CN1631906A - Method for preparing monodisperse core/shell composite particle emulsion by using polystyrene coated nano silicon dioxide microspheres - Google Patents

Abstract

The invention belongs to the technical field of preparation and application of nanocomposite materials, and in particular relates to a method for preparing monodisperse core/shell composite particle emulsion by coating nano silicon dioxide spheres with polystyrene or vinyl monomer polymers. The present invention uses coupling agent methacryloyl (3-trimethoxysilane) propyl ester to modify the surface of nano-silica particle microspheres; then adds vinyl monomers to carry out soap-free emulsion polymerization coating to obtain monodisperse A core/shell composite particle emulsion with a particle diameter of 80-900 nanometers. The method of the invention not only has low energy consumption, high product purity, good dispersibility and no pollution to the environment, but also can control the coating state of styrene on the surface of nano silicon dioxide particles by changing the reaction conditions.

Description

Method for preparing monodisperse core/shell composite particle emulsion by polystyrene-coated nano-silica microspheres

Technical field

The invention belongs to the technical field of preparation and application of nanocomposite materials, and in particular relates to a method for preparing monodisperse core/shell composite particle emulsion by coating nano silicon dioxide spheres with polystyrene or vinyl monomer polymers.

Background technique

Now people are increasingly demanding energy-saving, less pollution, high added value, and high-functional products, and the requirements for materials are getting higher and higher. Therefore, composite materials have gradually become the focus of people's research. Composite polymer emulsions, especially organic-inorganic composite polymer emulsions, have attracted more and more attention due to their wide applications in coatings, adhesives, biomedicine, electronics, fiber and paper processing. Using this composite emulsion as a coating not only overcomes many shortcomings of general-purpose coatings, but also develops many new uses. In short, when used as a coating, the inorganic-organic composite emulsion has the following advantages:

①The minimum film-forming temperature is low (without film-forming aids), and the formed film has excellent anti-blocking property;

② It has good adhesion to various substrates, especially cement substrates, and also has good adhesion to metal surfaces;

③The water resistance, solvent resistance, heat resistance and flame retardancy of the coating film are greatly improved compared with ordinary emulsions;

④ The temperature sensitivity of the coating film is small, and its strength changes little with temperature;

⑤The air permeability and moisture permeability of the coating film are improved;

⑥Excellent mechanical properties of the coating film.

In recent years, there have been many new materials that coat inorganic microparticles with organic polymers. Generally, adsorption is the most direct particle coating method, and polymers can form a better coating layer under certain conditions. However, when coating nanoparticles, the agglomeration of core particles is not easy to solve. There have been many reports on coating polymers on silica particles. Recently, it has been reported to prepare fine silica-polystyrene composite particles by atom transfer polymerization. Please see the article in Colloid and Interface Science, Vol. 210, p. 281, 1998 (Bourgeat Lmi, E.; Lang, J.J. colloid Interface Sci. 1998, 210, 281) and 2000, vol. 16, p. 9031 of Langmuir (Ican Sondi; Theodore, H.; Fedynyshyn; Roger Sinta; Langmuir 2000, 16, 9031). However, the synthesis route of this method is cumbersome and the preparation conditions are harsh, making it difficult to control and thus unable to be used in mass production. The people such as Tsubokawa and Ye Zhaoquan, Xie Zhilan have introduced the preparation method of silica-polystyrene composite emulsion, please refer to the article (Tsubokawa.N.T.Kimoto and K. Koyama.J.colloid Interface Sci.1993,271,940-946) and Chinese Patent Publication No. CN 1056883 (application 90103692); Kai Zhang et al. used emulsion polymerization to coat MPS modified silica particles to prepare core Shell composite particles, but the emulsifier on the surface of the particles tends to affect the further use of this particle, see page 380 of the 288 issue of "Macromolecular Material Eng" in 2003; and the core-shell bonding strength of the composite particles obtained by these methods is very high Poor, or these methods are unable to obtain monodisperse composite particle emulsion, thereby limiting the application of this composite particle in high-tech fields.

Generally, soap-free emulsion polymerization can obtain polymer latex particles with good monodispersity, so the preparation of inorganic/organic (core/shell) composite particles by using it has occupied a certain position in the field of material compounding. The method utilizes the electrostatic principle to obtain polymer coating through the electrostatic interaction (opposite charge) between the surface charge of the nuclear particle and the ionic group at the end of the macromolecular chain. In order to improve the coating effect, Bourgeat-lami et al. used MPS coupling modification to disperse nano-silica particles in isopropanol (see Bourgeat Lmi, E.; Lang, JJcolloid Interface Sci.1998, 197, 293). However, under this dispersion system, it is necessary to use hollow fiber membrane dialysis to remove unreacted MPS, so that the content of MPS on the surface of _SiO2 particles can be analyzed by thermogravimetric (TGA) method, which takes 3 to 4 weeks, so the preparation process of this method Very cumbersome; and cross-linked monodisperse composite particles cannot be obtained.

Contents of Invention

The object of the present invention is to provide a method for coating cross-linked polystyrene on the surface of nano-silica particle microspheres to obtain a monodisperse core/shell composite particle emulsion.

The invention adopts a soap-free emulsion polymerization method to prepare monodisperse organic-inorganic composite particle emulsion. Firstly, the surface of nano-silica particle microspheres is modified with coupling agent methacryloyl (3-trimethoxysilane) propyl ester (MPS); then, vinyl monomers are added for soap-free emulsion polymerization.

The polystyrene-coated nano silica microspheres of the present invention prepare the method for the monodisperse core/shell composite particle emulsion comprising the following steps:

(1). Coupling modification of silica spheres

Mix nano-silica microsphere particles (25-400 nanometers) with an organic solvent, put them into an ultrasonic pool for full ultrasonic dispersion for 10-50 minutes; then add MPS coupling agent, and react at room temperature for dozens of hours, among which, nano The molar ratio of silica microsphere particles to MPS coupling agent is 1:1-10; after the reaction, the reaction solution is centrifuged for 10-30 minutes, the supernatant is poured off, and then an organic solvent is added for washing, and this is repeated three times to obtain Nano silica microsphere particles modified by surface coupling.

(2). Soap-free emulsion polymerization coating

Put the surface-coupling-modified nano-silica microsphere particles in step (1) into deionized water 200 to 500 times its weight, and then place it in an ultrasonic pool for full ultrasonic dispersion for 10 to 50 minutes, and then add triggering agent and vinyl monomer, wherein the weight ratio of monomer: initiator: deionized water is 1-3: 0.01-0.03: 10-20, and the temperature is slowly raised to 50-90°C under stirring for polymerization to obtain milky white poly Monodisperse core/shell composite particle emulsion of styrene-coated nano-silica microspheres.

The organic solvent is absolute ethanol, isopropanol, tetrahydrofuran or cyclohexanol and the like.

The initiator includes potassium persulfate (KPS) or ammonium persulfate (APS).

The coupling agent is methacryloyl (3-trimethoxysilane) propyl ester.

The vinyl monomer includes styrene, methacrylic acid, methyl methacrylate, butyl methacrylate, acrylic acid or methyl acrylate.

The particle diameter of the SiO ₂ spherical particles is 25-400 nanometers.

The obtained core/shell composite particle emulsion has a particle size of 80-900 nanometers.

The polydispersity index of the obtained core/shell composite particle emulsion particle size is less than 0.2.

The emulsion prepared by the invention can be widely used in many fields such as coatings, adhesives, electronics, fiber and paper processing, etc., especially in the high-tech field of developing photonic crystals, and has a unique effect.

The method of the invention not only has low energy consumption, high product purity, good dispersibility and no pollution to the environment, but also can control the coating state of styrene on the surface of nano silicon dioxide particles by changing the reaction conditions.

Monodisperse silica-crosslinked polystyrene composite particles are obtained by the method of the present invention, as shown in accompanying drawings 1 and 2.

Description of drawings

Fig. 1. electron micrograph of the monodisperse silica-polystyrene composite particle of embodiment 2 of the present invention;

Fig. 2. Transmission electron micrograph of the polystyrene-coated composite particles of Example 4 of the present invention. Monodisperse mononuclear particles are about 310 nm and dinuclear particles are about 330 nm. The upper left panel is a magnified view of a mononuclear particle.

Specific implementation plan

Example 1

(1). Coupling modification of silica spherical particles

Add 0.025 moles of SiO ₂ spherical particles (25 nanometers) and 2.5 moles of absolute ethanol to the reaction bottle, and put them into an ultrasonic pool for full ultrasonic dispersion for 30 minutes. Add 30 mmol of MPS coupling agent and react at room temperature for 36 hours. Then pour the reaction solution into a centrifuge tube, centrifuge at 4000rps for 30 minutes, pour off the supernatant, add 2.5% absolute ethanol to wash, and then centrifuge to remove the supernatant. This was repeated three times to obtain coupling-modified SiO ₂ spherical particles.

(2). Coating with soap-free emulsion polymerization

The above-mentioned _SiO2 spherical particles were added to 12 moles of deionized water, placed in an ultrasonic pool for sufficient ultrasonic dispersion, and then 0.43 mmoles of potassium persulfate, 96 mmoles of styrene, and 15 mmoles of methacrylic acid were added, and heated to 80° C., and kept at this temperature for 24 hours to react to obtain a milky white, monodisperse core/shell composite particle emulsion with a particle diameter of 90-110 nanometers and a polydispersity index of 0.0356.

Example 2

(1). Coupling modification of silica spherical particles

Add 0.045 moles of SiO ₂ spherical particles (80 nanometers) and 2.5 moles of absolute ethanol to the reaction bottle, and put them into an ultrasonic pool for full ultrasonic dispersion for 30 minutes. Add 4.0 mmol of MPS coupling agent and react at room temperature for 36 hours. Then pour the reaction solution into a centrifuge tube, centrifuge at 4000rps for 30 minutes, pour off the supernatant, add 2.5 moles of absolute ethanol to wash, and then centrifuge to remove the supernatant. This was repeated three times to obtain coupling-modified SiO ₂ spherical particles.

(2). Coating with soap-free emulsion polymerization

Add the above-mentioned _SiO2 spherical particles to 16 moles of deionized water, place them in an ultrasonic pool for sufficient ultrasonic dispersion, then add 0.50 mmoles of potassium persulfate, 110 mmoles of styrene and 18 mmoles of methacrylic acid, and heat to 80° C., and kept at this temperature for 24 hours to obtain a milky white, monodisperse core/shell composite particle emulsion with a particle diameter of 240-270 nanometers and a polydispersity index of 0.1377.

Example 3

(1). Coupling modification of silica spherical particles

Add 0.045 moles of SiO ₂ spherical particles (80 nanometers) and 2.5 moles of absolute ethanol to the reaction bottle, and put them into an ultrasonic pool for full ultrasonic dispersion for 30 minutes. Add 4.0 mmol of MPS coupling agent and react at room temperature for 36 hours. Then pour the reaction solution into a centrifuge tube, centrifuge at 4000rps for 30 minutes, pour off the supernatant, add 2.5 moles of absolute ethanol to wash, and then centrifuge to remove the supernatant. This was repeated three times to obtain coupling-modified SiO ₂ spherical particles.

(2). Coating with soap-free emulsion polymerization

Add the above-mentioned _SiO2 spherical particles to 18 moles of deionized water, place them in an ultrasonic pool for sufficient ultrasonic dispersion, then add 0.45 mmoles of potassium persulfate, 115 mmoles of styrene and 20 mmoles of methacrylic acid, and heat to 70° C., and kept at this temperature for 36 hours to react to obtain a milky white monodisperse core/shell composite particle emulsion with a particle diameter of 310-330 nanometers and a polydispersity index of 0.1742.

Example 4

(1). Coupling modification of silica spherical particles

Add 0.075 moles of SiO ₂ spherical particles (150 nanometers) and 2.5 moles of absolute ethanol to the reaction bottle, and put them into an ultrasonic pool for full ultrasonic dispersion for 30 minutes. Add 6.0 mmol of MPS coupling agent and react at room temperature for 36 hours. Then pour the reaction solution into a centrifuge tube, centrifuge at 4000rps for 30 minutes, pour off the supernatant, add 2.5 moles of absolute ethanol to wash, and then centrifuge to remove the supernatant. This was repeated three times to obtain coupling-modified SiO ₂ spherical particles.

(2). Coating with soap-free emulsion polymerization

Add the above-mentioned _SiO2 spherical particles to 16 moles of deionized water, place them in an ultrasonic pool for sufficient ultrasonic dispersion, then add 0.55 millimoles of potassium persulfate, 115 millimoles of styrene and 20 millimoles of methacrylic acid, and heat to 80° C., and kept at this temperature for 24 hours to obtain a milky white monodisperse core/shell composite particle emulsion.

Claims (10)

1. a polystyrene clad nano silicon dioxide microsphere prepares the method for monodispersity nuclear/shell composite particles emulsion, it is characterized in that: with coupling agent methacryloyl (3-Trimethoxy silane) propyl ester the nanometer silicon dioxide particle microballoon is carried out surface modification; Add vinyl monomer again and carry out the emulsifier-free emulsion polymerization coating, obtain monodispersity nuclear/shell composite particles emulsion.

2. the method for claim 1 is characterized in that: the coupling modification of described nano silica microsphere is that nano silica microsphere particle and organic solvent are mixed, and puts into fully ultra-sonic dispersion of ultrasonic pond; Add coupling agent methacryloyl (3-Trimethoxy silane) propyl ester again, reaction at room temperature, wherein, the mol ratio of nano silica microsphere particle and coupling agent methacryloyl (3-Trimethoxy silane) propyl ester is 1: 1～10; Reaction is centrifugal with reaction solution after finishing, and outwells supernatant liquor, adds organic solvent washing again, obtains the nano silica microsphere particle of surperficial coupling modification.

3. the method for claim 1, it is characterized in that: it is to be in the deionized water of its 200～500 times of weight with inserting through the nano silica microsphere particle of surperficial coupling modification that described emulsifier-free emulsion polymerization coats, place fully ultra-sonic dispersion of ultrasonic pond then, add initiator and vinyl monomer again, monomer wherein: initiator: the weight ratio of deionized water is 1～3: 0.01～0.03: 10～20, stir, be warming up to 50～90 ℃ and carry out polymerization, obtain the monodispersity nuclear/shell composite particles emulsion of milky polystyrene clad nano silicon dioxide microsphere.

4. method as claimed in claim 2 is characterized in that: described organic solvent is dehydrated alcohol, Virahol, tetrahydrofuran (THF) or hexalin.

5. method as claimed in claim 3 is characterized in that: described initiator comprises Potassium Persulphate or Ammonium Persulfate 98.5.

6. as claim 1 or 3 described methods, it is characterized in that: described vinyl monomer comprises vinylbenzene, methacrylic acid, methyl methacrylate, butyl methacrylate, vinylformic acid or methyl acrylate.

7. as claim 1 or 3 described methods, it is characterized in that: described nano silica microsphere particle grain size is 25～400 nanometers.

8. as claim 1 or 3 described methods, it is characterized in that: the grain diameter of the described nuclear that obtains/shell composite particles emulsion is 80～900 nanometers.

9. as claim 1 or 3 described methods, it is characterized in that: the polydispersity index of the described nuclear that obtains/shell composite particles emulsion particle diameter is less than 0.2.

10. as claim 2 or 3 described methods, it is characterized in that: described ultrasonic time is 10～50 minutes.

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