A method for preparing a color-tunable total internal reflection structural color droplet

Abstract

The application belongs to the field of structural color materials, and discloses a preparation method of color-adjustable total internal reflection structural color liquid drops, which comprises the following steps: S1: preparing a surfactant solution as a continuous phase; S2: dissolving liquid hydrocarbons and liquid fluorocarbons in a cosolvent to obtain a mixed solution as a dispersed phase; S3: connecting the surfactant solution with an outer tube sample inlet of a microfluidic chip; connecting the mixed solution with an inner tube sample inlet of the microfluidic chip; adjusting the flow rates of the continuous phase and the dispersed phase, so that oil-in-water emulsion drops with uniform dispersion size can be obtained at the sample outlet; and after the organic solvent volatilizes, Janus liquid drops are formed, which are total internal reflection structural color liquid drops. The application can obtain total internal reflection structural color liquid drops with uniform size by improving the structures of components in the microfluidic chip, the setting modes of the components, and the overall cooperation modes between the components.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of structural color materials, more particularly, to a preparation method of color-tunable total internal reflection structural color droplets. BACKGROUND

[0002] The colors in nature are mainly divided into chemical color and physical color. Physical color, also known as structural color, is a color produced by the interaction of incident light and micro-nano structures such as interference, diffraction and scattering. Compared with chemical color which is easily affected by photochemical degradation, structural color is not easy to fade, has extremely high durability, and has unique metallic luster and extremely high color purity. Therefore, it is widely used in intelligent display, optical anti-counterfeiting, artificial flexible devices and many other fields. At present, the research of structural color materials mainly focuses on photonic crystals, however, the regular periodic structure and complex preparation process of photonic crystals hinder their high-throughput application. Therefore, developing new structural color materials and reducing their preparation period and cost is of great significance for further expanding the application of structural color materials.

[0003] The present inventors have previously developed a preparation method and application of responsive structural color droplets (see Chinese Patent Application CN202310306447.0). This achievement is achieved by using liquid hydrocarbons and liquid fluorocarbons as oil phase materials (both of which need to meet certain density and refractive index requirements and are not mutually soluble at room temperature), and using a first surfactant and a second surfactant (specifically, using one of FC-4430, FC301, Capstone FS-30, Capstone62MA, ZY-FC327, ZY-823, ZONLY FS300, TF282, TF328 as the first surfactant, and using one of SDS, PVA, CTAB, F-108, F-127, TWEEN 20, TWEEN 40, TWEEN 60, TWEEN 80 as the second surfactant), by uniformly mixing the above four to form an oil-in-water system, according to the mass ratio of the first surfactant to the second surfactant in the system, the droplets can have structural color or not (specifically: when the mass ratio of the first surfactant to the second surfactant in the oil-in-water system meets 1:1-1:5, the droplets are Janus droplets with structural color; when the mass ratio of the first surfactant to the second surfactant in the oil-in-water system does not meet 1:1-1:5, the droplets do not have structural color). Although this early achievement has achieved the preparation of responsive structural color droplets, the size of the structural color droplets obtained by vortex or hand shaking is not uniform, resulting in low color saturation observed by macroscopic observation and difficulty in distinguishing the specific color. SUMMARY

[0004] To address the aforementioned deficiencies or improvement needs of existing technologies, the present invention aims to provide a method for preparing a color-tunable total internal reflection (TIR) ​​structural color droplet. This method involves improving the structure and arrangement of components within a microfluidic chip, as well as the overall interaction between these components. Using microfluidic technology, uniformly sized oil-in-water droplets are prepared. Subsequently, the organic solvent in the oil-in-water emulsion droplets is evaporated, forming Janus droplets, which are TIR structural color droplets characterized by uniform size and controllable color. Since these TIR structural color droplets are hydrocarbon / fluorocarbon Janus droplets, they leverage the fact that hydrocarbons have a lower density but a higher refractive index than fluorocarbons, enabling the generation of structural color based on a combination of total internal reflection and interference mechanisms. Furthermore, based on the microfluidic chip of this invention, the diameter of the oil-in-water emulsion droplets can be controlled by varying the flow rates of the dispersed and continuous phases, thereby controlling the diameter of the TIR structural color droplets and ultimately achieving tunable structural color. The structural color produced by the total internal reflection structural color droplet prepared by the method of this invention exhibits size dependence; within a size period, changing the droplet size can yield a full spectrum of colors. The method of this invention is simple, and the resulting structural color possesses high saturation, is environmentally friendly, and resists fading, showing potential application prospects in optical anti-counterfeiting, display, and other fields.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a color-tunable total internal reflection structured color droplet is provided, characterized by comprising the following steps:

[0006] S1: Dissolve the surfactant in deionized water to obtain a surfactant solution; this surfactant solution corresponds to the continuous phase of the microfluidic system;

[0007] S2: An organic solvent capable of dissolving liquid hydrocarbons and liquid fluorocarbons is selected as a co-solvent. The liquid hydrocarbons and liquid fluorocarbons are dissolved together in the organic solvent to obtain a mixed solution. The hydrocarbons have a lower density and a higher refractive index than the fluorocarbons, and the hydrocarbons and fluorocarbons are immiscible at room temperature. The mixed solution serves as the dispersed phase of the microfluidic system.

[0008] S3: Prepare a microfluidic chip, which includes an outer tube, an input inner tube, and an output inner tube. The input and output inner tubes are nested within the outer tube, and their center lines are collinear. The input and output inner tubes are arranged alternately, each with a round opening at one end and a tapered opening at the other.

[0009] The inner tube is used to input liquid flow, with its round end extending out of the outer tube and serving as the sample inlet of the inner tube, and its conical end extending into the interior of the outer tube;

[0010] The output inner tube is used for outputting liquid flow, and its round end extends out of the outer tube and serves as an outlet, and its tapered end extends into the interior of the outer tube;

[0011] The outer tube is closed at both ends, and the outer tube is further connected with an outer tube sample inlet and an exhaust port, wherein the projection of the outer tube sample inlet on the outer tube center line is covered by the projection of the input inner tube on the outer tube center line, and the projection of the exhaust port on the outer tube center line is covered by the projection of the output inner tube on the outer tube center line;

[0012] The diameter of the tapered end of the input inner tube is 30-80 μm, the diameter of the tapered end of the output inner tube is greater than that of the input inner tube, and the distance between the projections of the two tapered ends on the outer tube center line is 100-200 μm;

[0013] The surfactant solution obtained in step S1 is loaded into a syringe and connected with the outer tube sample inlet of the microfluidic chip; at the same time, the mixed solution obtained in step S2 is loaded into a syringe and connected with the inner tube sample inlet of the microfluidic chip; then, the flow rates of the continuous phase and the dispersed phase are adjusted by a microfluidic injection pump, and the flow rates of the continuous phase and the dispersed phase are kept stable, so that the oil-in-water emulsion droplets with uniform size dispersed in the surfactant are obtained at the outlet of the microfluidic chip; after the organic solvent component in the oil-in-water emulsion droplets volatilizes, the Janus liquid droplet with total internal reflection structural color is formed.

[0014] As a further preferred embodiment of the present application, in step S3, the diameter of the oil-in-water emulsion droplets can be adjusted by changing the flow rate of the dispersed phase and the flow rate of the continuous phase, thereby adjusting the diameter of the total internal reflection structural color liquid droplet, and finally adjusting the structural color color of the total internal reflection structural color liquid droplet;

[0015] Preferably, the flow rate of the dispersed phase is 5-100 μL / min; the flow rate of the continuous phase is 150-500 μL / min; the diameter of the oil-in-water emulsion droplets is 200-400 μm; and the diameter of the total internal reflection structural color liquid droplet is 10-150 μm.

[0016] As a further preferred embodiment of the present application, in step S1, the surfactant comprises a first surfactant component and a second surfactant component simultaneously, wherein the first surfactant component is any one or more of Capstone FS-30, Triton X-100, F68, F127, F108, FC-4430, FC301, Capstone 62MA, ZY-FC327, ZY-823, ZONLY FS300, TF282, TF328; the second surfactant component is any one or more of polyvinyl alcohol, sodium dodecyl sulfate, sodium dodecyl sulfonate, dodecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide, didodecyl dimethyl ammonium bromide;

[0017] The mass ratio of the first surfactant component to the second surfactant component is 1:10 to 2:1;

[0018] The total concentration of the surfactant solution is 1-100 mg / mL.

[0019] As a further preferred embodiment of the present application, in step S2, the hydrocarbon is one of heptane, octane, nonane, decane, undecane, dodecane, tridecane, n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, methyl methacrylate octadecyl ester, ethoxylated trimethylolpropane triacrylate, ethylene glycol dimethacrylate, tert-butyl bromoacetate, n-butyl acrylate, dodecyl acrylate;

[0020] The fluorocarbon is one of perfluorohexane, perfluorooctane, methyl nonafluorobutoxy acrylate, 1H, 1H, 2H, 2H-heptadecafluorodecyl ester, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 2,2,2-trifluoroethyl methacrylate, hexafluorobutyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl acrylate, trifluoroethyl methacrylate;

[0021] The organic solvent is any one of dichloromethane, trichloromethane, toluene.

[0022] As a further preferred embodiment of the present application, in step S2, the volume ratio of the hydrocarbon to the fluorocarbon is 1:20-3:1;

[0023] The total concentration of the hydrocarbon and the fluorocarbon dissolved in the organic solvent is 50-300 mg / mL.

[0024] As a further preferred embodiment of the present application, in step S3, the temperature for volatilization is room temperature to 30°C.

[0025] As a further preferred embodiment of the present application, the diameter of the tapered end of the output inner tube in the microfluidic chip is 100-250 μm.

[0026] As a further preferred embodiment of the present application, the input inner tube in the microfluidic chip is further subjected to hydrophilic treatment, and the output inner tube is further subjected to hydrophobic treatment.

[0027] Compared with the prior art, the preparation method of the present application is based on a microfluidic chip with a specific component structure and a combined use mode, a co-solvent of hydrocarbons and fluorocarbons is used as a dispersed phase of a microfluidic system, a surfactant solution is used as a continuous phase of the microfluidic system, and an oil-in-water emulsion droplet with uniform size is prepared by using the microfluidic chip. After the organic solvent in the oil-in-water emulsion droplet is volatilized, a Janus droplet is formed, which is a total internal reflection structural color droplet. The present application introduces a co-solvent in the preparation process of the structural color droplet and uses a microfluidic chip to prepare a droplet with uniform size and color. Unlike the structural color droplet obtained by vortex or hand shaking, the droplet prepared by the microfluidic method is controllable in size, has uniform color and high saturation, and the structural color can be adjusted, especially the cyclic adjustment of the structural color.

[0028] Based on the preparation method of the present application, the diameter of the oil-in-water emulsion droplet can be adjusted by changing the flow rate of the dispersed phase (i.e. the internal phase) and the flow rate of the continuous phase (i.e. the external phase), thereby adjusting the diameter of the total internal reflection structural color droplet and finally adjusting the structural color of the total internal reflection structural color droplet. In a color change cycle of color cycle change, the smaller the flow rate of the dispersed phase and the larger the flow rate of the continuous phase, the smaller the size and the more blue the structural color. The structural color produced by the total internal reflection structural color droplet prepared by the present application has size dependence, different sizes of droplets produce different structural colors, which can cover the entire visible light region, and within a certain size cycle range, the cycle from blue to green to red to blue can be realized. The preparation method is simple, the technical requirements are low, and the continuous batch preparation can be realized. At the same time, the structural color produced by the total internal reflection structural color droplet through total internal reflection and interference has the characteristics of not easy to fade, bright color and high saturation, and is very suitable for many application fields such as intelligent display and optical anti-counterfeiting.

[0029] Specifically, the present application has the following beneficial effects:

[0030] (1) The structural color liquid drops prepared by the application have size-dependent structural color, and by adjusting the flow rate of the inner and outer phases during the preparation of the oil-in-water emulsion drops, oil-in-water emulsion drops of different sizes can be prepared, and after the organic solvent is volatilized, oil-in-water emulsion drops of different sizes can be obtained. The size of the total internal reflection structural color liquid drops is different, and the color produced is different, which can cover the entire visible light region, and within a certain size period, it can realize the cycle from blue to green to red to blue.

[0031] (2) The preparation method of the total internal reflection structural color liquid drops provided by the application is simple, easy to operate, low in technical requirements, and the required raw materials are cheap and easy to obtain, which is suitable for continuous and large-scale production.

[0032] (3) The total internal reflection structural color liquid drops prepared by the application do not require periodic structures, and can produce structural color through the synergistic effect of total internal reflection and interference within a single drop. The structural color produced by the total internal reflection structural color liquid drops prepared by the application has the characteristics of not easy to fade, can be stored for a long time, environmental protection, high saturation and the like. In the application, the specific materials of the hydrocarbons and fluorocarbons are not limited, as long as they are not mutually soluble at room temperature, and the density of the hydrocarbons is less than that of the fluorocarbons, and the refractive index of the hydrocarbons is greater than that of the fluorocarbons. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structural schematic diagram and a physical diagram of the microfluidic chip used in the examples; wherein, Figure 1 (a) in the above is a structural schematic diagram of the microfluidic chip, Figure 1 (b) in the above is a physical diagram of the microfluidic chip.

[0034] Figure 2 is a process diagram of the oil-in-water emulsion drops prepared by the microfluidic chip in Example 1 and the total internal reflection structural color liquid drops obtained by solvent volatilization induced phase separation. From left to right in the figure, Time = 0 s, Time = 2-3 d, Time = 4 d.

[0035] Figure 3 is the optical microscope picture, macroscopic physical picture and spectrum of the structural color liquid drops in Example 2; wherein, Figure 3 (a) in the above corresponds to the optical microscope picture, Figure 3 (b) in the above corresponds to the physical picture of the liquid drops in the culture dish, Figure 3 (c) in the above corresponds to the spectrum.

[0036] Figure 4 is the optical microscope picture, macroscopic physical picture and spectrum of the structural color liquid drops in Example 3; wherein,Figure 4 (a) corresponds to the optical microscope picture, Figure 4 (b) corresponds to the real picture of the droplet located in the culture dish, Figure 4 (c) corresponds to the spectrum.

[0037] Figure 5 The macroscopic real pictures of the total internal reflection structural color droplets of different sizes prepared in Example 4, the structural color cycles from blue to green to red to blue. DETAILED DESCRIPTION

[0038] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0039] As shown in Figure 1 The microfluidic chip in the present application includes an input inner tube, an output inner tube and an outer tube, and the outer tube is provided with an outer tube sample inlet and an exhaust port. The input inner tube and the output inner tube are both nested in the outer tube, and the centers of the input inner tube, the output inner tube and the outer tube are collinear. One end of the input inner tube and the output inner tube is a round port, and the other end is a tapered port with a controllable diameter.

[0040] The round port end of the input inner tube extends out of the outer tube as an inner tube sample inlet for passing in a mixed solution (this is a dispersed phase) obtained by dissolving hydrocarbons and fluorocarbons in an organic solvent; the tapered port end of the input inner tube extends into the inner tube.

[0041] The round port end of the output inner tube extends out of the outer tube as a sample outlet; the tapered port end of the output inner tube extends into the outer tube.

[0042] The outer tube sample inlet is connected to one end of the outer tube close to the input inner tube sample inlet for passing in a surfactant solution (this is a continuous phase) into the outer tube. The exhaust port is connected to one end of the outer tube close to the sample outlet for exhausting the gas in the chip. In addition, both ends of the outer tube are closed by epoxy resin glue.

[0043] In addition, the input inner tube can be preferably hydrophilic treated (for example, can be soaked in 3-aminopropyl triethoxysilane for hydrophilic treatment) to improve the yield of the preparation process, and the diameter of the tip of the end of the input inner tube is 30-80 μm; the output inner tube can be preferably hydrophobic treated (for example, can be soaked in middle octadecyl trichlorosilane for hydrophobic treatment) to improve the yield of the preparation process, and the diameter of the tip of the end of the output inner tube is 100-250 μm; the distance between the tip of the end of the input inner tube and the tip of the end of the output inner tube is 100-200 μm.

[0044] Using the above device, based on the present application, taking Capstone FS-30 and sodium dodecyl sulfate (SDS) as the surfactant, n-hexadecane as the hydrocarbon, and methyl nonafluorobutyl ether as the fluorocarbon as examples, the preparation method of the total internal reflection structural color droplet with adjustable structural color can include the following steps:

[0045] (1) Configure a surfactant solution:

[0046] Dissolve a certain mass of Capstone FS-30 and sodium dodecyl sulfate in a certain volume of deionized water to obtain an aqueous solution of the continuous phase of the total internal reflection structural color droplet; the total concentration of the surfactant can be 1-100 mg / mL.

[0047] Based on the previous research results CN202310306447.0, Capstone FS-30 belongs to the first surfactant, and sodium dodecyl sulfate belongs to the second surfactant. In order to obtain a Janus droplet with structural color, the mass ratio of the first surfactant to the second surfactant needs to meet 1:1-1:5. Since the preparation method of the present application introduces a cosolvent, the mass ratio of the first surfactant to the second surfactant can be extended to 1:10 to 2:1.

[0048] (2) Configure a mixture solution:

[0049] Add n-hexadecane and methyl nonafluorobutyl ether to the organic solvent according to a certain volume ratio to obtain a mixture solution of the dispersed phase of the total internal reflection structural color droplet; the volume ratio of n-hexadecane to methyl nonafluorobutyl ether can be 1:20-3:1. The organic solvent can be dichloromethane, trichloromethane, or toluene. The concentration of n-hexadecane and methyl nonafluorobutyl ether dissolved in the organic solvent is 50-300 mg / mL.

[0050] (3) Connect the syringe filled with the surfactant solution to the outer tube inlet of the microfluidic chip using a silicone hose, and connect the syringe filled with the mixed solution to the inner tube inlet of the microfluidic chip using a silicone hose, and set the inner and outer phase flow rates using a microfluidic syringe pump to prepare oil-in-water emulsion droplets of different sizes. The dispersed phase flow rate is 5-100 μL / min; the continuous phase flow rate is 150-500 μL / min.

[0051] (4) After the oil-in-water emulsion droplets are prepared, volatilize the organic solvent at 30°C to obtain total internal reflection structural color droplets. The diameter of the total internal reflection structural color droplet is 10-150 μm.

[0052] In the performance test of the structural color droplet, the prepared total internal reflection structural color droplet can be dropped on a glass slide, and the color of the droplet can be observed under a reflection mode optical microscope. The prepared total internal reflection structural color droplet can also be collected in a culture dish, and a macroscopic picture of the structural color produced by the droplet can be taken by an electronic device such as a mobile phone, and the reflection spectrum of the structural color produced by the droplet can be tested by using a fiber optic spectrometer.

[0053] The following is a specific embodiment:

[0054] Embodiment 1

[0055] The total internal reflection structural color droplet in this embodiment is prepared according to the following method:

[0056] (1) Prepare a surfactant solution:

[0057] A certain mass of Capstone FS-30 and sodium dodecyl sulfate is dissolved in a certain volume of deionized water to obtain an aqueous solution of the continuous phase of the total internal reflection structural color droplet; the total concentration of the surfactant is 10 mg / mL; in this embodiment, the Capstone FS-30 solution and the sodium dodecyl sulfate solution are mixed in equal volumes, wherein the concentration of the Capstone FS-30 solution is 5 mg / mL, and the concentration of the sodium dodecyl sulfate solution is 15 mg / mL.

[0058] (2) Prepare a mixture solution:

[0059] A certain volume ratio of n-hexadecane and methyl nonafluorobutyl ether is added to an organic solvent to obtain a mixture solution of the dispersed phase of the total internal reflection structural color droplet; the volume ratio of the n-hexadecane and the methyl nonafluorobutyl ether is 1:1. The organic solvent can be chloroform. The concentration of the n-hexadecane and the methyl nonafluorobutyl ether dissolved in the organic solvent is 60 mg / mL.

[0060] (3) Connect the syringe filled with the surfactant solution to the outer tube inlet of the microfluidic chip by using a silicone hose, and connect the syringe filled with the mixture solution to the inner tube inlet of the microfluidic chip by using a silicone hose, and set the flow rates of the inner and outer phases by using a microfluidic injection pump to prepare oil-in-water emulsion droplets of different sizes. The dispersed phase flow rate is 10 μL / min; the continuous phase flow rate is 150 μL / min.

[0061] (4) After the oil-in-water emulsion droplet is prepared, the organic solvent is volatilized at 30°C to obtain the total internal reflection structural color droplet. The diameter of the total internal reflection structural color droplet is 100 μm.

[0062] As Figure 2The series of optical microscope images shown indicate that the water-in-oil emulsion droplets prepared by the microfluidic device are homogeneous monodisperse chloroform droplets. As chloroform volatilizes, it induces phase separation between n-hexadecane and methyl nonafluorobutyl ether until finally generating total internal reflection structural color droplets that produce structural color, which is green.

[0063] Example 2

[0064] The total internal reflection structured color droplet in this embodiment is prepared according to the following method:

[0065] (1) Prepare the surfactant solution:

[0066] A certain mass of Capstone FS-30 and sodium dodecyl sulfate were dissolved in a certain volume of deionized water to obtain an aqueous solution of the continuous phase of the total internal reflection structured color droplet; the total concentration of the surfactant was 9 mg / mL; in this embodiment, it was obtained by mixing equal volumes of Capstone FS-30 solution and sodium dodecyl sulfate solution, wherein the concentration of Capstone FS-30 solution was 6 mg / mL and the concentration of sodium dodecyl sulfate solution was 12 mg / mL.

[0067] (2) Prepare the mixture solution:

[0068] Hexadecane and methylnonafluorobutyl ether are added to an organic solvent at a specific volume ratio to obtain a mixture solution of the dispersed phase of the total internal reflection structural color droplets; the volume ratio of hexadecane to methylnonafluorobutyl ether is 1:1. The organic solvent can be chloroform. The concentration of hexadecane and methylnonafluorobutyl ether in the organic solvent is 65 mg / mL.

[0069] (3) Connect a syringe filled with surfactant solution to the outer inlet of the microfluidic chip using a silicone tubing, and connect a syringe filled with mixed solution to the inner inlet of the microfluidic chip using a silicone tubing. Prepare oil-in-water emulsion droplets of different sizes using a microfluidic syringe pump with the internal and external phase flow rates set. The dispersed phase flow rate is 15 μL / min; the continuous phase flow rate is 200 μL / min.

[0070] (4) After the water-in-oil emulsion droplets are prepared, the organic solvent is evaporated at 30°C to obtain total internal reflection structural color droplets. The diameter of the total internal reflection structural color droplets is 60.5 μm.

[0071] like Figure 3 The optical microscope images, macroscopic images, and reflectance spectra shown indicate that the structural color produced by the prepared total internal reflection structural color droplets is pink.

[0072] Example 3

[0073] The total internal reflection structural color droplet in this embodiment is prepared according to the following method:

[0074] (1) Prepare a surfactant solution:

[0075] A certain mass of Capstone FS-30 and sodium dodecyl sulfate is dissolved in a certain volume of deionized water to obtain an aqueous solution of the continuous phase of the total internal reflection structural color droplet; the total concentration of the surfactant is 10 mg / mL; in this embodiment, the Capstone FS-30 solution and the sodium dodecyl sulfate solution are mixed in equal volumes, wherein the concentration of the Capstone FS-30 solution is 5 mg / mL, and the concentration of the sodium dodecyl sulfate solution is 15 mg / mL.

[0076] (2) Prepare a mixture solution:

[0077] A certain volume ratio of n-hexadecane and methyl nonafluorobutyl ether is added to an organic solvent to obtain a mixture solution of the dispersed phase of the total internal reflection structural color droplet; the volume ratio of the n-hexadecane and the methyl nonafluorobutyl ether is 1:1. The organic solvent can be chloroform. The concentration of the n-hexadecane and the methyl nonafluorobutyl ether dissolved in the organic solvent is 65 mg / mL.

[0078] (3) Connect the syringe filled with the surfactant solution to the outer tube inlet of the microfluidic chip using a silicone hose, and connect the syringe filled with the mixture solution to the inner tube inlet of the microfluidic chip using a silicone hose, and set the flow rates of the inner and outer phases using a microfluidic injection pump to prepare oil-in-water emulsion droplets of different sizes. The dispersed phase flow rate is 15 μL / min; the continuous phase flow rate is 260 μL / min.

[0079] (4) After the oil-in-water emulsion droplets are prepared, the organic solvent is volatilized at 30°C to obtain the total internal reflection structural color droplet. The diameter of the total internal reflection structural color droplet is 47.8 μm.

[0080] As shown in the optical microscope image, the macroscopic image, and the reflectance spectrum image, the structural color produced by the prepared total internal reflection structural color droplet is green. Figure 4

[0081] Embodiment 4

[0082] The total internal reflection structural color droplet in this embodiment is prepared according to the following method:

[0083] (1) Prepare a surfactant solution:

[0084] ​A certain mass of Capstone FS-30 and sodium dodecyl sulfate were dissolved in a certain volume of deionized water to obtain an aqueous solution of the continuous phase of the total internal reflection structured color droplet; the total concentration of the surfactant was 15 mg / mL; in this embodiment, it was obtained by mixing equal volumes of Capstone FS-30 solution and sodium dodecyl sulfate solution, wherein the concentration of Capstone FS-30 solution was 15 mg / mL and the concentration of sodium dodecyl sulfate solution was 15 mg / mL.

[0085] (2) Prepare the mixture solution:

[0086] Hexadecane and methylnonafluorobutyl ether are added to an organic solvent at a specific volume ratio to obtain a mixture solution of the dispersed phase of the total internal reflection structural color droplets; the volume ratio of hexadecane to methylnonafluorobutyl ether is 1:1. The organic solvent can be chloroform. The concentration of hexadecane and methylnonafluorobutyl ether in the organic solvent is 70 mg / mL.

[0087] (3) Connect a syringe filled with surfactant solution to the outer inlet of the microfluidic chip using a silicone tubing, and connect a syringe filled with mixed solution to the inner inlet of the microfluidic chip using a silicone tubing. Prepare oil-in-water emulsion droplets of different sizes using a microfluidic injection pump with the internal and external phase flow rates set. The dispersed phase flow rate is 20 μL / min; the continuous phase flow rate is 150-400 μL / min.

[0088] (4) After the water-in-oil emulsion droplets are prepared, the organic solvent is evaporated at 30°C to obtain total internal reflection structural color droplets. The diameter of the total internal reflection structural color droplets is 40.3-62.7 μm.

[0089] like Figure 5 The series of macroscopic images shown demonstrates that different sizes of total internal reflection structured color droplets were obtained due to varying continuous phase flow velocities. The structured color produced was purple when the droplet size was 40.3 μm, green when the droplet size was 47.8 μm, and orange when the droplet size was 57.4 μm. This indicates that the total internal reflection structured color droplets exhibit size dependence; different droplet sizes produce different colors, and within a certain size range, they can complete a cycle from blue to green to red and back to blue.

[0090] Since the dispersed phase flow rate remains constant in step (3), within a color change cycle (such as a cycle in which the structural color changes from purple to red), the larger the continuous phase flow rate, the smaller the size of the water-in-oil emulsion droplets obtained, and correspondingly, the smaller the size of the total internal reflection structural color droplets.

[0091] The above examples are merely examples, for example, the hydrophilic treatment of the input inner tube, the hydrophobic treatment of the output inner tube, other known ways can also be used. The preparation process of each of the above examples is that the process of volatilizing organic solvent is at 30°C, and the remaining operations are carried out at room temperature (i.e. 25°C). In addition, the above examples are merely examples, in addition to the examples of the combination of hydrocarbons and fluorocarbons, other hydrocarbons and fluorocarbons can also be used according to the needs, as long as they are not mutually soluble at room temperature, and the density of the hydrocarbon is less than that of the fluorocarbon, and the refractive index is greater than that of the fluorocarbon.

[0092] Those skilled in the art will readily understand that the above description is merely preferred embodiments of the present application, and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a color-tunable total internal reflection structured droplet, characterized in that, Includes the following steps: S1: Dissolve the surfactant in deionized water to obtain a surfactant solution; this surfactant solution corresponds to the continuous phase of the microfluidic system; S2: An organic solvent capable of dissolving liquid hydrocarbons and liquid fluorocarbons is selected as a co-solvent. The liquid hydrocarbons and liquid fluorocarbons are dissolved together in the organic solvent to obtain a mixed solution. The hydrocarbons have a lower density and a higher refractive index than the fluorocarbons, and the hydrocarbons and fluorocarbons are immiscible at room temperature. The mixed solution serves as the dispersed phase of the microfluidic system. S3: Prepare a microfluidic chip, which includes an outer tube, an input inner tube, and an output inner tube. The input and output inner tubes are nested within the outer tube, and their center lines are collinear. The input and output inner tubes are arranged alternately, each with a round opening at one end and a tapered opening at the other. The inner tube is used to input liquid flow, with its round end extending out of the outer tube and serving as the sample inlet of the inner tube, and its conical end extending into the interior of the outer tube; The inner output tube is used to output liquid flow, with its round end extending out of the outer tube and serving as a sample outlet, and its conical end extending into the interior of the outer tube. The outer tube is closed at both ends and is also connected to an outer tube inlet and an exhaust port. The projection of the outer tube inlet on the center line of the outer tube is covered by the projection of the input inner tube on the center line of the outer tube, and the projection of the exhaust port on the center line of the outer tube is covered by the projection of the output inner tube on the center line of the outer tube. Furthermore, the diameter of the conical end of the input inner tube is 30-80 μm, the diameter of the conical end of the output inner tube is larger than the diameter of the conical end of the input inner tube, and the distance between the projections of the two conical ends on the center line of the outer tube is 100-200 μm. The surfactant solution obtained in step S1 is loaded into a syringe and connected to the sample inlet of the outer tube of the microfluidic chip; simultaneously, the mixed solution obtained in step S2 is loaded into the syringe and connected to the sample inlet of the inner tube of the microfluidic chip; then, the flow rates of the continuous phase and the dispersed phase are adjusted by the microfluidic injection pump and kept stable, thereby obtaining uniformly sized oil-in-water emulsion droplets dispersed in the surfactant at the sample outlet of the microfluidic chip; after the organic solvent components in the oil-in-water emulsion droplets evaporate, the Janus droplets formed are total internal reflection structural color droplets; In step S3, the diameter of the oil-in-water emulsion droplets can be controlled by changing the flow rate of the dispersed phase and the flow rate of the continuous phase, thereby controlling the diameter of the total internal reflection structural color droplets and ultimately controlling the structural color of the total internal reflection structural color droplets.

2. The preparation method according to claim 1, characterized in that, In step S3, the flow rate of the dispersed phase is 5-100 μL / min; the flow rate of the continuous phase is 150-500 μL / min; the diameter of the water-in-oil emulsion droplets is 200-400 μm; and the diameter of the total internal reflection structural color droplets is 10-150 μm.

3. The preparation method according to claim 1, characterized in that, In step S1, the surfactant simultaneously comprises a first surfactant component and a second surfactant component, wherein the first surfactant component is any one or more of Capstone FS-30, Triton X-100, F68, F127, F108, FC-4430, FC301, Capstone 62MA, ZY-FC327, ZY-823, ZONLY FS300, TF282, and TF328; and the second surfactant component is any one or more of polyvinyl alcohol, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and bis(dodecyldimethylammonium bromide). The mass ratio of the first surfactant component to the second surfactant component is between 1:10 and 2:

1. The total concentration of the surfactant solution is 1-100 mg / mL.

4. The preparation method according to claim 1, characterized in that, In step S2, the hydrocarbon is one of heptane, octane, nonane, decane, undecane, dodecane, tridecane, n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, octadecyl methacrylate, ethoxylated trimethylolpropane triacrylate, ethylene glycol dimethacrylate, tert-butyl bromoacetate, n-butyl acrylate, and dodecyl acrylate. The fluorocarbon compound is one of perfluorohexane, perfluorooctane, methyl nonafluorobutyl ether acrylate, 1H,1H,2H,2H-heptadecyl methacrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 2,2,2-trifluoroethyl methacrylate, hexafluorobutyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate, and trifluoroethyl methacrylate. The organic solvent is any one of dichloromethane, trichloromethane, and toluene.

5. The preparation method according to claim 1, characterized in that, In step S2, the volume ratio of the hydrocarbon to the fluorocarbon is 1:20 - 3:1; The total concentration of the hydrocarbon and the fluorocarbon dissolved in the organic solvent is 50-300 mg / mL.

6. The preparation method according to claim 1, characterized in that, In step S3, the temperature at which the evaporation occurs is between room temperature and 30°C.

7. The preparation method according to claim 1, characterized in that, In the microfluidic chip, the diameter of the conical end of the output inner tube is 100-250 μm.

8. The preparation method according to claim 1, characterized in that, In the microfluidic chip, the input inner tube has undergone hydrophilic treatment, and the output inner tube has undergone hydrophobic treatment.

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