A method for preparing conductive microspheres based on microfluidics and application thereof

Abstract

The application discloses a method for preparing conductive microspheres based on microfluidic technology and application, and relates to the technical field of microfluidic technology, and the method comprises the following steps: S1, preparing materials, wherein the materials comprise an inner phase, an outer phase and a chemical plating solution; S2, preparing the inner phase and the outer phase into droplet microspheres by using microfluidic technology; S3, receiving the droplet microspheres, and performing redox chemical plating in the chemical plating solution to form conductive microspheres; and S4, cleaning and collecting the conductive microspheres. The conductive microspheres are prepared by using the microfluidic technology, the modification, sensitization and activation processes of the microspheres are simplified, the purpose of avoiding the uneven distribution of functional monomers possibly generated by a functional monomer introduction method and the breakage or deformation of the microspheres possibly caused by the modification of the microspheres is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of microfluidics, and in particular to a method for preparing conductive microspheres based on microfluidics and applications thereof. BACKGROUND

[0002] The polystyrene conductive microspheres are formed by adsorbing a layer of conductive metal on the surface of polystyrene microspheres. The process for preparing polystyrene conductive microspheres using traditional electroless plating technology is as follows:

[0003] (1) Monomer polymerization to prepare polystyrene;

[0004] (2) Sulfonation: using concentrated sulfuric acid to modify polystyrene microspheres to obtain sulfonated polystyrene microspheres;

[0005] (3) Sensitization: placing the sulfonated microspheres in a SnCl2 solution to adsorb Sn 2+ ;

[0006] (4) Activation: placing the sensitized microspheres in a PdCl2 solution to plate palladium;

[0007] (5) Metal plating: using the palladium layer as a catalyst to prepare a metal nickel layer by oxidation-reduction.

[0008] The entire process is complex and difficult to control, especially the sulfonation step, which can cause the microspheres to carbonize, break, or significantly shrink, failing to meet the use requirements.

[0009] Functionalized microspheres have extremely wide applications in drug delivery, biological detection, pollution treatment, electronic devices, etc. For example, in the biomedical field, functionalized magnetic microspheres and fluorescent microspheres can be used for drug carriers, cell separation, fluorescent probe labeling, biological catalysis, enzyme immobilization, etc. For example, in the industrial material field, functionalized carbon microspheres are used for adsorption and catalytic reaction, and functionalized chromatographic packing microspheres are used for high-efficiency separation media, such as biological pharmaceutical separation and purification. Currently, the preparation methods of functionalized microspheres mainly include the following two types:

[0010] One type of functionalized monomer polymerization method is to directly add a functionalized monomer during the monomer polymerization process to synthesize microspheres with functional groups. During the polymerization process, on the one hand, the uneven distribution of the functionalized monomer may be caused by uneven stirring and dispersion, and on the other hand, the functionalized groups on the surface of the microspheres are constantly covered due to the continuous growth of the microspheres, making it difficult to effectively control the degree of modification.

[0011] The second type is a microsphere modification method, in which a functional group (such as an amino group (-NH2), a hydroxyl group (-OH), a mercapto group (-SH), a carboxyl group (-COOH), a sulfonic acid group (-SO3H), a chloromethyl group (-CH3Cl), an aminomethyl group (-CH2NH2), or an epoxy group) is introduced into an existing microsphere. This method modifies the surface of the microsphere, and the modification process is complex, and may also cause the microsphere to break and deform.

[0012] In view of this, the present application is proposed. SUMMARY

[0013] The present application aims to provide a method for preparing conductive microspheres based on microfluidics and applications, in which polystyrene microdroplets prepared by microfluidics are received and then subjected to redox electroless plating in an electroless plating solution to form conductive microspheres, thereby solving the problems of uneven distribution of functional monomers, easy breakage and deformation of microspheres in the prior art.

[0014] First, the present application provides a method for preparing conductive microspheres based on microfluidics, which comprises the following steps:

[0015] S1: preparing materials, which include an inner phase, an outer phase, and an electroless plating solution;

[0016] S2: using microfluidic technology to prepare the inner phase and the outer phase into droplet microspheres;

[0017] S3: receiving the droplet microspheres and subjecting them to redox electroless plating in an electroless plating solution to form conductive microspheres;

[0018] S4: cleaning and collecting the conductive microspheres.

[0019] As an optional implementation, the inner phase includes a solute and a solvent, the solute includes a functional polymer, and the solvent includes a volatile organic solvent.

[0020] The functional group of the functional polymer includes at least one of an amino group, a hydroxyl group, a mercapto group, a carboxyl group, an ester bond, a sulfonic acid group, a chloromethyl group, and an aminomethyl group.

[0021] The polymer structure of the functional polymer includes at least one of polystyrene, polyacrylate, and polyacrylamide.

[0022] The volatile organic solvent includes at least one of acetone, cyclohexanone, methyl ethyl ketone, chloroform, dimethylbenzene, toluene, carbon tetrachloride, ethyl acetate, and tetrahydrofuran.

[0023] As an optional implementation, the inner phase includes a polymer monomer, a functional monomer, an initiator, and a crosslinking agent.

[0024] The polymer monomer includes at least one of an alkenyl aromatic monomer, an acrylate monomer, an acrylic monomer, a vinyl acetate monomer, and an acrylamide monomer;

[0025] The functional monomer includes a monomer with both a double bond and a functional group, the functional group including at least one of an amino group, a hydroxyl group, a mercapto group, a carboxyl group, an ester bond, a sulfonic acid group, a chloromethyl group, and an aminomethyl group;

[0026] The initiator includes at least one of azobisisobutyronitrile, azobisisoheptyl nitrile, dibenzoyl peroxide, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide, and dicumyl peroxide;

[0027] The crosslinking agent includes at least one of divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, isoprene, and butadiene.

[0028] As an optional implementation, the double bond in the functional monomer is a carbon-carbon double bond, and the functional group is a carboxyl group; preferably, the functional monomer is methacrylic acid.

[0029] The amount of the crosslinking agent is 0.1-20 wt%.

[0030] As an optional implementation, the outer phase includes an activation solution and / or a sensitization solution, and the electroless plating solution includes at least one of an electroless nickel plating solution, an electroless silver plating solution, and an electroless gold plating solution.

[0031] As an optional implementation, the outer phase is an activation solution, and the electroless plating solution is an electroless nickel plating solution.

[0032] The activation solution includes a non-ionic polymer surfactant mixed solution of PdCl2 and HCl;

[0033] The concentration of the PdCl2 is 0.001-0.05 mol / L, and the concentration of the HCl is 0.1-5 mol / L.

[0034] The electroless nickel plating solution includes 0.01-1 M nickel sulfate, 0.01-0.1 M sodium citrate, 0.01-0.2 M sodium acetate, and 0.01-5 M sodium hypophosphite, and the pH value of the electroless nickel plating solution is 4-6.

[0035] The non-ionic polymer surfactant includes an aqueous solution with a solvent being at least one of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, and hydroxyethyl cellulose, and the concentration of the non-ionic polymer surfactant is 0.1-3 wt%.

[0036] As an optional implementation, the outer phase is a sensitization solution, and the electroless plating solution is an electroless silver plating solution.

[0037] The sensitization solution comprises a non-ionic polymer surfactant mixed solution of SnCl2 and HCl.

[0038] The concentration of SnCl2 is 0.001-0.05 mol / L, and the concentration of HCl is 0.1-5 mol / L.

[0039] The electroless silver plating solution comprises a silver ammonia solution, which is formed by adding 1-10 wt% ammonia water drop by drop into 1-10 wt% silver nitrate solution until the generated AgOH precipitate just dissolves.

[0040] The non-ionic polymer surfactant comprises an aqueous solution of at least one of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone and hydroxyethyl cellulose as a solvent, and the concentration of the non-ionic polymer surfactant is 0.1-3 wt%.

[0041] As an optional implementation, the preparation method of the conductive microspheres in S3 comprises receiving liquid droplet microspheres using an electroless plating solution, stirring at a speed of 100-400 rpm for 0.5-12 h under heating conditions of 40-80 ℃, and simultaneously achieving solidification and electroless plating of the microspheres in the electroless plating solution.

[0042] The washing and collecting in S4 comprises filtering the reaction solution in which the electroless plating is completed in S3 using a filter screen with a pore size of 0.6-1.0 μm, and then drying and collecting the filtered conductive microspheres after alternatingly centrifuging the conductive microspheres using anhydrous ethanol and pure water.

[0043] As an optional implementation, the preparation method of the conductive microspheres in S3 comprises receiving liquid droplet microspheres using pure water, achieving solidification and activation of the microspheres under heating conditions of 40-80 ℃ at a stirring speed of 100-400 rpm for 0.5-12 h, and then transferring the microspheres into the electroless plating solution to achieve electroless plating after centrifuging the microspheres using pure water for at least twice.

[0044] The washing and collecting in S4 comprises filtering the reaction solution in which the electroless plating is completed in S3 using a filter screen with a pore size of 0.6-1.0 μm, and then drying and collecting the filtered conductive microspheres after alternatingly centrifuging the conductive microspheres using anhydrous ethanol and pure water.

[0045] Secondly, the embodiment of the present application also provides an application of the conductive microspheres prepared based on microfluidic control, wherein the conductive microspheres are prepared by the above method, and the conductive microspheres are used in at least one of the following fields: biomedical field, biological detection, pollution treatment, electronic device and industrial material.

[0046] Compared with the prior art, the embodiment of the present application has the following advantages and beneficial effects:

[0047] 1、The conductive microspheres are prepared by the microfluidic one-step method, the modification, sensitization and activation processes of the microspheres are simplified, the uneven distribution of the functional monomers possibly caused by the functional monomer polymerization method is avoided, and the breakage or deformation possibly caused by the modification of the microspheres is avoided, and the process flow is simpler and easier to operate compared with the traditional conductive microsphere preparation method.

[0048] 2、The polystyrene microdroplets prepared by the droplet microfluidic method are directly received into the chemical plating solution, the microsphere solidification, modification, activation and chemical plating are realized in one step, the sensitization step is saved, and the process steps are optimized and simplified.

[0049] 3、The conductive microspheres with a size of 1 μm to 2 mm can be prepared by the method, the breakage, shrinkage and heterogeneity probability of the microspheres is less than 2%, and the CV value of the microspheres is less than 5%, and the breakage, shrinkage, deformation and other conditions of the use of the finished microspheres for sulfonation modification are avoided. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the example embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments, and it should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings:

[0051] Figure 1 is a morphology diagram of the microspheres collected without chemical plating in example 1 of the present application;

[0052] Figure 2 is a morphology diagram of the conductive nickel spheres prepared in example 1 of the present application;

[0053] Figure 3 is a partial enlarged view of Figure 2 ;

[0054] Figure 4 is a partial enlarged view of Figure 2 ;

[0055] Figure 5 is a morphology diagram of the conductive nickel spheres prepared in example 2 of the present application;

[0056] Figure 6 is a morphology diagram of the conductive nickel spheres prepared in example 3 of the present application;

[0057] Figure 7 is a morphology diagram of the conductive nickel spheres prepared in example 4 of the present application;

[0058] Figure 8Morphology of the conductive nickel spheres prepared in Example 5 of the present application;

[0059] Figure 9 Morphology of the conductive nickel spheres prepared in Example 6 of the present application;

[0060] Figure 10 Morphology of the conductive nickel spheres prepared in Example 7 of the present application;

[0061] Figure 11 Morphology of the conductive nickel spheres prepared in Example 8 of the present application;

[0062] Figure 12 Morphology of the conductive nickel spheres prepared in Example 9 of the present application;

[0063] Figure 13 Morphology of the broken polystyrene spheres in Comparative Example 1, wherein Figure 13 a is Figure 13 a partial enlarged view of b;

[0064] Figure 14 Morphology of the wrinkled conductive nickel spheres prepared in Comparative Example 1;

[0065] Figure 15 a partial enlarged view of Figure 14 a partial enlarged view of

[0066] Figure 16 a partial enlarged view of Figure 14 a partial enlarged view of DETAILED DESCRIPTION

[0067] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application.

[0068] Therefore, the detailed description of the embodiments of the present application provided below is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0069] The embodiments of the present application provide a method for preparing conductive microspheres based on microfluidic technology, which comprises the following contents:

[0070] S1: preparing materials, wherein the materials comprise an inner phase, an outer phase and a chemical plating solution;

[0071] S2: preparing the inner phase and the outer phase into droplet microspheres using microfluidic technology;

[0072] S3: receiving the droplet microspheres, and performing redox electroless plating in an electroless plating solution to form conductive microspheres;

[0073] S4: cleaning and collecting the conductive microspheres.

[0074] (1) Inner phase formula one: solute is a functional polymer, and solvent is a volatile organic solvent;

[0075] The functional groups of the functional polymer include at least one of amino, hydroxyl, mercapto, carboxyl, ester bond, sulfonic acid group, chloromethyl and aminomethyl;

[0076] The polymer structure of the functional polymer includes at least one of polystyrene, polyacrylate and polyacrylamide;

[0077] The volatile organic solvent includes at least one of acetone, cyclohexanone, methyl ethyl ketone, chloroform, dimethylbenzene, toluene, carbon tetrachloride, ethyl acetate and tetrahydrofuran.

[0078] (2) Inner phase formula two: including a polymer monomer, a functional monomer, an initiator and a crosslinking agent;

[0079] The polymer monomer includes at least one of alkenyl aromatic monomer, acrylate monomer, acrylic monomer, vinyl acetate and acrylamide monomer;

[0080] The functional monomer includes a monomer with both a double bond and a functional group, and the functional group includes at least one of amino, hydroxyl, mercapto, carboxyl, ester bond, sulfonic acid group, chloromethyl and aminomethyl; preferably, the double bond in the functional monomer is a carbon-carbon double bond, and the functional group is a carboxyl group; more preferably, the functional monomer is an acrylic acid, which can not only maintain good water insolubility and enhance the mutual solubility with styrene, but also directly introduce a carboxyl group.

[0081] The initiator includes at least one of azobisisobutyronitrile, azobisisoheptyl nitrile, dibenzoyl peroxide, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide and dicumyl peroxide;

[0082] The crosslinking agent includes at least one of divinylbenzene, ethylene glycol dimethyl acrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, isoprene and butadiene, and the amount of the crosslinking agent is 0.1-20wt%, and a suitable amount of the crosslinking agent can be selected according to the requirement of the compression strength of the microspheres.

[0083] It should be noted that the inner phase formula one and the inner phase formula two can be mixed in a corresponding proportion according to the requirement, which is not limited here.

[0084] (3) Outer phase formula one: Sensitizing liquid, the sensitizing liquid includes non-ionic high molecular surfactant mixed solution of SnCl2 and HCl;

[0085] The concentration of SnCl2 is 0.001-0.05 mol / L, the concentration of HCl is 0.1-5 mol / L; the non-ionic high molecular surfactant includes aqueous solution of which the solvent is at least one of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone and hydroxyethyl cellulose, the concentration of the non-ionic high molecular surfactant is 0.1-3 wt%;

[0086] (4) Outer phase formula two: Activating liquid, the activating liquid includes non-ionic high molecular surfactant mixed solution of PdCl2 and HCl;

[0087] The concentration of PdCl2 is 0.001-0.05 mol / L, the concentration of HCl is 0.1-5 mol / L; the non-ionic high molecular surfactant includes aqueous solution of which the solvent is at least one of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone and hydroxyethyl cellulose, the concentration of the non-ionic high molecular surfactant is 0.1-3 wt%.

[0088] (5) Electroless plating liquid formula one: Electroless nickel plating liquid, the electroless nickel plating liquid includes 0.01-1 M nickel sulfate, 0.01-0.1 M sodium citrate, 0.01-0.2 M sodium acetate and 0.01-5 M sodium hypophosphite, the pH value of the electroless nickel plating liquid is 4-6.

[0089] (6) Electroless plating liquid formula two: The electroless silver plating liquid includes silver ammonia solution, the silver ammonia solution is set to be formed by adding 1-10 wt% ammonia water drop by drop in 1-10 wt% silver nitrate solution until the generated AgOH precipitate just dissolves.

[0090] (7) Electroless plating liquid formula three: Electroless gold plating liquid.

[0091] (8) Conductive microsphere preparation method one: including using chemical plating liquid to receive liquid drop microspheres, under the heating condition of 40-80℃, stirring at the speed of 100-400 rpm for 0.5-12 h, realizing the solidification and electroless plating of the microspheres in the chemical plating liquid at the same time;

[0092] Using filter screen with pore size of 0.6-1.0 μm to filter the reaction liquid after electroless plating, using anhydrous ethanol and pure water to alternately centrifugal clean the filtered conductive microspheres, then drying and collecting.

[0093] (9) The second method for preparing the conductive microspheres comprises using pure water to receive the liquid droplet microspheres, stirring at a speed of 100-400 rpm under heating conditions of 40-80℃ for 0.5-12 h to realize solidification and activation of the microspheres, using pure water to centrifugally clean the microspheres for at least two times, and then transferring the microspheres into a chemical plating solution to realize chemical plating.

[0094] The reaction solution after the chemical plating is filtered using a filter screen with a pore size of 0.6-1.0 μm, and the filtered conductive microspheres are cleaned by using anhydrous ethanol and pure water alternately, and then dried and collected.

[0095] As a preferred embodiment of the present application, in S2 and S3, when the liquid droplet microfluidic external phase is an activation solution, the chemical plating solution is a chemical plating nickel solution. In this way, the sensitization process in the traditional process can be omitted, and the reason is that Sn 2+ is introduced in the sensitization process in the traditional process to reduce Pd 2+ on the surface of the microspheres, and the present application omits the sensitization step and directly adsorbs Pd 2+ on the surface of the microspheres in the microfluidic external phase. 2+ Pd

[0096] As a preferred embodiment of the present application, in S2 and S3, when the liquid droplet microfluidic external phase is a sensitization solution, the chemical plating solution is a chemical plating silver solution. In this way, the activation process in the traditional process can be omitted, and Sn 2+ catalyzes reduction of silver ammine ions to generate elemental silver, and Sn 2+ plays a role of both a catalyst and a reducing agent in the silver mirror reaction and promotes the silver mirror reaction, while Pd 2+ competes for electrons with the silver ammine ions in the silver mirror reaction and destroys the metal silver deposition process.

[0097] Example 1: A method for preparing conductive microspheres based on microfluidics is provided, and specifically a method for preparing conductive nickel microspheres, which comprises the following contents:

[0098] (1) Preparation of materials

[0099] Internal phase: 89wt% styrene, 1wt% divinylbenzene, 5wt% acrylic acid, and 5wt% AIBN;

[0100] External phase: a polyvinyl alcohol solution of PdCl2 and HCl, the concentration of PdCl2 is 0.01 mol / L, the concentration of HCl is 0.2 mol / L, and the concentration of polyvinyl alcohol is 1%;

[0101] Chemical plating nickel solution: 0.1M nickel sulfate, 0.08M sodium citrate, 0.12 sodium acetate, and 0.5M sodium hypophosphite dihydrogen, and the pH value is 5.5.

[0102] (2) Using microfluidic to prepare droplet microspheres, the outer phase and the inner phase are flowed out at the same time, the flow ratio of the inner phase to the outer phase is 1:10, and the outer phase shears the inner phase to form microdroplets.

[0103] (3) Using a chemical nickel plating solution to directly receive the droplet microspheres generated in step (2), the receiving solution has a temperature of 70°C, and stirring is continuously performed at 200 rpm for 8 h. AIBN polymerization is initiated at 70°C to generate carboxylated polystyrene. Meanwhile, the carboxyl group can adsorb Pd in the droplet 2+ , and the sodium hypophosphite in the nickel plating solution reduces the Pd point to Pd, which catalyzes the reduction of nickel ions into a nickel metal layer on the surface of the microspheres.

[0104] (4) Using a filter screen with a pore size of 1 μm to filter the reaction solution in which chemical plating is completed in step (3), to remove nanoscale metal particles and waste liquid in the plating solution, and using anhydrous ethanol and pure water to alternately centrifugally clean the filtered conductive nickel spheres, and drying at 60°C to complete collection.

[0105] The embodiment of the present application omits the sensitization step, and Sn 2+ is introduced in the traditional process to reduce Pd 2+ to generate Pd metal point on the surface of the microspheres. The embodiment directly adsorbs Pd 2+ in the microfluidic outer phase, and Pd 2+ can also catalyze the reduction of nickel plating, and can also be reduced to Pd catalyst by a reducing agent in the chemical nickel plating solution. Figure 1 is a scanning diagram of the microspheres collected without step (3) chemical plating, Figure 2 is a scanning diagram of the conductive microspheres collected in step (4), Figure 3 , Figure 4 is a local enlarged view of Figure 2 , it can be seen that the conductive microspheres prepared in the embodiment have good morphology, and basically do not have the phenomena of microsphere breakage, shrinkage and abnormality, and the probability of microsphere breakage, shrinkage and abnormality prepared in the embodiment is <2%, and the CV value of the microspheres is <5%.

[0106] Embodiment 2: A method for preparing conductive microspheres based on microfluidics is provided, and specifically, a conductive silver sphere is prepared, including the following contents:

[0107] (1) Material preparation

[0108] The inner phase: 89wt% styrene, 1wt% divinylbenzene, 5wt% acrylic acid, and 5wt% AIBN;

[0109] The outer phase: a polyvinyl alcohol solution of SnCl2 and HCl, the concentration of SnCl2 is 0.01 mol / L, the concentration of HCl is 0.2 mol / L, and the concentration of polyvinyl alcohol is 1%.

[0110] Chemical silver plating solution: silver ammonia solution, 20ml of 5wt% ammonia water is added dropwise into 40ml of 1wt% AgNO3, brown-black precipitate is generated, then stop adding dropwise until the solution is clear, finally 0.1g of glucose is added dropwise to obtain silver ammonia solution;

[0111] (2) The liquid droplet microspheres are prepared by using microfluidic control, the outer phase and the inner phase are simultaneously flowed out, the flow rate ratio of the inner phase to the outer phase is 1:10, and the outer phase shears the inner phase to form microdroplets.

[0112] (3) The liquid droplet microspheres generated in step (2) are directly received by using the chemical silver plating solution, the receiving liquid has a temperature of 70 DEG C, and stirring is continuously performed at 200 rpm for 8h. AIBN polymerization is initiated at 70 DEG C to generate carboxylated polystyrene. Meanwhile, the carboxyl group can adsorb Sn 2+ in the silver ammonia solution to catalyze the reduction of silver ammonia ions to generate elemental silver, and silver is chemically plated on the surface of the microspheres;

[0113] (4) The reaction liquid in which the chemical plating is completed in step (3) is filtered by using a filter screen with a pore size of 1um to remove nanoscale metal particles and waste liquid in the plating solution, the conductive silver spheres filtered out are cleaned by using anhydrous ethanol and pure water alternately by centrifugation, and drying is performed at 60 DEG C to complete collection.

[0114] The embodiment of the application omits the activation step and directly uses Sn 2+ to catalyze the reduction of silver ammonia ions to generate elemental silver, and the reason is that Sn 2+ plays a role of catalyst and reducing agent in the silver mirror reaction, promotes the silver mirror reaction, and the introduction of Pd 2+ in the activation step competes with silver ammonia ions for electrons in the silver mirror reaction, and destroys the metal silver deposition process. Figure 5 As shown in the scanning electron microscope image of the conductive microspheres prepared in the embodiment, the conductive microspheres prepared in the embodiment have good morphology, and the phenomena of microsphere breakage, shrinkage and abnormality basically do not occur, and the probability of microsphere breakage, shrinkage and abnormality prepared in the embodiment is less than 2%, and the CV value of the microspheres is less than 5%.

[0115] Embodiment 3: A method for preparing conductive microspheres based on microfluidic control is provided, and specifically, conductive gold microspheres are prepared, and the method comprises the following contents:

[0116] The surface of the conductive nickel microspheres prepared in embodiment 1 is reduced and plated with gold, specifically, 1g of the conductive nickel microspheres prepared in embodiment 1 is taken, 20ml of 1wt% chloroauric acid is added, and stirring is performed at 200rpm for 1h to perform displacement reaction, and conductive gold microspheres are obtained.

[0117] As shown in the scanning electron microscope image of the conductive microspheres prepared in the embodiment, the conductive microspheres prepared in the embodiment have good morphology, and the phenomena of microsphere breakage, shrinkage and abnormality basically do not occur, and the probability of microsphere breakage, shrinkage and abnormality prepared in the embodiment is less than 2%, and the CV value of the microspheres is less than 5%. Figure 6The image shown is a scanning electron microscope (SEM) image of the conductive gold spheres prepared in this embodiment. The conductive microspheres prepared in this embodiment have good morphology, and there are basically no phenomena of microsphere breakage, shrinkage, or anomaly. Statistical analysis shows that the probability of breakage, shrinkage, and anomaly of the microspheres prepared in this embodiment is <2%, and the microsphere CV value is <5%.

[0118] Example 4: A method for preparing conductive microspheres based on microfluidics is provided, specifically for preparing conductive gold spheres, including the following:

[0119] Gold was reduced and plated on the surface of the conductive silver balls prepared in Example 2. Specifically, 1g of the conductive silver balls prepared in Example 2 was taken, 20ml of chloroauric acid with a concentration of 1wt% was added, and the mixture was stirred at 200rpm for 1h to carry out a displacement reaction, thereby obtaining conductive gold balls.

[0120] like Figure 7 The image shown is a scanning electron microscope (SEM) image of the conductive gold spheres prepared in this embodiment. The conductive microspheres prepared in this embodiment have good morphology, and there are basically no phenomena of microsphere breakage, shrinkage, or anomaly. Statistical analysis shows that the probability of breakage, shrinkage, and anomaly of the microspheres prepared in this embodiment is <2%, and the microsphere CV value is <5%.

[0121] Example 5: A method for preparing conductive microspheres based on microfluidics is provided, specifically for preparing conductive nickel spheres of different polymers, including the following:

[0122] (1) Material preparation

[0123] Internal phase: 50wt% styrene, 35wt% methacrylate, 5wt% divinylbenzene, 5wt% amino-modified p-styrene, 5wt% AIBN;

[0124] External phase: a polyvinyl alcohol solution of PdCl2 and HCl, with PdCl2 concentration of 0.01 mol / L, HCl concentration of 0.2 mol / L, and polyvinyl alcohol concentration of 1%.

[0125] Electroless nickel plating solution: 0.1M nickel sulfate, 0.08M sodium citrate, 0.12M sodium acetate, 0.5M sodium hypophosphite, pH 5.5.

[0126] (2) Use microfluidics to prepare droplet microspheres so that the external phase and the internal phase flow out at the same time. The flow ratio of the internal phase to the external phase is 1:10. The external phase shears the internal phase to form microdroplets.

[0127] (3) The droplet microspheres generated in step (2) were directly received using a chemical nickel plating solution at a temperature of 70°C and stirred continuously at 200 rpm for 8 hours. AIBN polymerization was initiated at 70°C to generate carboxylated polystyrene. Simultaneously, the carboxyl groups adsorbed Pd from the droplets. 2+In the plating nickel liquid, sodium hypophosphite is reduced to Pd point position, and nickel ions are catalytically reduced to nickel metal layer on the surface of the microspheres.

[0128] (4) The reaction solution in which the electroless plating is completed in step (3) is filtered by using a filter screen with a pore size of 1 μm to remove the nanoscale metal particles and waste liquid in the plating solution, and the filtered conductive nickel spheres are cleaned by using anhydrous ethanol and pure water alternately by centrifugation, dried at 60°C, and collected.

[0129] As shown in FIG. 1, it is a scanning electron microscope image of the conductive microspheres prepared in this embodiment. The conductive microspheres prepared in this embodiment have good morphology, and the phenomena of microsphere breakage, shrinkage and abnormality basically do not occur. Through statistics, the probability of breakage, shrinkage and abnormality of the microspheres prepared in this embodiment is <2%, and the CV value of the microspheres is <5%. Figure 8

[0130] Embodiment 6: A method for preparing conductive microspheres based on microfluidics is provided, specifically for preparing conductive nickel spheres, which includes the following contents:

[0131] (1) Material preparation

[0132] Inner phase: 89wt% styrene, 1wt% divinylbenzene, 5wt% acrylic acid, 5wt% AIBN;

[0133] Outer phase: PdCl2 and HCl polyvinyl alcohol solution, PdCl2 concentration is 0.01 mol / L, HCl concentration is 0.2 mol / L, polyvinyl alcohol concentration is 1%;

[0134] Electroless nickel plating solution: 0.1M nickel sulfate, 0.08M sodium citrate, 0.12 sodium acetate, 0.5M sodium hypophosphite, pH value is 5.5.

[0135] (2) Using microfluidics to prepare droplet microspheres, the outer phase and the inner phase flow out at the same time, the flow rate ratio of the inner phase to the outer phase is 1:10, and the outer phase shears the inner phase to form microdroplets.

[0136] (3) Using pure water to receive the droplet microspheres generated in step (2), under the condition of heating at 60°C, stirring at 200 rpm for 2h, and washing and centrifuging with pure water for 3 times, carboxylated microspheres with Pd 2+ adsorbed on the surface are obtained; 1g of the carboxylated microspheres with Pd 2+ adsorbed on the surface are placed in the electroless nickel plating solution, the temperature is 60°C, and the stirring is continuously carried out at 200 rpm for 8h, and nickel ions are reduced to a nickel metal layer on the surface of the microspheres.

[0137] (4) The reaction solution in which the electroless plating is completed in step (3) is filtered by using a filter screen with a pore size of 1 μm to remove the nanoscale metal particles and waste liquid in the plating solution, and the filtered conductive nickel spheres are cleaned by using anhydrous ethanol and pure water alternately by centrifugation, dried at 60°C, and collected. ​

[0138] As shown in Figure 9 The scanning electron micrograph of the conductive microspheres prepared in this example is shown in the figure. The conductive microspheres prepared in this example have good morphology, and the phenomena of microsphere breakage, shrinkage and abnormality basically do not occur. The probability of microsphere breakage, shrinkage and abnormality prepared in the example of the present application is <2%, and the CV value of the microspheres is <5%.

[0139] Example 7: A method for preparing conductive microspheres based on microfluidics is provided, specifically for preparing conductive nickel spheres. The difference from Example 1 is that the internal phase formula is a linear aminomethyl polystyrene dichloromethane solution, and the mass concentration of aminomethyl polystyrene is 10%, and the remaining steps remain unchanged.

[0140] As shown in Figure 10 The scanning electron micrograph of the conductive microspheres prepared in this example is shown in the figure. The conductive microspheres prepared in this example have good morphology, and the phenomena of microsphere breakage, shrinkage and abnormality basically do not occur. The probability of microsphere breakage, shrinkage and abnormality prepared in the example of the present application is <2%, and the CV value of the microspheres is <5%.

[0141] Example 8: A method for preparing conductive microspheres based on microfluidics is provided, specifically for preparing conductive nickel spheres. The difference from Example 1 is that the internal phase is 89.9wt% styrene, 0.1wt% isoprene, 5wt% acrylic acid, and 5wt% AIBN, and the remaining steps remain unchanged.

[0142] As shown in Figure 11 The scanning electron micrograph of the conductive microspheres prepared in this example is shown in the figure. The conductive microspheres prepared in this example have good morphology, and the phenomena of microsphere breakage, shrinkage and abnormality basically do not occur. The probability of microsphere breakage, shrinkage and abnormality prepared in the example of the present application is <2%, and the CV value of the microspheres is <5%.

[0143] Example 9: A method for preparing conductive microspheres based on microfluidics is provided, specifically for preparing conductive nickel spheres. The difference from Example 1 is that the internal phase is 85wt% styrene, 20wt% ethylene glycol dimethyl acrylate, 5wt% acrylic acid, and 5wt% AIBN, and the remaining steps remain unchanged.

[0144] As shown in Figure 12 The scanning electron micrograph of the conductive microspheres prepared in this example is shown in the figure. The conductive microspheres prepared in this example have good morphology, and the phenomena of microsphere breakage, shrinkage and abnormality basically do not occur. The probability of microsphere breakage, shrinkage and abnormality prepared in the example of the present application is <2%, and the CV value of the microspheres is <5%.

[0145] Comparative Example 1: Conductive nickel spheres were prepared by sulfuric acid sulfonation chemical plating, including the following contents:

[0146] (1) using concentrated sulfuric acid to sulfonate polystyrene microspheres: take 1g of polystyrene microspheres, add 20mL of concentrated sulfuric acid, ultrasonic dispersion at 40Hz for 10min, then stir at 60℃ and 200rpm for 2h, and wash with pure water for 5 times; using concentrated sulfuric acid to sulfonate polystyrene microspheres will cause the microspheres to shrink and break (see Figure 13

[0147] (2) add 1g of sulfonated microspheres to 20mL of a mixture of SnCl2 with a concentration of 0.01mol / L and HCl with a concentration of 0.2mol / L, stir at 200rpm for 30min, and centrifugal wash with pure water for 3 times to obtain sensitized microspheres.

[0148] (3) add the sensitized microspheres in step (2) to 20mL of a mixture of PdCl2 with a concentration of 0.01mol / L and HCl with a concentration of 0.2mol / L, stir at 200rpm for 1h, and centrifugal wash with pure water for 3 times to obtain activated microspheres.

[0149] (4) disperse the activated polymer microspheres in step (3) in 50mL of electroless plating solution, the composition of the electroless nickel plating solution is 0.1M nickel sulfate, 0.08M sodium citrate, 0.12 sodium acetate, and 0.5M sodium hypophosphite, and the pH value is 5.5; stir at 40℃ for 1h, and wash and dry to obtain conductive microspheres with a nickel layer on the surface.

[0150] The scanning diagram of the conductive nickel spheres prepared by sulfuric acid sulfonation and electroless plating is shown in Figure 14 , Figure 15 and Figure 16 , the conductive nickel spheres have serious shrinkage, and the total probability of microsphere shrinkage and breakage is >50% after statistics.

[0151] Overall, the conductive microspheres with a size of 10~2mm can be prepared by the embodiment of the present application, the probability of breakage, shrinkage and deformation of the conductive microspheres is <2%, and the CV value of the microspheres is <5%, which avoids the breakage, shrinkage and deformation of the microspheres during sulfonation modification using finished microspheres.

[0152] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.​

Claims

1. A method for the preparation of electrically conductive microspheres based on microfluidics, characterized by, The method comprises the following steps: S1: preparing materials, the materials comprising an inner phase, an outer phase and a chemical plating solution; S2: preparing the inner phase and the outer phase into droplet microspheres using microfluidic control technology; S3: receiving the droplet microspheres and performing redox chemical plating in the chemical plating solution to form conductive microspheres; S4: cleaning and collecting the conductive microspheres; the outer phase comprising an activation solution and / or a sensitization solution, and the chemical plating solution comprising at least one of a chemical plating nickel solution, a chemical plating silver solution and a chemical plating gold solution.

2. The method for fabricating conductive microspheres based on microfluidic control according to claim 1, wherein, The inner phase comprises a solute and a solvent, the solute comprising a functionalized polymer, and the solvent comprising a volatile organic solvent; the functionalized group of the functionalized polymer comprising at least one of an amino group, a hydroxyl group, a mercapto group, a carboxyl group, an ester bond, a sulfonic acid group, a chloromethyl group and an aminomethyl group; the polymer structure of the functionalized polymer comprising at least one of polystyrene, polyacrylate and polyacrylamide; the volatile organic solvent comprising at least one of acetone, cyclohexanone, methyl ethyl ketone, chloroform, dimethylbenzene, toluene, carbon tetrachloride, ethyl acetate and tetrahydrofuran.

3. The method for fabricating conductive microspheres based on microfluidics according to claim 1, wherein, The inner phase comprises a polymer monomer, a functionalized monomer, an initiator and a crosslinking agent; the polymer monomer comprising at least one of an alkenyl aromatic monomer, an acrylate monomer, an acrylic monomer, vinyl acetate and an acrylamide monomer; the functionalized monomer comprising a monomer with both a double bond and a functionalized functional group, the functionalized functional group comprising at least one of an amino group, a hydroxyl group, a mercapto group, a carboxyl group, an ester bond, a sulfonic acid group, a chloromethyl group and an aminomethyl group; the initiator comprising at least one of azobisisobutyronitrile, azobisisoheptyl nitrile, dibenzoyl peroxide, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide and dicumyl peroxide; the crosslinking agent comprising at least one of divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, isoprene and butadiene.

4. The method for fabricating conductive microspheres based on microfluidic according to claim 3, characterized in that, The double bond in the functionalized monomer is a carbon-carbon double bond, and the functionalized functional group is a carboxyl group; the amount of the crosslinking agent being 0.1-20wt%.

5. The method for fabricating conductive microspheres based on microfluidics according to claim 1, wherein, The outer phase is an activation solution, and the chemical plating solution is a chemical plating nickel solution; the activation solution comprising a non-ionic polymer surfactant mixed solution of PdCl2 and HCl; the concentration of the PdCl2 being 0.001-0.05mol / L, and the concentration of the HCl being 0.1-5mol / L; the chemical plating nickel solution comprising 0.01-1M nickel sulfate, 0.01-0.1M sodium citrate, 0.01-0.2M sodium acetate and 0.01-5M sodium hypophosphite, and the pH value of the chemical plating nickel solution being 4-6; the non-ionic polymer surfactant comprising an aqueous solution with at least one of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone and hydroxyethyl cellulose as a solvent, and the concentration of the non-ionic polymer surfactant being 0.1-3wt%.

6. The method for fabricating conductive microspheres based on microfluidics according to claim 1, wherein, The outer phase is a sensitization solution, and the chemical plating solution is a chemical plating silver solution; the sensitization solution comprising a non-ionic polymer surfactant mixed solution of SnCl2 and HCl; The concentration of SnCl2 is 0.001-0.05 mol / L, and the concentration of HCl is 0.1-5 mol / L. The chemical silver plating solution comprises a silver-ammonia solution, which is prepared by adding 1-10 wt% ammonia water drop by drop into 1-10 wt% silver nitrate solution until the generated AgOH precipitate just dissolves; The non-ionic polymer surfactant comprises a water solution of at least one of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone and hydroxyethyl cellulose, and the concentration of the non-ionic polymer surfactant is 0.1-3 wt%.

7. The method for fabricating conductive microspheres based on microfluidics according to claim 1, wherein, The preparation method of the conductive microspheres in S3 comprises receiving liquid droplet microspheres by using a chemical plating solution, stirring at a speed of 100-400 rpm for 0.5-12 h under heating conditions of 40-80 ℃, and simultaneously achieving solidification and chemical plating of the microspheres in the chemical plating solution; The cleaning and collecting in S4 comprises filtering the reaction liquid in which the chemical plating is completed in S3 by using a filter screen with a pore size of 0.6-1.0 μm, cleaning the filtered conductive microspheres by using anhydrous ethanol and pure water alternately, and then drying and collecting.

8. The method for fabricating conductive microspheres based on microfluidics according to claim 1, wherein, The preparation method of the conductive microspheres in S3 comprises receiving liquid droplet microspheres by using pure water, achieving solidification and activation of the microspheres under heating conditions of 40-80 ℃ at a speed of 100-400 rpm for 0.5-12 h, transferring the microspheres into a chemical plating solution after centrifugal cleaning at least twice by using pure water, and then achieving chemical plating; The cleaning and collecting in S4 comprises filtering the reaction liquid in which the chemical plating is completed in S3 by using a filter screen with a pore size of 0.6-1.0 μm, cleaning the filtered conductive microspheres by using anhydrous ethanol and pure water alternately, and then drying and collecting.

9. Use of electrically conductive microspheres prepared on the basis of microfluidics, which are prepared by the method according to any one of claims 1 to 8, characterized in that, The conductive microspheres are used in at least one of the fields of biomedicine, biological detection, pollution treatment, electronic devices and industrial materials.

Images