Droplet generation microchannel design method and device based on critical fracture interface matching

Abstract

The application discloses a droplet generation microchannel design method and device based on critical fracture interface matching. The design method is based on the principle of interface energy minimization, takes the continuous phase filling volume as the control variable, identifies the critical fracture interface of the limited liquid filament, extracts the liquid filament interface overhead projection profile and quantifies the critical neck thickness, determines the arc structure of the channel intersection based on the projection profile as a template, accurately matches the arc structure with the critical fracture interface, and minimizes the compatible volume of the external phase of the channel intersection. The device comprises a dispersed phase inlet channel, two symmetrical continuous phase inlet channels and an outlet channel, and the channel intersection has an arc structure, so that the continuous phase triggers the capillary instability fracture of the liquid filament after filling a smaller volume, and the droplet spacing is significantly smaller than that of the traditional straight-wall cross channel under the same flow ratio condition. The high internal phase emulsion can be directly generated on the chip.

Description

Technical Field

[0001] This invention relates to the field of microfluidics, specifically to a method and apparatus for designing droplet generation microchannels based on critical fracture interface matching. Background Technology

[0002] Microfluidic droplet generation technology is widely used in digital biological detection, drug encapsulation, precision emulsion synthesis, and multiphase displacement in porous media. In rectangular cross-section microchannels, dispersed phase filaments neck and eventually break under the compression of the continuous phase, forming discrete droplets. This breakage process is dominated by capillary instability. Existing microfluidic droplet generation technologies have the following shortcomings: 1. In traditional cross-shaped microchannels, the continuous phase needs to fill a large volume at the channel intersection to trigger droplet breakage, resulting in high continuous phase consumption, wide droplet spacing, and difficulty in increasing the dispersed phase volume fraction. This problem is particularly prominent in applications requiring high internal phase emulsions.

[0003] 2. Existing methods for increasing the volume fraction of the dispersed phase each have limitations: increasing the flow ratio is limited by the transition from liquid filament flow to jet flow, resulting in a narrow operating window and a tendency to generate polydisperse droplets; step emulsification has limited flexibility in controlling droplet size; and downstream extraction of the continuous phase increases the complexity of the device and the need for additional components.

[0004] 3. Some existing technologies attempt to reduce the amount of continuous phase used by modifying the channel layout at the continuous phase supply end. For example, Chinese utility model patent CN221108304U, entitled "Microfluidic Chip and Microfluidic Chip System," sets up a continuous phase buffer channel composed of multiple interconnected curved channels on the continuous phase supply path to stabilize the continuous phase flow rate, and makes the width of the continuous phase exit channel smaller than the width of the continuous phase inlet channel, thereby reducing the overall amount of continuous phase used in single-cell / single-particle droplet encapsulation scenarios. However, the effective point of this type of solution is located at the continuous phase supply end, and what is reduced is the overall amount of continuous phase used at the system level. It does not change the interfacial dynamics conditions of filament breakage at the channel intersection. The reduction in continuous phase usage depends on the additional buffer channels and variable-width channel structures, which increases the complexity of the chip layout. Moreover, the continuous phase filling volume required to trigger capillary instability in a single breakage event is still determined by the intersection structure and has not been optimized.

[0005] 4. Existing technologies lack a systematic design method for determining the optimal intersection profile based on quantitative interfacial mechanics analysis, starting from the geometry of the intersection itself. Neither traditional straight-walled cross intersections nor the aforementioned schemes that regulate continuous phase flow through supply-side channel layout achieve precise matching between the channel structure and the critical fracture interface shape of the liquid filament at the intersection. Consequently, the external phase containment volume required for a single fracture cannot be directly controlled, leading to the intersection structure design relying primarily on experience and making it difficult to quickly determine the unique optimal configuration for different channel sizes. Summary of the Invention

[0006] To address the aforementioned shortcomings in the prior art, the droplet generation microchannel design method and device based on critical fracture interface matching provided by this invention solves the problems of large external phase capacity, large continuous phase consumption, inability to accurately control droplet size, and inability to achieve high dispersed phase volume fraction droplet generation.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for designing microchannels for droplet generation based on critical fracture interface matching is provided, comprising the following steps: S1. Determine the height of the dispersed phase channel, the width of the dispersed phase channel, and the width of the continuous phase channel; S2. Use interface energy minimization software to establish a calculation model, and set the volume of the dispersed liquid filament to be constant in the calculation model; S3. In the calculation model, the dispersed phase filament is placed at the center of the intersection of the dispersed phase channel and the continuous phase channel; the continuous phase channel is filled with a volume of... The continuous phase; wherein the dispersed phase filaments and the continuous phase are confined within the channel walls corresponding to the dispersed phase channel height, dispersed phase channel width, and continuous phase channel width determined in step S1; S4. In the computational model, the interface between the dispersed liquid filament and the continuous phase is allowed to evolve freely under the drive of surface tension until the interface converges to a minimum value, thus obtaining the continuous phase. Quasi-steady-state interface at time; S5. In the calculation model, the continuous phase filling volume is gradually increased, and step S4 is repeated to obtain a series of quasi-steady interfaces. The last quasi-steady interface is defined as the critical fracture interface. S6. Extract the projection profile of the critical fracture interface in the top view plane; record the critical neck thickness; where the critical neck thickness is the minimum width of the projection profile. S7. Design the intersecting arc structure based on the projected profile and critical neck thickness to obtain a microchannel matching the critical fracture interface.

[0008] Furthermore, the interface can be minimized to the Surface Evolver program.

[0009] A device for generating microchannels for droplet formation based on critical fracture interface matching is provided, comprising: One dispersed phase inlet channel is used to input the dispersed phase; two continuous phase inlet channels are symmetrically arranged on both sides of the dispersed phase inlet channel for inputting the continuous phase; the dispersed phase inlet channel and the continuous phase inlet channel are intersected to form an intersection; one outlet channel is connected to the intersection for outputting the generated droplets; the intersection has an arc-shaped structure in the top view plane, and the arc-shaped structure is designed according to the top view projection profile of the critical fracture interface.

[0010] Furthermore, the device is made of polydimethylsiloxane.

[0011] Furthermore, the channel walls of the device are treated with hydrophobic material.

[0012] A method for manufacturing a device for droplet generation microchannels based on critical fracture interface matching is provided, comprising the following steps: P1. Convert the top-view projection outline into a photomask pattern and create a silicon mold with the photomask pattern engraved on it. P2. Mix polydimethylsiloxane with a curing agent, degas under vacuum, and pour the mixture onto a silicon mold engraved with a mask pattern. After curing and demolding, create a fluid interface to obtain a channel layer. P3. The channel layer and the substrate are bonded after plasma surface treatment to obtain a microfluidic chip with a critical fracture interface matching.

[0013] Furthermore, in step P2, the mass ratio of polydimethylsiloxane to curing agent is 10:1, the curing temperature is 80℃, and the curing time is 40 minutes.

[0014] A droplet generation method is provided using a device for droplet generation microchannels based on critical fracture interface matching, comprising the following steps: A1. Select the dispersion channel height and dispersion channel width based on the target droplet size and the target dispersed phase volume fraction; A2. Inject the dispersed phase and the continuous phase into the intersection through the dispersed phase inlet and the continuous phase inlet, respectively; A3. Adjust the dispersed phase flow rate With continuous phase flow Flow ratio This ensures that the size and spacing of the generated droplets meet the target requirements.

[0015] The beneficial effects of this invention are as follows: 1. The critical fracture interface matching design ensures that the arc-shaped structure of the channel intersection corresponds precisely to the shape of the critical fracture interface of the liquid filament in the top view, reducing the effective containment volume at the channel intersection. Under the same fluid properties and flow rate conditions, droplet fracture can be triggered earlier than in traditional channels, and the droplet spacing is significantly reduced, achieving a more compact droplet arrangement. This advantage stems from the direct control of the intersection geometry on the triggering conditions of capillary instability. It can significantly improve the dispersed phase distribution density without widening the flow operating window, effectively avoiding the instability risk brought about by the transition from liquid filament flow to jet flow.

[0016] 2. The device of the present invention can directly generate high internal phase emulsions with a volume fraction exceeding the face-centered cubic close packing limit (74%) on the chip, realizing one-step on-chip preparation of high internal phase emulsions.

[0017] 3. The aspect ratio of the dispersed phase channel can be used as a means of controlling the droplet size. Under the same flow ratio, a larger aspect ratio of the dispersed phase channel reduces the flow rate of the dispersed phase, shortens the distance the droplet travels before breaking at the arc-shaped intersection, and makes the volume of a single liquid filament smaller before breaking and separating, thus providing a flexible geometric control dimension for the preparation of multi-scale droplets.

[0018] 4. The design method provided by this invention is based on the principle of interface energy minimization and has universal applicability. It can determine the optimal arc-shaped intersection structure for any channel cross-sectional size, providing a general theoretical tool for the customized design of microfluidic chips and breaking through the limitations of traditional design methods that rely on experience or specific dimensions.

[0019] 5. The device of the present invention has a simple structure, can be manufactured by standard soft lithography process, is compatible with existing microfluidic platforms, and is easy to mass-produce. Attached Figure Description

[0020] Figure 1 This is a flowchart of the design method of the present invention; Figure 2 A graph showing the relationship between the liquid filament interfacial energy and the continuous phase filling volume for Surface Evolver under different aspect ratios; Figure 3 This is a schematic diagram of the arc-shaped structure of the intersection; Figure 4 The results show a comparison of droplet generation between the device of the present invention and a traditional straight-walled cross channel under different aspect ratios; where A is an aspect ratio of 1.0, B is an aspect ratio of 1.5, C is an aspect ratio of 2.0, and D is an aspect ratio of 3.0. Figure 5 The results of droplet generation experiments of the device of the present invention under different aspect ratios and flow rates are shown; where A is an aspect ratio of 1.0, B is an aspect ratio of 1.5, C is an aspect ratio of 2.0, and D is an aspect ratio of 3.0. Detailed Implementation

[0021] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0022] like Figure 1 As shown, a method for designing droplet generation microchannels based on critical fracture interface matching is provided, including the following steps: S1. Determine the height of the dispersed phase channel, the width of the dispersed phase channel, and the width of the continuous phase channel; S2. Use interface energy minimization software to establish a calculation model, and set the volume of the dispersed liquid filament to be constant in the calculation model; S3. In the calculation model, the dispersed phase filament is placed at the center of the intersection of the dispersed phase channel and the continuous phase channel; the continuous phase channel is filled with a volume of... The continuous phase; wherein the dispersed phase filaments and the continuous phase are confined within the channel walls corresponding to the dispersed phase channel height, dispersed phase channel width, and continuous phase channel width determined in step S1; S4. In the computational model, the interface between the dispersed liquid filament and the continuous phase is allowed to evolve freely under the drive of surface tension until the interface converges to a minimum value, thus obtaining the continuous phase. Quasi-steady-state interface at time; S5. In the calculation model, the continuous phase filling volume is gradually increased, and step S4 is repeated to obtain a series of quasi-steady interfaces. The last quasi-steady interface is defined as the critical fracture interface. S6. Extract the projection profile of the critical fracture interface in the top view plane; record the critical neck thickness; where the critical neck thickness is the minimum width of the projection profile. S7. Design the intersecting arc structure based on the projected profile and critical neck thickness to obtain a microchannel matching the critical fracture interface.

[0023] In this embodiment, as Figure 2 As shown, the relationship between the interfacial energy of the liquid filament and the continuous phase filling volume under different aspect ratios (dispersed phase channel width W / dispersed phase channel height H) was calculated using the Surface Evolver program. Figures A, B, C, and D correspond to the interfacial energy of the liquid filament under four aspect ratios (W / H = 1.0, 1.5, 2.0, and 3.0). Dimensionless filling volume of continuous phase ( The change is normalized. The red line represents the minimum interfacial energy calculated from the quasi-steady-state interface for each continuous phase-filled volume. The blue 3D schematic shows the interfacial morphology of the liquid filament for the corresponding continuous phase-filled volume, varying with... As the volume gradually increases, the interfacial energy continues to rise, and all interfaces are in a quasi-steady state, with the neck of the liquid filament gradually contracting; when When the value increases to a critical value, the interface energy minimization calculation no longer converges to a quasi-steady state. Instead, an instability phenomenon occurs where the neck interface spontaneously collapses from the center, and the liquid filament breaks into two sub-droplets. This is the critical fracture state triggered by capillary instability. The last convergent quasi-steady interface before this critical value, i.e., the highest point of the red line, corresponds to the critical fracture interface.

[0024] In one embodiment of the present invention, an apparatus for droplet generation microchannels based on critical fracture interface matching is provided, comprising: One dispersed phase inlet channel is used to input the dispersed phase; two continuous phase inlet channels are symmetrically arranged on both sides of the dispersed phase inlet channel for inputting the continuous phase; the dispersed phase inlet channel and the continuous phase inlet channel are intersected to form an intersection; one outlet channel is connected to the intersection for outputting the generated droplets; the intersection has an arc-shaped structure in the top view plane, and the arc-shaped structure is designed according to the top view projection profile of the critical fracture interface.

[0025] like Figure 3 The diagram shows four schematic representations of curved intersection structures, where A has a W / H ratio of 1.0 (width 100μm, height 100μm); B has a W / H ratio of 1.5 (width 150μm, height 100μm); C has a W / H ratio of 2.0 (width 200μm, height 100μm); and D has a W / H ratio of 3.0 (width 300μm, height 100μm). The critical neck thickness is the minimum width of the critical fracture interface projected onto the top plane. The blue line in the figure represents the critical fracture interface. With a continuous phase channel width of 50 μm, the corresponding aspect ratios are calculated. As shown in Table 1: Table 1

[0026] In one embodiment of the present invention, a microfluidic chip is fabricated using a standard soft lithography process. Specifically, the top-view projection contour is converted into a photomask pattern, and a silicon mold with the photomask pattern is fabricated. Polydimethylsiloxane and a curing agent are mixed at a mass ratio of 10:1, degassed under vacuum, and then poured onto the silicon mold with the photomask pattern. After curing at 80°C in a forced-air drying oven for 40 minutes, the mold is demolded and trimmed. Holes are drilled at the channel inlet and outlet positions using a punch with a flat-headed needle. A layer of polydimethylsiloxane film is spin-coated onto a glass substrate and pre-baked at 80°C for 15 minutes in a forced-air drying oven. The channel layer and the film layer are bonded after plasma surface treatment. The bonding strength is enhanced by heating at 80°C for 30 minutes. A polytetrafluoroethylene tube is inserted and sealed. The channel surface is treated with Aquapel hydrophobic agent for 1 minute. Subsequently, the surface is rinsed with mineral oil and dried with pressurized air. Finally, an arc-shaped cross-shaped microchannel chip is fabricated.

[0027] The intersecting arc-shaped structure designed in this invention minimizes the volume of the external phase (i.e., the neck of the liquid filament) within the channel during deformation, allowing the continuous phase to fill a smaller volume before triggering capillary instability fracture of the liquid filament. To verify the effect of the critical fracture interface matching design on improving droplet spacing and density, at the same flow ratio ( Under the condition of W / H = 3), a comparative experiment was conducted on the arc-shaped intersection microchannel and the traditional straight-wall cross channel. Specifically, 1. A comparison was conducted under the condition of completely identical absolute flow rates (W / H = 2.0 group); 2. It was examined whether the arc-shaped channel could still maintain its droplet arrangement advantage when the absolute flow rate was higher than that of the cross channel (W / H = 1.0, 1.5 groups); 3. Conversely, it was examined whether the arc-shaped channel could still maintain its droplet arrangement advantage when the absolute flow rate was lower than that of the cross channel, to rule out the possibility that the advantage of the arc-shaped channel was solely due to a higher output rate (W / H = 3.0 group). The specific experimental flow rate settings for each aspect ratio are as follows: When W / H = 1.0, the arc-shaped channel adopted... = 60 μL / h = 20 μL / h, cross channel using = 30 μL / h = 10 μL / h, the absolute flow rate of the arc-shaped channel is twice that of the cross-shaped channel; when W / H = 1.5, the arc-shaped channel uses = 60 μL / h = 20 μL / h, cross channel using = 45 μL / h = 15 μL / h, the absolute flow rate of the arc-shaped channel is higher; when W / H = 2.0, both the arc-shaped channel and the cross-shaped channel are used. = 60 μL / h = 20 μL / h, both have the same absolute flow rate, serving as a strictly parameter-comparative group; when W / H = 3.0, the arc-shaped channel adopts = 60 μL / h = 20 μL / h, cross channel using = 90 μL / h = 30 μL / h, with a higher absolute flow rate in the cross channel.

[0028] Figure 4 The top row of each sub-plot shows the results for the curved intersection channel, and the bottom row shows the results for the traditional straight-walled cross channel. It can be seen that for all four aspect ratios, the droplet spacing in the curved intersection channel is significantly smaller than that in the traditional straight-walled cross channel, resulting in a more densely packed droplet arrangement. Specifically: At W / H = 1.0, the arc-shaped channel, with an absolute flow rate twice that of the cross channel, produces significantly smaller droplet spacing. The length of the continuous phase interval between droplets is much smaller than the corresponding value in the cross channel, indicating that the arc-shaped intersection can still achieve better droplet arrangement quality at higher output rates. At W / H = 1.5, the arc-shaped channel also maintains a significant advantage in droplet spacing at higher absolute flow rates. At W / H = 2.0, comparing the arc-shaped channel and the cross channel at the same absolute flow rate, the droplet spacing in the arc-shaped channel is still significantly smaller, proving the improvement effect of the arc-shaped intersection geometry on droplet arrangement. At W / H = 3.0, even though the absolute flow rate of the cross channel is higher than that of the arc-shaped channel, the droplet arrangement in the arc-shaped channel is still more compact than that in the cross channel. The consistent presentation of the above results across the four aspect ratios indicates that the curved intersection has broad applicability to improving droplet arrangement, and this advantage does not depend on higher continuous phase flow rates, but rather stems from the optimization of the fracture process by the intersection geometry itself.

[0029] In one embodiment of the present invention, a droplet generation method is provided using a device for droplet generation microchannels based on critical fracture interface matching, comprising the following steps: A1. Select the dispersion channel height and dispersion channel width based on the target droplet size and the target dispersed phase volume fraction; A2. Inject the dispersed phase and the continuous phase into the intersection through the dispersed phase inlet and the continuous phase inlet, respectively; A3. Adjust the dispersed phase flow rate With continuous phase flow Flow ratio This ensures that the size and spacing of the generated droplets meet the target requirements.

[0030] like Figure 5As shown, droplet generation experiments of the device of the present invention were conducted under different aspect ratios and flow rates, with deionized water as the dispersed phase and mineral oil with 3% w / w Span 80 added as the continuous phase. The experimental results show that when the flow rate ratio... At lower levels, the generated droplets have uniform spacing and good monodispersity; increasing... This increases the dispersed phase volume fraction, while simultaneously increasing the volume of individual droplets and reducing the spacing between droplets, resulting in a denser droplet arrangement. Under the same flow rate conditions, a larger channel aspect ratio leads to smaller droplet sizes. Increasing the channel width reduces the dispersed phase flow rate, shortens the travel distance of the liquid filaments before breaking at the arc-shaped intersection, and ultimately results in smaller individual droplet volumes. Under given fluid properties and flow ratio conditions, compared to traditional channels, this device minimizes the external phase capacity, directly producing smaller droplet spacing and higher dispersed phase density. The dispersed phase volume fraction of the emulsion prepared using this device can reach 85.7%, exceeding the face-centered cubic closest packing limit (74%), thus directly yielding a high internal phase emulsion.

[0031] This invention presents a progressive technical solution from design method to device to application. Based on the arc-shaped structure of the channel intersection determined by interface energy minimization calculations, it matches the shape of the critical fracture interface of the liquid filament, minimizing the external phase volume at the intersection and reducing the consumption of continuous phase in a single fracture event. This results in smaller droplet spacing and denser droplet arrangement under the same flow rate ratio. Even under the unfavorable condition of higher absolute flow rate (i.e., higher dispersed phase production rate) in the arc-shaped channel, its droplet density is still superior to that of the traditional cross-shaped channel, highlighting the direct control effect of the optimized arc-shaped structure of the intersection on the capillary instability triggering conditions. This differs fundamentally from solutions that simply adjust the flow rate ratio; the critical fracture interface-matched intersection directly controls the capillary instability triggering conditions by reducing the amount of continuous phase required for a single fracture, rather than relying on the flow rate ratio to compensate for droplet spacing after fracture. Therefore, it can significantly improve the dispersed phase density without widening the flow rate operating window, effectively avoiding the instability risk brought about by the transition from liquid filament flow to jet flow.

Claims

1. A microchannel design method for droplet generation based on critical fracture interface matching, characterized in that, Includes the following steps: S1. Determine the height of the dispersed phase channel, the width of the dispersed phase channel, and the width of the continuous phase channel; S2. Use interface energy minimization software to establish a calculation model, and set the volume of the dispersed liquid filament to be constant in the calculation model; S3. In the calculation model, the dispersed phase liquid filament is placed at the center of the intersection of the dispersed phase channel and the continuous phase channel; The volume of filling the continuous phase channel is Continuous phase; The dispersed phase liquid filament and the continuous phase are confined within the channel wall corresponding to the dispersed phase channel height, dispersed phase channel width, and continuous phase channel width determined in step S1. S4. In the computational model, the interface between the dispersed liquid filament and the continuous phase is allowed to evolve freely under the drive of surface tension until the interface converges to a minimum value, thus obtaining the continuous phase. Quasi-steady-state interface at time; S5. In the calculation model, the continuous phase filling volume is gradually increased, and step S4 is repeated to obtain a series of quasi-steady interfaces. The last quasi-steady interface is defined as the critical fracture interface. S6. Extract the projection profile of the critical fracture interface on the top plane; record the critical neck thickness; The critical neck thickness is the minimum width of the projected profile. S7. Design the intersecting arc structure based on the projected profile and critical neck thickness to obtain a microchannel matching the critical fracture interface.

2. The droplet generation microchannel design method based on critical fracture interface matching according to claim 1, characterized in that, The interface can be minimized to make the software a Surface Evolver program.

3. An apparatus based on the droplet generation microchannel design method based on critical fracture interface matching as described in claim 1 or 2, characterized in that, include: A dispersed phase inlet channel is provided for inputting the dispersed phase; Two continuous phase inlet channels are symmetrically arranged on both sides of the dispersed phase inlet channel for inputting the continuous phase; The dispersed phase inlet channel and the continuous phase inlet channel intersect to form an intersection; An outlet channel, connected to the intersection, is used to output the generated droplets; The intersection has an arc-shaped structure in the top view plane, and the arc-shaped structure is designed according to the top view projection profile of the critical fracture interface.

4. The apparatus according to claim 3, characterized in that, The device is made of polydimethylsiloxane.

5. The apparatus according to claim 3, characterized in that, The channel walls of the device are treated with hydrophobic coating.

6. A method for manufacturing the apparatus according to any one of claims 3-5, characterized in that, Includes the following steps: P1. Convert the top-view projection outline into a photomask pattern and create a silicon mold with the photomask pattern engraved on it. P2. Mix polydimethylsiloxane with a curing agent, degas under vacuum, and pour the mixture onto a silicon mold engraved with a mask pattern. After curing and demolding, create a fluid interface to obtain a channel layer. P3. The channel layer and the substrate are bonded after plasma surface treatment to obtain a microfluidic chip with a critical fracture interface matching.

7. The manufacturing method according to claim 6, characterized in that, In step P2, the mass ratio of polydimethylsiloxane to curing agent is 10:

1.

8. The manufacturing method according to claim 6, characterized in that, In step P2, the curing temperature of polydimethylsiloxane and curing agent is 80℃.

9. The manufacturing method according to claim 6, characterized in that, In step P2, the curing time for polydimethylsiloxane and the curing agent is 40 minutes.

10. A droplet generation method based on the apparatus according to any one of claims 3-5, characterized in that, Includes the following steps: A1. Select the dispersion channel height and dispersion channel width based on the target droplet size and the target dispersed phase volume fraction; A2. Inject the dispersed phase and the continuous phase into the intersection through the dispersed phase inlet and the continuous phase inlet, respectively; A3. Adjust the dispersed phase flow rate With continuous phase flow Flow ratio This ensures that the size and spacing of the generated droplets meet the target requirements.

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