JP2010001555A - Nanoparticle coated with silica, nanoparticle deposited substrate, and method for producing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nanoparticle coated with silica, which has high dispersing properties in a solvent and is easily fixed on a substrate and the like. <P>SOLUTION: The nanoparticle coated with silica includes: a core formed of a nanoparticle; a shell which is made from a silicon compound and is provided around the core so as to cover the core; and a first silane coupling agent which deposits around the shell and has 7 or more carbon atoms. One end of the first silane coupling agent is coupled with a Si element in the shell, and the other end has a reactive functional group. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to silica-coated nanoparticles in which the surface of nanoparticles coated with silica is modified with an organic compound, a method for producing the same, and a dispersion of silica-coated nanoparticles. The silica-coated nanoparticles of the present invention can be applied to high-density magnetic recording media, magnetoresistive elements, nonlinear optical devices, fuel cell electrodes, and the like by arranging them on a substrate.

  In recent years, many studies have been made on nanoparticles having a size of 1 nm to several hundreds of nm produced by chemical synthesis methods, and many production methods have been reported.

  In particular, magnetic nanoparticles such as iron oxide, Co, and FePt are attracting attention not only for high-density magnetic recording media and magnetoresistive elements, but also for medical-related technologies such as MRI contrast agents and heating elements for magnetic thermotherapy. ing.

  In order to apply magnetic nanoparticles to these technologies, it is preferable to coat the surfaces of the nanoparticles with a chemically stable oxide shell such as silica in order to improve weather resistance and suppress biotoxicity.

  In addition, when the nanoparticle surface is modified with an organic ligand, it is usually used that the metal atom on the nanoparticle surface and the coordination atom (N, O, S, etc.) of the organic ligand form a coordinate bond. Thus, an organic ligand is immobilized on the nanoparticle surface. Here, when the organic ligand is immobilized after the nanoparticle surface is coated with silica, the organic ligand and the silica on the nanoparticle surface are immobilized by a stronger covalent bond via a silane coupling agent. Therefore, it is possible to prevent a decrease in solvent dispersibility due to elimination of the organic ligand.

  In Patent Document 1, after a metal oxide core is coated with silica, alcohol washing is performed, a hydroxyl group is introduced to the surface, a silane coupling agent is added in large excess, and the reaction is performed at 130 ° C. for 20 hours. Modification is performed.

In Patent Document 2, polyoxyethylene nonylphenyl ether (commercially available as IGEPAL (registered trademark) CO-520) is added to cyclohexane, an aqueous AgNO ₃ solution is added, and the mixture is stirred at room temperature, whereby water-in-oil reverse micelles are Forming this, adding hydrazine to reduce AgNO ₃ , thereby producing a dispersion containing a nano-particle reverse micelle composite in which Ag nanoparticles are incorporated in reverse micelles, and tetraethyl orthosilicate (TEOS) and ammonia therein. By adding water and stirring at room temperature for 24 hours, a silica shell is formed on the surface of the Ag nanoparticles, and a reverse micelle composite dispersion containing silica-coated Ag nanoparticles is prepared. Next, the silica shell surface is modified with the silane coupling agent by adding an ethanol solution of the silane coupling agent to the reverse micelle composite dispersion and causing the reaction.

  As described above, the purpose of modifying the surface of the nanoparticle with an organic ligand is to improve the solvent dispersibility of the nanoparticle. However, as another purpose, the bonding mechanism when the fine particles are arranged on the substrate is mentioned. It is also known to give the organic ligand the role of In Patent Document 3, a monomolecular film having a functional group at the molecular end is formed on the surface of the substrate, while a monomolecular film having a functional group at the molecular end is formed on the nanoparticle surface. A method for arranging nanoparticles on a substrate using a chemical bond is described. According to this method, since the bonding between the substrate and the nanoparticles is performed using the terminal functional group on the substrate, it is possible to form a monolayer film of the nanoparticles on the substrate. It is attracting attention as a forming method. In Patent Document 3, the solvent dispersibility of the nanoparticles is not mentioned, but it is essential to have a reactive functional group at the terminal as an organic ligand that modifies the nanoparticle surface.

JP 2007-269770 JP Special table 2008-501509 gazette Japanese Patent No. 3597507

  In the method of Patent Document 1, since the silane coupling agent is reacted in a homogeneous system, a dehydration condensation reaction of the silane coupling agent occurs everywhere in the reaction system, and the polymer obtained by polymerizing the silane coupling agent is a secondary agent. There is a disadvantage that it is generated in large quantities as a product.

  Further, in the method of Patent Document 1, when a silane coupling agent having a reactive functional group at the terminal is used, a high temperature of 130 ° C. is required when modifying the surface of the silica-coated nanoparticles with the silane coupling agent. The reactive functional group at the terminal of the silane coupling agent may be decomposed or oxidized and cannot be used.

  In the method of Patent Document 2, hydrolysis and dehydration condensation of the silane coupling agent occurs only in the reverse micelle, so that the silane coupling agent is easily bonded only to the silica shell surface. However, in the method of Patent Document 2, as a result of experiments conducted by the present inventor using a silane coupling agent having a reactive functional group at the terminal, it has been found that the solvent dispersibility is remarkably lowered. Observation of the obtained dispersion by TEM revealed that a plurality of particles aggregated to form a composite.

  When manufacturing a high-density magnetic recording medium, a magnetoresistive effect element, or a nonlinear optical device, since it is necessary to regularly arrange individual particles on a substrate, a composite including a plurality of particles is formed. If you do not use it.

  An object of the present invention is to provide silica-coated nanoparticles that are difficult to form a composite and have high solvent dispersibility, and dispersions thereof. Another object of the present invention is to provide a silica-coated nanoparticle capable of forming a chemical bond with a substrate or the like by having a reactive functional group at the terminal, and a dispersion thereof. Moreover, an object of this invention is to provide the manufacturing method which can manufacture these easily.

  An object of the present invention is to provide nanoparticles for immobilization on a substrate or the like. The primary purpose of introducing reactive functional groups at the end of the silane coupling agent attached to the surface of the silica shell that coats the nanoparticles is to form bonds with the substrate and other molecules. In order to achieve that purpose, the reactive functional groups must be aligned to the outside of the particle. In order to align the direction of the reactive functional group in this way, when the alkoxide part of the silane coupling agent (that is, the other end of the reactive functional group) is hydrolyzed into silanol, only those parts are Needs to enter the reverse reverse micelle of ammonia water and dehydrate and condense with the silica shell surface.

  As described above, in the method of Patent Document 2, the present inventor conducted an experiment using a silane coupling agent having a reactive functional group at the terminal, and as a result, it was found that the solvent dispersibility was significantly reduced. Observation of the obtained dispersion by TEM revealed that a plurality of particles aggregated to form a composite. The present inventors considered this as follows. That is, the aminopropyltrimethoxysilane (APS) used in Patent Document 2 has one aminopropyl group having 3 carbon atoms, but the proportion of hydrophobic sites in the molecule is 3 in 3 molecules. Since the polarity is small and the whole APS molecule is strong, the molecule can easily enter the reverse micelle of ammonia water. In such a case, since the orientation of the molecules of APS is random, it is difficult to align the amino groups and face them outward. In addition, when the orientation of the APS molecules in the ammonia water reverse micelle is random, the silanol group generated when the APS is hydrolyzed can be directed outward, so that it binds to the silica shell of the adjacent particle or the surface of the adjacent particle. It was presumed that the particles were connected by dehydration condensation with APS to form a composite containing a plurality of particles.

  When manufacturing a high-density magnetic recording medium, a magnetoresistive effect element, or a nonlinear optical device, since it is necessary to regularly arrange individual particles on a substrate, a composite including a plurality of particles is formed. If you do not use it.

  In addition, since the functional functional group (or reactive functional group) is often polar, when the functional functional group is aligned outward, the dispersibility of the silica-coated nanoparticles in the nonpolar solvent decreases, Functional functional groups form hydrogen bonds and the like, and particles tend to aggregate.

  The present inventors considered that such a problem can be solved by reducing the polarity of the entire silane coupling agent molecule. Specifically, an increase in the proportion of hydrophobic sites in the silane coupling agent molecule was studied.

  In view of these circumstances, the inventors of the present invention have intensively studied and found that the surface of the silica-coated nanoparticles is terminated with a reactivity such as amino group, mercapto group, hydroxyl group, epoxy group, cyano group, isocyanate group or vinyl group. It has been found that the object can be achieved by using a silane coupling agent having a functional group-containing alkyl chain having 7 or more carbon atoms (first silane coupling agent in the present invention). In such a silane coupling agent, the silane coupling agent molecule itself is large, and the polarity of the silane coupling agent molecule as a whole is dispersed (has a long hydrophobic site). It is considered that when a molecule enters, the silanol group side can preferentially enter, and as a result, it is possible to obtain silica-coated nanoparticles with reactive functional groups facing outward.

  Furthermore, in addition to the first silane coupling agent, a silane coupling agent having no reactive functional group (second silane coupling agent in the present invention) may be further mixed and used. And found it preferable from the viewpoint of immobilization on a substrate. In the case of only the first silane coupling agent, the formation of a composite was sometimes confirmed when stored for a long time, but such a phenomenon was confirmed when the second silane coupling agent was used in combination. No solvent dispersibility was found. In addition, in the case of only the first silane coupling agent, the density of the nanoparticles may not be significantly improved when immobilized on the substrate, but when the second silane coupling agent is used in combination, Such a phenomenon was not confirmed, and it was found that nanoparticles can be immobilized on the substrate at a high density. For this reason, the present inventors say that if there are reactive functional groups at the ends of all silane coupling agents, aggregation occurs in the solvent or on the substrate due to the interaction between the reactive functional groups. thinking. Therefore, in order to improve the solvent dispersibility, it was considered preferable to mix a silane coupling agent having no reactive functional group. Since the second silane coupling agent is used in combination for this purpose, the molecular length is expressed as much as possible on the solvent side and does not hinder the binding of the reactive functional group at the terminal of the first silane coupling agent. It is necessary to select the second silane coupling agent so as to have Therefore, it is preferable that the first and second silane coupling agents have the same carbon number.

In addition, the difference (N _C1 −N _C2 ) between the carbon number (N _C1 ) of the first silane coupling agent and the carbon number (N _C2 ) of the second silane coupling agent is −1, 0, One of 1, 2, and 3 is preferable. When the difference is −1, the lengths of “silica shell to the reactive functional group terminal of the first silane coupling agent” and “silica shell to the terminal of the second silane coupling agent” are substantially equal. As described above, it is preferable from the viewpoint of coexistence of “improving solvent dispersibility” and “improving the degree of fixation to a substrate”. When the difference is 0 to 3, it is preferable that the difference is smaller from the viewpoint of coexistence of “improvement of solvent dispersibility” and “improvement of fixing degree to the substrate”. is doing.

  In addition, the hydrocarbon groups in the first and second silane coupling agents of the present invention are straightforward from the viewpoint that a hexagonal close-packed structure can be easily formed by self-assembly when they are immobilized on a substrate. It has been found that it is preferably a chain hydrocarbon.

  Moreover, it turned out that the hydrocarbon group in the 1st and 2nd silane coupling agent of this invention has the more preferable branched structure hydrocarbon from a viewpoint of the dispersibility to a solvent. However, in view of the object of the present invention, when the first silane coupling agent has a branched structure, it is necessary that a reactive functional group is provided at the end of the side chain far from the nanoparticle. Of course.

  Examples of the core material (nanoparticle material) in the present invention include metals (including single-component and multi-component systems) and oxide materials. Examples thereof include FePt, CoPt, InP, CdSe, ZnSe, ZnS, Co, Au, Ag, iron oxide, titanium oxide, and zirconia oxide.

  An object of the present invention is to provide nanoparticles for immobilization on a substrate or the like. Since immobilization of the substrate and the nanoparticles is performed by chemical bonding, a reactive functional group is introduced at the terminal of the silane coupling agent attached to the silica-coated nanoparticles as a bond for chemical bonding. Examples of the combination of the substrate and the like for chemical bonding and the reactive functional group include the following combinations. Au and mercapto group (coordination bond), Pt and mercapto group (coordination bond), Pt and amino group (coordination bond), alumina (having a hydroxyl group on the surface) and hydroxyl group (covalent bond by dehydration condensation), titania (surface) Hydroxyl group) and hydroxyl group (covalent bond by dehydration condensation), alumina (having a hydroxyl group on the surface) and isocyanate group (covalent bond), Pt and cyano group (covalent bond), Ru and cyano group (covalent bond), Si (surface And a vinyl group (covalent bond). In addition, the bond type in the above description is a bond type that has a high possibility of being equivalent to the end, and is not limited thereto. As described above, when the nanoparticles of the present invention are immobilized on a substrate or the like, it is not necessary to previously form a reactive functional group on the surface of the substrate, so that it can be immobilized on the substrate or the like by a simple method. Become.

  The method for producing silica-coated nanoparticles of the present invention comprises (I) a nonionic surfactant after uniformly dispersing metal or oxide nanoparticles whose surface is protected with an organic ligand in a nonpolar organic solvent. And adding a base-added water and stirring (for example, at room temperature) to prepare a dispersion containing a nanoparticle reverse micelle composite incorporating nanoparticles, and a solution of (II) (I) An orthosilicate compound (for example, tetraethylorthosilicate (TEOS)) and stirring (for example, at room temperature) to form a silica shell on the nanoparticle surface; and (III) an alkyl chain having a reactive functional group By adding a first silane coupling agent having an alkyl chain and a second silane coupling agent having an alkyl chain having no reactive functional group, Introducing a silane coupling agent on the peripheral, and having a.

The present invention has the following configuration.
(Configuration 1) A core composed of nanoparticles,
A shell made of a silicon compound provided to cover the core around the core;
A first silane coupling agent having a hydrocarbon group having 7 or more carbon atoms attached around the shell;
Have
The first silane coupling agent is
One end is bonded to the Si element in the shell, and the other end is a silica-coated nanoparticle having a reactive functional group.
(Configuration 2) Around the shell,
A structure in which a second silane coupling agent having a hydrocarbon group having the same carbon number as the hydrocarbon group of the first silane coupling agent and not having a reactive functional group is attached. 1 silica-coated nanoparticles.
(Configuration 3) The silica-coated nanoparticles according to Configuration 1 or 2, wherein the reactive functional group is a functional group selected from an amino group, a mercapto group, a hydroxyl group, an epoxy group, a cyano group, an isocyanate group, and a vinyl group.
(Configuration 4) Any one of Configurations 1 to 3, wherein the core is any one of FePt, CoPt, InP, CdSe, ZnSe, ZnS, Co, Au, Ag, iron oxide, titanium oxide, and zirconia oxide. Silica coated nanoparticles.
(Configuration 5) Difference (N _C1 ) between the carbon number (N _C1 ) of the hydrocarbon group of the first silane coupling agent and the carbon number (N _C2 ) of the hydrocarbon group of the second silane coupling agent -N _C2 ) is a silica-coated nanoparticle according to any one of constitutions 1 to 4, wherein the compound is −1 to 3.
(Configuration 6) A silica-coated nanoparticle deposition substrate in which the silica-coated nanoparticles according to any one of Configurations 1 to 5 are immobilized on the substrate in a single layer by chemical bonding via the reactive functional group.
(Configuration 7) (A) A step of adding a nonionic surfactant, nanoparticles, and an alkaline aqueous solution to an organic solvent to form alkaline reverse micelle water enclosing the nanoparticles,
(B) A step of adding an orthosilicate compound to the reaction solution of the step (A) to form a silicon compound around the nanoparticles,
(C) a first silane coupling agent having a hydrocarbon group having 7 or more carbon atoms having a reactive functional group at the tip thereof in the reaction solution obtained in the step (B), and the carbon number of the silane cup Adding a second silane coupling agent having the same number of carbon atoms as the ring agent and not having a reactive functional group at the tip, and modifying the surface of the silicon compound with the silane coupling agent;
The manufacturing method of the silica coating nanoparticle in any one of the structures 1-6 which have these.
(Configuration 8) In the step (C), the addition ratio (molar ratio) of the first silane coupling agent and the second silane coupling agent is 0.5: 9.5 to 5: 5. The manufacturing method of the silica coating nanoparticle of the structure 7 to do.
(Configuration 9) In the step (C), the addition ratio (molar ratio) of the first silane coupling agent and the second silane coupling agent is 2: 8 to 4: 6. A method for producing silica-coated nanoparticles.
(Configuration 10) A method for producing a nanoparticle-deposited substrate in which only a single layer of the silica-coated metal nanoparticles according to configurations 1 to 6 is fixed by forming a chemical bond between the reactive functional group and the substrate. .

  According to the present invention, it is possible to provide a silica-coated nanoparticle, a silica-coated nanoparticle dispersion liquid having high solvent dispersibility and easy to be immobilized on a substrate, and an efficient production method thereof.

  Representative examples of the present invention are as follows, but are not limited to these examples.

  After uniformly dispersing metal or oxide nanoparticles whose surface is protected with an organic ligand in a nonpolar organic solvent such as cyclohexane, polyoxyethylene nonylphenyl ether (commercially available as IGEPAL (registered trademark) CO-520), etc. The nonionic surfactant is added, water to which a base such as ammonia is added, and the mixture is stirred at room temperature for 10 to 30 minutes to form water-in-oil reverse micelles. A dispersion containing the incorporated nanoparticle reverse micelle composite was prepared.

  To the dispersion containing the nanoparticle reverse micelle composite, tetraethyl orthosilicate (TEOS) is added and stirred at room temperature for 2 to 5 days to form a silica shell on the surface of the nanoparticle, and the reverse micelle composite containing silica-coated nanoparticles. A dispersion was prepared.

  In the reverse micelle composite dispersion containing the silica-coated nanoparticles, a first silane coupling agent having a reactive functional group at the tip of a long chain alkyl group and a second silane coupling agent having a long chain alkyl group are added. Add the mixture, stir at room temperature for 2-5 days, modify the silica shell surface with a silane coupling agent, remove the nonpolar organic solvent with an evaporator, wash the particles with methanol, and centrifuge The silica-coated nanoparticles surface-modified with were recovered.

  As a first silane coupling agent having a reactive functional group at the tip of the long chain alkyl group, it has a mercapto group, an amino group, a hydroxyl group, an epoxy group, a cyano group, an isocyanate and a double bond at the end, and Examples thereof include silane coupling agents having 1 to 3 alkyl chains having 7 to 17 carbon atoms. These silane coupling agents having a reactive functional group at the tip of the long chain alkyl group can be used alone or in combination of two or more.

  Examples of the second silane coupling agent having the long chain alkyl group include silane coupling agents having 1 to 3 alkyl chains having 8 to 18 carbon atoms. These silane coupling agents having a long-chain alkyl group can also contain one or more unsaturated bonds in the alkyl chain. These silane coupling agents having a long chain alkyl group can be used alone or in combination of two or more.

  Examples Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1
(1) Coating process of FePt nanoparticles with SiO ₂ shell To 20 ml of cyclohexane, 0.94 ml of IGEPAL (registered trademark) CO-520 and 0.8 mg of FePt nanoparticles having an average particle diameter of 6 nm were added and uniformly dispersed. Thereafter, 80 μl of 25% aqueous ammonia was added and stirred at room temperature for 30 minutes, and 80 μl of TEOS was added and stirred at room temperature for 3 days.

(2) Coating step with SiO ₂ coated FePt nanoparticles After adding 24 μl (38 μmol) of dodecyltrimethoxysilane and 10 μl (16 μmol) of 11-mercaptoundecyltrimethoxysilane to the reaction solution obtained in (1) above. The mixture was stirred at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in methylene chloride. The results of observation of the obtained particles by a transmission electron microscope (TEM) are shown in FIG. It was confirmed that the SiO ₂ shell was coated with a thickness of about 10 nm around the FePt core portion having an average particle diameter of 6 nm.

(3) Immobilization of surface-modified SiO ₂ coated FePt nanoparticles on Au substrate A glass substrate whose surface was coated with Au was immersed in a methylene chloride dispersion of the obtained nanoparticles for 1 day. After removal from the dispersion, the substrate was ultrasonically cleaned in methylene chloride for 5 minutes. FIG. 2 shows the results of scanning electron microscope (SEM) observation of the surface of the Au-coated glass substrate after ultrasonic cleaning. It was confirmed that the particles were closely attached to the substrate surface, and it was confirmed that the nanoparticles could be immobilized on the Au-coated glass substrate.

Comparative Example 1
To the reaction solution obtained in Example 1 (1), 13 μl (54 μmol) of 3-mercaptopropyltrimethoxysilane (MPS) was added, followed by stirring at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in toluene. As a result of TEM observation, aggregation of nanoparticles was observed as shown in FIG.

Example 2
To the reaction solution obtained in Example 1 (1), 31 μl (49 μmol) of dodecyltrimethoxysilane and 3 μl (5 μmol) of 11-mercaptoundecyltrimethoxysilane were added, followed by stirring at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in toluene. As a result of TEM observation, it was confirmed that the SiO ₂ shell was coated with a thickness of about 10 nm around the FePt core portion having an average particle diameter of 6 nm as in Example 1. Further, as in Example 1 (3), an attempt was made to immobilize nanoparticles on an Au-coated glass substrate. As a result of SEM observation, it was confirmed that the particles were closely attached to the substrate surface, and it was confirmed that the nanoparticles could be immobilized on the Au-coated glass substrate.

Example 3
After adding 17 μl (27 μmol) of dodecyltrimethoxysilane and 17 μl (27 μmol) of 11-mercaptoundecyltrimethoxysilane to the reaction solution obtained in Example 1 (1), the mixture was stirred at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in methylene chloride. As a result of TEM observation, it was confirmed that the SiO ₂ shell was coated with a thickness of 10 nm around the FePt core portion having an average particle diameter of 6 nm as in Example 1. Further, as in Example 1 (3), an attempt was made to immobilize nanoparticles on an Au-coated glass substrate. As a result of SEM observation, it was observed that the particles were closely attached to the substrate surface, and it was found that the nanoparticles could be immobilized on the Au-coated glass substrate.

Example 4
After adding 24 μl (38 μmol) of octyltrimethoxysilane and 10 μl (16 μmol) of 7-mercaptoheptyltrimethoxysilane to the reaction solution obtained in Example 1 (1), the mixture was stirred at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in methylene chloride. As a result of TEM observation, it was confirmed that the SiO ₂ shell was coated with a thickness of 10 nm around the FePt core portion having an average particle diameter of 6 nm as in Example 1. Further, as in Example 1 (3), an attempt was made to immobilize nanoparticles on an Au-coated glass substrate. As a result of SEM observation, it was observed that the particles were closely attached to the substrate surface, and it was found that the nanoparticles could be immobilized on the Au-coated glass substrate.

Example 5
After adding 24 μl (38 μmol) of octyltrimethoxysilane and 10 μl (16 μmol) of 11-mercaptoundecyltrimethoxysilane to the reaction solution obtained in Example 1 (1), the mixture was stirred at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in methylene chloride. As a result of TEM observation, it was confirmed that the SiO ₂ shell was coated with a thickness of about 10 nm around the FePt core portion having an average particle diameter of 6 nm as in Example 1. Further, as in Example 1 (3), an attempt was made to immobilize nanoparticles on an Au-coated glass substrate. As a result of SEM observation, it was observed that the particles were closely attached to the substrate surface, and it was found that the nanoparticles could be immobilized on the Au-coated glass substrate.

Example 6
After adding 24 μl (38 μmol) of dodecyltrimethoxysilane and 10 μl (16 μmol) of 11-aminoundecyltrimethoxysilane to the reaction solution obtained in Example 1 (1), the mixture was stirred at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in methylene chloride. As a result of TEM observation, it was confirmed that the SiO ₂ shell was coated with a thickness of about 10 nm around the FePt core portion having an average particle diameter of 6 nm as in Example 1. In addition, nanoparticle immobilization on a Pt-coated glass substrate was attempted in the same manner as in Example 1 (3). As a result of SEM observation, it was found that the particles were closely attached to the substrate surface, and it was found that the nanoparticles could be immobilized on the Pt-coated glass substrate.

Example 7
After adding 24 μl (38 μmol) of dodecyltrimethoxysilane and 10 μl (16 μmol) of 11-hydroxyundecyltrimethoxysilane to the reaction solution obtained in Example 1 (1), the mixture was stirred at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in methylene chloride. As a result of TEM observation, it was confirmed that the SiO ₂ shell was coated with a thickness of about 10 nm around the FePt core portion having an average particle diameter of 6 nm as in Example 1. In addition, an attempt was made to immobilize nanoparticles on an Al ₂ O ₃ coated glass substrate in the same manner as in Example 1 (3). As a result of SEM observation, it was found that the particles were closely attached to the substrate surface, and it was found that the nanoparticles could be immobilized on the Al ₂ O ₃ coated glass substrate.

Example 8
(1) Coating process of CoPt nanoparticles with SiO ₂ shell To 20 ml of cyclohexane, 0.94 ml of IGEPAL (registered trademark) CO-520 and 0.9 mg of CoPt nanoparticles having an average particle diameter of 4 nm were added and uniformly dispersed. Thereafter, 80 μl of 25% aqueous ammonia was added and stirred at room temperature for 30 minutes, and 80 μl of TEOS was added and stirred at room temperature for 3 days.

(2) Coating step with SiO ₂ coated CoPt nanoparticles After adding 24 μl (38 μmol) of dodecyltrimethoxysilane and 10 μl (16 μmol) of 11-mercaptoundecyltrimethoxysilane to the reaction solution obtained in (1) above. The mixture was stirred at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in methylene chloride. The results of observation of the obtained particles with a transmission electron microscope (TEM) were the same as those in FIG. It was confirmed that the SiO ₂ shell was coated with a thickness of about 10 nm around the CoPt core portion having an average particle diameter of 4 nm. Further, as in Example 1 (3), an attempt was made to immobilize nanoparticles on an Au-coated glass substrate. As a result of SEM observation, it was observed that the particles were closely attached to the substrate surface, and it was found that the nanoparticles could be immobilized on the Au-coated glass substrate.

Example 9
(1) Coating step of Fe ₂ O ₃ nanoparticles with SiO ₂ shell Uniform dispersion by adding 0.94 ml of IGEPAL (registered trademark) CO-520 and 1.0 mg of Fe ₂ O ₃ nanoparticles with an average particle diameter of 10 nm to 20 ml of cyclohexane I let you. Thereafter, 80 μl of 25% aqueous ammonia was added and stirred at room temperature for 30 minutes, and 60 μl of TEOS was added and stirred at room temperature for 3 days.

(2) Coating step with SiO ₂ coated Fe ₂ O ₃ nanoparticles To the reaction solution obtained in (1) above, 24 μl (38 μmol) of dodecyltrimethoxysilane and 10 μl (16 μmol) of 11-mercaptoundecyltrimethoxysilane were added. After the addition, the mixture was stirred at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in methylene chloride. The results of observation of the obtained particles with a transmission electron microscope (TEM) were the same as those in FIG. It was confirmed that the SiO ₂ shell was coated with a thickness of about 8 nm around the Fe ₂ O ₃ core portion having an average particle diameter of 10 nm. Further, as in Example 1 (3), an attempt was made to immobilize nanoparticles on an Au-coated glass substrate. As a result of SEM observation, it was observed that the particles were closely attached to the substrate surface, and it was found that the nanoparticles could be immobilized on the Au-coated glass substrate.

Example 10
(1) Coating step of Au nanoparticles with SiO ₂ shell To 20 ml of cyclohexane, 0.94 ml of IGEPAL (registered trademark) CO-520 and 1.0 mg of Au nanoparticles having an average particle diameter of 4 nm were added and uniformly dispersed. Thereafter, 80 μl of 25% aqueous ammonia was added and stirred at room temperature for 30 minutes, and 80 μl of TEOS was added and stirred at room temperature for 3 days.

(2) Coating step with SiO ₂ -coated Au nanoparticles After adding 24 μl (38 μmol) of dodecyltrimethoxysilane and 10 μl (16 μmol) of 11-mercaptoundecyltrimethoxysilane to the reaction solution obtained in (1) above The mixture was stirred at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in methylene chloride. The results of observation of the obtained particles with a transmission electron microscope (TEM) were the same as those in FIG. It was confirmed that the SiO ₂ shell was coated with a thickness of about 10 nm around the Au core portion having an average particle diameter of 4 nm. Further, as in Example 1 (3), an attempt was made to immobilize nanoparticles on an Au-coated glass substrate. As a result of SEM observation, it was observed that the particles were closely attached to the substrate surface, and it was found that the nanoparticles could be immobilized on the Au-coated glass substrate.

Example 11
After adding 17 μl (54 μmol) of 11-mercaptoundecyltrimethoxysilane to the reaction solution obtained in Example 1 (1), the mixture was stirred at room temperature for 3 days. The product was isolated by adding methanol to the obtained reaction solution and centrifuging, and uniformly dispersed in toluene. The result of transmission electron microscope (TEM) observation of the obtained particles is shown in FIG. Although it was confirmed that the SiO ₂ shell was coated with a thickness of about 10 nm around the FePt core portion having an average particle diameter of 6 nm, it was found that the dispersibility was inferior to that of Example 1. Further, as in Example 1 (3), an attempt was made to immobilize nanoparticles on an Au-coated glass substrate. FIG. 5 shows the results of scanning electron microscope (SEM) observation of the surface of the Au-coated glass substrate after ultrasonic cleaning. It was confirmed that the particles were densely adhered to the substrate surface, and it was confirmed that the nanoparticles could be immobilized on the Au-coated glass substrate, but it was found that the immobilization density was inferior to that of Example 1.

  The silica-coated nanoparticle of the present invention can provide a silica-coated nanoparticle, a silica-coated nanoparticle dispersion liquid, and a method for efficiently producing the silica-coated nanoparticle that have high solvent dispersibility and can be easily immobilized on a substrate or the like. According to the present invention, silica-coated nanoparticles that are easy to handle can be provided. By arranging the silica-coated nanoparticles of the present invention on a substrate or the like, it can be applied to high-density magnetic recording media, magnetoresistive elements, nonlinear optical devices, fuel cell electrodes, and the like.

It is a TEM photograph which shows the silica coating nanoparticle obtained in Example 1 of this invention. It is a SEM photograph which shows the silica coating nanoparticle fixed in Au coated glass substrate obtained in Example 1 of this invention. 4 is a TEM photograph showing aggregated nanoparticles obtained in Comparative Example 1. It is a TEM photograph which shows the silica coating nanoparticle obtained in Example 11 of this invention. It is a SEM photograph which shows the silica coating nanoparticle fixed in Au coated glass substrate obtained in Example 11 of this invention.

Claims (10)

A core of nanoparticles,
A shell made of a silicon compound provided to cover the core around the core;
A first silane coupling agent having a hydrocarbon group having 7 or more carbon atoms attached around the shell;
Have
The first silane coupling agent is
One end is combined with the Si element in the shell, and the other end is provided with a reactive functional group. Around the shell,
A second silane coupling agent having a hydrocarbon group having the same carbon number as the hydrocarbon group of the first silane coupling agent and not having a reactive functional group is attached. The silica-coated nanoparticles according to claim 1.   The silica-coated nanoparticle according to claim 1 or 2, wherein the reactive functional group is a functional group selected from an amino group, a mercapto group, a hydroxyl group, an epoxy group, a cyano group, an isocyanate group, and a vinyl group. .   4. The core according to claim 1, wherein the core is any one of FePt, CoPt, InP, CdSe, ZnSe, ZnS, Co, Au, Ag, iron oxide, titanium oxide, and zirconia oxide. The silica-coated nanoparticles according to claim 1. Difference between the number of carbon atoms (N _C1 ) of the hydrocarbon group of the first silane coupling agent and the number of carbon atoms (N _C2 ) of the hydrocarbon group of the second silane coupling agent (N _C1 −N _C2 ) The silica-coated nanoparticles according to any one of claims 1 to 4, wherein -1 to -3.   A nanoparticle-deposited substrate, wherein the silica-coated nanoparticles according to any one of claims 1 to 5 are immobilized on the substrate in a single layer by chemical bonding via the reactive functional group. (A) A step of adding a nonionic surfactant, nanoparticles, and an aqueous alkaline solution in an organic solvent to form alkaline reverse micelle water enclosing the nanoparticles,
(B) A step of adding an orthosilicate compound to the reaction solution of the step (A) to form a silicon compound around the nanoparticles,
(C) a first silane coupling agent having a hydrocarbon group having 7 or more carbon atoms having a reactive functional group at the tip thereof in the reaction solution obtained in the step (B), and the carbon number of the silane cup Adding a second silane coupling agent having the same number of carbon atoms as the ring agent and not having a reactive functional group at the tip, and modifying the surface of the silicon compound with the silane coupling agent;
The method for producing silica-coated nanoparticles according to any one of claims 1 to 6, wherein:   In the step (C), an addition ratio (molar ratio) between the first silane coupling agent and the second silane coupling agent is set to 0.5: 9.5 to 5: 5. The method for producing silica-coated nanoparticles according to claim 7.   The addition ratio (molar ratio) of the first silane coupling agent and the second silane coupling agent in the step (C) is set to 2: 8 to 4: 6. 8. The method for producing silica-coated nanoparticles according to 7.   Nanoparticle deposition characterized by immobilizing only a single layer of silica-coated metal nanoparticles according to any one of claims 1 to 6 by forming a chemical bond between the reactive functional group and a substrate. A method for manufacturing a substrate.