Liquid crystal microsphere with multiple optical signals as well as preparation method and application of liquid crystal microsphere

Abstract

The invention provides a liquid crystal microsphere with multiple optical signals as well as a preparation method and application of the liquid crystal microsphere. The microsphere is composed of the liquid crystal compound and the hydrocarbon which are immiscible with each other, the density of the hydrocarbon is smaller than that of the liquid crystal compound, and the refractive index of the hydrocarbon is smaller than that of the liquid crystal compound, so that the microsphere can generate structural color based on total internal reflection and interference mechanism synergy; the formation of the total internal reflection structural color mainly depends on interface reflection between a liquid crystal compound and water; moreover, after an oil-in-water system is formed through uniform mixing, the form of the microspheres and the arrangement mode of the liquid crystal texture in the microspheres can be further changed by simply adjusting the volume ratio of two phases and the proportion of the surfactant in the system, so that the microspheres have the characteristics of the liquid crystal texture while having the total internal reflection structural color; the obtained structural color microspheres have the characteristic of being difficult to copy, and a new solution is provided for the security identification and anti-counterfeiting technology.

Description

Technical Field

[0001] The present invention relates to the technical field of structural color materials, and particularly to a liquid crystal microsphere with multiple optical signals, a preparation method thereof, and an application thereof. Background Art

[0002] As a new type of structural color mechanism, total internal reflection structural color presents bright and highly saturated colors through the reflection and interference effects of coherent light within a specific wavelength range. It has the advantages of environmental protection, anti-fading, bright colors, and no periodic structure, which has attracted great attention and exploration from researchers. However, in a changing and complex application environment, a single total internal reflection structural color can no longer meet the actual application needs. Especially in the field of password anti-counterfeiting, designing and introducing other optical mechanisms into the total internal reflection structural color system to develop new total internal reflection structural colors is undoubtedly a huge technical challenge. Multiple optical mechanisms can endow anti-counterfeiting labels with more complexity, greatly increasing the difficulty of counterfeiting. For a highly secure anti-counterfeiting system, this is the key to achieving efficient anti-counterfeiting, ensuring the effectiveness and non-replicability of anti-counterfeiting measures in actual applications.

[0003] Currently, the preparation methods of materials with total internal reflection structural color are simple, and the optical mechanisms are single, which are extremely easy to be imitated and are not sufficient to meet the highly secure anti-counterfeiting system. In view of this, it is necessary to improve this situation. Summary of the Invention

[0004] Aiming at the above defects or improvement requirements of the prior art, the purpose of the present invention is to provide a liquid crystal microsphere with multiple optical signals, a preparation method thereof, and an application thereof. The present invention consists of two monomers with different refractive indices, one of which is a liquid crystal phase, and two different surfactants. By adjusting the surfactant ratio, the composition of the two phases, and the volume ratio, the structure of the microspheres is regulated to obtain Janus microspheres with structural color. At the same time, under the action of two different surfactants, different arrangement modes of textures will appear in the liquid crystal phase. The liquid crystal microspheres obtained by the present invention have multiple optical signals. They can not only directly observe bright and vivid total internal reflection structural colors with the naked eye, but also clearly observe the liquid crystal texture at the microscopic level with the aid of a polarized light microscope. This unique optical property makes it difficult to be replicated or imitated, so it shows broad application potential in the field of anti-counterfeiting. In addition, the preparation process of the present invention is simple, the raw material cost is low, and it is convenient to realize large-scale production. Compared with other types of structural colors, the structural color in the present invention has the advantages of anti-fading, environmental protection, high saturation, etc., and does not require a complex periodic structure, further enhancing its application value.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing liquid crystal microspheres with multiple optical signals, comprising the following steps:

[0007] Adding a first surfactant to water to obtain a first surfactant solution;

[0008] Adding a second surfactant to water to obtain a second surfactant solution;

[0009] Mixing the first surfactant solution and the second surfactant solution to obtain an aqueous phase mixture;

[0010] Adding a liquid crystal compound and a hydrocarbon to a co-solvent to obtain an oil phase mixture;

[0011] Feeding the aqueous phase mixture and the oil phase mixture into a microfluidic chip respectively to prepare liquid crystal microspheres with multiple optical signals;

[0012] Wherein, the density of the hydrocarbon is less than that of the liquid crystal compound, and the refractive index of the hydrocarbon is less than that of the liquid crystal compound.

[0013] Preferably, the microfluidic chip comprises:

[0014] An outer pipe, one end of which is communicated with an aqueous phase mixture feed pipe;

[0015] A first inner pipe, one end of which is sleeved inside the outer pipe and the other end extends outside the outer pipe;

[0016] A second inner pipe, one end of which is sleeved inside the outer pipe and the other end extends outside the outer pipe;

[0017] The first inner pipe and the second inner pipe are distributed on both sides of the outer pipe, and the ends of the first inner pipe and the second inner pipe located inside the outer pipe form a gap;

[0018] Injecting the aqueous phase mixture into the outer pipe through the aqueous phase mixture feed pipe, injecting the oil phase mixture into the first inner pipe, the oil phase mixture is sheared by the aqueous phase mixture at the gap and flows out through the second inner pipe to form emulsion microspheres with uniform size; waiting for the co-solvent in the emulsion microspheres to volatilize and phase separation occurs to obtain liquid crystal microspheres with multiple optical signals.

[0019] Preferably, the first surfactant comprises at least one of PVA, PEO, and PEG;

[0020] And / or, the second surfactant comprises at least one of SDS, CTAB, CTAC, DTAC, sodium stearate, and PSS.

[0021] Preferably, the liquid crystal compound includes at least one of 1CB, 2CB, 3CB, 4CB, 5CB, 6CB, 7CB, 8CB, RM257, LC756, 4-n-pentylbenzoic acid, RM82, RM105, LC242;

[0022] And / or, the hydrocarbon includes at least one of PDMS, PDMS-OH, n-decane, n-heptane, n-octane, n-nonane, n-decane, n-dodecane, n-tridecane, ethoxylated trimethylolpropane triacrylate, octadecyl methacrylate.

[0023] Preferably, the co-solvent includes at least one of chloroform, dichloromethane, n-hexane, toluene.

[0024] Preferably, the concentration of the first surfactant solution is 1 - 30 mg / mL;

[0025] The concentration of the second surfactant solution is 1 - 30 mg / mL;

[0026] The mass ratio of the liquid crystal compound to the hydrocarbon is (1:9) - (1:1).

[0027] Preferably, the mass ratio of the first surfactant to the second surfactant is (0:1) - (1:4);

[0028] Or, the mass ratio of the first surfactant to the second surfactant is (3:7) - (7:3);

[0029] Or, the mass ratio of the first surfactant to the second surfactant is (4:1) - (1:0).

[0030] Preferably, the aqueous phase mixture is injected into the outer pipe through the aqueous phase mixture feed pipe at a rate of 50 - 500 μL / min;

[0031] The oil phase mixture is injected into the first inner pipe at a rate of 5 - 30 μL / min.

[0032] In a second aspect, the present invention also provides a liquid crystal microsphere with multiple optical signals, which is prepared by using the preparation method described above.

[0033] In a third aspect, the present invention also provides an application of the liquid crystal microsphere with multiple optical signals prepared by using the preparation method described above or the liquid crystal microsphere with multiple optical signals in the preparation of anti-counterfeiting materials.

[0034] The liquid crystal microsphere with multiple optical signals of the present invention, its preparation method and application have the following beneficial effects compared with the prior art:

[0035] 1. The liquid crystal microspheres with multiple optical signals prepared by the present invention are composed of two monomers with different refractive indices (i.e., liquid crystal compounds and hydrocarbons), one of which is a liquid crystal phase, and two different surfactants. By adjusting the ratio of surfactants, the composition and volume ratio of the two phases, the structure of the microspheres is regulated to obtain Janus microspheres with structural color. At the same time, under the action of two different surfactants, different arrangement patterns will appear in the texture of the liquid crystal phase. The liquid crystal microspheres obtained by the present invention have multiple optical signals. They can not only directly observe bright and vivid total internal reflection structural color with the naked eye, but also clearly observe the liquid crystal texture at the microscopic level with the aid of a polarized light microscope. This unique optical property makes it difficult to be replicated or imitated, so it shows broad application potential in the field of anti-counterfeiting. In addition, the preparation process of the present invention is simple, the raw material cost is low, and it is convenient to realize large-scale production. Compared with other types of structural colors, the structural color in the present invention has the advantages of anti-fading, environmental protection, high saturation, etc., and does not require a complex periodic structure, further enhancing its application value;

[0036] 2. The microspheres in the present invention are composed of immiscible liquid crystal compounds and hydrocarbons. By using the characteristics that the density of hydrocarbons is less than that of liquid crystal compounds and the refractive index is less than that of liquid crystal compounds, the microspheres can generate structural color based on the synergistic effect of total internal reflection and interference mechanisms. The formation of total internal reflection structural color mainly depends on the interface reflection between liquid crystal compounds and water. And after forming a water-in-oil system uniformly, the morphology of the microspheres and the arrangement pattern of the internal liquid crystal texture can be further changed by simply adjusting the volume ratio of the two phases and the surfactant ratio in the system, so that the microspheres have the characteristics of liquid crystal texture while having total internal reflection structural color. The structural color microspheres obtained by the present invention can have the characteristics of liquid crystal texture while having total internal reflection structural color by adjusting the mass ratio of surfactants and the volume ratio of liquid crystal compounds and hydrocarbons. It has the characteristics of being difficult to replicate, providing a new solution for security identification and anti-counterfeiting technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0038] Figure 1 It is a schematic structural diagram of the microfluidic chip of the present invention;

[0039] Figure 2Optical microscope images and polarized light microscope images of the liquid crystal microspheres with multiple optical signals prepared in Example 1;

[0040] Figure 3 Optical microscope images and polarized light microscope images of the liquid crystal microspheres with multiple optical signals prepared in Example 2. Detailed implementation manners

[0041] The following will describe the technical solutions in the embodiments of the present invention clearly and completely in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0042] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "upper" is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the present invention is usually placed during use, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0043] The description order of the following embodiments does not limit the preferred order of the embodiments. In addition, in the description of the present application, the term "including" means "including but not limited to". The various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present invention; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0044] The embodiments of the present application provide a preparation method for liquid crystal microspheres with multiple optical signals, including the following steps:

[0045] S1. Add a first surfactant to water to obtain a first surfactant solution;

[0046] S2. Add a second surfactant to water to obtain a second surfactant solution;

[0047] S3. Mix the first surfactant solution and the second surfactant solution to obtain an aqueous phase mixture;

[0048] S4. Add a liquid crystal compound and a hydrocarbon to a co-solvent to obtain an oil phase mixture;

[0049] S5. Introduce the aqueous phase mixture and the oil phase mixture into a microfluidic chip respectively to prepare liquid crystal microspheres with multiple optical signals;

[0050] Wherein, the density of the hydrocarbon is less than that of the liquid crystal compound, and the refractive index of the hydrocarbon is less than that of the liquid crystal compound.

[0051] The present invention consists of two monomers with different refractive indexes (i.e., a liquid crystal compound and a hydrocarbon), one of which is a liquid crystal phase, and two different surfactants. By adjusting the proportion of the surfactants, the composition, volume ratio or mass ratio of the two phases, the structure of the microspheres is regulated to obtain Janus microspheres with structural color. At the same time, under the action of two different surfactants, different arrangement patterns will appear in the texture of the liquid crystal phase. The liquid crystal microspheres obtained by the present invention have multiple optical signals. They can not only directly observe bright and vivid total internal reflection structural color with the naked eye, but also clearly observe the liquid crystal texture at the microscopic level with the aid of a polarized light microscope. This unique optical property makes it difficult to be replicated or imitated, so it shows broad application potential in the anti-counterfeiting field. In addition, the preparation process of the present invention is simple, the raw material cost is low, and it is convenient to realize large-scale production. Compared with other types of structural colors, the structural color in the present invention has the advantages of anti-fading, environmental protection, high saturation, etc., and does not require a complex periodic structure, further enhancing its application value.

[0052] Through the above technical solution conceived by the present invention, compared with the prior art, by using two different surfactants and utilizing the cooperation of the first surfactant, the second surfactant, the liquid crystal compound and the hydrocarbon, liquid crystal microspheres with multiple optical signals are obtained, and bright and vivid total internal reflection structural color can be observed both with the naked eye and under an optical microscope. At the same time, with the aid of a polarized light microscope, the liquid crystal texture can also be clearly observed.

[0053] The present invention can precisely control structural color and liquid crystal texture by regulating the morphology of microspheres and the surfactant ratio, achieving multiple optical signals. The first surfactant of the present invention has no preference for the arrangement of liquid crystals, but it can stabilize the interface between water and liquid crystal molecules, resulting in a structure in which liquid crystal molecules finally form a bipolar arrangement; during the formation of microspheres, the second surfactant adsorbs on the surface of the liquid crystal microspheres, extends the hydrophobic alkyl chains into the liquid crystal phase, causing the liquid crystal molecules to exhibit an arrangement perpendicular to the surface of the microspheres, and finally forming a radial arrangement structure from the inside out. By regulating the mass ratio of the two surfactants in the system, the arrangement mode of liquid crystal molecules can be changed; secondly, the first surfactant and the second surfactant can effectively reduce the interfacial tension between the liquid crystal compound and the hydrocarbon and water, thereby changing the morphology of the microspheres. The microspheres in the present invention are composed of immiscible liquid crystal compounds and hydrocarbons. By utilizing the characteristics that the density of hydrocarbons is less than that of liquid crystal compounds and the refractive index is less than that of liquid crystal compounds, structural color can be generated by the cooperation of total internal reflection and interference mechanisms. The formation of total internal reflection structural color mainly depends on the interfacial reflection between the liquid crystal compound and water. Moreover, after forming a water-in-oil system by mixing evenly, the morphology of the microspheres and the arrangement mode of the internal liquid crystal texture can be further changed by simply adjusting the volume ratio of the two phases and the surfactant ratio in the system, endowing the microspheres with the characteristics of liquid crystal texture while having total internal reflection structural color.

[0054] In some embodiments, as Figure 1 shown, the microfluidic chip includes:

[0055] An outer pipe 1, one end of which is connected with an aqueous phase mixture feed pipe 2;

[0056] A first inner pipe 4, one end of which is sleeved inside the outer pipe 1 and the other end extends outside the outer pipe 1;

[0057] A second inner pipe 5, one end of which is sleeved inside the outer pipe 1 and the other end extends outside the outer pipe 1;

[0058] The first inner pipe 4 and the second inner pipe 5 are distributed on both sides of the outer pipe, and the ends of the first inner pipe 4 and the second inner pipe 5 located inside the outer pipe form a gap 11; the aqueous phase mixture is injected into the outer pipe 1 through the aqueous phase mixture feed pipe 2, and the oil phase mixture is injected into the first inner pipe 4. The oil phase mixture is sheared by the aqueous phase mixture at the gap and flows out through the second inner pipe to form emulsion microspheres with uniform size; after the co-solvent in the emulsion microspheres volatilizes and phase separation occurs, liquid crystal microspheres with multiple optical signals are obtained.

[0059] Specifically, the microfluidic chip of the present invention includes an outer pipe 1, a first inner pipe 4, and a second inner pipe 5; both ends of the outer pipe 1 are closed. Among them, one end of the outer pipe 1 is communicatively provided with an aqueous phase mixture feed pipe 2, and the other end is communicatively provided with an exhaust pipe 3; the first inner pipe 4 and the second inner pipe 5 are distributed on both sides of the outer pipe 1, and the ends of the first inner pipe 4 and the second inner pipe 5 close to each other both extend into the interior of the outer pipe 1, while the ends of the first inner pipe 4 and the second inner pipe 5 far from each other both extend out of the outer pipe 1, and a gap 11 is formed between the ends of the first inner pipe 4 and the second inner pipe 5 close to each other; the aqueous phase mixture is injected into the outer pipe 1 through the aqueous phase mixture feed pipe 2, the oil phase mixture is injected into the first inner pipe 4, the oil phase mixture is sheared by the aqueous phase mixture at the gap 11 and flows out through the second inner pipe to form emulsion microspheres with uniform size; the emulsion microspheres are volatilized at (20 - 25 °C), and after the co-solvent is completely volatilized, the immiscible liquid crystal compounds and hydrocarbons undergo phase separation to form microspheres with a Janus structure (the Janus structure is a material or particle with asymmetry or anisotropy characteristics. The Janus structure usually consists of two or more different parts, each part having different physical, chemical, or functional characteristics), and the diameter of the microspheres is 5 - 200 μm, obtaining liquid crystal microspheres with multiple optical signals.

[0060] In some embodiments, the first surfactant includes at least one of PVA, PEO, and PEG.

[0061] Specifically, PVA is polyvinyl alcohol, PEO is polyethylene oxide, and PEG is polyethylene glycol.

[0062] In some embodiments, the second surfactant includes at least one of SDS, CTAB, CTAC, DTAC, sodium stearate, and PSS.

[0063] Specifically, SDS is sodium dodecyl sulfate, CTAB is cetyltrimethylammonium bromide, CTAC is cetyltrimethylammonium chloride, DTAC is dodecyltrimethylammonium chloride, sodium stearate is sodium octadecanoate, and its chemical formula is C 17 H 35 COONa, and PSS is sodium polystyrene sulfonate. In some embodiments, the liquid crystal compound includes at least one of 1CB, 2CB, 3CB, 4CB, 5CB, 6CB, 7CB, 8CB, RM257, LC756, 4-n-pentylbenzoic acid, RM82, RM105, and LC242.

[0064] Specifically, the nCB series (n = 1, 2, …, 8); 1CB is 4-cyano-4'-methylbiphenyl, 2CB is 4'-ethyl-4-cyanobiphenyl, 3CB is 4-cyano-4'-propylbiphenyl, 4CB is 4-cyano-4'-butylbiphenyl, 5CB is 4-cyano-4'-pentylbiphenyl, 6CB is 4-cyano-4'-hexylbiphenyl, 7CB is 4-cyano-4'-heptylbiphenyl, 8CB is 4-cyano-4'-octylbiphenyl; RM257 is 1,4-bis-(4-(3-acryloyloxypropoxy)benzoyloxy)-2-methylbenzene, LC756 is 2,5-bis-O-[4-[[4-[[[4-(acryloyloxy)butoxy]carbonyl]oxy]benzoyl]oxy]benzoyl]-1,4:3,6-dianhydro-D-glucitol, RM82 is 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (1,4-bis-[4-(6-RM105 is 4-methoxyphenyl 4-[[6-[(1-oxo-2-propenyl)oxy]hexyl]oxy]benzoate, LC242 is 2-methyl-1,4-diphenol (4-(((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoate).

[0065] In some embodiments, the hydrocarbon includes at least one of PDMS, PDMS-OH, n-decane, n-heptane, n-octane, n-nonane, n-decane, n-dodecane, n-tridecane, ethoxylated trimethylolpropane triacrylate, and octadecyl methacrylate.

[0066] Specifically, PDMS is polydimethylsiloxane, and PDMS-OH is hydroxyl-terminated polydimethylsiloxane, which is a derivative of polydimethylsiloxane (PDMS) and contains hydroxyl (-OH) functional groups at both ends of the molecular chain.

[0067] In some embodiments, the co-solvent includes at least one of chloroform, dichloromethane, n-hexane, and toluene. Specifically, the amount of the co-solvent added is not limited and can be selected according to the actual situation. For example, the added amount is 5 times the sum of the masses of the liquid crystal compound and the hydrocarbon.

[0068] In some embodiments, the concentration of the first surfactant solution is 1 - 30 mg / mL;

[0069] The concentration of the second surfactant solution is 1 - 30 mg / mL;

[0070] The mass ratio of the first surfactant to the second surfactant is (0:1) - (1:4);

[0071] Or, the mass ratio of the first surfactant to the second surfactant is (3:7) - (7:3);

[0072] Alternatively, the mass ratio of the first surfactant to the second surfactant is (4:1) to (1:0).

[0073] In some embodiments, the mass ratio of the liquid crystal compound to the hydrocarbon is (1:9) to (1:1).

[0074] Specifically, when the mass ratio of the first surfactant to the second surfactant in the system is (0:1) to (1:4), the Janus microspheres do not have structural color, and their liquid crystal texture is radially arranged from the inside out; when the mass ratio of the first surfactant to the second surfactant in the system is (3:7) to (7:3), the Janus microspheres have total internal reflection structural color, and their color rings are complete circles, and at the same time the liquid crystal texture is a mixed arrangement; when the mass ratio of the first surfactant to the second surfactant in the system is (4:1) to (1:0), the Janus microspheres have total internal reflection structural color, but the color ring is a circle with light emitting at both ends, and at the same time the liquid crystal texture is a bipolar arrangement; secondly, when the mass ratio of the liquid crystal compound to the hydrocarbon in the system is (1:9) to (1:1), the Janus microspheres have total internal reflection structural color, otherwise the Janus microspheres do not have total internal reflection structural color. Thus, by controlling the mass ratio of the surfactants in the system and the mass ratio of the liquid crystal compound to the hydrocarbon, Janus liquid crystal microspheres with multiple optical signals can be prepared, and bright and vivid total internal reflection structural color can be observed both with the naked eye and under an optical microscope. At the same time, with the aid of a polarizing microscope, the liquid crystal texture can also be clearly observed.

[0075] In some embodiments, the volume ratio of the first surfactant solution to the second surfactant solution is (3 - 4):(2 - 3).

[0076] In some embodiments, the aqueous phase mixture is injected into the outer pipe at a rate of 50 - 500 μL / min through the aqueous phase mixture feed pipe.

[0077] The oil phase mixture is injected into the first inner pipe at a rate of 5 - 30 μL / min.

[0078] In some embodiments, the inner diameter of the outer pipe 1 is 1 - 1.1 mm; the inner diameter of the larger end of the first inner pipe 4 (i.e., the end close to the aqueous phase mixture feed pipe 2) is 700 - 900 μm, and the inner diameter of the smaller end (i.e., the end close to the spacer 11) is 50 - 70 μm; the inner diameter of the smaller end of the second inner pipe 5 (i.e., the end close to the spacer 11) is 100 - 140 μm, and the inner diameter of the larger end (i.e., the end close to the exhaust pipe 3) is 800 - 950 μm.

[0079] Specifically, a co-solvent (i.e., oil-phase mixture) dissolving a liquid crystal compound and a hydrocarbon is used as the dispersed phase, and two mutually miscible surfactants (i.e., water-phase mixture) are used as the continuous dispersed phase. A microfluidic chip is connected through a silica gel hose. The two mutually miscible surfactants serve as the outer phase, and the flow rate of the outer phase is 50 - 500 μL / min; the co-solvent dissolving the liquid crystal compound and the hydrocarbon is the inner phase, and the flow rate of the inner phase is 5 - 30 μL / min; the dispersed phase is sheared by the continuous-phase solution to form emulsion microspheres with uniform and stable sizes; emulsion microspheres with different sizes can be obtained by adjusting the flow rates of the dispersed phase and the continuous phase; the obtained emulsion microspheres are left at room temperature to volatilize for 24 h. After the co-solvent completely volatilizes, the microspheres form a Janus structure, and the diameter of the microspheres is 5 - 200 μm; when the Janus liquid crystal microspheres with multiple optical signals are placed under an optical microscope, bright and vivid total internal reflection structural colors can be observed. At the same time, with the aid of a polarized light microscope, the liquid crystal texture can be clearly observed.

[0080] The microspheres in the present invention are composed of immiscible liquid crystal compounds and hydrocarbons. Utilizing the characteristics that the density of the hydrocarbon is less than that of the liquid crystal compound and the refractive index is also less than that of the liquid crystal compound, the microspheres can generate structural colors synergistically based on the mechanisms of total internal reflection and interference. The formation of the total internal reflection structural color mainly depends on the interfacial reflection between the liquid crystal compound and water. Moreover, after forming a water-in-oil system by mixing evenly, the morphology of the microspheres and the arrangement of the internal liquid crystal texture can be further changed by simply adjusting the volume ratio of the two phases and the surfactant ratio in the system, endowing the microspheres with the characteristics of liquid crystal texture while having the total internal reflection structural color.

[0081] Specifically speaking, the present invention can achieve the following beneficial effects:

[0082] (1) The preparation method of the structural color microspheres provided by the present invention is simple, with simple operation and low technical requirements. Micro-nano scale structural color microspheres with uniform and controllable sizes can be easily prepared, and the required raw materials are cheap and easily available, suitable for large-scale production.

[0083] (2) The structural color microspheres obtained by the present invention can endow the microspheres with the characteristics of liquid crystal texture while having the total internal reflection structural color by adjusting the mass ratio of the surfactant and the volume ratio of the liquid crystal compound and the hydrocarbon. It has the characteristics that are difficult to replicate, providing a new solution for security identification and anti-counterfeiting technologies.

[0084] Based on the same inventive concept, the present invention also provides a liquid crystal microsphere with multiple optical signals, which is prepared by using the above preparation method.

[0085] Based on the same inventive concept, the present invention also provides an application of the multi-optical-signal liquid crystal microspheres prepared by the above preparation method or the above multi-optical-signal liquid crystal microspheres in the preparation of anti-counterfeiting materials.

[0086] The following further illustrates the multi-optical-signal liquid crystal microspheres of the present application, their preparation methods and applications with specific examples. This part further illustrates the content of the present invention in combination with specific examples, but should not be construed as a limitation of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0087] In the following examples, the inner diameter of the outer pipe 1 is 1.1 mm; the inner diameter of the larger end of the first inner pipe 4 is 800 μm, and the inner diameter of the smaller end is 60 μm; the inner diameter of the smaller end of the second inner pipe 5 is 120 μm, and the inner diameter of the larger end is 900 μm.

[0088] Example 1

[0089] The embodiment of the present application provides a preparation method of multi-optical-signal liquid crystal microspheres, including the following steps:

[0090] S1. Add the first surfactant PVA (polyvinyl alcohol) to water to obtain a first surfactant solution; the concentration of the first surfactant solution is 10 mg / mL;

[0091] S2. Add the second surfactant SDS (sodium dodecyl sulfate) to water to obtain a second surfactant solution; the concentration of the second surfactant solution is 10 mg / mL;

[0092] S3. Mix the first surfactant solution and the second surfactant solution to obtain an aqueous phase mixture; the volume ratio of the first surfactant solution to the second surfactant solution is 3:2;

[0093] S4. Add the liquid crystal compound 5CB and the hydrocarbon PDMS to the co-solvent dichloromethane to obtain an oil phase mixture; the mass ratio of 5CB to PDMS is 3:7; the addition amount of the co-solvent dichloromethane is not limited. In this example, for the convenience of the experiment, the addition amount of the co-solvent dichloromethane is 5 times the sum of the masses of 5CB and PDMS;

[0094] S5. Provide Figure 1 the microfluidic chip shown;

[0095] Inject the aqueous phase mixture in S3 into the outer pipe at a rate of 240 μL / min through the aqueous phase mixture feed pipe;

[0096] Inject the oil-phase mixture in S4 into the first inner pipe at a rate of 15 μL / min. The water-phase mixture and the oil-phase mixture are mixed at the interval and flow out through the second inner pipe to form emulsion microspheres with a diameter of 19 μm.

[0097] Place the prepared emulsion microspheres at room temperature (25 °C) for volatilization. After the co-solvent dichloromethane is completely volatilized, the microspheres undergo phase separation to form microspheres with a Janus structure. At this time, the prepared microspheres have a total internal reflection structural color, and Janus liquid crystal microspheres with multiple optical signals are obtained.

[0098] Drop the microsphere solution system prepared in Example 1 onto a petri dish and observe it under a reflection-mode optical microscope. The color of its total internal reflection structural color is blue; place the blue Janus liquid crystal microspheres under a polarized light microscope to observe the arrangement of the liquid crystal texture in the microspheres, and the internal liquid crystal texture is a mixed arrangement.

[0099] As Figure 2 shown, Figure 2 in (a) is an optical microscope picture (top view) of the Janus microspheres with a total internal reflection structural color of blue obtained in step S5 of Example 1; Figure 2 in (b) is a macroscopic picture of the Janus microspheres with a total internal reflection structural color in step S5 of Example 1; Figure 2 in (c) is a microscope picture (top view) of the Janus liquid crystal microspheres with a total internal reflection structural color of blue obtained in step S5 of Example 1 placed under a polarized light microscope, and the internal liquid crystal texture is a mixed arrangement.

[0100] Example 2

[0101] This application example provides a preparation method of liquid crystal microspheres with multiple optical signals, including the following steps:

[0102] S1. Add the first surfactant PVA (polyvinyl alcohol) to water to obtain a first surfactant solution; the concentration of the first surfactant solution is 15 mg / mL;

[0103] S2. Add the second surfactant PSS (sodium polystyrene sulfonate) to water to obtain a second surfactant solution; the concentration of the second surfactant solution is 5 mg / mL;

[0104] S3. Mix the first surfactant solution and the second surfactant solution to obtain a water-phase mixture; the volume ratio of the first surfactant solution to the second surfactant solution is 4:3;

[0105] S4. Add the liquid crystal compound RM257 and the hydrocarbon n-decane into the co-solvent dichloromethane to obtain an oil-phase mixture; the mass ratio of RM257 to n-decane is 2:8; the addition amount of the co-solvent dichloromethane is not limited. In this embodiment, for the convenience of the experiment, the addition amount of the co-solvent dichloromethane is 5 times the sum of the masses of RM257 and n-decane.

[0106] S5. Provide Figure 1 the microfluidic chip shown in

[0107] Inject the aqueous-phase mixture in S3 into the outer pipe at a rate of 230 μL / min through the aqueous-phase mixture feed pipe.

[0108] Inject the oil-phase mixture in S4 into the first inner pipe at a rate of 20 μL / min. The aqueous-phase mixture and the oil-phase mixture are mixed at the interval and flow out through the second inner pipe to form emulsion microspheres with a diameter of 23 μm.

[0109] Place the prepared emulsion microspheres at room temperature (25 °C) for volatilization. After the co-solvent dichloromethane is completely volatilized, the microspheres undergo phase separation to form microspheres with a Janus structure. At this time, the prepared microspheres have a total internal reflection structural color, and Janus liquid crystal microspheres with multiple optical signals are obtained.

[0110] Drop the microsphere solution system prepared in Example 2 onto a petri dish and observe it under a reflection-mode optical microscope. Its total internal reflection structural color is light blue, and at the same time, its color ring is not a complete circle; place the blue Janus liquid crystal microspheres under a polarized light microscope to observe the liquid crystal texture arrangement in the microspheres, and its internal liquid crystal texture is bipolar arrangement.

[0111] As Figure 3 shown, Figure 3 (a) in is an optical microscope picture (top view) of the Janus microspheres with a total internal reflection structural color of light blue prepared in step S5 of Example 2, and its color ring is not a complete circle; Figure 3 (b) in is a macroscopic picture of the Janus microspheres with a total internal reflection structural color prepared in step S5 of Example 2, Figure 3 (c) in is a microscope picture (top view) of the Janus microspheres with a total internal reflection structural color prepared in step S5 of Example 2 placed under a polarized light microscope, and its internal liquid crystal texture is bipolar arrangement.

[0112] The above embodiments are only examples. In addition to those shown above, surfactant 1 can also be any one of PEO and PEG. Similar to PVA, these surfactants can all stabilize the interface between water and liquid crystal molecules, resulting in the final formation of a structure with bipolar arrangement of liquid crystal molecules; surfactant 2 can also be any one of SDS, CTAB, CTAC, DTAC, sodium stearate, and PSS. Similar to SDS, these surfactants can all extend the hydrophobic alkyl chain into the liquid crystal phase, resulting in the final formation of a radial arrangement structure from the inside out of liquid crystal molecules; the specific types of liquid crystal compounds and the specific types of hydrocarbons can also be flexibly adjusted as long as they are all in a liquid state at room temperature and are immiscible with each other, and the density of the hydrocarbon is less than that of the liquid crystal compound and the refractive index is less than that of the liquid crystal compound. In addition, the preparation process and subsequent detection process of each of the above embodiments are all carried out under room temperature conditions.

[0113] The foregoing is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing liquid crystal microspheres with multiple optical signals, characterized in that: The following steps are involved: adding a first surfactant into water to obtain a first surfactant solution; adding a second surfactant into water to obtain a second surfactant solution; Mixing the first surfactant solution and the second surfactant solution to obtain an aqueous phase mixture; adding a liquid crystal compound and a hydrocarbon compound into a co-solvent to obtain an oil phase mixture; The aqueous phase mixture and the oil phase mixture are respectively introduced into the microfluidic chip to prepare liquid crystal microspheres with multiple optical signals; The density of the hydrocarbon compound is smaller than that of the liquid crystal compound, and the refractive index of the hydrocarbon compound is smaller than that of the liquid crystal compound.

2. The method for preparing liquid crystal microspheres with multiple optical signals according to claim 1, characterized in that: The microfluidic chip comprises: An external pipeline, one end of which is connected to a water phase mixture feed pipe; A first inner pipe, one end of which is sleeved inside the outer pipe and the other end of which extends outside the outer pipe; A second inner pipe, one end of which is sleeved inside the outer pipe and the other end of which extends outside the outer pipe; The first inner pipe and the second inner pipe are distributed on both sides of the outer pipe, and the ends of the first inner pipe and the second inner pipe located in the outer pipe form a gap; The aqueous phase mixture is injected into the outer pipe through the aqueous phase mixture feed pipe, and the oil phase mixture is injected into the first inner pipe. The oil phase mixture is sheared by the aqueous phase mixture at the interval and flows out through the second inner pipe to form emulsion microspheres with uniform size. The co-solvent in the emulsion microspheres evaporates and phase separation occurs to obtain liquid crystal microspheres with multiple optical signals.

3. The method for preparing liquid crystal microspheres with multiple optical signals according to claim 1, characterized in that: The first surfactant includes at least one of PVA, PEO, and PEG; And / or, the second surfactant includes at least one of SDS, CTAB, CTAC, DTAC, sodium stearate, and PSS.

4. The method for preparing liquid crystal microspheres with multiple optical signals according to claim 1, characterized in that: The liquid crystal compound includes at least one of 1CB, 2CB, 3CB, 4CB, 5CB, 6CB, 7CB, 8CB, RM257, LC756, 4-n-pentylbenzoic acid, RM82, RM105, and LC242; And / or, the hydrocarbon includes at least one of PDMS, PDMS-OH, n-decane, n-heptane, n-octane, n-nonane, n-decane, n-dodecane, n-tridecane, ethoxylated trimethylolpropane triacrylate, and octadecyl methacrylate.

5. The method for preparing liquid crystal microspheres with multiple optical signals according to claim 1, characterized in that: The co-solvent includes at least one of chloroform, dichloromethane, n-hexane and toluene.

6. The method for preparing liquid crystal microspheres with multiple optical signals according to claim 1, characterized in that: The concentration of the first surfactant solution is 1 to 30 mg / mL; The concentration of the second surfactant solution is 1 to 30 mg / mL; The mass ratio of the liquid crystal compound to the hydrocarbon compound is (1:9) to (1:1).

7. The method for preparing liquid crystal microspheres with multiple optical signals according to claim 1, characterized in that: The mass ratio of the first surfactant to the second surfactant is (0:1) to (1:4); Or, the mass ratio of the first surfactant to the second surfactant is (3:7) to (7:3); Alternatively, the mass ratio of the first surfactant to the second surfactant is (4:1) to (1:0).

8. The method for preparing liquid crystal microspheres with multiple optical signals according to claim 1, characterized in that: Injecting the aqueous phase mixture into the outer pipe through the aqueous phase mixture feed pipe at a rate of 50 to 500 μL / min; The oil phase mixture was injected into the first inner channel at a rate of 5-30 μL / min.

9. A liquid crystal microsphere with multiple optical signals, characterized in that: The preparation is obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the liquid crystal microspheres with multiple optical signals prepared by the preparation method according to any one of claims 1 to 8 or the liquid crystal microspheres with multiple optical signals according to claim 9 in the preparation of anti-counterfeiting materials.

Images