JP4580359B2 - Magnetic nanoparticle composite - Google Patents

Description

The present invention relates to a magnetic nanoparticle composite.

Ferromagnetic nanoparticles such as iron oxide are used in a wide range of applications such as magnetic recording media and electrostatic imaging toners. Increasing the surface area of magnetite as nanoparticles is useful in a wide range of fields such as high-density data storage materials, ferrofluids, magnetic resonance materials, bioseparation techniques, magnetic paints, and pharmaceuticals. Specifically, application examples of magnetite nanoparticles have been introduced in the pharmaceutical field (see Non-Patent Document 1).

However, since magnetic nanoparticles do not dissolve in various liquids such as water, organic solvents, monomers, and liquid polymers, they were dispersed in liquids using low molecular surfactants, polymer dispersants, etc. However, since it inherently easily aggregates, it has been difficult to prepare a liquid material by forcibly dispersing it. For this reason, what surface-treated by various methods is known in order to provide solubility of magnetite particles in a solvent. However, such surface-treated magnetite particles settle in the solution over time and phase separate, and it is difficult to maintain a dispersed state. In particular, it is difficult to prepare and maintain a molding material uniformly dispersed at the nano level. (See Patent Document 1)

JP-A-8-31629 Tomoaki, “Detection and purification of biomolecules using nanoparticles”, Oreoscience, Vol. 4, No. 1 (2004)

An object of the present invention is to provide magnetic nanoparticles that can be dispersed at a nano level in a dispersion medium such as water, an organic solvent, and other organic liquids and that can be dispersed at a nano level for a long time. is there.

As a result of intensive studies to obtain the magnetic nanoparticles as described above, the present inventors have found that dispersibility in various dispersion media can be achieved by coating the surface of the magnetic nanoparticles with a protective agent having a cationic heterocyclic structure. As a result, the inventors have found a property that the dispersion stability in the medium can be drastically improved.

That is, the present invention provides a magnetic nanoparticle composite in which the surface of a magnetic nanoparticle (P) is coated with a protective agent (A) having a heterocyclic cationic group (a) , the heterocyclic cationic The magnetic nanoparticle composite (C) in which the group (a) is an imidazolium group or a pyridinium group, and the magnetic nanoparticles (P) and the protective agent (A) are bonded by a Fe—O—Si bond. .

The magnetic nanoparticle composite of the present invention is excellent in dispersibility in water, organic solvents, and other organic liquids, and has high dispersion stability. The magnetic nanoparticle composite of the present invention can provide a magnetic nanoparticle dispersion liquid, a magnetic nanoparticle dispersion paste, and a magnetic nanoparticle dispersion solid.

The magnetic nanoparticles (P) in the present invention are composed of nano-sized particles containing a metal or alloy containing an iron group or manganese group element as an essential component or an iron group element oxide (p).
As (p), specifically, Fe, Co, Ni metals or alloys selected from the group consisting of FePt, CoPt, FePd, MnAl, FePtM, CoPtM, FePdM, and MnAlM (in the chemical formula, M Represents a metal element, and M is Li, Mg, Al, Si, P, S, Mn, Ni, Cu, Zn, Ga, Ge, As, Se, Ag, Cd, In, Sn, Sb, Te, I , Au, Tl, Bi, Po, and At.) Or a metal oxide containing iron oxide Fe ₂ O ₃ . Among these, metal oxides containing iron oxide Fe ₂ O ₃ are preferable. Examples of the metal oxide are represented by the general formula: (NO) m · Fe ₂ O ₃ (wherein N represents a divalent metal atom and m is a number of 0 ≦ m ≦ 1). Examples of the divalent metal atom N include magnesium, calcium, manganese, iron, nickel, cobalt, copper, zinc, strontium, barium and the like. In particular, magnetic iron oxide (for example, magnetite Fe ₃ O ₄ , γ-Fe ₂ O ₃ etc.) when N is divalent iron is preferably used in the present invention. The magnetic nanoparticles (P) may contain crystal water in addition to (p).

The volume average particle size of the magnetic nanoparticles (P) is preferably from 3 to 1000 nm, more preferably from 4 to 500 nm, still more preferably from 5 to 100 nm. When the magnetic nanoparticles (P) are 3 nm or more, the influence of the demagnetization phenomenon due to thermal fluctuation can be suppressed to a small value, and when the magnetic nanoparticles (P) are smaller than 1000 nm, long-term dispersibility can be further improved. The measurement of the volume average particle size was performed by calculation from the result of measuring the particle size of 100 particles by observing with a transmission electron microscope.
There is no restriction | limiting in particular as a shape of (P), A perfect spherical shape, spindle shape, plate shape, needle shape, etc. are mentioned. Among these, a true spherical shape is preferable.

When the magnetic nanoparticle (P) is a metal or an alloy, since there is no functional group on the particle surface, the bond between the protective agent (A) and the magnetic nanoparticle (P) is not a covalent bond but an electrostatic interaction. , Physical adsorption by van der Waals force.
When the magnetic nanoparticles (P) contain iron oxide, since iron oxide has a hydroxyl group on the surface, it can form covalent bonds with various protective agents (A). ) Has a large dispersion stabilizing effect. The equipotential point of iron oxide is pH = 5.7 to 6.9, and a hydroxyl group exists on the particle surface in a pH range higher than this. Since the hydroxyl group and the functional group of the protective agent (A) form a covalent bond, the protective agent coats the surface of the iron oxide nanoparticles, so that the dispersion stability is improved as compared with nanoparticles other than iron oxide. .

For the production of the magnetic nanoparticle composite of the present invention, an aqueous sol consisting only of magnetic nanoparticles is prepared. The method for preparing this aqueous sol is not particularly defined. In the case of iron oxide, examples include an alkali coprecipitation method and an ion exchange resin method. In the case of metals and alloys, a liquid phase reduction method can be exemplified. In the alkali coprecipitation method, for example, about 0.1 to 2 mol of an aqueous solution containing iron chloride (III) and iron chloride (II) in a molar ratio of about 1: 3 to 2: 1, NaOH, KOH, A base such as NH ₄ OH is mixed so as to have a pH of about 7 to 12, and heated and aged as necessary. Then, the produced magnetic iron oxide is separated, washed with water, and then water or water and a water-soluble solvent. The mixture is re-dispersed, a protective agent is added, and optionally, the reaction between the protective agent and the iron oxide surface is performed to obtain iron oxide nanoparticles coated with the protective agent. This aqueous sol may be purified or concentrated by dialysis, ultrafiltration, centrifugation or the like, if necessary.
In the liquid phase reduction method, for example, a protective agent is dissolved in advance in an aqueous solution of a metal salt such as iron acetate or platinum acetylacetonate, and a reducing agent such as sodium borohydride is added thereto to reduce metal ions. Thus, metal nanoparticles coated with a protective agent are obtained. In the case of an alloy, alloy nanoparticles can be obtained by using a plurality of metal ion species to be dissolved. This aqueous sol may also be purified or concentrated by dialysis, ultrafiltration, centrifugation or the like, if necessary, as in the case of iron oxide.

The surface of the magnetic nanoparticle (P) is coated with the protective agent (A) using an intermolecular interaction such as electrostatic interaction, and the protective agent (A) is shared on the surface of the magnetic nanoparticle (P). Among them, those utilizing bonding are preferred, but those in which a protective agent is covalently bonded to the particle surface are more preferred from the viewpoint of the protective power of the particles. As the protective agent (A), generally known surfactants and the like can be used. From the above viewpoint, at least one functional group that forms a covalent bond by reaction with a functional group on the surface of the magnetic nanoparticle is included in the molecule. What is contained is desirable. For example, an epoxy group, an amino group, a sulfone group, a sulfonyl group, a phosphoryl group, an alkoxysilane group, a carboxyl group, an isocyanate group, or the like is preferable as a functional group that reacts with the surface of the iron oxide nanoparticles (P). However, when the magnetic nanoparticles are iron oxide, such as amino groups and carboxyl groups, a covalent bond is formed by reaction, but when the magnetic nanoparticles are an alloy such as FePt, both properties are covered by adsorption. Also includes what you have. In addition to the thiol group, examples of the functional group that does not react with the surface of the magnetic nanoparticle (P) and interacts between molecules such as electrostatic interaction include the carboxyl group and amino group described above. The molecular weight of the protective agent (A) is preferably 500 to 1,000,000, more preferably 100 to 100,000, and more preferably 500 to 10,000.
Examples of the protective agent (A) include a protective agent (A2) that forms a covalent bond with a protective agent (A1) that does not form a covalent bond with the surface of the magnetic nanoparticle (P).

The surface of the magnetic nanoparticle (P) is coated with the protective agent (A1) using physical adsorption or chemical adsorption excluding covalent bonds. In order to coat, the magnetic nanoparticles (P) and the protective agent (A1) are mixed in a predetermined ratio, and are usually stirred at room temperature and optionally with heating. The ratio between the magnetic nanoparticles (P) and the protective agent (A) is preferably 1: 0.01 to 1: 6, more preferably 1: 0.1 to 1: 1 by weight.

The coating of the protective agent (A2) on the surface of the magnetic nanoparticles (P) is usually performed by mixing these at a predetermined ratio and heating. The ratio between the magnetic nanoparticles (P) and the protective agent (A) is preferably 1: 0.01 to 1: 6, more preferably 1: 0.1 to 1: 1 by weight. The reaction may be performed at a temperature of room temperature to 120 ° C. for 10 minutes to 10 hours, and usually it is sufficient to heat and reflux for about 1 hour. The concentration of the magnetic nanoparticle composite (C) in the reaction solution is usually in the range of 0.1 to 20% by weight, preferably 1 to 10% by weight as a metal.

After coating, a known operation such as ultrafiltration is used to carry out a purification operation for separating unreacted polysaccharides and low-molecular compounds to obtain an aqueous sol having a predetermined purity and concentration. To this, a solvent such as methanol, ethanol, tetrahydrofuran, or acetone is added to preferentially precipitate and precipitate the magnetic nanoparticle composite (C), which is separated, and then the precipitate is redissolved in water. Dialyze, and if necessary, concentrate under reduced pressure to obtain an aqueous sol of the complex (C). Then, if necessary, centrifugation, filtration, pH adjustment and the like may be performed.

The protective agent (A) that binds to the surface of the magnetic nanoparticle (P) is preferably a molecule having a functional group as described above. Among them, a molecule having an alkoxysilane group easily proceeds in water. This is more preferable from the viewpoint of a large number of binding sites with the iron oxide surface per molecule. This is because an Fe—O—Si bond is formed between the iron oxide surface and the protective agent by the reaction with the alkoxysilane group, and this bond is relatively stable in water.

Since the protective agent (A) improves the dispersibility in the medium together with the binding site with the surface of the magnetic nanoparticles (P), the protective agent (A) is not only influenced by the excluded volume effect of the protective agent, but also has a complex electrostatic repulsion. It has a cyclic cationic group (a) in the molecule. Specifically, examples of the cationic group (a) include an imidazolium group (a1), a pyridinium group, an imidazolinium group, a thiazolium group, and a pyrazolium group. In particular, the imidazolium group (a1) is a salt of imidazole, which is a typical organic strong base, and the solubility in the dispersion medium can be changed by changing the substituent at the 1-position or 3-position of the imidazolium group. It can be adjusted by changing the anion species of the counter ion. Thus, a protective agent having an imidazolium group introduced into the molecule can easily adjust and enhance the dispersibility of magnetic nanoparticles in various dispersion media by adjusting the molecular structure. Moreover, since imidazolium has a resonance structure in the heterocyclic ring and the stability of the cation is very high, an imidazolium group is particularly preferable.

The imidazolium group (a1) is a structure represented by the following general formula (1). In the general formula (1), R is an alkyl group having 1 to 15 carbon atoms, or a total of carbon and oxygen including an ether bond. Represents an alkyl group having a number of 15 or less, Q represents an alkyl group having 1 to 4 carbon atoms or a hydrogen atom, and S represents an alkyl chain, a polyether chain or the like directly at a site bonded to the surface of the magnetic nanoparticle. This is a site that binds via a spacer.

Examples of the alkyl group having 1 to 15 carbon atoms of R include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, a tert-butyl group, an n-octyl group, and a 2-ethylhexyl group. Is mentioned. Examples of the alkyl group containing an ether bond and having a total number of carbon and oxygen of 15 or less include a group represented by-(CH2) n- (OCH2CH2) mOH (n is an integer of 4 or less, m is an integer of 7 or less). Can be mentioned. Examples of the alkyl group having 1 to 4 carbon atoms of Q include a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, and a tert-butyl group.

By adjusting the carbon number of R, the solubility in the dispersion medium can be adjusted. For example, when aiming at dispersion in an aqueous dispersion medium, when Q is a hydrogen atom, R is preferably a hydrogen atom, a methyl group, an ethyl group, or a propyl group, and more preferably a hydrogen atom or a methyl group. . When aiming at dispersion in an organic solvent, dispersibility in an organic solvent is enhanced by making R an alkyl group having 4 or more carbon atoms, and the longer alkyl chain is preferred.

In addition, the magnetic nanoparticle composite of the present invention does not particularly specify the counter anion species, but the solubility of the protective agent in the dispersion medium changes depending on the selection of the counter anion, so that the dispersion is similar to the alkyl chain length of the imidazolium group. The solubility in the medium can be adjusted. Specifically as an anion, a well-known anion can be used and the anion remove | excluding the proton from the acid which is illustrated below is mentioned.
Inorganic strong acids such as HCl, HBr, HClO ₄ , HBF ₄ , HPF ₆ , HAsF ₆ , HSbF ₆ ; acetic acid, trifluoromethanesulfonic acid, pentafluoroethanesulfonic acid, heptafluoropropanesulfonic acid, trichloromethanesulfonic acid, pentachloropropanesulfone Acid, heptachlorobutanesulfonic acid, trifluoroacetic acid, pentafluoropropionic acid, pentafluorobutanoic acid, trichloroacetic acid, pentachloropropionic acid, heptachlorobutanoic acid and the like halogen-containing sulfonic acids having 1 to 30 carbon atoms; bis (tri C1-C30 halogen-containing sulfonylimides such as fluoromethylsulfonyl) imide; C1-C30 halogen-containing sulfonylmethides such as tris (trifluoromethylsulfonyl) methide; and the like. Regarding the dispersibility, when the dispersion medium is aqueous, the anion is preferably HCl, HClO ₄ , HBF ₄ , acetic acid or the like, and when the dispersion medium is an organic solvent, HPF ₆ , trifluoromethanesulfonic acid, pentafluoroethanesulfonic acid, hepta. Fluoropropanesulfonic acid, bis (trifluoromethylsulfonyl) imide and the like are preferable.

Specific examples of the protective agent (A2) that forms a covalent bond with the protective agent (A1) that does not form a covalent bond with the surface of the magnetic nanoparticle (P) include the following.
Specific examples of (A1) include carboxyl group-containing imidazolium salt compounds (such as 1-methyl-3-carboxyhexylimidazolium chloride), carboxyl group-containing pyridinium salt compounds (such as N-carboxyhexyl pyridinium chloride), and carboxyl group-containing compounds. Imidazolinium salt compounds (1-methyl-3-carboxyhexylimidazolinium chloride, etc.), carboxyl group-containing thiazolium salt compounds, carboxyl group-containing pyrazolium salt compounds, amino group-containing imidazolium salt compounds (1-methyl-3-amino Hexylimidazolium chloride), amino group-containing pyridinium salt compound (N-aminohexylpyridinium chloride, etc.), amino group-containing imidazolinium salt compound (1-methyl-3-aminohexylimidazolium chloride) Um chloride), amino group-containing thiazolium salt compound, amino group-containing pyrazolium salt compound, thiol group-containing imidazolium salt compound (1-methyl-3-mercaptohexylimidazolium chloride, etc.), thiol group-containing pyridinium salt compound (N- Mercaptohexylpyridinium chloride, etc.), thiol group-containing imidazolinium salt compounds (1-methyl-3-mercaptohexylimidazolinium chloride, etc.), thiol group-containing thiazolium salt compounds, thiol group-containing pyrazolium salt compounds, and the like.

Specific examples of (A2) include alkoxysilane group-containing imidazolium salts (1-methyl-3-trimethoxysilane hexylimidazolium chloride, etc.), alkoxysilane group-containing pyridinium salt compounds (N-trimethoxysilane hexyl pyridinium chloride, etc.) ), Alkoxysilane group-containing imidazolinium salt compound (1-methyl-3-trimethoxysilane hexylimidazolinium chloride, etc.), alkoxysilane group-containing thiazolium salt compound, alkoxysilane group-containing pyrazolium salt compound, epoxy group-containing imidazolium Salt compounds (1-methyl-3-hexyl oxide imidazolium chloride, etc.), epoxy group-containing pyridinium salt compounds (N-hexyl oxide pyridinium chloride, etc.), epoxy group-containing imidazolinium Salt compounds (1-methyl-3-hexyl oxide imidazolinium chloride, etc.), epoxy group-containing thiazolium salt compounds, epoxy group-containing pyrazolium salt compounds, isocyanate group-containing imidazolium salt compounds, isocyanate group-containing pyridinium salt compounds, isocyanate group-containing Examples include imidazolinium salt compounds and isocyanate group-containing pyridinium salt compounds.

Specific examples of the protective agents (A1) and (A2) have been described above, but before reacting with the magnetic nanoparticles, not only the salt but also the magnetic nanoparticles (P) and the composite (C) were formed. Thereafter, a molecule that is exemplified as a salt is also included. In other words, after the formation of the magnetic nanoparticles (P) and the complex (C) in the state of basic molecules, the state of the salt neutralized with acidic molecules is a compound as exemplified above. .

The volume average particle diameter of the magnetic nanoparticle composite (C) is preferably 4 to 1100 nm, more preferably 5 to 600 nm, and still more preferably 6 to 110 nm.

As an example of use of the magnetic nanoparticle composite (C), the magnetic nanoparticle composite (C) is dispersed in the dispersion medium (S), thereby imparting a function such as magnetism to the dispersion medium (S). Use as an additive is considered. The dispersion medium (S) may be used as it is, or may be used as a solid in which magnetic nanoparticles are dispersed by curing. Examples of applications include magnetic fluids used for sealing agents, dampers, speakers, etc., drug transport system base materials, nuclear magnetic resonance imaging agents, and the like that are dispersed in a liquid and used as they are. Also, after being dispersed in a liquid, it is solidified by removing the dispersion medium and used for high-density magnetic recording media, magnetic coating materials used for high-frequency electromagnetic wave shielding, etc., dispersed in resin beads, and then cured. Magnetic toners obtained by this method.

Examples of the dispersion medium (S) include liquid materials such as water, organic solvents, monomers, and liquid polymers. By selecting a protective agent that easily dissolves in each dispersion medium and making the magnetic nanoparticle composite (C) coated with the surface of the magnetic nanoparticle (P), it is easy to disperse and has a stable dispersion over time. A high magnetic nanoparticle dispersion liquid can be obtained. Although there is no specific designation as an organic solvent, those commonly used are mentioned, such as methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutyl alcohol, ethyl cellosolve, butyl cellosolve, ethyl carbitol, butyl carbitol, methyl acetate, acetic acid Examples include ethyl, propyl acetate, isopropyl acetate, isobutyl acetate, cellosolve acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, hexane, heptane, cyclohexane, cyclohexanone, dioxane, isophorone, tetrahydrofuran, toluene, xylene, dimethylformamide, pyridine and the like. The monomer is not particularly specified, but vinyl monomers such as styrene, vinyl chloride, methyl acrylate, methyl methacrylate, and butadiene, cyclic monomers such as ε-caprolactone and ε-caprolactam, and other functional groups in the molecule. One or more polyaddition and polycondensation polymer precursor monomers such as 1,4 butanediol, bisphenol A, adipic acid, terephthalic acid, hexamethylenediamine, isophoronediamine, hexamethylene diisocyanate, diphenylmethane diisocyanate, etc. . These may be used alone or in combination. Examples of the liquid polymer include polyethylene glycol, polypropylene glycol, perfluoroether, and polydimethylsiloxane.

In a preferred embodiment of the present invention, when the magnetic nanoparticle composite (C) is used as a dispersion, paste, water, or an organic solvent, the magnetic nanoparticle composite (C) and the dispersion medium (S) are used. Is preferably 0.01 to 150 parts by weight of the magnetic nanoparticle composite with respect to 100 parts by weight of the dispersion medium. The concentration used depends on the application, but if it is 0.01% or more, even when used for medical imaging agents, etc., it has sufficient detection sensitivity, and when used for the purpose of imparting magnetism to polymers, The concentration should be as high as possible, but if it is 150% or less, the dispersibility is good.

The method of dispersing the magnetic nanoparticle composite (C) of the present invention in the dispersion medium (S) can be dispersed by simple stirring at a low concentration of about 5% or less, but can be dispersed at a higher concentration than that. In the case where it is desired to carry out the dispersion, it is also possible to carry out the dispersion efficiently, for example, by using a tool such as a sand mill, a colloid mill, a visco mill, a motor mill, a dyno mill, a spike mill, or a cosmo mill.

Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to the examples without departing from the gist of the present invention.

(Method for producing iron oxide nanoparticles)
541 mg of iron (III) chloride hexahydrate and 397 mg of iron (II) chloride tetrahydrate were dissolved in 150 ml of ion-exchanged water. The temperature was adjusted to 40 ° C. under a nitrogen stream, 16 ml of 25% aqueous ammonia was added, and the mixture was reacted for 30 minutes. The resulting black precipitate was magnetically separated and washed several times with water to obtain iron oxide nanoparticles (P-1). The volume average particle diameter was 8.5 nm.

(Method for producing protective agent (A-1))
The following operation was performed under N ₂ atmosphere.
60.4 mmol of 1-methylimidazole and 54.9 mmol of 3-chloropropyltrimethoxysilane were mixed and reacted at 90 ° C. for 72 hours. After washing several times with ethyl acetate, the ethyl acetate was removed under reduced pressure to obtain 53.1 mmol of 1-methyl-3-trimethoxysilanepropylimidazolium chloride (A-1) represented by the following molecular formula (2). .

(Method for producing protective agent (A-2))
Borhard Shore Modern organic chemistry According to the method of p816, 10-bromodecanoic acid is synthesized from dodecanedioic acid and purified. 50 mmol of synthesized 10-bromodecanoic acid and 40 mmol of 1-methylimidazole were mixed and reacted at 90 ° C. for 72 hours. After washing several times with ethyl acetate, ethyl acetate was removed under reduced pressure to obtain 37 mmol of 1-methyl-3-carboxydecylimidazolium bromide (A-2) represented by the following molecular formula (3).

(Method for producing protective agent (A-3))
The following operation was performed under N ₂ atmosphere.
60.4 mmol of 1-butylimidazole and 54.9 mmol of 3-chloropropyltrimethoxysilane were mixed and reacted at 90 ° C. for 72 hours. After washing several times with ethyl acetate, the ethyl acetate was removed under reduced pressure to obtain 53.1 mmol of 1-butyl-3-trimethoxysilanepropylimidazolium chloride. The synthesized 1-butyl-3-trimethoxysilanepropyl imidazolium chloride (50 mmol), sodium hexafluorophosphate (50 mmol) and 50 g of acetone were put into a reaction vessel having a reflux tube and stirred at 27 ° C. for 24 hours. The resulting reaction mixture was filtered to remove precipitates, and then acetone was distilled off under reduced pressure. 20 g of toluene was added to the residue, and the mixture was stirred for 15 minutes, and toluene was separated and removed twice. Subsequently, it dried under reduced pressure of 1 Pa at 70 ° C., thereby obtaining 42.5 mmol of 1-butyl-3-trimethoxysilanepropylimidazolium hexafluorophosphate (A-3) represented by the following molecular formula (4).

(Method for producing protective agent (A-4))
50 mmol of 10-bromodecanoic acid and 40 mmol of 1-butylimidazole were mixed and reacted at 90 ° C. for 72 hours. After washing several times with ethyl acetate, the ethyl acetate was removed under reduced pressure to obtain 37 mmol of 1-butyl-3-carboxynonylimidazolium bromide. This 1-butyl-3-carboxynonylimidazolium bromide (50 mmol), sodium hexafluorophosphate (50 mmol) and 50 g of acetone were put in a reaction vessel having a reflux tube and stirred at 27 ° C. for 24 hours. The resulting reaction mixture was filtered to remove precipitates, and then acetone was distilled off under reduced pressure. 20 g of toluene was added to the residue, and the mixture was stirred for 15 minutes, and toluene was separated and removed twice. Subsequently, 200 g of ion-exchanged water was added, and the mixture was stirred for 15 minutes to separate and remove water twice. This was dried at 70 ° C. under reduced pressure of 1 Pa to obtain 44 mmol of 1-butyl-3-carboxydecylimidazolium hexafluorophosphate (A-4) represented by the following molecular formula (5).

(Method for producing protective agent (A-5))
Pyridine (60.4 mmol) and 3-chloropropyltrimethoxysilane (54.9 mmol) were mixed and reacted at 90 ° C. for 72 hours. After washing several times with ethyl acetate, ethyl acetate was removed under reduced pressure to obtain 53.1 mmol of N-trimethoxysilanepropylpyridinium chloride (A-5) represented by the following molecular formula (6).

(Method for producing protective agent (A-6))
50 mmol of 10-bromodecanoic acid and 40 mmol of pyridine were mixed and reacted at 90 ° C. for 72 hours. After washing several times with ethyl acetate, ethyl acetate was removed under reduced pressure to obtain 37 mmol of N-carboxydecylpyridinium bromide (A-6) represented by the following molecular formula (7).

Example 1
300 mg of the prepared iron oxide nanoparticles (P-1) are dispersed in 150 ml of a mixed solvent of water / ethanol = 1/1 by applying ultrasonic waves, and 200 mg of the protective agent (A-1) is added and reacted at 80 ° C. for 10 hours. Thus, the surface was coated with the molecule (A-1). The dispersion was washed with ion-exchanged water five times using an ultra filter unit USY-1.5-2.0 manufactured by Advantech, and then dried under reduced pressure to obtain a magnetic nanoparticle composite (C -1) was obtained.

Example 2
200 mg of protective agent (A-2) was used in place of 200 mg of (A-1) as the protective agent, and the protective agent (A-2) and iron oxide nanoparticles (P-1) were mixed at room temperature. Thereafter, magnetic nanoparticle composite (C-2) was obtained in the same manner as in Example 1.

Example 3
300 mg of the produced iron oxide nanoparticles (P-1) are dispersed in 150 ml of a mixed solvent of water / ethanol = 1/9 by applying ultrasonic waves, and 200 mg of the protective agent (A-3) is added and reacted at 80 ° C. for 10 hours. Thus, the surface was coated with the molecule (A-3). Thereafter, the same procedure as in Example 1 was performed to obtain a magnetic nanoparticle composite (C-3).

Example 4
A magnetic nanoparticle composite (C-4) was obtained in the same manner as in Example 2 except that 200 mg of the protective agent (A-4) was used instead of 200 mg of (A-2) as the protective agent.

Example 5
A magnetic nanoparticle composite (C-5) was obtained in the same manner as in Example 1 except that the protective agent (A-5) was used instead of the protective agent (A-1).

Example 6
A magnetic nanoparticle composite (C-6) was obtained in the same manner as in Example 2 except that 200 mg of the protective agent (A-6) was used instead of 200 mg of (A-2) as the protective agent.

Example 7
Particulate iron oxide (FRO-20, manufactured by Sakai Chemical Industry Co., Ltd., average particle size 200 nm) 25 parts, dispersing agent (A-1) 2.5 parts, 72.1 parts of water is blended and painted with glass beads The mixture was dispersed with a shaker for 6 hours and reacted at 90 ° C. for 72 hours. After washing several times with ethyl acetate, ethyl acetate was distilled off under reduced pressure to obtain a magnetic nanoparticle composite (C-7).

Example 8
Fine iron oxide (BIO-MAG, manufactured by NIPPN Technocluster Co., Ltd., average particle diameter 1000 nm) 25 parts, dispersant (A-1) 0.1 part, 72.1 parts of water are blended and painted with glass beads The mixture was dispersed with a shaker for 6 hours and reacted at 90 ° C. for 72 hours. After washing several times with ethyl acetate, ethyl acetate was distilled off under reduced pressure to obtain a magnetic nanoparticle composite (C-8).

Example 9
The following operation was performed under N ₂ atmosphere.
After dissolving 93 mg of H ₂ PtCl ₆ hexahydrate, 59.7 mg of FeCl ₂ tetrahydrate and 0.2 g of the protective agent (A-2) in 100 ml of distilled water: ethanol = 1: 1 solution. And refluxed at 100 ° C. for 5 hours. Next, 10 ml of a 12 μmol / ml aqueous solution of FeSO ₄ heptahydrate was added. Thereafter, 0.07 g NaBH ₄ dissolved in 50 ml distilled water was added. This obtained the FePt nanoparticle composite (C-9). The volume average particle diameter was 3.9 nm.

Comparative Example 1
The trade name Feridex [manufactured by Tanabe Seiyaku Co., Ltd.] obtained by coating magnetic nanoparticles that are iron oxide with dextran was used as the magnetic nanoparticle composite (C-1 ′) of Comparative Example 1.

Comparative Example 2
The surface of iron oxide nanoparticles (volume average particle size 8.5 nm) is coated with water with Poise 520 [manufactured by Kao Corporation], a polycarboxylic acid type polymer dispersant for ferrite, then dried and magnetic nanoparticle composites Got the body. This was designated as the magnetic nanoparticle composite (C-2 ′) of Comparative Example 2.

The magnetic nanoparticle composites (C-1) to (C-9) of Examples 1 to 9 and the magnetic nanoparticle composites (C-1 ′) and (C-2 ′) of Comparative Examples 1 and 2 are as follows. The dispersibility and the dispersion stability were evaluated by the evaluation methods described above. (C-1), (C-2), (C-5) to (C-9) are water (ion-exchanged water, water adjusted to pH 2 with hydrochloric acid, pH adjusted to 10 with sodium hydroxide). Evaluation of dispersibility in water), (C-3) and (C-4) are evaluations of dispersibility in organic solvents (ethanol, acetone) and organic liquid [polyethylene glycol (weight average molecular weight = 2000)], (C-1 ′) and (C-2 ′) were evaluated for dispersibility in water, organic solvents, and organic liquids by the following method. The results are shown in Tables 1 and 2.

<Evaluation of dispersibility>
The medium and the magnetic nanoparticle composite are placed in a screw tube so that the magnetic nanoparticle composite is 1.0% by mass with respect to each medium. The medium and the magnetic nanoparticle composite are shaken by hand for 1 minute and allowed to stand for 30 minutes. Filtration was performed with a filter having a pore size of 5 μm manufactured by the company, and the determination was made based on the presence or absence of black lumps on the filter. In the case where no lump was observed, it was marked as ◯, and in other cases, it was marked as x.

<Method for evaluating dispersion stability>
With respect to those in which dispersion was confirmed in the dispersibility evaluation test, the dispersion stability over time was evaluated. After leaving at 25 ° C. for 1 month, after leaving at 50 ° C. for 1 month, each volume average particle size before standing was measured and evaluated. The volume average particle size was measured after shaking for 1 minute by hand before measuring the particle size.

<Measurement method of volume average particle diameter>
The volume average particle diameters of the magnetic nanoparticles (P) and the magnetic nanoparticle composite (C) were measured as follows. The magnetic nanoparticles (P) were calculated by calculation from the results of observation with a transmission electron microscope (Hitachi, H-7100) and measurement of the particle size of 100 particles. The measurement sample was prepared by dropping a drop of the dispersion containing the magnetic nanoparticles (P) with a dropper on a copper mesh treated with a collodion film and air-drying it as it was.
The magnetic nanoparticle composite (C) is a magnetic nanoparticle using a dynamic light scattering particle size measuring device (Horiba, LB-550) and the same solvent as the solvent in which each of the samples is dispersed. The dispersion liquid diluted so as to have a concentration of 0.1% by weight was injected into the measurement cell and measured.

From the results in the above table, the magnetic nanoparticle composite of the present invention can drastically improve the dispersibility in water and organic solvents by selecting a protective agent. It can also be seen that the dispersion stability over time is very excellent compared to the conventional products.

The magnetic nanoparticle composite of the present invention is excellent in dispersibility in water, organic solvents, and other organic liquids, and has high dispersion stability. New magnetic materials, particularly for electronic materials, for recording, for sealing, It is useful as a medical magnetic material.

Claims (3)

A magnetic nanoparticle composite in which the surface of a magnetic nanoparticle (P) is coated with a protective agent (A) having a heterocyclic cationic group (a) , wherein the heterocyclic cationic group (a) is A magnetic nanoparticle composite (C) which is an imidazolium group or a pyridinium group, and is formed by binding the magnetic nanoparticles (P) and the protective agent (A) with Fe—O—Si bonds . The magnetic nanoparticle composite (C) according to claim 1, wherein the magnetic nanoparticle (P) has a volume average particle diameter of 3 to 1000 nm. The magnetic nanoparticle composite (C) according to claim 1 or 2, wherein the magnetic nanoparticle (P) is a particle containing iron oxide.