Method for preparing multifunctional nanometer shell-core particles based on anti-solvent self-assembly strategy and application of multifunctional nanometer shell-core particles

Abstract

The invention discloses a method for preparing multifunctional nanometer shell-core particles based on an anti-solvent self-assembly strategy and application of the multifunctional nanometer shell-core particles. Oligomer containing an ammonium phosphate structure is prepared through condensation polymerization, and uniform and stable nanometer emulsion is prepared to serve as a core material through a method that solute is separated out from a good solvent to a poor solvent; carrying out hydrolytic condensation on tetraethyl orthosilicate under an alkaline condition to form small-particle-size nano silicon dioxide sol as a shell material; the core material and the shell material are stirred and mixed, so that silicon dioxide is loaded on the surface of the emulsion to form nano particles with a shell-core structure, and the multifunctional nano shell-core particles are obtained after freeze drying. The core-shell particle has a pore structure and a high specific surface area, after the core-shell particle is compounded with liquid silicone rubber vulcanized at room temperature, the mechanical property and the flame retardant property of the organic silicone elastomer can be remarkably improved, and compared with a traditional filler, the core-shell particle enhances the elastomer and avoids reduction of the elongation at break at the same time, and the core-shell particle shows a wide application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of polymer composite materials, and particularly relates to a method for preparing multifunctional nanoshell-core particles based on an anti-solvent self-assembly strategy and its applications. Background Art

[0002] Liquid silicone rubber (LSR) has been widely used in the fields of hydrophobic modification of hydrophilic material surfaces and electronic component encapsulation due to its excellent properties such as low surface energy, easy processing and molding, and resistance to high and low temperatures. With the development of microelectronic devices towards miniaturization, light weight, high integration, electrical insulation, excellent heat dissipation and flame retardancy, higher requirements are put forward for the properties of elastomer materials. Among them, room temperature vulcanized silicone rubber (RTV), a polymer composed of hydroxyl-terminated dimethylsiloxane (PDMS-OH) and methyltrimethoxysilane (MTMS), has attracted wide attention in academia and industry due to the high bond energy of its Si-O-Si chain, showing excellent mechanical flexibility, high temperature stability and water resistance. However, LSR elastomers generally have problems of weak mechanical properties and poor flame retardancy, which limit their applications in high-performance fields. Therefore, it is urgent to improve their mechanical properties and flame retardant characteristics through composite modification.

[0003] At present, the preparation method of shell-core particles mainly uses monomers to form a core through free radical emulsion polymerization, and then adds a second monomer to polymerize to form a shell, finally obtaining shell-core particles. For example, the team of Wei Yi from Donghua University prepared two types of shell-core particles, hard-soft and soft-hard, using methyl methacrylate and butyl acrylate monomers to fill epoxy resin, significantly improving the toughness of epoxy resin (Impressive epoxy toughening by a structure-engineered core / shell polymer nanoparticle). However, these methods have problems such as complex processes, easy agglomeration, large amounts of emulsifiers used, difficult control of reaction rates, and difficult regulation of shell layer thickness and structure, and organic solvents need to be used, increasing costs and environmental burdens.

[0004] In addition, the shell-core particles prepared by traditional methods have a smooth surface and low specific surface area, with weak interfacial interaction with the matrix material, limited enhancement effect, and single function, only being able to improve mechanical properties. Summary of the Invention

[0005] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Simplifications or omissions may be made in this part, as well as in the abstract and title of the present application, to avoid obscuring the purpose of this part, the abstract and the title, and such simplifications or omissions shall not be used to limit the scope of the present invention.

[0006] In view of the above and / or problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the object of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing multifunctional nano core-shell particles based on an anti-solvent self-assembly strategy.

[0008] To solve the above technical problems, the present invention provides the following technical solutions: A method for preparing multifunctional nano core-shell particles based on an anti-solvent self-assembly strategy, including,

[0009] Preparing oligomer PAPTS: Slowly drop N-aminoethyl-γ-aminopropyltrimethoxysilane into water, and carry out a condensation reflux reaction to obtain oligomer PAPTS;

[0010] Preparing siloxane oligomer PPAP with ammonium phosphate salt: Drop phosphoric acid into PAPTS at a molar ratio of amine group to phosphoric acid of 1:1, carry out a condensation reflux reaction, and dry to remove the water solvent to generate siloxane oligomer PPAP with ammonium phosphate salt;

[0011] Preparing nanoemulsion C: Dissolve PPAP in water to prepare solution A; Add an emulsifier to ethanol to prepare solution B; Quickly pour solution A into solution B under stirring to obtain a homogeneous and stable nanoemulsion C;

[0012] Preparing nano core-shell particles: Pour emulsion C into nano-silica sol, stir at room temperature to make nano-silica fully loaded on the surface of emulsion microspheres to form a core-shell structure;

[0013] Let it stand for precipitation, pour off the supernatant, add deionized water to reduce the ethanol concentration, freeze with liquid nitrogen and then freeze-dry to obtain nano core-shell particles with a porous structure.

[0014] As a preferred embodiment of the method of the present invention, wherein: in the preparation of oligomer PAPTS, the ratio of N-aminoethyl-γ-aminopropyltrimethoxysilane to water is 22.2 g: 12 ml, the dropping rate is 1 drop / second, the condensation reflux temperature is 90 °C, and the reflux reaction time is 12 h.

[0015] As a preferred embodiment of the method of the present invention, wherein: in the preparation of siloxane oligomer PPAP with ammonium phosphate salt, the condensation reflux temperature is 90 °C and the reflux reaction time is 12 h.

[0016] As a preferred embodiment of the method of the present invention, wherein: in solution A, the ratio of PPAP to water is 10 g: 100 ml; in solution B, the ratio of the emulsifier to ethanol is 0.3 g: 100 ml.

[0017] As a preferred embodiment of the method of the present invention, wherein: the volume ratio of solution A to solution B is 6:2, 5:3, 4:4, 3:5 or 2:6.

[0018] As a preferred embodiment of the method of the present invention, wherein: the preparation method of the nano-silica sol includes,

[0019] Dissolve 8 g of tetraethyl orthosilicate in a mixed solution of 100 ml of ethanol and 40 ml of water, add 750 - 1500 μl of ammonia water dropwise, and stir at 40 °C and 500 r / min for 6 hours to obtain nano-silica sol.

[0020] As a preferred embodiment of the method of the present invention, wherein: the mass ratio of tetraethyl orthosilicate to PPAP is 4:5.

[0021] Another object of the present invention is to overcome the deficiencies in the prior art and provide a multifunctional nano-core-shell particle prepared by a method for preparing multifunctional nano-core-shell particles based on an anti-solvent self-assembly strategy.

[0022] Another object of the present invention is to overcome the deficiencies in the prior art and provide an application of nano-core-shell particles in the preparation of silicone elastomers, including,

[0023] Mix 25 g of 15000 cst hydroxyl-terminated siloxane, 1 g of methyltrimethoxysilane, 0.25 g of dibutyltin dilaurate with nano-core-shell particles, stir at 500 r / min for 5 minutes, pour into a polytetrafluoroethylene mold after evacuating, and cure at room temperature;

[0024] Wherein, the addition amount of nano-core-shell particles is 0.1 - 100 phr based on 100 g of hydroxyl-terminated silicone oil.

[0025] Advantages of the present invention:

[0026] (1) Simple process, controllable morphology: The present invention ingeniously utilizes the transformation characteristics from a good solvent (water) to a poor solvent (ethanol) to prepare nano-emulsions, and forms a core-shell structure through the adsorption of large particles on small particles, successfully preparing spherical nano-particles with uniform particle size and full shape. The process is simple and the morphology is controllable.

[0027] (2) High specific surface area, strong interfacial interaction: The prepared nano-core-shell particles have a high specific surface area and a porous structure, can form a strong interfacial interaction with the silicone elastomer matrix, and significantly improve the mechanical properties of the composite material.

[0028] (3) Multifunctional integration: The porous nano core-shell particles prepared by the present invention can not only enhance the mechanical properties (such as strength and stretchability) of silicone elastomers, but also endow them with excellent flame retardant properties by introducing phosphorus and nitrogen elements, realizing the synergistic improvement of mechanical properties and flame retardant properties, and breaking through the technical bottleneck of the single function of traditional fillers. Description of the Drawings

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. 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. Among them:

[0030] Figure 1 It is a process flow chart for the preparation of the core-shell particles of the present invention.

[0031] Figure 2 It is a diagram showing the influence of the preparation conditions on the particle size of the nanoemulsion of the present invention. Among them, (a) shows the influence of the volume of ammonia water on the particle size of silica, (b) shows the influence of the volume ratio of ethanol to water of the particles on the particle size of the emulsion, and (c) shows the influence of the amount of emulsifier on the particle size of the nanoemulsion.

[0032] Figure 3 It is (a) the nanoemulsion of PPAP, and (b) the nanoemulsion of PPAP standing for 5 h.

[0033] Figure 4 It is a diagram showing the influence of the mass ratio of PPAP to TEOS on the core-shell particles.

[0034] Figure 5 It is (a) the scanning electron microscope and (b) the transmission electron microscope of the core-shell nanoparticles.

[0035] Figure 6 It is (a) the specific surface area and pore size and (b) the particle size distribution of the nano core-shell particles.

[0036] Figure 7 It is (a) the tensile curve, (b) the tensile strength, and (c) the elongation at break of the silicone elastomer filled with 0 phr, 25 phr, 50 phr, 75 phr, and 100 phr of the core-shell particles.

[0037] Figure 8 It is (a) the limiting oxygen index, (b) the thermogravimetry, and (c) the weight loss rate of the silicone composite elastomer with 0 phr, 25 phr, 50 phr, 75 phr, and 100 phr.

[0038] Figure 9 It is the influence of excessive ammonia water on the success of the preparation of the core-shell particles.

[0039] Figure 10 Effect of a small amount of emulsifier on the particle size distribution of core-shell particles.

[0040] Figure 11 Effect of different drying methods on the success of preparing core-shell particles. Specific embodiments

[0041] To make the above objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below in conjunction with the embodiments of the specification.

[0042] Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0043] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation manner of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they separate or selectively exclusive embodiments from other embodiments.

[0044] The object of the present invention is to provide a nanoparticle with a porous core-shell structure and its preparation method, which are used to significantly improve the mechanical properties and flame retardancy of silicone elastomers. The present invention cleverly utilizes the property that ammonium phosphate salt dissolves in a good solvent (water) and precipitates in a poor solvent (ethanol) to prepare nano-scale stable and uniform emulsion particles; at the same time, tetraethyl orthosilicate is hydrolyzed under alkaline conditions to generate nano-scale silica sol, which is adsorbed and loaded on the surface of the emulsion particles to form a nano-scale core-shell structure. By reducing the ethanol concentration and combining with the freeze-drying process, core-shell particles with a porous structure are finally obtained. This preparation process is simple and does not require harsh reaction conditions, and spherical and plump nanoparticles with uniform particle size can be obtained.

[0045] The prepared core-shell particles have a high specific surface area and a porous structure, and can form good interfacial interactions with the matrix material; at the same time, the phosphorus and nitrogen elements in the core material endow it with excellent flame retardancy. Adding this filler to silicone elastomers can significantly improve the strength, stretchability, and flame retardancy of the composite material. Compared with the elastomer without adding the filler, the performance is significantly improved, which has important application value.

[0046] The experimental raw materials used in the embodiments of the present invention are shown in Table 1.

[0047] Table 1

[0048]

[0049] Example 1

[0050] (1) Preparation of nano-silica:

[0051] Weigh 10 g of TEOS and dissolve it in a mixed solution of 100 ml of ethanol and 40 ml of water. Add 1500 ul, 1250 ul, 1000 ul, and 750 ul of ammonia water, and stir at 40 °C and 500 r / min for 6 hours to obtain a nano-silica suspension.

[0052] (2) Measurement of the particle size of nano-silica

[0053] Use a Malvern laser particle size analyzer to measure the particle size and distribution of the emulsion. The test results are as Figure 2 (a) shown. The particle size decreases with the increase in the volume of ammonia water. When the volume of ammonia water is 750 ul, the particle size of silica is 34.5 ± 8.1 nm.

[0054] Example 2

[0055] (1) Preparation of PPAP:

[0056] Take 22.2 g of PAPTS in a 250 ml three-necked flask, add 12 ml of H2O dropwise (1 drop per second) under stirring at 500 r / min, reflux at 90 °C for 12 h, then add 19.8 g of phosphoric acid dropwise (1 drop per second), and continue to react for 12 h. Remove the solvent and dry to obtain PPAP.

[0057] (2) Preparation of nano-emulsion:

[0058] Take 10 g of PPAP and dissolve it in 150 ml, 125 ml, 100 ml, 75 ml, and 50 ml of water respectively to obtain solutions A1, A2, A3, A4, and A5;

[0059] Measure 50 ml, 75 ml, 100 ml, 125 ml, and 150 ml of ethanol as solutions B1, B2, B3, B4, and B5, without adding the emulsifier Triton;

[0060] Quickly pour solution A into the corresponding solution B under stirring at 500 r / min to prepare emulsions C1, C2, C3, C4, and C5, and stir for 10 min (pour A into B to get C).

[0061] (2) Measurement of the particle size of nano-emulsion

[0062] Use a Malvern laser particle size analyzer to measure the particle size and distribution of the emulsion. The test results are as Figure 2 (b) shown. The particle size of the emulsion gradually decreases and tends to be stable with the increase in the proportion of ethanol, and the outer periphery of the distribution becomes narrower.

[0063] When the volume ratio of water to ethanol is 1:1, the particle size and distribution of the emulsion have stabilized. For the convenience of subsequent freeze-drying, the volume ratio of water to ethanol of 1:1 is comprehensively considered.

[0064] Example 3

[0065] (1) Preparation of nanoemulsion

[0066] Take 10 g of PPAP and dissolve it in 100 ml of water respectively to obtain solutions A1, A2, A3, A4, and A5;

[0067] Measure 5 portions of 100 ml of ethanol and add 0.1 g, 0.2 g, 0.3 g, 0.4 g, and 0.5 g of Triton respectively to obtain solutions B1, B2, B3, B4, and B5;

[0068] Quickly pour the A solution into the corresponding B solution under stirring at 500 r / min to prepare emulsions C1, C2, C3, C4, and C5, and stir for 10 min.

[0069] (2) Measurement of the particle size of nanoemulsion

[0070] Use a Malvern laser particle size analyzer to test the particle size and distribution of the emulsion. The test results are as Figure 2 (c) shown. The particle size first decreases and then increases with the increase of the emulsifier, and the distribution range also changes accordingly, reaching the best at a PPAP mass fraction of 3%.

[0071] When 3% of the emulsifier is added, the formed emulsion is as Figure 3 shown. Even after standing for 5 h, the state of the emulsion remains stable.

[0072] Example 4

[0073] (1) Preparation of nanoshell-core particles:

[0074] Take 10 g of PPAP and dissolve it in 100 ml of water to obtain solution A;

[0075] Weigh 0.3 g of Triton and dissolve it in 100 ml of ethanol to prepare solution B;

[0076] Weigh 10 g, 8 g, and 6 g of TEOS and dissolve them in a mixed solution of 100 ml of ethanol and 40 ml of water. Add 750 μl of ammonia water, stir at 40 °C and 500 r / min for 6 hours to obtain a nano-silica suspension;

[0077] Quickly pour the A solution into the B solution under stirring at 500 r / min to prepare emulsion C, and stir for 10 min;

[0078] At room temperature, pour emulsion C into the silica suspension at 500 r / min for 8 h, let it settle naturally for 24 h, pour off the supernatant, add a certain amount of water, freeze it with liquid nitrogen, and freeze-dry to obtain nanospheres with a core-shell structure.

[0079] (2) Characterization of morphology

[0080] Use transmission electron microscopy to observe the morphology of the nanospheres with core-shell structure, as Figure 4 shown. When the mass ratio of PPAP to TEOS is 5:5, the core-shell particles prepared have an overly thick shell due to the excess of the shell material, and the granularity is not obvious. When the ratio is 5:3, the shell material cannot completely coat the emulsion, and emulsion leakage leads to serious agglomeration between particles. When the ratio is 5:4, the prepared core-shell particles have obvious granularity.

[0081] Example 5

[0082] (1) Preparation of nanospheres with core-shell structure:

[0083] Dissolve 10 g of PPAP in 100 ml of water to obtain solution A;

[0084] Weigh 0.3 g of Triton and dissolve it in 100 ml of ethanol to prepare solution B;

[0085] Weigh 8 g of TEOS and dissolve it in a mixed solution of 100 ml of ethanol and 40 ml of water, add 750 μl of ammonia water, and stir at 40 °C and 500 r / min for 6 h to obtain a silica suspension;

[0086] Quickly pour solution A into solution B under stirring at 500 r / min to prepare emulsion C, and stir for 10 min;

[0087] At room temperature, pour emulsion C into the silica suspension at 500 r / min for 8 h, let it settle naturally for 24 h, pour off the supernatant, add a certain amount of water, freeze it with liquid nitrogen, and freeze-dry to obtain nanospheres with a core-shell structure. For the process flow chart, see Figure 1 .

[0088] (2) Characterization of morphology

[0089] Use scanning electron microscopy and transmission electron microscopy to observe the morphology of the nanospheres with core-shell structure, as Figure 5 shown. The prepared nanospheres with core-shell structure have obvious granularity, and the core-shell structure is clear at a glance. The particle size distribution of the core-shell particles is 383 ± 66 nm.

[0090] (3) Specific surface area measurement

[0091] Use a specific surface area and porosity tester to measure the specific surface area and porosity of the nanospheres with core-shell structure, as Figure 6 shown. The nanospheres show a relatively high specific surface area of 29.532 m2 / g, and at the same time, the nanoparticles also exhibit a certain void structure.

[0092] Example 6

[0093] Application of the porous nanoshell-core particle liquid in the preparation of room temperature vulcanized silicone rubber:

[0094] (1) Preparation of the organosilicon elastomer composite:

[0095] Weigh 50 g of hydroxy-terminated siloxane, 0 g, 12.5 g, 25 g, 37.5 g, 50 g of nanoshell-core particles and a certain amount of n-heptane, mix them and stir at 800 r / min for 20 min;

[0096] Add 2 g of methyltrimethoxysilane and 0.2 g of dibutyltin dilaurate, stir for 5 min, remove the bubbles under vacuum, pour them into a polytetrafluoroethylene mold, and crosslink at room temperature for 12 hours to obtain 0 phr, 25 phr, 50 phr, 75 phr, 100 phr organosilicon elastomer composites.

[0097] (2) Mechanical property testing:

[0098] Perform all mechanical tests on the organosilicon elastomer composite using a universal testing tensile machine.

[0099] The test results of the tensile stress-strain curve are as Figure 7 shown. With the addition of the nanoshell-core particles, the mechanical properties of the composite organosilicon elastomer increase accordingly. The tensile strength of the organosilicon elastomer without filled nanoshell-core particles (0 phr) is 0.33 ± 0.02 MPa, and the fracture strain is 294 ± 45%.

[0100] The tensile strength of the 75 phr composite organosilicon elastomer is 1.21 ± 0.05 MPa, and the fracture strain is 403 ± 22%.

[0101] Reinforcement and toughening mechanism of the nanoshell-core particles in the composite organosilicon elastomer: Due to the high specific surface area of the shell-core particles, the similar structure to the Si-O bond of the silicone rubber, and the porous structure, there is a good interfacial interaction between the shell-core particle liquid and the silicone rubber, which can promote the stress transfer during the stretching process, thus improving the strength of the composite organosilicon elastomer. Thanks to the porous structure of the nanoshell-core particles, the molecular chains of the silicone elastomer can pass through and form a movable buckle that restricts multiple molecular chains. When stretched, the molecular chains under this physical constraint can move, thus increasing the tensile strain of the composite organosilicon elastomer.

[0102] (3) Limiting oxygen index

[0103] The limiting oxygen index of the silicone elastomer composite material was tested using a limiting oxygen index tester.

[0104] The test results of the limiting oxygen index are as Figure 8 (a) shown. The limiting oxygen index of the silicone elastomer without filled nano-core-shell particles at 0 phr was 19.6%. With the addition of the core-shell particles, the flame retardancy of the composite silicone rubber material gradually increased and reached a 28% flame retardant effect at 75 phr. At high temperatures, the phosphorus element in the core material of the nano-core-shell particles catalyzes the carbonization of the methyl groups on the side chains of the silicone rubber and the main chain of the silicone rubber, forming a dense silica layer, which plays the effect of condensed-phase flame retardancy. At the same time, the nitrogen element turns into non-combustible ammonia gas when heated, reducing the concentration of combustible gases around, and then playing the effect of gas-phase flame retardancy. The condensed-phase and gas-phase flame retardancy greatly improve the flame retardancy of the nano-core-shell particles on the silicone rubber composite material.

[0105] (4) Thermogravimetric test

[0106] The thermal stabilities of the silicone rubber composite materials at 0 phr, 25 phr, 50 phr, 75 phr, and 100 phr were determined using a thermogravimetric thermal analyzer under a nitrogen atmosphere.

[0107] As Figure 8 (b) and 8(c) shown, for 0 phr, there was an obvious thermal degradation stage at 350 - 550 °C, and two stages of the maximum decomposition rate appeared. This is the result of the prior depolymerization of the methyl groups on the side chains of the silicone rubber main chain and then the depolymerization of the main chain.

[0108] In contrast, the decomposition temperature and the temperature of the maximum decomposition rate of the 25 phr, 50 phr, 75 phr, and 100 phr samples decreased slightly, and the decomposition temperature range advanced. This is because phosphorus catalyzes the rapid carbonization of the side methyl groups and the main chain at low temperatures, causing the decomposition temperature to advance, but the residual carbon content of the silicone rubber composite material increased significantly after carbonization, forming more dense protective layers. The rapidly formed carbon layer can isolate the entry of flames and combustible gases, which is beneficial for more effectively protecting the interior from further decomposition.

[0109] Comparative Example 1

[0110] The other conditions were the same as in Example 5, and the variable was the volume of ammonia water of 1250 μl. When emulsion C was poured into the silica suspension, agglomeration occurred within one minute and sedimented at the bottom of the cup, and nano-core-shell particles could not be prepared, as Figure 9 shown.

[0111] Comparative Example 2

[0112] The other conditions were the same as in Example 5, and the variable was 0.1 g of emulsifier. The prepared nano-core-shell particles had a non-uniform particle size distribution, as Figure 10 shown.

[0113] Comparative Example 3

[0114] The remaining conditions were the same as those in Example 5. Instead of using the freeze-drying method for drying, drying was carried out by baking. During the drying process of the prepared nano core-shell particles, the core material leaked and was mixed with the shell material. The preparation of the core-shell particles failed, as Figure 11 shown.

[0115] By designing a new type of multifunctional core-shell particle, the present invention not only solves the problems of complex preparation process and single function in the traditional method, but also endows the core-shell particles with dual functions of both mechanical enhancement and flame retardancy. Compared with the prior art, the core-shell particles prepared by the present invention have a high specific surface area and a pore structure, significantly enhancing the interfacial interaction with the matrix material. At the same time, by introducing flame retardant elements (such as phosphorus and nitrogen), the synergistic improvement of mechanical properties and flame retardancy is realized, providing an innovative solution for the application of liquid silicone rubber in high-performance fields.

[0116] The present invention prepared multifunctional nano core-shell particles with a high specific surface area and a porous structure through the strategy of solute precipitation from a good solvent to a poor solvent and automatic adsorption. Briefly, first, an oligomer with ammonium phosphate salt on the side chain was prepared. Then, the oligomer with ammonium phosphate salt on the side chain was dissolved in the good solvent water. Next, the aqueous solution of the oligomer was poured into the poor solvent ethanol containing an emulsifier under stirring, and the solute automatically precipitated in the poor solvent to form a stable and uniform nanoemulsion. Appropriate particle size silica nanoparticles were prepared by using ammonia water. Subsequently, the nanoemulsion was poured into the silica suspension and stirred for several hours, naturally precipitated at room temperature, the supernatant was poured off, a certain amount of water was added to reduce the ethanol concentration, and it was quickly frozen with liquid nitrogen. Finally, multifunctional nano core-shell particles with a high surface area and a porous structure were obtained by freeze-drying. Due to the high specific surface area and pore structure, the nano core-shell particles have good interfacial interaction with the liquid room temperature vulcanized silicone rubber, greatly improving the tensile strength and modulus of the silicone rubber composite material. In addition, on the one hand, the addition of the filler will reduce the reaction degree between the molecular active functional groups in the matrix material and the cross-linking agent, resulting in a decrease in the number of cross-linking points formed by chemical cross-linking and an increase in the distance between the chemical cross-linking points. On the other hand, the molecular chains of the liquid silicone rubber infiltrate through the pores of the nano core-shell particles and are bound, forming a physical cross-linking point. The bound molecular chains undergo relative slippage when subjected to external force stretching. These two reasons make the addition of the core-shell particles have the effect of enhancing the elongation at break of the silicone rubber composite material within a certain range when the silicone rubber composite material is stretched. Since the core material of the added nano core-shell particles contains phosphorus and nitrogen elements, when the silicone rubber composite material is attacked by a flame, the nitrogen element participates in the conversion to ammonia gas, reducing the concentration of combustible gases, and the phosphorus oxygen free radicals formed by the phosphorus element can catalyze the rapid carbonization of the matrix material, achieving the synergistic flame retardant effect in the gas phase and the condensed phase.

[0117] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the present invention.

Claims

1. A method for preparing multifunctional nanoshell-core particles based on an anti-solvent self-assembly strategy, characterized in that: Including, Preparing oligomer PAPTS: Slowly drop N-aminoethyl-γ-aminopropyltrimethoxysilane into water, carry out condensation reflux reaction to obtain oligomer PAPTS; Preparing siloxane oligomer PPAP with ammonium phosphate salt: Drop phosphoric acid into PAPTS at a molar ratio of amine group to phosphoric acid of 1:1, carry out condensation reflux reaction, dry to remove the water solvent to generate siloxane oligomer PPAP with ammonium phosphate salt; Preparing nanoemulsion C: Dissolve PPAP in water to prepare solution A; Add an emulsifier to ethanol to prepare solution B; Quickly pour solution A into solution B under stirring to obtain a homogeneous and stable nanoemulsion C; Preparing nano core-shell particles: Pour emulsion C into nano silica sol, stir at room temperature to make nano silica fully loaded on the surface of emulsion microspheres to form a core-shell structure; Let it stand for precipitation, pour off the supernatant, add deionized water to reduce the ethanol concentration, freeze with liquid nitrogen and then freeze-dry to obtain porous nano core-shell particles.

2. The method according to claim 1, characterized in that: In the preparation of oligomer PAPTS, the ratio of N-aminoethyl-γ-aminopropyltrimethoxysilane to water is 22.2 g:12 ml, the dropping rate is 1 drop / second, the condensation reflux temperature is 90 °C, and the reflux reaction time is 12 h.

3. The method according to claim 1, characterized in that: In the preparation of siloxane oligomer PPAP with ammonium phosphate salt, the condensation reflux temperature is 90 °C and the reflux reaction time is 12 h.

4. The method according to claim 1, wherein: In solution A, the ratio of PPAP to water is 10 g:100 ml; in solution B, the ratio of the emulsifier to ethanol is 0.3 g:100 ml.

5. The method according to claim 4, wherein: The volume ratio of solution A to solution B is 6:2, 5:3, 4:4, 3:5 or 2:

6.

6. The method according to claim 1, characterized in that: The preparation method of the nano silica sol includes, Dissolve 8 g of tetraethyl orthosilicate in a mixed solution of 100 ml of ethanol and 40 ml of water, drop 750-1500 μl of ammonia water, stir at 40 °C and 500 r / min for 6 hours to obtain nano silica sol.

7. The method according to claim 6, wherein: The mass ratio of tetraethyl orthosilicate to PPAP is 4:

5.

8. Porous nano core-shell particles prepared by the method according to any one of claims 1 to 7.

9. Use of the nano core-shell particles according to claim 8 in the preparation of silicone elastomers.

10. The application according to claim 9, wherein: Including, Mix 25 g of 15000 cst hydroxyl-terminated siloxane, 1 g of methyltrimethoxysilane, 0.25 g of dibutyltin dilaurate with the nano core-shell particles, stir at 500 r / min for 5 minutes, evacuate and then pour into a polytetrafluoroethylene mold for curing at room temperature; Among them, the addition amount of the nano core-shell particles is 0.1-100 phr based on 100 g of hydroxyl-terminated silicone oil.

Images