing the flow field distribution to prevent gelation and blockage of easily condensable liquids under laminar flow conditions. The inner tube inlet connection port 11 is connected to the inner capillary tube 121. Hole A is connected to the intermediate phase output threaded connector 16. The intermediate phase output threaded connector 16 is connected to the pre-emulsion flow outlet port 18. The intermediate phase inlet port 15 is connected to the intermediate phase inlet threaded connector 14. The intermediate phase inlet threaded connector 14 is connected to hole b, which is connected to the outer capillary tube 122. Hole B is connected to the movable slider 31 by bolts to achieve overall movement of the coaxial premixing module 1. Hole C and hole c are sealed by a glass plate to form an observation window for the liquid level. The inner phase fluid enters the capillary inner tube 121 through the inner tube inlet 11, and the intermediate phase liquid enters the capillary outer tube 122 through the intermediate phase inlet 15. It is premixed and stabilized with the inner phase in the annular gap disturbed by the turbulent alloy wire 17.

[0029] The flow focusing module 2 includes a perforated silicone plug 21, a liquid collecting tube 22, an external phase inlet 23, an external phase inlet threaded connector 24, a hexahedral nut 25, an outlet pipe threaded connector 26, an outlet pipe 27, and a transparent glass tube 28.

[0030] The hexahedral nut 25 has three sets of through holes: Aa, Bb, and Cc. The Aa through hole is parallel to the slide rail and perpendicular to the base, which is the vertical direction in the front view of the device. The upper end is hole a, and the lower end is hole A, which are connected. The Bb through hole is perpendicular to the sliding surface of the moving slider, which is the front-back direction in the front view. The front is hole b, and the back is hole B, which are connected. The Cc through hole is parallel to the sliding surface of the moving slider and perpendicular to the slide rail, which is the left-right direction in the front view. The left side is hole c, and the right side is hole C, which are connected. A transparent glass tube 28 is connected to hole a, and a perforated silicone plug 21 is fixed inside the transparent glass tube 28 (fluid cavity inlet). The pre-emulsion outlet 18 of the coaxial premixing module 1 is inserted into the central hole of the perforated silicone plug 21. When the focusing distance adjustment mechanism 100 drives the pre-emulsion outlet 18 to move axially along the central hole of the perforated silicone plug 21, the elastic material of the perforated silicone plug 21 can always fit against the outer wall of the pre-emulsion outlet 18 to achieve dynamic sealing and ensure that there is no fluid leakage during the adjustment of the focusing distance D. A-hole connects to outlet pipe threaded connector 26, which in turn connects to outlet pipe 27. Collection pipe 22 is fixed inside outlet pipe threaded connector 26 and is integrated with outlet pipe 27. The upper end of collection pipe 22 extends into transparent glass tube 28, with the upper opening gradually narrowing. External phase inlet 23 connects to external phase inlet threaded connector 24, which in turn connects to port b. Port B is connected to static slider 33 via bolts. Ports C and c are sealed with a glass plate, forming an observation window for liquid level. External phase liquid enters through external phase inlet 23, is guided by collection pipe 22, forms a counter-current flow within collection pipe 22, mixes with the pre-emulsion from coaxial premixing module 1, and flows out through outlet pipe 27.

[0031] The focusing distance adjustment mechanism 100 adjusts the distance between the coaxial premixing module 1 and the flow focusing module 2 to change the axial distance between the discrete phase capillary outlet (emulsion flow outlet 18) and the continuous phase focusing hole (collecting tube 22 port), i.e. the focusing distance D, thereby achieving fine control of the droplet morphology.

[0032] The following describes in more detail the method of using the coaxial copolymer microfluidic droplet generation device with adjustable focusing distance of the present invention, taking the preparation of water-in-oil-in-water (W / O / W) type dual emulsion microcapsule droplets as an example.

[0033] The internal phase is an aqueous solution of polyethylene glycol containing fluorescent dye, with a viscosity range of 10–20 mPa·s. The intermediate phase is liquid paraffin with added surfactant, with a viscosity range of 40–120 mPa·s. The external phase is a 2 wt% aqueous solution of polyvinyl alcohol containing surfactant, with a viscosity range of 60–150 mPa·s.

[0034] Step 1: Place the inner phase (W), intermediate phase (O), and outer phase (W) into the syringes respectively. Start the device; the three-phase fluids will be input by independent precision injection pumps at the set flow rates.

[0035] Step 2: Turn on the external phase input, set the external phase flow rate to 400 μL / min, input through the external phase input port 23 of the flow focusing module 2, and flow back into the transparent glass tube 28 under the action of the collecting tube 22. After being blocked by the perforated silicone plug 21, it is output through the outlet tube 27.

[0036] Step 3: Turn on the intermediate phase input. The intermediate phase flow rate is 15 μL / min. The intermediate phase is input into the capillary outer tube 122 through the intermediate phase inlet 15, and then enters the annular gap between the capillary outer tube 122 and the capillary inner tube 121, which is surrounded by the turbulence-supported alloy winding wire 17.

[0037] Step 4: Turn on the internal phase input, the internal phase flow rate is 15 μL / min, and the internal phase is input into the capillary inner tube 121 through the inner tube input connection port 11.

[0038] The intermediate phase and the inner phase initially coat each other at the annular gap to form a W / O fluid. The outer phase and the W / O fluid merge in the focusing area (inside the transparent glass tube 28), and the hydraulic shearing action of the outer phase fluid during flow forms a double emulsion droplet (W / O / W).

[0039] Step 5: The transmission input source 45 drives the lead screw 44 to rotate, which in turn drives the coaxial premixing module 1 to move up and down, thereby achieving precise changes in the distance between the coaxial premixing module 1 and the flow focusing module 2. Figure 3 As shown, when the distance between the two modules decreases, the pre-emulsion outlet 18 and the inner collection pipe 22 are closer, the shear zone formed by the outer phase fluid is strengthened, the generated droplet size is reduced and the shell is thinner; when the distance increases, the focusing distance D is extended, the droplet generation rate decreases, the droplet size increases and the shell thickness increases.

[0040] Step 6: Adjust the focusing distance D from 0.0 mm to 10.0 mm, and adjust the equivalent diameter of the dual emulsion droplets from 260 μm to 650 μm, with a coefficient of variation of less than 5%.

[0041] The device of this invention is applicable to the preparation of droplets or microcapsules in various multiphase systems, and is especially suitable for scenarios requiring control of the ratio and thickness of the inner and outer shells, or the generation of microspheres, drug sustained-release particles, and functionalized emulsions.

[0042] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A coaxial copolymer microfluidic droplet generation device with adjustable focusing distance, characterized in that, include: The system comprises a focusing distance adjustment mechanism (100), a coaxial premixing module (1), and a flow focusing module (2). The coaxial premixing module (1) and the flow focusing module (2) are mounted on the focusing distance adjustment mechanism (100) and are dynamically sealed together. The coaxial premixing module (1) is used to coaxially and stably pre-form internal phase droplets uniformly dispersed in the intermediate phase of the pre-emulsion flow by the internal phase fluid and the intermediate phase fluid. The flow focusing module (2) is used to introduce the external phase and, under the hydraulic focusing and shearing action of the external phase fluid, shear the pre-emulsion flow into target droplets. The focusing distance adjustment mechanism (100) is used to adjust the distance between the coaxial premixing module (1) and the flow focusing module (2). The focusing distance D of the droplet is adjusted to achieve precise control over the size and shell thickness of the target droplet. The coaxial premixing module (1) is provided with a pre-emulsion flow output port (18) for outputting the pre-emulsion flow. The pre-emulsion flow output port (18) is connected to the fluid cavity inlet of the flow focusing module (2) through a dynamic sealing structure. The focusing distance adjustment mechanism (100) includes a base (41), a slide rail (42), a lead screw slider (43), a lead screw (44), a transmission input source (45), a moving slider (31), and a stationary slider (33). The slide rail (42) is vertically fixed on the base (41). The moving slider (31) and the stationary slider (33) are both mounted on the slide rail (42). The lead screw slider... Block (43) is threadedly connected to lead screw (44). The transmission input source (45) is installed on one side of the upper end of slide rail (42), and the output end is fixedly connected to lead screw (44) for driving lead screw (44) to rotate. The moving slider (31) is fixedly connected to lead screw slider (43). The coaxial premixing module (1) is installed on the moving slider (31), and the flow focusing module (2) is installed on the stationary slider (33). The coaxial premixing module (1) also includes: hexahedral nut (13), capillary inner tube (121) and capillary outer tube (122), turbulence support alloy winding (17), inner tube input connection port (11), and intermediate phase input port (15). The hexahedral nut (13) is provided with Aa, Bb, Three sets of through holes Cc; the inner capillary tube (121) and the outer capillary tube (122) are coaxially arranged and connected to the a hole and A hole of the hexahedral nut (13) respectively; the turbulence support alloy winding (17) is arranged in the annular gap between the inner capillary tube (121) and the outer capillary tube (122); the inner tube input connection port (11) is connected to the inner capillary tube (121); the intermediate phase input port (15) and the pre-emulsion flow output port (18) are connected to the b hole and A hole of the hexahedral nut (13) respectively through threaded joints; the hexahedral nut (13) is fixedly connected to the movable slider (31) through the B hole; the C hole and c hole of the hexahedral nut (13) are sealed with transparent material to form an observation window.

2. The apparatus according to claim 1, characterized in that, The moving slider (31) and the stationary slider (33) are respectively provided with a sliding resistance adjustment knob one (32) and a sliding resistance adjustment knob two (34) to adjust the resistance between the moving slider (31) and the stationary slider (33) and the slide rail (42).

3. The apparatus according to claim 1, characterized in that, The transmission input source (45) is a stepper motor. The transmission input source (45) drives the lead screw (44) to rotate, which drives the lead screw slider (43) to slide along the slide rail (42), thereby driving the moving slider (31) to move the coaxial premixing module (1) closer to or further away from the flow focusing module (2) on the stationary slider (33), so as to achieve precise adjustment of the focusing distance D.

4. The apparatus according to claim 1, characterized in that, The flow focusing module (2) includes a hexahedral nut (25), a perforated silicone plug (21), a collection tube (22), an external phase inlet (23), an outlet tube (27), and a transparent glass tube (28). The hexahedral nut (25) is provided with three sets of through holes Aa, Bb, and Cc. The transparent glass tube (28) is connected to hole a. The pre-emulsion flow outlet (18) is dynamically sealed to the transparent glass tube (28) through the perforated silicone plug (21). The external phase inlet (23) and the outlet tube (27) are respectively connected to hole b and hole A of the hexahedral nut (25) through threaded joints. The hexahedral nut (25) is fixedly connected to the static slider (33) through hole B. The collection tube (22) and the outlet tube (27) are integrally set, with the upper end extending into the transparent glass tube (28). The upper end of the collection tube (22) gradually narrows.

5. The apparatus according to claim 4, characterized in that, The C-hole and c-hole of the hexahedral nut 2 (25) are sealed with transparent material to form an observation window.

6. The apparatus according to claim 1, characterized in that, The focusing distance adjustment mechanism (100) can drive the focusing distance D to be continuously adjusted in the range of 0.0 mm to 10.0 mm, and when the focusing distance D increases from 0.0 mm to 10.0 mm, the equivalent diameter of the target droplet increases continuously from 260 μm to 650 μm.

7. A method for preparing droplets using the apparatus according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Input the inner phase, intermediate phase and outer phase into the independent flow path device respectively. The inner phase and intermediate phase enter the coaxial premixing module (1) to form a pre-emulsion flow, and the outer phase enters the flow focusing module (2). Step 2: Start the focusing distance adjustment mechanism (100) to drive the coaxial premixing module (1) to move relative to the flow focusing module (2) and adjust the droplet focusing distance D to the target value; Step 3: Keep the focusing distance D stable, and the external phase fluid generates hydraulic shear on the pre-emulsion flow through the collection pipe (22) to form the target droplet; Step 4: If it is necessary to adjust the droplet size or shell thickness, repeat step 2 and adjust the size by changing the value of the focusing distance D: when the focusing distance D increases, the droplet size increases and the shell thickness increases; when the focusing distance D decreases, the droplet size decreases and the shell thickness decreases.

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