JP2011094212A - Method for producing solvent-dispersible particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing solvent-dispersible particles, which can effectively produce the solvent-dispersible particles that have high dispersibility in a solvent having high polarity such as water in spite of showing ferromagnetism. <P>SOLUTION: This production method includes: the first step of forming a shell (temporary coating film) 72 which covers the surface of a multicomponent alloy particle 71 to obtain a core-shell particle (coated particle) 7; the second step of heat-treating the core-shell particle 7 to regulate the arrangement of atoms in the multicomponent alloy particle 71 and make the particle develop the ferromagnetism; and the third step of simultaneously removing the shell 72 of the core-shell particle 7 and making a surface modifier (m) bond to the surface of the multicomponent alloy particle 71 in the same liquid phase (in treatment liquid 6) to obtain the solvent-dispersible particle 1. The multicomponent alloy particle 71 includes, for instance, an FePt particle. If the surface modifier (m) has a functional group having an affinity for a polar solvent, the solvent-dispersible particle 1 can disperse in the polar solvent without causing agglomeration, in spite of showing the ferromagnetism. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing solvent-dispersible particles. More specifically, the present invention relates to a method for producing ferromagnetic ordered alloy nanocrystal particles that are excellent in dispersibility in polar solvents such as water and are expected to be applied to biochemistry and medical fields.

  In alloy particles such as FePt, the atomic arrangement has an irregular phase and a regular phase. However, when it has an ordered structure, it exhibits a relatively large magnetic anisotropy and has a particle size of 10 nm or less. However, since its magnetic properties are not lost, it is considered to be applied to high-density magnetic recording media using the properties (hereinafter, particles having such properties are referred to as “ordered alloy nanoparticles”). .)

  On the other hand, it is expected that such magnetic properties of alloy particles are applied to fields such as biochemistry, medical care, and diagnostic agents (magnetic beads) in recent years. In order to apply to these fields, it is required that the ordered alloy nanoparticles can be uniformly dispersed in a polar solvent, particularly water. When this requirement is satisfied, the ordered alloy nanoparticles and the dispersion liquid thereof are biocompatible.

  When producing alloy nanocrystal particles such as FePt by a liquid phase synthesis method, the atomic arrangement of the particles usually has an irregular structure (fcc phase), and the magnetic anisotropy of the particles is relatively small (superparamagnetism). However, when this is subjected to heat treatment, it transitions to an ordered structure (fct phase) in which Fe and Pt are alternately laminated. As a result, the ordered alloy nanoparticles exhibit large magnetic anisotropy (ferromagnetism).

Usually, this heat treatment requires a temperature of 500 ° C. or higher, so that there is a problem that the particles are fused and the particle size is increased. As one of solutions to this problem, a method is known in which particles are covered with a metal oxide such as SiO ₂ and heat treatment is performed. In this method, even if heat treatment at 500 ° C. or higher is performed, the particles can be transferred to a regular structure while suppressing the fusion of the particles. However, since the fusion of the coating layers occurs, the coating layer must be removed in order to disperse the particles in the solvent. Since the particles from which the coating layer has been removed have strong spontaneous magnetization, magnetic aggregation occurs. Even if ultrasonic waves are used, it is difficult to eliminate this aggregation. Therefore, it is very difficult to uniformly disperse the particles in a solvent in the same manner as for irregularly-structured particles.

  In order to deal with this problem, Patent Document 1 prevents aggregation of particles by a method of binding a cationic surfactant to the particle surface while dissolving the coating layer of the core-shell particles after heat treatment in an aqueous sodium hydroxide solution. Has been proposed. This method is performed in a system separated into two phases of an alkaline solution (aqueous sodium hydroxide) phase and an organic solvent (chloroform) phase. After dissolving the metal oxide coating layer in the alkaline solution phase, the organic solvent is then added. In this phase, a cationic surfactant is bonded to the surface of the bare particle from which the coating layer has been peeled off. As a result, the organic solvent phase includes ordered alloy nanoparticles having a cationic surfactant bonded to the surface.

WO2006 / 070572

  However, the ordered alloy nanoparticles obtained by the above method have a structure in which the hydrophobic group of the cationic surfactant is oriented toward the solvent side. Although it has dispersibility with respect to a solvent, it does not have dispersibility with respect to a highly polar solvent such as water.

  In the above method, the dissolution of the coating layer and the binding of the cationic surfactant are performed in different phases, but when the coating layer is peeled off in the alkaline solution phase, bare particles (such as a surfactant on the surface) The ordered alloy nanoparticles to which the qualifier is not attached are more likely to be close to each other, so that a stronger magnetic attractive force is generated and immediately aggregates before moving to the organic solvent phase.

  An object of the present invention is to provide a method for producing solvent-dispersible particles capable of efficiently producing solvent-dispersible particles having high dispersibility in a highly polar solvent such as water, despite exhibiting ferromagnetism. It is in.

Such an object is achieved by the present inventions (1) to (12) below.
(1) A method for producing solvent-dispersible particles obtained by bonding a surface modifier to multi-component alloy particles composed of two or more metal components,
Forming a temporary coating so as to cover the multi-component alloy particles, and obtaining coated particles;
Applying a heat treatment to the coated particles to regularize the atomic arrangement in the multi-component alloy particles and to develop ferromagnetism;
Removing the temporary coating in the liquid phase, exposing the surface of the multi-component alloy particles, and bonding the surface modifier to the surface;
In the third step, the removal of the temporary coating and the bonding of the surface modifier are simultaneously performed in the same liquid phase.

  Thereby, despite exhibiting ferromagnetism, the solvent-dispersible particles can be efficiently produced by a simple method.

(2) The said liquid phase is a manufacturing method of the solvent dispersible particle | grains as described in said (1) which is the process liquid which contains the said surface modifier and can melt | dissolve the said temporary film.
Thereby, removal of a temporary film and introduction of a surface modifier can be easily performed.

  (3) The said temporary film is a manufacturing method of the solvent dispersible particle | grains in any one of said (1) or (2) comprised by the oxide.

  An oxide is suitable as a constituent material for a temporary coating because it has high chemical stability, and is hardly altered or deteriorated even in heat treatment at a high temperature or hardly reacts with multi-component alloy particles.

  (4) The method for producing solvent-dispersible particles according to the above (3), wherein the oxide is a metal oxide having a higher ionization tendency than Fe.

  Thereby, when removing a temporary film using an acid solution or an alkali solution, a temporary film can be reliably removed, without attacking the multicomponent alloy particle with a small ionization tendency.

(5) The method for producing solvent-dispersible particles according to (3) or (4), wherein the oxide is SiO ₂ .

Since SiO ₂ has a simple coating method and can be dissolved in an alkaline solution, it is suitable as a temporary film.

  (6) The said temporary coating film is a manufacturing method of the solvent dispersible particle | grains in any one of said (1) or (2) comprised by the hydroxyapatite.

  Since hydroxyapatite can be dissolved even in a relatively weak acid solution, the work can be easily performed in a short time when the temporary coating is removed.

  (7) The method for producing solvent-dispersible particles according to any one of (1) to (6), wherein the surface modifier is soluble in the treatment liquid.

  As a result, each molecule of the surface modifier is uniformly dispersed in every corner of the processing liquid, so that the contact probability between the bare multicomponent alloy particles after removing the temporary coating and the molecule of the surface modifier Can be significantly increased. As a result, aggregation of multi-component alloy particles can be prevented more reliably.

  (8) The said surface modifier has the functional group which can be couple | bonded with any of a covalent bond, an ionic bond, and a coordinate bond with respect to the said multi-component alloy particle of said (1) thru | or (7). The manufacturing method of the solvent dispersible particle in any one.

  These bonds have higher bond strength than electrostatic interactions, which are the adsorption principle of surfactants, and interactions such as intermolecular forces, so the bonding state between the multi-component alloy particles and the surface modifier Can be maintained for a long time. In addition, these bonds are bonded in a shorter time than electrostatic interaction or intermolecular force (van der Waals force), so that the multi-component alloy particles are exposed and the surface modifier is bonded at the same time. As a result, solvent-dispersible particles can be reliably obtained.

  (9) The method for producing solvent-dispersible particles according to any one of (1) to (8), wherein the multicomponent alloy particles have an average particle diameter of 1 to 30 nm.

  If the particle size of the multicomponent alloy particles is within the above range, the magnetic properties of the multicomponent alloy particles are excellent in various applications in order to sufficiently reduce the mass of each multicomponent alloy particle while ensuring sufficient magnetic properties. The properties are exhibited and the dispersion state can be maintained for a long time in the dispersion.

  (10) The multi-component alloy particles include at least one element group A selected from transition metal elements other than Cu belonging to the fourth period of the long-period periodic table, the platinum group, and the elements of the long-period periodic table. The method for producing solvent-dispersible particles according to any one of the above (1) to (9), which is alloy particles containing at least one element group B selected from transition metal elements belonging to Group 11.

  Such an alloy particle can maintain ferromagnetism even when the particle size is reduced to the order of nm, because the atomic arrangement has a regular structure.

  (11) The method for producing solvent-dispersible particles according to (10), wherein the element group A includes Fe or Co, and the element group B includes Pt or Pd.

  When an ordered structure in which these element groups A and these element groups B are alternately stacked has a strong magnetic anisotropy in the direction of the easy axis of magnetization, the coercive force is as high as several kOe even when the particle diameter is 10 nm or less. Can have.

  (12) The method for producing solvent-dispersible particles according to any one of (1) to (11), wherein the multi-component alloy particles after the second step have a coercive force of 1 kOe or more.

  Multi-component alloy particles having such a coercive force are useful because they exhibit better magnetic properties in the use of solvent-dispersible particles.

  According to the present invention, the surface modifier can be efficiently introduced into the multi-component alloy particles, so that the multi-component alloy particles exhibit ferromagnetism, but do not aggregate and polar solvents such as water It is possible to provide a method for producing solvent-dispersible particles capable of producing ferromagnetic ordered alloy nanocrystal particles (solvent-dispersible particles) that are excellent in dispersibility.

It is a figure which shows typically the coupling | bonding state of the multicomponent alloy particle and surface modifier in this invention. It is a figure which shows typically a mode that a coating particle is made to contact the process liquid stored in the container. It is a XRD pattern of the coating particle before heat processing, the coating particle after heat processing, and the solvent dispersible particle | grains obtained by this invention. It is a TEM observation image of the coating particle after heat processing, and the solvent dispersible particle | grains obtained by this invention. It is the HM curve of the coating particle after heat processing, and the solvent dispersible particle | grains obtained by this invention.

  Hereinafter, the method for producing solvent-dispersible particles of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

  Solvent dispersible particles obtained by the method for producing solvent dispersible particles of the present invention include multi-component alloy particles (particles composed of two or more metal components) having an ordered atomic structure, and the surface of the particles. And a surface modifier to be coated.

Such solvent-dispersible particles have multi-component alloy particles exhibiting ferromagnetism, but their surfaces are covered with a surface modifier, so that even when dispersed in a polar solvent such as water, the particles are aggregated. Is prevented. For this reason, the solvent-dispersible particles obtained by the present invention can be applied to biochemistry and medical fields by utilizing the feature of ferromagnetic particles that can be dispersed in a polar solvent.
Hereinafter, the configuration of the solvent-dispersible particles will be sequentially described.

[Multi-component alloy particles]
The multi-component alloy particle in the present invention is not particularly limited as long as it contains two or more kinds of metal components and has a composition in which the atomic arrangement can take a regular structure by heat treatment. At least one element group A selected from transition metal elements other than Cu belonging to four periods, and at least one element group selected from platinum group and transition metal elements belonging to Group 11 of the long-period periodic table Alloy particles containing B may be mentioned. Such alloy particles can maintain ferromagnetism even if the particle size is reduced to the order of nm due to the atomic arrangement of the ordered structure.

  Specific examples of the element belonging to the element group A include Sc, Ti, V, Cr, Mn, Fe, Co, and Ni. These elements constitute element group A by one kind or two or more kinds. Among the above elements, at least one selected from Fe, Co, and Ni is preferable, and at least one selected from Fe and Co is more preferable. Since these elements each exhibit ferromagnetism alone, they are useful elements in consideration of the magnetic properties of multicomponent alloy particles.

  On the other hand, specific examples of elements belonging to element group B include Ru, Rh, Pd, Os, Ir and Pt as elements belonging to the platinum group, and as transition metal elements belonging to group 11 of the long-period periodic table Cu, Ag, and Au are mentioned. These elements constitute one or more element groups B. Among the above elements, at least one selected from Ru, Rh, Pd, Os, Ir and Pt is preferable, and at least one selected from Pd and Pt is more preferable.

  In particular, particles of FePd alloy, FePt alloy, CoPd alloy, CoPt alloy, etc. exhibit strong magnetic anisotropy in the direction of the easy axis of magnetization when the atomic arrangement has a regular structure. Therefore, even if the particle diameter is 10 nm or less, several kOe It can have a high coercive force. Therefore, these particles are suitable not only for high-density magnetic recording media and magnetoresistive elements, but also as magnetic alloy particles used in biochemistry, medical fields, and the like.

Here, when the alloy particles containing the element group A and the element group B are synthesized by a normal liquid phase synthesis method, the atomic arrangement thereof has a face-centered cubic structure (fcc structure). In this structure, the elements belonging to the element group A and the elements belonging to the element group B are irregularly arranged, and the magnetic anisotropy is relatively small. However, when such multi-component alloy particles are subjected to heat treatment, the atomic arrangement is regularized, and regular L1 in which layers composed of elements belonging to element group A and layers composed of elements belonging to element group B are alternately stacked. Transition to a _0- type face-centered tetragonal structure (fct structure). Such an ordered structure shows a large magnetic anisotropy in the direction of the easy axis of magnetization, and this magnetic anisotropy is not lost even if the particle diameter is reduced to 10 nm or less. For this reason, if it is multicomponent alloy particles as described above, magnetic alloy particles of the order of nm having a high coercive force can be obtained.

  The average particle size of such multi-component alloy particles is preferably about 1 to 30 nm from the viewpoint of dispersibility in a solvent. Further, the preferred particle size varies depending on the purpose, and when used for a magnetic recording medium, it is preferably about 5 to 10 nm, and when used in the biochemistry / medical field, it is preferably about 10 to 20 nm, depending on the application. If the particle size of the multi-component alloy particles is within the above range, the magnetic properties of the particles are exhibited in various applications in order to sufficiently reduce the mass of each particle while ensuring sufficient magnetic properties. The dispersion state for a long time can be maintained in the dispersion liquid.

  When the particle size of the multi-component alloy particles is below the lower limit, the particle size is too small, so that the magnetic properties of each particle become insufficient. On the other hand, when the particle diameter of the multi-component alloy particles exceeds the upper limit, sedimentation is likely to occur in the dispersion, and it may be difficult to produce solvent-dispersible particles having uniform dispersibility.

The coercive force of the multi-component alloy particles is preferably 3 kOe (2.39 × 10 ⁵ A / m) or more when used for a magnetic recording medium, and is 5 kOe (3.98 × 10 ⁵ A / m) or more. It is more preferable that On the other hand, when used in the biochemistry and medical fields, it is preferably 1 kOe (7.96 × 10 ⁴ A / m) or more. The multi-component alloy particles having such a coercive force exhibit more excellent magnetic properties in the above-described applications, and the usefulness of the solvent-dispersible particles is enhanced. That is, according to the present invention, solvent dispersible particles having good dispersibility with respect to a polar solvent can be obtained even when the multicomponent alloy particles having a high coercive force as described above are included.

[Surface modifier]
The surface modifier in this invention is couple | bonded so that the surface of the multicomponent alloy particle mentioned above may be coat | covered. Such a surface modifier has two or more functional groups that interact with each other for two or more kinds of metal components in the multicomponent alloy particles, and a solvent affinity for dispersing the multicomponent alloy particles in a polar solvent. It has one or more functional groups in one molecule.

  Here, examples of the interaction include an action of binding and adsorbing on the surface of the multi-component alloy particle, such as a covalent bond, an ionic bond, and a coordination bond. These bonds have higher bond strength than electrostatic interactions, which are the adsorption principle of surfactants, and interactions such as intermolecular forces, so the bonding state between the multi-component alloy particles and the surface modifier Can be maintained for a long time.

  The polar solvent refers to a liquid containing polar molecules (molecules having a permanent dipole) having a high relative dielectric constant, and examples thereof include water, methanol, acetic acid, and acetone.

  Here, two or more functional groups that interact with each other with respect to two or more metal components in the multi-component alloy particle will be described. Here, as an example, a binary alloy particle having an element a belonging to the element group A and an element b belonging to the element group B as metal components is described, and a functional group interacting with the particle will be described. A functional group that interacts with the element a is X, and a functional group that interacts with the element b is Y. A functional group having affinity for a polar solvent is Z. That is, in the following description, a surface modifier having a functional group X, a functional group Y, and a functional group Z in one molecule will be described. The functional group Z may also have a function of binding to a specific substance such as a protein. Furthermore, the functional group Z may be the same type of functional group as the functional group X or the functional group Y.

  By introducing such a surface modifier having each functional group into the surface of the multi-component alloy particle, the functional group X is bonded to the element a, and the functional group Y is bonded to the element b. In addition, since the functional group Z having solvent affinity exists as a residue, the multi-component alloy particles into which the surface modifier is introduced are well dispersed in the polar solvent.

  Examples of the functional group X include functional groups corresponding to hard bases, specifically, primary amino group, secondary amino group, carboxyl group and deprotonated product, hydroxy group and deprotonated product, ether group, phosphine Examples thereof include an oxide group, phosphonic acid group, phosphinic acid group, phosphoric acid group, sulfonic acid group, β-diketone group and the like. A hard base is a base classified based on the HSAB rule (hard and soft acids and based rule), is relatively difficult to polarize, has a high electronegativity, and forms a stable compound with a hard acid. To get. On the other hand, according to the HSAB rule, metal ions can be handled as acids, and their hardness and softness are considered to correspond to the ionization tendency of metals. For this reason, the functional group X has a larger ionization tendency among the element group A and the element group B, and causes a stable interaction with the element a belonging to the element group A corresponding to a hard acid.

  On the other hand, examples of the functional group Y include functional groups corresponding to soft bases, and specifically include aromatic amino groups, pyridyl groups, amide groups, mercapto groups and their deprotonated products, sulfide groups, phosphine groups, Examples thereof include a phosphate group, a thiophene group, an ethene group, an alkyl group, a cyano group, a thiocyano group, a sulfoxide group, and a sulfone group. A soft base is a base that is classified based on the HSAB rule, is relatively easily polarized, has a low electronegativity, and can form a stable compound with a soft acid. For this reason, the functional group Y has a smaller ionization tendency among the element group A and the element group B, and causes a stable interaction with the element b belonging to the element group B corresponding to the soft acid.

  The classification of hard bases and soft bases is relative as described above. Depending on the combination of functional groups, even the same functional groups may be classified as hard bases, or soft bases. It may be classified as

In addition, examples of the functional group Z include functional groups having affinity for polar solvents. Specifically, —COO ⁻ , —NH ₃ ⁺ , —SO ₃ ⁻ , —PO ₃ ²⁻ , —R _{^{3 N +, -O -, -O-}} , ethylene glycol group, and the like.

  Each functional group as described above is bonded to one molecular chain and constitutes a surface modifier. The form of this molecular chain may be any of linear, branched, cyclic and the like.

  By the way, when the functional group X interacts with the element a and the functional group Y interacts with the element b in this way, the surface modifier is firmly fixed to the surface of the multi-component alloy particle through two bonds. Is done. As a result, it is possible to prevent the surface modifier from being removed from the multicomponent alloy particles. That is, even if one of the two bonds is removed, the surface modifier is fixed through the remaining one bond, so that the probability that the surface modifier will be removed is reduced.

  Further, when two functional groups (functional group X and functional group Y) among functional groups in one molecule interact with the surface of the multi-component alloy particle, the remaining functional group Z is necessarily directed to the solvent side. The probability of orientation increases. As a result, the surface is surely covered with the functional group Z, and solvent dispersible particles with higher solvent dispersibility can be obtained.

  Here, since the multi-component alloy particle having the regular structure has a structure in which the layer of the element a and the layer of the element b are alternately laminated as described above, the element a and the element are formed on the particle surface. It is considered that it is easy to take a structure in which b is alternately arranged. For this reason, the probability that the element a and the element b are adjacent or close to each other is high, and the probability that the functional group X and the functional group Y of one molecule are bonded to the element a and the element b is high. .

  In other words, when the atomic arrangement of the multi-component alloy particle has an irregular structure (fcc structure), the element a and the element b are not necessarily adjacent or close to each other on the particle surface. Therefore, even if the functional group X interacts with the element a, the functional group Y may not reach the element b because the element b is separated from the element a. In this case, since there is only one coupling portion and the surface modifier is not sufficiently fixed, the surface modifier may be removed.

  On the other hand, when the multi-component alloy particle has an ordered structure (fct structure), as described above, there is a probability that two bonds are formed between the surface modifier and the surface of the multi-component bonded particle. Get higher. For this reason, the surface modifier is firmly fixed to the surface of the multi-component alloy particle.

  Here, the figure which shows typically the coupling | bonding state of the multicomponent alloy particle and surface modifier in this invention is shown in FIG.

  FIG. 1 shows an arrangement example of four surface modifiers m and the atoms of element a and element b to which they are bonded in the solvent-dispersible particle 1. FIG. 1 (ii) shows an example in which the surface modifier m is introduced on the surface of the multi-component alloy particle 11 having an irregular structure. As shown in this example, the surface modification bonded with one bond s. There is a child m. In this case, the surface modifier m is not sufficiently fixed.

  On the other hand, FIG. 1 (i) shows an example in which the surface modifier m is introduced on the surface of the multi-component alloy particle 10 having an ordered structure. As shown in this example, the element a and the element b are ordered. Since the surface modifiers m are regularly arranged according to the arrangement, the functional group X and the atom of the element a, and the functional group Y and the atom of the element b inevitably approach each other. There is a high possibility that s is formed in two places. As a result, the surface modifier m is bonded without a gap so as to cover the surface of the multi-component alloy particle 10 having an ordered structure, and the functional group Z is arranged on the surface of the solvent-dispersible particle 1 without a gap. . Such solvent-dispersible particles 1 exhibit particularly excellent dispersibility with respect to a polar solvent and can reliably maintain the inter-particle distance, so that aggregation thereof can be prevented.

  Further, from the viewpoint of the bonding between the surface modifier and the multi-component alloy particles, the present inventor has found an optimum range for the number of carbons between the functional group X and the functional group Y. This carbon number is preferably 1 to 4, and more preferably 1 to 3. If the number of carbons between the functional group X and the functional group Y is within this range, the distance between the functional group X and the functional group Y and the distance between the atom of the element a and the atom of the element b in the multi-component alloy particle The surface modifier has a structure in which both the functional group X and the functional group Y can interact with the surface of the multi-component alloy particle having a regular structure.

  When the number of carbons exceeds the upper limit, a plurality of surface modifiers are sterically hindered and easily interfere with each other, which may hinder the formation of bonds or reduce the introduction density of surface modifiers. There is. Further, depending on the type of functional group, for example, the functional group Y and the functional group Z may be the same type of functional group, and in that case, the functional group Y cannot be specified, so the number of carbons counted is two. In that case, the smaller one may be the above carbon number. In the above, the number of carbons is defined on the assumption that the main chain (molecular chain) of the surface modifier is a carbon chain, but the main chain between the functional group X and the functional group Y is an atom other than carbon. When it contains (for example, a sulfur atom), it is preferable that it is the same range as the said carbon number including the number of atoms.

  As described above, the functional group Z may be the same type as the functional group X or the functional group Y, and examples of such a functional group include a carboxyl group. This carboxyl group is preferably located at at least one end of the molecular chain (surface modifier). As described above, since the carboxyl group can be the functional group X or the functional group Y or the functional group Z, it is suitable for the surface modifier regardless of whether the carboxyl group is directed to the particle side or the solvent side. It becomes a state. That is, since the carboxyl group is positioned at the end of the molecular chain, the functional group Z can be reliably arranged on the solvent side.

  The surface modifier having the functional group X, the functional group Y, and the functional group Z as described above is not particularly limited, but 2-mercaptosuccinic acid, 2,3-dimercaptosuccinic acid, (S) -2-mercapto Glutaric acid, (S) -4-amino-6-mercaptohexanoic acid, 5-mercaptosalicylic acid, 2,4-diaminobenzoic acid, 2,4-pyridinedicarboxylic acid, homocysteine, carbocysteine, aspartic acid, glutamic acid, etc. Can be mentioned.

[Method for Producing Solvent Dispersible Particles]
Next, a method for producing the solvent-dispersible particles as described above (a method for producing the solvent-dispersible particles of the present invention) will be described.

  The manufacturing method includes [1] a first step of obtaining multi-component alloy particles by a liquid phase synthesis method, and [2] forming a shell (temporary coating) that covers the surface of the multi-component alloy particles. ), [3] a third step of ordering the atomic arrangement in the multi-component alloy particles by heat-treating the core-shell particles, and [4] And a fourth step of simultaneously performing removal and bonding of the surface modifier to the surface of the multi-component alloy particle in the same liquid phase.

Hereinafter, each process will be described sequentially.
[1] First, multi-component alloy particles are produced using a liquid phase synthesis method. The method for producing the particles is not particularly limited, and a known method such as a reverse micelle method, a polyol reduction method, or a thermal decomposition method can be employed.

  [2] Next, a shell is formed so as to cover the surface of the multi-component alloy particles. By forming this shell, it is possible to prevent the particles from fusing when the multi-component alloy particles are heat-treated in the second step described later. The shell protects the multi-component alloy particles from heat treatment and is removed in a process described later, and thus has a function as a heat-resistant coating and a temporary coating.

  Although there is no restriction | limiting in particular as a formation method of a shell, Nonpatent literature 1 (Q. Yan et al., Adv. Mater. 2006, 18, 2569-2573) and Nonpatent literature 2 (DC Lee et al., Appl. Phys. Chem. B2006, 110, 11160-11166) can be used. In particular, when the reverse micelle method is used as a method for producing particles, if the method described in Non-Patent Document 1 is applied, it is possible to form a shell while synthesizing particles using reverse micelles. The production process of solvent dispersible particles can be simplified. This method will be described.

  First, a nonpolar solvent such as isooctane is prepared as a solvent, a nonionic surfactant such as polyethylene glycol is prepared as a surfactant, and a mixed solution is prepared.

  Next, an aqueous solution of at least one metal salt selected from element group A is added to the mixed solution to obtain a reverse micelle solution. Further, the above mixed solution is prepared separately, and an aqueous solution of at least one metal salt selected from element group B is added to this mixed solution to prepare a reverse micelle solution.

The W ₀ value (= [water (mol)] / [surfactant (mol)]) used as an index of the size of the reverse micelle is correlated with the particle diameter of the multi-component alloy particles obtained by the reaction. By changing ₀ , the particle size can be controlled. In the present invention, W ₀ is preferably 1 to 5.

  Next, each reverse micelle solution is mixed, and a reaction solution is prepared by adding a small amount of alcohol (about 1-2% of the amount of solvent). When a reducing agent such as hydrazine is added to the reaction solution and stirred for about 3 hours, multicomponent alloy particles are produced in the reverse micelle (first step).

  Thereafter, a shell raw material such as tetraethyl orthosilicate is added to the reaction solution to form a shell so as to cover the multi-component alloy particles in reverse micelles, thereby obtaining core-shell particles (second step).

  After completion of the reaction, the reaction solution is sufficiently washed with ethanol or the like, and then subjected to solid-liquid separation treatment by a known means such as centrifugation. Thereby, the core-shell particle | grains which coat | covered the multi-component alloy particle | grains with the shell of a metal oxide are recoverable.

The constituent material of the shell is determined according to the raw material added to the reaction solution. For example, when silicon alkoxide is used, a shell of SiO ₂ is formed. Examples of the raw material for producing such a metal oxide include a corresponding metal halide, carboxylate, metal amide and the like in addition to the corresponding metal alkoxide. Moreover, as a raw material for producing | generating apatites, calcium hydroxide, calcium nitrate, etc. and phosphoric acid are mentioned.

By using such raw materials, it is composed of oxides such as SiO ₂ , TiO ₂ , Al ₂ O ₃ , MgO, ZrO ₂ , CeO ₂ and ZnO, and apatites such as hydroxyapatite and fluoroapatite. Shell is obtained. Oxides are suitable as a constituent material of the shell because they have high chemical stability, are not deteriorated or deteriorated even in heat treatment at high temperatures, and do not easily react with multicomponent alloy particles. In particular, SiO ₂ is suitable as a shell because it has a simple coating method and can be dissolved in an alkaline solution. On the other hand, since apatites, particularly hydroxyapatite, can be dissolved even in a relatively weak acid solution, when the shell is removed in the process described later, the work can be easily performed in a short time.

  The shell preferably has a melting temperature higher than the ordering temperature of the multi-component alloy particles and can be decomposed (dissolved) with an acid or an alkali. Therefore, it is preferable to appropriately select a shell raw material from this viewpoint. .

  When a metal oxide is used as the shell, it is preferable to use a metal oxide having a higher ionization tendency than Fe as the metal oxide. Thereby, when removing a shell by a liquid phase process in the process mentioned later, a shell can be removed reliably, without attacking the multicomponent alloy particle with a small ionization tendency.

  The average thickness of such a shell is preferably about 1 to 50 nm, and more preferably about 5 to 20 nm. By setting the thickness of the shell within the above range, the shell becomes a partition wall having a necessary and sufficient thickness between the multi-component alloy particles in the second step described later, so that the particles are fused. Can be surely prevented.

  [3] Next, the obtained core-shell particles are heat-treated. Thereby, the atomic arrangement in the multi-component alloy particles is ordered to obtain particles having a regular structure (third step).

  Here, when the heat treatment is performed on the core-shell particles, it is preferable that the core-shell particles are mixed with the inorganic salt particles and the core-shell particles. Thereby, it can prevent that core-shell particle | grains seize on wall surfaces, such as a container.

  Although the heat treatment conditions are not particularly limited, for example, the heat treatment is performed at 550 to 700 ° C. for about 0.5 to 12 hours. The heat treatment atmosphere is preferably an inert atmosphere or a reducing atmosphere, and more preferably a reducing atmosphere.

  Examples of inorganic salts include sodium chloride, potassium chloride, calcium chloride and the like. Since these inorganic salts have a relatively high water solubility and are inexpensive, they are useful because they can be removed simply by washing with water.

  The inorganic salt particles used are preferably finely pulverized in advance with a ball mill or mortar. Thereby, the inorganic salt particles can fill the gaps between the core-shell particles without gaps, and the seizure of the core-shell particles can be more reliably prevented.

  The average particle size of the inorganic salt is not particularly limited, but it is preferably about 0.5 to 5 times, more preferably about 0.7 to 3 times the average particle size of the multicomponent alloy particles.

  After the heat treatment, the reaction product is washed several times with a washing solution such as water to obtain core-shell particles having multi-component alloy particles in which the atomic arrangement is changed to an ordered structure.

  When the heat treatment is performed as described above, the atomic arrangement in the multi-component alloy particles is ordered, and ferromagnetism is exhibited.

  [4] Next, the heat-treated core-shell particles are brought into contact with the treatment liquid. This replaces the shell and surface modifier.

  FIG. 2 is a diagram schematically showing how the core-shell particles 7 are brought into contact with the treatment liquid 6 stored in the container. The core-shell particle 7 shown in FIG. 2 has multi-component alloy particles 71 and a shell 72 that covers the surface thereof.

  The processing liquid 6 shown in FIG. 2 (I) is a liquid that contains the surface modifier m described above and can dissolve the shell 72. When the core-shell particles 7 are brought into contact with such a treatment liquid 6, the shell 72 is dissolved (see FIG. 2 (II)). When the shell 72 is dissolved, the multi-component alloy particles 71 are exposed in a bare state, and the surface modifier m in the processing liquid 6 is immediately bonded to the exposed surface by interaction. The bond at this time is due to the interaction such as covalent bond, ionic bond and coordination bond as described above, and the bond strength is higher than that of electrostatic interaction or intermolecular force (van der Waals force). The bonding is relatively high and takes a short time. Therefore, at the same time as the multi-component alloy particles 71 are exposed, the surface modifier m is bonded, and as shown in FIG. 2 (III), the surface of the multi-component alloy particle 71 is coated with the surface modifier m. Dispersible particles 1 will be obtained (fourth step).

  As described above, in the present invention, the removal of the shell 72 and the bonding of the surface modifier m are simultaneously performed in one processing liquid (same liquid phase) 6, so that the multi-component alloy particle 71 is dissolved after the shell 72 is dissolved. It is possible to prevent the particles from aggregating with each other due to the magnetic attraction, and to ensure the dispersibility of the multi-component alloy particles 71.

  In other words, since the multi-component alloy particles 71 having an ordered atomic structure have a large magnetic attraction (magnetic property), the multi-component alloy particles 71 are likely to move in the liquid, and the multi-component alloy particles 71 begin to aggregate as the shell 72 dissolves. However, in the present invention, since the surface modifier m is dissolved and dispersed around the multi-component alloy particle 71, the surface modifier m is bonded to the surface of the multi-component alloy particle 71 as soon as the shell 72 is dissolved. Thereby, a sufficient physical distance is secured between the multi-component alloy particles 71. As a result, aggregation of the multi-component alloy particles 71 can be prevented.

  In addition, when there is a time difference between the removal of the shell and the bonding of the surface modifier, the aggregation of particles starts with the removal of the shell. Once aggregated, it is difficult to return to the separated state again even if an external force is applied to the aggregate.

  The same applies to the case where the removal of the shell and the bonding of the surface modifier are sequentially performed in different liquid phases. When the shell is removed in one of the two liquid phases and then the surface modifier is bonded in the other liquid phase, it takes some time for the particles to move between the liquid phases. Therefore, as in the case where there is a time difference, particle aggregation is unavoidable.

  When multi-component alloy particles aggregate in this way, surface modifiers bind to cover the aggregates, but such aggregates have low dispersibility and are not suitable for the applications described above. It becomes.

  As described above, the treatment liquid is not particularly limited as long as it contains a surface modifier and can dissolve the shell. For example, an acid solution or an alkali solution to which the surface modifier is added is preferably used. An acid solution or an alkali solution is suitable as a treatment liquid because it dissolves the above-described metal oxide or apatite reliably and has little influence on the multicomponent alloy particles.

  Although it does not specifically limit as an acid solution, Hydrochloric acid, nitric acid, a sulfuric acid, phosphoric acid etc. are mentioned. On the other hand, the alkaline solution is not particularly limited, and examples thereof include aqueous ammonia and aqueous sodium hydroxide.

  The concentration of the surface modifier in the treatment liquid is not particularly limited, but is preferably about 2 to 20% by mass, more preferably about 5 to 10% by mass.

  The ratio between the core-shell particles and the treatment liquid is preferably such that the ratio between the multi-component alloy particles and the surface modifier is 1:10 to 1: 100 in terms of mass ratio.

  The temperature of the treatment liquid to be contacted is preferably less than the decomposition temperature of the surface modifier (for example, less than 70 ° C.). In addition, the temperature of the treatment liquid can be controlled efficiently and simply by using a hot plate or the like and immersing the core-shell particles in the treatment liquid placed on the hot plate and stirring them. it can. In addition, by applying ultrasonic waves or vibration during stirring, particle aggregation associated with the salting-out effect can be eliminated.

  In addition, although the contact time of a process liquid is determined according to the density | concentration of a process liquid and it does not specifically limit, It is preferable that it is about 5-200 hours, and it is more preferable that it is about 10-100 hours.

  Further, the surface modifier used in the present invention is preferably one that dissolves in the above-described treatment liquid. As a result, each molecule of the surface modifier is uniformly dispersed in every corner of the processing solution. Therefore, in this step, the contact probability between the bare particle after removing the shell and the molecule of the surface modifier Can be significantly increased. As a result, aggregation of particles can be prevented more reliably.

  After the core-shell particles are brought into contact with the treatment liquid, the treatment liquid is subjected to solid-liquid separation treatment such as centrifugation as necessary, and the supernatant liquid is removed. Thereby, the melt | dissolution substance of a shell can be removed and solvent dispersible particles can be collect | recovered.

  In order to completely remove the remaining shell that has not been dissolved, it may be washed again with a diluted acid solution or alkaline solution. Thereafter, the recovered solvent dispersible particles are added to a polar solvent such as water and dispersed. When the polar solvent is water, impurities in the dispersion can be removed by performing dialysis treatment on the dispersion several times. On the other hand, when the polar solvent is a solvent other than water, impurities can be removed by performing a solid-liquid separation process such as centrifugation. In addition, since the particles have a large magnetization, impurities can be removed using magnetic separation.

  As described above, since the method for producing solvent-dispersible particles of the present invention simultaneously removes the shell and binds the surface modifier in one treatment liquid (the same liquid phase), immediately after the shell is removed, the multi-component Surface modifiers can be bonded to the surface of the alloy particles. Thereby, a sufficient physical distance is secured so that the multi-component alloy particles do not aggregate.

  Since the solvent-dispersible particles obtained by the method for producing solvent-dispersible particles of the present invention exhibit high ferromagnetism in spite of exhibiting ferromagnetism, these properties are utilized. Can be applied to biochemistry and medical fields.

  Applications of solvent-dispersible particles include, for example, contrast agents used in nuclear magnetic resonance imaging (MRI), magnetic beads used in magnetic hyperthermia using heat generated by alternating magnetic fields, and drugs on the particle surface. And a carrier for a drug delivery system to be administered into the body in a dry state. In any of these applications, since the solvent-dispersible particles are dispersed in a polar solvent such as water and the ferromagnetism of the particles is used, the solvent-dispersible particles obtained in the present invention are preferably used.

  As mentioned above, although embodiment of the manufacturing method of the solvent dispersible particle | grains of this invention was described, this invention is not limited to these.

  For example, the method for producing solvent-dispersible particles of the present invention may be one obtained by adding an arbitrary step to the embodiment.

Hereinafter, specific examples of the present invention will be described.
Production and evaluation of solvent-dispersible particles

Example 1
<1> Preparation of FePt / SiO ₂ core-shell particles 60 ml of isooctane (manufactured by Wako Pure Chemical Industries) and 8.528 g (= 0.0125 mol) of nonionic surfactant polyethylene glycol hexadecyl ether (manufactured by Aldrich) are mixed. Divided into. To one of them, 41.5 mg (= 0.10 mmol) of potassium chloroplatinate (K ₂ PtCl ₄ , manufactured by Wako Pure Chemical Industries, Ltd.) and water were added to prepare a platinum salt reverse micelle solution. Other hand the iron chloride hexahydrate _(FeCl 3 · _6H 2 O, manufactured by Kanto Kagaku) to prepare a Tetsushiogyaku micelle solution 29 mg (= 0.106 mmol) and added to the water. W ₀ was set to 5. Thereafter, two reverse micelle solutions and 700 μl of hexanol were mixed and stirred for a while, and then 0.4 ml (= 8 mmol) of hydrazine monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was added. It turned black. After stirring for 3 hours, 60 μl (= 0.27 mmol) of tetraethyl orthosilicate (TEOS, Tokyo Chemical Industry) was added, and the mixture was stirred for 60 hours with a stirrer. The product was washed with ethanol and acetone and then dispersed in ethanol. Thereby, FePt / SiO ₂ core-shell particles dispersed in ethanol were obtained.

<2> was dispersed in ethanol ordering FePt / SiO ₂ core-shell particles of FePt / SiO ₂ core-shell particles by heat treatment, the resulting dispersion mixed with sodium chloride 2g was pulverized in a mortar, it was volatilized solvent thereafter evaporator . The mixture was annealed at 600 ° C. for 4 hours in a forming gas (N ₂ : 96.5% by volume, H ₂ : 3.5% by volume mixed gas) atmosphere. After annealing, the mixture was washed several times with water and acetone to obtain FePt / SiO ₂ core-shell particles having an ordered structure.

  The crystal structure of the obtained particles was evaluated by X-ray diffraction (XRD) measurement, the particle size was observed by a transmission electron microscope (TEM), and the magnetic properties were evaluated by superconducting quantum interference magnetic flux (SQUID) measurement. The average particle size obtained was 15 nm.

<3> Preparation of FePt alloy particle dispersion water by peeling SiO ₂ shell and introducing surface modifier First, 0.75 g (concentration 0.5M) of 2-mercaptosuccinic acid (MSA, Wako Pure Chemical Industries), tetramethylammonium A processing solution was prepared by dissolving 3.6 g (concentration 2M) of hydroxide pentahydrate (TMAOH · 5H ₂ O, manufactured by Tokyo Chemical Industry Co., Ltd.) in 10 ml of water.

Next, 5 mg of the FePt / SiO ₂ core-shell particles after the heat treatment were immersed in this treatment solution, and the obtained reaction solution was left on a hot plate at 70 ° C. for 2 days. Thereby, the removal of the SiO ₂ shell and the introduction of the surface modifier were simultaneously performed in the same reaction solution. Since the particles aggregate due to the salting out effect, the reaction solution was appropriately dispersed by ultrasonic irradiation.

After the reaction, the reaction solution was centrifuged, and the supernatant was removed. In order to remove residual SiO ₂ , it was washed with 1M NaOH aqueous solution. Then, after washing with water again, when water was added, the obtained particles were well dispersed in water. Thereafter, dialysis was performed 5 times, and finally dispersed in water to obtain dispersed water obtained by dispersing 2-mercaptosuccinic acid-modified FePt alloy particles (solvent dispersible particles) in water.

<4> Evaluation of Solvent Dispersible Particles Regarding the obtained solvent dispersible particles, the crystal structure was evaluated by XRD measurement, the particle form was observed by TEM, and the magnetic properties were evaluated by SQUID measurement.

FIG. 3 shows the XRD result. In FIG. 3, (1) is an XRD pattern of FePt / SiO ₂ core-shell particles before heat treatment, (2) is an XRD pattern of FePt / SiO ₂ core-shell particles after heat treatment, and (3) is an aqueous dispersion treatment (SiO ₂ removal and It is an XRD pattern of 2-mercaptosuccinic acid modified FePt alloy particles (solvent dispersible particles) after introduction of a surface modifier. By comparing the XRD pattern of (1) and the XRD pattern of (2), it was confirmed that the crystal structure was transformed into an ordered phase by heat treatment. A characteristic peak was observed in the XRD pattern of (2), and the arrangement of this peak was in good agreement with the card data of the FePt alloy having an ordered structure (fct structure). Further, by comparing the XRD pattern of (2) and the XRD pattern of (3), the crystal structure of the particles dispersed in water is not changed from the crystal structure after the heat treatment, and the introduction of the surface modifier is the FePt alloy. It was confirmed that the crystal structure of the particles was not affected.

FIG. 4 shows the TEM observation results. 4A is an observation image of FePt / SiO ₂ core-shell particles after heat treatment, and FIG. 4B is an observation image of 2-mercaptosuccinic acid-modified FePt alloy particles after water dispersion treatment. In (a), it can be confirmed that the FePt alloy particles in the dark color region are covered with the SiO ₂ shell in the light color region. In (b), it is considered that SiO ₂ could be removed because no shell in the light color region was observed around the FePt alloy particles. It is thought that the particles are arranged in a bead shape due to magnetic interaction, but since there are gaps between the particles, the surface modifier is bonded to the particle surface to prevent aggregation of the particles This is probably because of this.

FIG. 5 shows an HM curve obtained by SQUID measurement. In FIG. 5, (1) is an HM curve of FePt / SiO ₂ core-shell particles after heat treatment, and (2) is an HM curve of 2-mercaptosuccinic acid-modified FePt alloy particles after water dispersion treatment. . The HM curves of (1) and (2) almost overlap, the coercivity is 5.6 kOe for (1), 5.5 kOe for (2), the residual magnetization is 498 emu / cc for (1), (2 ) Was 427 emu / cc, and the magnetic characteristics were almost the same between (1) and (2). From the above results, it was confirmed that the solvent-dispersible particles obtained in Example 1 were composed of a ferromagnetic material.

  Further, the obtained solvent-dispersible particles were dispersed in water and allowed to stand for 1 day. However, formation of precipitates and the like was not observed, and after that, they were left for 7 days, but no change was observed.

(Example 2)
The same process as in Example 1 was performed until the preparation of the FePt / SiO ₂ core-shell particles after the heat treatment.

  Subsequently, 0.6 g (concentration 0.5M) of L-cysteine (Cys, manufactured by Tokyo Chemical Industry Co., Ltd.) and 3.6 g of tetramethylammonium hydroxide pentahydrate (concentration 2M) were dissolved in 10 ml of water, Was prepared.

Next, 5 mg of the FePt / SiO ₂ core-shell particles after the heat treatment were immersed in this treatment solution, and the obtained reaction solution was left on a hot plate at 70 ° C. for 2 days. The following operation was performed in the same manner as in Example 1 to obtain dispersed water obtained by dispersing L-cysteine-modified FePt alloy particles (solvent dispersible particles) in water.

When the crystal structure of the obtained solvent-dispersible particles was evaluated by XRD measurement, the particle structure was a regular phase, and there was no change before and after the water dispersion treatment. It was confirmed by TEM observation that the SiO ₂ shell was removed. The magnetic characteristics were evaluated by SQUID measurement, the coercive force was 5.5 kOe, the residual magnetization was 431 emu / cc, and there was almost no change before and after water treatment.

  Further, the obtained solvent-dispersible particles were dispersed in water and allowed to stand for 1 day. However, formation of precipitates and the like was not observed, and after that, they were left for 7 days, but no change was observed.

(Example 3)
The same process as in Example 1 was performed until the preparation of the FePt / SiO ₂ core-shell particles after the heat treatment.

  Next, 0.73 g (concentration 0.5M) of L-glutamic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) and 3.6 g of tetramethylammonium hydroxide pentahydrate (concentration 2M) are dissolved in 10 ml of water to prepare a treatment solution. did.

Next, 5 mg of the FePt / SiO ₂ core-shell particles after the heat treatment were immersed in this treatment solution, and the obtained reaction solution was left on a hot plate at 75 ° C. for 1 day. The following operations were carried out in the same manner as in Example 1 to obtain dispersed water obtained by dispersing L-glutamic acid-modified FePt alloy particles (solvent dispersible particles) in water.

When the crystal structure of the obtained solvent-dispersible particles was evaluated by XRD measurement, the particle structure was a regular phase, and there was no change before and after the water dispersion treatment. It was confirmed by TEM observation that the SiO ₂ shell was removed.

  Further, the obtained solvent-dispersible particles were dispersed in water and allowed to stand for 1 day. However, formation of precipitates and the like was not observed, and after that, they were left for 7 days, but no change was observed.

Example 4
Core-shell particles were obtained in the same manner as in Example 1 except that a mixed solution of an aqueous phosphoric acid solution and a calcium hydroxide suspension was used instead of tetraethyl orthosilicate. The obtained core-shell particles are FePt / HAp core-shell particles in which a shell of hydroxyapatite (HAp) is formed so as to cover the FePt alloy particles.

  Hereinafter, heat treatment, shell peeling, and introduction of a surface modifier were sequentially performed in the same manner as in Example 1. However, when shell peeling and surface modifier were introduced, tetramethylammonium hydroxide pentahydrate was added. Instead, the same procedure as in Example 1 was performed except that hydrochloric acid (concentration 1% by weight) was used.

  When the crystal structure of the obtained solvent-dispersible particles was evaluated by XRD measurement, the particle structure was a regular phase, and there was no change before and after the water dispersion treatment. It was confirmed by TEM observation that the HAp shell was removed.

  Further, the obtained solvent-dispersible particles were dispersed in water and allowed to stand for 1 day. However, formation of precipitates and the like was not observed, and after that, they were left for 7 days, but no change was observed.

(Comparative Example 1)
The same process as in Example 1 was performed until the preparation of the FePt / SiO ₂ core-shell particles after the heat treatment.

Then, to remove the SiO ₂ shell, it is immersing the FePt / SiO ₂ core-shell particles 5mg tetramethylammonium hydroxide aqueous solution (2M) 10 ml, allowed to stand for 2 days to 70 ° C. on a hot plate. After the reaction, the reaction solution was centrifuged, and the supernatant was removed. After washing with a 1M NaOH aqueous solution to remove residual SiO ₂ , water was added again, and centrifugation was performed at 4000 rpm for 10 minutes to collect FePt alloy particles. The particles were dried at room temperature for 12 hours.

  Next, 10 ml of water and 0.75 g of 2-mercaptosuccinic acid were mixed to prepare a reaction solution and stirred for 2 days. After stirring, after washing with water again, water was added, and particles obtained by irradiating with ultrasonic waves for 10 minutes were dispersed in water.

  When the obtained FePt alloy particles were dispersed in water and allowed to stand overnight, all the particles precipitated.

Moreover, when the crystal structure of the obtained FePt alloy particles was evaluated by XRD measurement, the particle structure was a regular phase. Moreover, it was confirmed by TEM observation that the SiO ₂ shell was removed. On the other hand, in the TEM observation image, it was recognized that the particles were aggregated.

(Comparative Example 2)
An attempt was made to disperse the particles in water by dispersing FePt alloy particles in an organic solvent using the method of Patent Document 1 and then performing surface modifier substitution.

The same process as in Example 1 was performed until the preparation of the FePt / SiO ₂ core-shell particles after the heat treatment.

Next, 0.03 g of the FePt / SiO ₂ core-shell particles, 3 g (4M) of aqueous sodium hydroxide, 5 g of chloroform, and 0.5 g of cetyltrimethylammonium bromide (CTAB) were mixed and stirred for 24 hours.

  After completion of stirring, 15 g of chloroform was added to the reaction solution, followed by centrifugation at 4000 rpm for 10 minutes to extract the chloroform phase. The yield of particles recovered in the chloroform phase was 12%, and most of the particles precipitated.

  Next, 0.75 g of 2-mercaptosuccinic acid and 10 ml of water were added to the chloroform dispersion of FePt alloy particles obtained by the above method, and the mixture was stirred for 24 hours. After the stirring was completed, the reaction solution was allowed to separate into two phases, and then the aqueous phase was extracted by sucking the upper phase with a pipette, but the particles were hardly present in the aqueous phase.

(Summary)
From the above results, it was revealed that the solvent-dispersible particles obtained in each Example showed high dispersibility with respect to polar solvents such as water.

  On the other hand, it was revealed that the particles obtained in each comparative example were already aggregated, and even when dispersed in a polar solvent such as water, precipitation occurred.

DESCRIPTION OF SYMBOLS 1 Solvent dispersible particle | grains 10 Multicomponent alloy particle which has a regular structure 11 Multicomponent alloy particle which has an irregular structure 6 Treatment liquid 7 Core shell particle 71 Multicomponent alloy particle 72 Shell a Element which belongs to element group A b It belongs to element group B Element m Surface modifier s Bond X, Y, Z Functional group

Claims (12)

A method of producing solvent-dispersible particles obtained by bonding a surface modifier to multi-component alloy particles composed of two or more metal components,
Forming a temporary coating so as to cover the multi-component alloy particles, and obtaining coated particles;
Applying a heat treatment to the coated particles to regularize the atomic arrangement in the multi-component alloy particles and to develop ferromagnetism;
Removing the temporary coating in the liquid phase, exposing the surface of the multi-component alloy particles, and bonding the surface modifier to the surface;
In the third step, the removal of the temporary coating and the bonding of the surface modifier are simultaneously performed in the same liquid phase.   The method for producing solvent-dispersible particles according to claim 1, wherein the liquid phase is a treatment liquid containing the surface modifier and capable of dissolving the temporary coating.   The method for producing solvent-dispersible particles according to claim 1, wherein the temporary coating is made of an oxide.   The method for producing solvent-dispersible particles according to claim 3, wherein the oxide is a metal oxide having a higher ionization tendency than Fe. The oxides, the production method of solvent-dispersible particle according to claim 3 or 4 is SiO _2.   The method for producing solvent-dispersible particles according to claim 1, wherein the temporary coating is composed of hydroxyapatite.   The method for producing solvent-dispersible particles according to claim 1, wherein the surface modifier is dissolved in the treatment liquid.   The solvent according to any one of claims 1 to 7, wherein the surface modifier has a functional group that can be bonded to the multicomponent alloy particle by any one of a covalent bond, an ionic bond, and a coordinate bond. A method for producing dispersible particles.   The method for producing solvent-dispersible particles according to any one of claims 1 to 8, wherein the multi-component alloy particles have an average particle size of 1 to 30 nm.   The multi-component alloy particles include at least one element group A selected from transition metal elements other than Cu belonging to the fourth period of the long-period periodic table, the platinum group, and the eleventh group of the long-period periodic table. The method for producing solvent-dispersible particles according to any one of claims 1 to 9, wherein the particles are alloy particles containing at least one element group B selected from the transition metal elements to which they belong.   The method for producing solvent-dispersible particles according to claim 10, wherein the element group A includes Fe or Co, and the element group B includes Pt or Pd.   The method for producing solvent-dispersible particles according to any one of claims 1 to 11, wherein the coercive force of the multi-component alloy particles after the second step is 1 kOe or more.

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