A method for preparing a water-in-oil-in-water composite droplet based on droplet impact

Abstract

The present application relates to a kind of based on parcel type water-in-oil composite droplet preparation method of droplet impact, including the impact platform for preparing water-in-oil composite droplet, prepare millimeter size oil-in-water composite droplet, oil-in-water double-layer composite droplet falls to the top surface of super-liquid-repellent surface body and obtains kinetic energy and impact the top surface of super-liquid-repellent surface body of inclined setting and generates three-layer composite droplet, adjust ethanol open container position, so that the three-layer composite droplet moves to the direction of downward direction of super-liquid-repellent surface inclination and falls into the ethanol in ethanol open container and is dissolved as micron size water-in-oil composite droplet.The beneficial effect is that: in open environment, sub-millimeter size parcel type water-in-oil composite droplet is prepared, hardware facilities are not changed, not dependent on microfluidic chip, controllable generation different sub-millimeter order water-in-oil composite liquid, operability is strong.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of composite droplet preparation, in particular to a preparation method of a wrapped water-in-oil composite droplet based on droplet impact. BACKGROUND

[0002] The wrapped composite droplet has very important applications in the biological field, such as drug transportation and cell array. The core-shell structure of the wrapped composite droplet can isolate the liquid core from the outside, so that the drug in the liquid core droplet is effectively protected and the composition is not contaminated during transportation. In addition, the composite droplet can be used as a carrier to provide an ideal platform for the biochemical reaction of the liquid core.

[0003] The wrapped composite droplet can be produced by three methods, coaxial method (such as through coaxial needle), injection method and microfluidic technology. The wrapped composite droplet with thermodynamic stability generally needs to satisfy γ 12 +γ 23 <γ 13 , wherein γ 12 , γ 23 and γ 13 are the interfacial tension of the interface of phase 1 and phase 2, the interface of phase 2 and phase 3, and the interface of phase 1 and phase 3. The water-in-silicone oil composite droplet is a stable system from the thermodynamic point of view. For a thermodynamically unstable system, a suitable amount of surfactant can be added to form a relatively stable wrapped composite droplet. The outer diameter of the droplet and the volume fraction of each phase liquid are important parameters for characterizing the wrapped composite droplet.

[0004] For the coaxial method, because of the difficulty in preparing the coaxial needle, the size of the coaxial needle used is generally large, so the size of the composite droplet obtained is also large. The overall radius of the liquid is generally greater than 1 mm. If the size of the coaxial needle is further reduced to obtain a smaller composite droplet, it is difficult in process, and the problem of blockage is easy to occur. The injection method is usually manually controlled to inject the internal liquid core, which is low in operability. For the microfluidic technology, although it is easy to prepare a sub-millimeter size composite droplet, there are problems of difficulty in channel preparation, difficulty in packaging and easy liquid residue in the channel to cause blockage. SUMMARY

[0005] The present application provides a preparation method of a wrapped water-in-oil composite droplet based on droplet impact, which mainly aims to realize the controllable preparation of a wrapped water-in-oil composite droplet with a sub-millimeter size in an open environment.

[0006] To achieve the above purpose, the present application provides a preparation method of a wrapped water-in-oil composite droplet based on droplet impact, which mainly aims to realize the controllable preparation of a wrapped water-in-oil composite droplet with a sub-millimeter size in an open environment.

[0007] Step S1, building an impact platform for preparing water-in-oil composite droplets;

[0008] Step S2, preparing millimeter-sized oil-in-water composite droplets, specifically comprising:

[0009] Step S21, preparing water phase liquid and oil phase liquid, injecting oil phase liquid into coaxial needle by injector one and microsyringe pump one, with constant flow rate and set as Q1, injecting water phase liquid into coaxial needle by injector two and microsyringe pump two, with constant flow rate and set as Q2;

[0010] Step S22, preparing oil-in-water double-layer composite droplets by coaxial needle and separating from coaxial needle, with outer layer of water phase liquid and inner layer of oil phase liquid;

[0011] Step S3, the oil-in-water double-layer composite droplets falling to the top surface of super-lyophobic surface body to obtain kinetic energy and impact the top surface of the super-lyophobic surface body to generate three-layer composite droplets.

[0012] Step S4, adjusting the position of ethanol open container, so that the three-layer composite droplets move downward to the ethanol in the ethanol open container, the outermost water shell dissolves rapidly, and the three-layer composite droplets dissolve into micron-sized water-in-oil composite droplets.

[0013] Further, the impact platform comprises the microsyringe pump one, the microsyringe pump two, the injector one, the injector two, the injection catheter, the coaxial needle, the lifting frame, the super-lyophobic surface body and the ethanol open container, the injector one is installed on the microsyringe pump one, the injector two is installed on the microsyringe pump two, the injection ports of the injector one and the injector two are connected to the coaxial needle through the injection catheter, the coaxial needle is installed on the lifting frame, the super-lyophobic surface body is arranged below the lifting frame and extends to the ethanol open container in an inclined manner.

[0014] Further, the top surface of the super-lyophobic surface body is a super-lyophobic surface, and the inclination angle of the super-lyophobic surface with the horizontal plane is in the range of 3°-10°.

[0015] Further, the Q1 is between 0 μL / min and 70 μL / min, and the Q2 is between 100 μL / min and 150 μL / min.

[0016] Further, the height adjustment range of the lifting frame is 0 mm-100 mm.

[0017] Further, the outer diameters of the inner and outer needles of the coaxial needle are 0.31 mm and 0.91 mm, respectively.

[0018] Beneficial effects:

[0019] 1. In an open environment, it can controllably prepare sub-millimeter size of encapsulated water-in-oil composite droplets, and the operation process is simpler than microfluidic technology;

[0020] 2. Without changing the hardware facilities, only by adjusting the injection speed of the micro-injection system and the impact speed of the composite droplets, it can controllably produce different sub-millimeter level of water-in-oil composite liquid, and the operability is strong;

[0021] 3. It does not depend on microfluidic chips, and utilizes the energy conversion between gravitational potential energy and liquid surface energy and the interaction between solid and liquid to produce sub-millimeter size of micro-droplets. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram of the preparation device system of the encapsulated water-in-oil composite droplets;

[0023] Figure 2 is a relationship diagram of the volume ratio of the oil core in the oil-in-water composite droplets and the flow rate ratio;

[0024] Figure 3 is a diagram of the water-in-oil composite droplets produced at each Weber number when α is 0.3;

[0025] Figure 4 is a diagram of the water-in-oil composite droplets produced at different values of α when the Weber number is 3.6;

[0026] Figure 5 is a relationship diagram of the radius of the water droplets in the water-in-oil composite droplets and the Weber number;

[0027] Figure 6 is a relationship diagram of the volume ratio of the water droplets in the water-in-oil composite droplets and the Weber number.

[0028] The reference signs are as follows:

[0029] 1. Micro-injection pump one; 2. Micro-injection pump two; 3. Syringe one; 4. Syringe two; 5. Injection catheter; 6. Coaxial needle; 7. Lifting frame; 8. Oil-in-water double-layer composite droplet; 9. Super-lyophobic surface body; 10. Three-layer composite droplet; 11. Ethanol opening container; 12. Water-in-oil composite droplet. DETAILED DESCRIPTION

[0030] It should be understood that the specific embodiments described herein are merely used to explain the present application, and are not used to limit the present application.

[0031] EMBODIMENT

[0032] As Figures 1-6An oil-in-water composite droplet preparation method based on droplet impact is shown, and the oil-in-water composite droplet preparation method based on droplet impact comprises:

[0033] Step S1, build an impact platform for preparing water-in-oil composite droplets, the impact platform comprises microsyringe pump one 1, microsyringe pump two 2, syringe one 3, syringe two 4, injection catheter 5, coaxial needle 6, lifting frame 7, super-lyophobic surface body 9 and ethanol open container 11, syringe one 3 is installed on microsyringe pump one 1, syringe two 4 is installed on microsyringe pump two 2, the injection ports of syringe one 3 and syringe two 4 are connected to coaxial needle 6 through injection catheter 5, the outer diameters of the inner and outer needles of coaxial needle 6 are 0.31mm and 0.91mm respectively, coaxial needle 6 is installed on lifting frame 7, lifting frame 7 is used for adjusting the height of coaxial needle 6, so as to adjust the potential energy of the internal liquid, thereby changing the falling speed of the droplet and the impact speed of the droplet to super-lyophobic surface body 9, the height adjustment range of lifting frame 7 is 0mm-100mm, the maximum droplet impact speed can be realized about 1.4m / s, ethanol open container 11 contains ethanol solution, the liquid outlet of coaxial needle 6 is vertically downward, super-lyophobic surface body 9 is placed vertically below coaxial needle 6, the top surface of super-lyophobic surface body 9 is super-lyophobic surface, and the inclination angle between the super-lyophobic surface and the horizontal plane is in the range of 3°-10°;

[0034] Step S2, prepare millimeter-sized oil-in-water composite droplets, specifically comprising:

[0035] Step S21, prepare water phase liquid and oil phase liquid, inject oil phase liquid into coaxial needle 6 through syringe one 3 and microsyringe pump one 1, the flow rate is constant and set as Q1, inject water phase liquid into coaxial needle 6 through syringe two 4 and microsyringe pump two 2, the flow rate is constant and set as Q2, wherein Q1 is between 0μL / min and 70μL / min (due to the stability requirement of composite droplets, higher than this value is unstable), Q2 is set to be between 100μL / min and 150μL / min, the setting of flow rate is determined according to the size calculation of target composite droplets, the larger Q1 is, the higher the volume ratio of oil phase liquid in oil-in-water double-layer composite droplet 8 is;

[0036] Step S22, prepare oil-in-water double-layer composite droplet 8 through coaxial needle 6 and separate from coaxial needle 6, the outer layer of oil-in-water double-layer composite droplet 8 is water phase liquid, and the inner layer is oil phase liquid;

[0037] Step S3, oil-in-water double-layer composite droplet 8 falls to the top surface of super-lyophobic surface body 9 to obtain kinetic energy and impacts the top surface of the inclined super-lyophobic surface body 9 to generate three-layer composite droplet 10, during the falling process, the gravitational potential energy is converted into kinetic energy, and the kinetic energy obtained by the droplet can be expressed as mgh=0.5mV 2where h is the falling height of the droplet, V is the impact velocity of the droplet, so the falling height of the oil-in-water double-layer composite droplet 8, i.e. the distance between the position of the center of gravity of the oil-in-water double-layer composite droplet 8 before falling off the coaxial needle 6 and the super-lyophobic surface, can be adjusted by the lifting frame 7, and different three-layer composite droplets 10 can be obtained by the oil-in-water double-layer composite droplets 8 with different impact velocities. Here, the Weber number We is used to represent the impact condition of the composite droplet, where We = [p o α+ρ w (1-α)]R0V 2 / γ w represents the ratio of the initial kinetic energy of the composite droplet to the surface energy, p o , p w and g w represent the density of the oil phase liquid, the density of the water phase liquid and the surface tension of water respectively, R0 represents the radius of the oil-in-water double-layer composite droplet 8, and a is the ratio of the volume of the oil phase liquid to the total volume of the oil-in-water double-layer composite droplet 8.

[0038] In this embodiment, the principle of generating the three-layer composite droplet 10 by the oil-in-water double-layer composite droplet 8 impacting the super-lyophobic surface is as follows:

[0039] After the oil-in-water double-layer composite droplet 8 impacts the inclined super-lyophobic surface, a capillary wave is excited from the bottom of the oil-in-water double-layer composite droplet 8 and propagates along the surface of the oil-in-water double-layer composite droplet 8, and at the same time, the oil-in-water double-layer composite droplet 8 rapidly spreads on the surface to form a pyramid shape under the action of the inertial force. Subsequently, the capillary wave converges into a small protrusion at the top of the droplet. When a > 0.05, it is observed that a small protrusion of the water phase is formed at the top of the droplet, and a water column can be formed inside the oil phase liquid. The formation of the water column is mainly determined by the competition of the pressure inside the water phase liquid and the oil phase liquid. When the pressure inside the water phase liquid at the top is greater than the pressure inside the oil phase liquid, the small protrusion at the top of the water shell will move to the oil phase liquid under the driving of the pressure, forming a water column. In the subsequent retraction process, the water column is finally trapped inside the oil phase liquid, forming a three-layer structure of the encapsulated composite droplet and bouncing off the super-lyophobic surface, i.e. the three-layer composite droplet 10, whose outer layer is the water phase liquid, the middle layer is the oil phase liquid, and the inner layer is the water phase liquid.

[0040] In step S4, the position of the ethanol open container 11 is adjusted so that the three-layer composite droplet 10 moves in the direction of tilting downward to the super-lyophobic surface and falls into the ethanol in the ethanol open container 11. The outermost water shell rapidly dissolves, and the three-layer composite droplet 10 is dissolved into micron-sized water-in-oil composite droplets 12.

[0041] In the embodiment, the experimental data and images are obtained by a high-speed camera placed in front of the super-omniphobic surface, and the experimental data are obtained by a video captured by the high-speed camera at a speed of 10000 frames per second, wherein different Q1 and Q2 are set and recorded in step S2, the oil core volume ratio in the oil-in-water double-layer composite droplet 8 is measured by the images captured by the high-speed camera, the discrete relationship between the oil core volume ratio a in the oil-in-water composite droplet and the flow rate is obtained, and the relationship formula a = 1-1 / [1+0.89(Q1 / Q2)] obtained by least square fitting is obtained. For details, please refer to Figure 2 .

[0042] The R0 radius of the oil-in-water double-layer composite droplet 8 finally generated in step S22 is about 1.55 mm, wherein a is between 0.0 and 0.30, Q1 is 0 μL / min, a is 0.0, Q1 is about 70 μL / min, a is about 0.30, and Q2 is 100 optimal, and the radius of the oil core is between 500 μm and 1.2 mm;

[0043] The size of the small water droplets wrapped in the oil core in the three-layer composite droplet 10 increases with the increase of the Weber number within a certain range, and when the oil-in-water double-layer composite droplet 8 with a given oil core volume ratio is given, such as a≈0.30, the radius of the small water droplets wrapped inside is between 150 μm and 400 μm. For details, please refer to Figure 3 Meanwhile, if the Weber number is the same, such as We≈3.6, the size of the small water droplets wrapped in the oil core increases with the increase of a, when a≈0.05, the radius of the oil droplet before impact is about 500 μm, and the radius of the small water droplets wrapped inside after impact is about 150 μm, when a≈0.24, the radius of the oil droplet before impact is about 1.0 mm, and the radius of the small water droplets wrapped inside after impact is about 270 μm. For details, please refer to Figure 4 Therefore, the size of the water-in-oil composite droplet can be adjusted by changing the Weber number We and the oil core volume ratio a in the oil-in-water double-layer composite droplet 8.

[0044] In the embodiment, R ew represents the water core radius of the water-in-oil composite droplet 12 (see Figure 3 ), when a≈0.30, the radius R ew of the water core in the sub-millimeter water-in-oil composite droplet 12 is generated, and the relationship between the Weber number and the radius R Figure 5 of the water core in the water-in-oil composite droplet 12 is specifically referred to Figure 6 .

[0045] From Figure 5 , 6It can be seen that the Weibull number is a critical value of the curve change at about 4.5, when the Weibull number is less than the critical value, R ew and β increase rapidly with the increase of the Weibull number, when the Weibull number is greater than the critical value, R ew and β increase slowly with the increase of the Weibull number, and tend to be a straight line with a smaller slope.

[0046] The above are only preferred embodiments of the present application, and do not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation made by using the specification and content of the present application, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing a water-in-oil-in-water composite droplet based on droplet impingement, characterized by The preparation method of the encapsulated water-in-oil composite droplet comprises the following steps: Step S1, an impact platform for preparing water-in-oil composite droplets is built, the impact platform comprises a microsyringe pump 1, a microsyringe pump 2, a syringe 1, a syringe 2, an injection catheter, a coaxial needle, a lifting frame, a super-omniphobic surface body and an ethanol open container, the syringe 1 is installed on the microsyringe pump 1, the syringe 2 is installed on the microsyringe pump 2, the injection ports of the syringe 1 and the syringe 2 are connected to the coaxial needle through the injection catheter, the coaxial needle is installed on the lifting frame, and the super-omniphobic surface body is placed obliquely below the coaxial needle and extends towards the ethanol open container; Step S2, millimeter-sized oil-in-water double-layer composite droplets are prepared, specifically comprising the following steps: S21, water phase liquid and oil phase liquid are prepared, the oil phase liquid is injected into the coaxial needle through the syringe 1 and the microsyringe pump 1 at a constant flow rate Q1, the water phase liquid is injected into the coaxial needle through the syringe 2 and the microsyringe pump 2 at a constant flow rate Q2, the Q1 is between 0 and 70 μL / min, and the Q2 is between 100 and 150 μL / min; S22, oil-in-water double-layer composite droplets are prepared through the coaxial needle and separated from the coaxial needle, the outer layer of the oil-in-water double-layer composite droplets is water phase liquid, and the inner layer is oil phase liquid; Step S3, the oil-in-water double-layer composite droplets fall to the top surface of the super-omniphobic surface body to obtain kinetic energy and impact the top surface of the obliquely arranged super-omniphobic surface body to generate three-layer composite droplets; Step S4, the position of the ethanol open container is adjusted, so that the three-layer composite droplets move in the direction of the obliquely downward of the super-omniphobic surface body and fall into the ethanol in the ethanol open container, the outermost water shell is quickly dissolved, and the three-layer composite droplets are dissolved into micron-sized water-in-oil composite droplets.

2. The droplet-impact-based, wrapped water-in-oil compound droplet preparation method according to claim 1, characterized by: The top surface of the super-omniphobic surface body is a super-omniphobic surface, and the inclination angle of the super-omniphobic surface with the horizontal plane is in the range of 3°-10°.

3. The encapsulated water-in-oil compound droplet preparation method based on droplet impingement according to claim 1, characterized by: The height adjustment range of the lifting frame is 0-100 mm.

4. The encapsulated water-in-oil compound droplet preparation method based on droplet impingement according to claim 1, characterized by: The coaxial needle comprises an inner needle and an outer needle, the outer diameters of the inner needle and the outer needle are 0.31 mm and 0.91 mm respectively, the oil phase liquid passes through the inner needle at a constant flow rate Q1, and the water phase liquid enters the outer needle at a constant flow rate Q2.

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