Methods for manufacturing coated metal nanoparticles and a composite material comprising same, use of such a material and device comprising same

Abstract

A method for preparing coated metal nanoparticles, each nanoparticle comprising a core constituted of at least one metal M and a layer constituted of at least one polymer, the layer coating the metal core. The method comprises the steps: (a.sub.1) preparing a solution A comprising the at least one metal M in the form of cations M.sup.n+, n being an integer comprised between 1 and 3, each metal M being a transition metal of atomic number comprised between 21 and 30, a polyol, and a noble metal salt; (a.sub.2) preparing a solution B comprising at least one organic monomer of the at least one polymer, in an organic solvent; (b) mixing solutions A and B, this mixture being heated to the boiling temperature of the polyol; and (c) recovering the coated metal nanoparticles.

Claims

1. A method for preparing coated metal nanoparticles, each nanoparticle comprising a core constituted of at least one metal M and a layer constituted of at least one polymer, the layer coating the metal core, which method comprises the following steps: (a.sub.1) preparing a solution A comprising: said at least one metal M in the form of cations M.sup.n+, n being an integer comprised between 1 and 3, each metal M being a transition metal of atomic number comprised between 21 and 30, a polyol, and a noble metal salt, (a.sub.2) preparing a solution B comprising at least one organic monomer of said at least one polymer, in an organic solvent, (b) mixing the solutions A and B, this mixture being heated to the boiling temperature of the polyol, whereby coated metal nanoparticles are obtained, and (c) recovering the coated metal nanoparticles.

2. The method according to claim 1, wherein each transition metal M is selected from the group constituted of Ni, Fe and Co.

3. The method according to claim 2, wherein the core is constituted of Ni, Fe, Co, NiFe, CoNi, FeCo or NiFeCo.

4. The method according to claim 3, wherein, the core being constituted of a CoNi alloy, the Co/Ni molar ratio is comprised between 50/50 and 90/10.

5. The method according to claim 1, wherein said at least one metal M in the form of cations M.sup.n+ is a metal salt.

6. The method according to claim 5, wherein said metal salt comprises at least one element selected from the group constituted of an acetate, an acetyl acetonate, a hydroxide and an oxide of the transition metal M.

7. The method according to claim 1, wherein the molar concentration of cations M.sup.n+ [M.sup.n+], in the solution A, is comprised between 0.02 mol/L and 1 mol/L.

8. Method according to claim 1, wherein the polyol is a diol.

9. The method according to claim 8, wherein the diol is an -diol.

10. The method according to claim 9, wherein the -diol is butane-1,2-diol.

11. The method according to claim 1, wherein the noble metal salt is selected from osmium chloride, ruthenium chloride and iridium chloride.

12. The method according to claim 1, wherein the ratio of molar concentrations between the noble metal and the cations M.sup.n+, noted [noble metal]/[M.sup.n+], is comprised between 0.005 and 0.1.

13. The method according to claim 1, wherein the solution A further comprises sodium hydroxide, in a molar concentration [NaOH] of at most 0.5 mol/L.

14. The method according to claim 1, wherein said at least one organic monomer is selected from the group constituted of styrene, an alkyl (meth)acrylate, a fluorocarbon monomer, norbornene and ethylene.

15. The method according to claim 1, wherein n is equal to 2.

16. A method for manufacturing a composite material, which method comprises the following steps: (1) preparing coated metal nanoparticles, each nanoparticle comprising a core constituted of at least one metal M and a layer constituted of at least one polymer, the layer coating the metal core, by the implementation of the preparation method according to claim 1, (2) mixing the nanoparticles prepared at step (1) in a polymeric matrix, whereby a formulation comprising the nanoparticles dispersed in the polymeric matrix is obtained, (3) obtaining a deposition of the formulation at the end of step (3), and (4) applying a heat treatment of the formulation deposited at step (3), whereby the composite material is obtained.

17. The method according to claim 16, wherein the polymeric matrix comprises at least one polymer selected from the group constituted of a polystyrene, a poly(methyl methacrylate), a fluorocarbon polymer, a polynorbornene and a polyethylene.

18. The method according to claim 16, wherein the polymer of the layer coating each nanoparticle and the polymer of the polymeric matrix are identical.

19. An antenna, comprising, as dielectric material, a composite material obtained by the implementation of the manufacturing method according to claim 17.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 corresponds to an image taken using a scanning electron microscope (SEM) of non-coated CoNi nanoparticles.

(2) FIG. 2 corresponds to an image taken using a scanning electron microscope (SEM) of CoNi nanoparticles coated with a layer of polystyrene, such as obtained by the implementation of the method according to the invention.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(3) 1. Preparation of Non-Coated CoNi Nanoparticles

(4) The CoNi nanoparticles were prepared from cobalt acetate tetrahydrate, Co(CH.sub.3COO).sub.2, 4 H.sub.2O, and nickel acetate tetrahydrate Ni(CH.sub.3COO).sub.2, 4 H.sub.2O.

(5) 1.59 g of cobalt acetate tetrahydrate and 0.398 g of nickel acetate tetrahydrate were dissolved in 100 mL of butane-1,4-diol, in a Co/Ni molar ratio of 80/20. To the mixture thereby obtained are next successively added 600 mg of sodium hydroxide NaOH pellets, so as to reach a molar concentration of NaOH, in the solution, of 0.15 mol/L, and 52 mg of ruthenium trichloride RuCl.sub.3. The resulting solution has the following characteristics: a molar concentration of cobalt-nickel [Co+Ni]=0.08 mol/L, a [Ru]/[Co+Ni] molar ratio=2.5%, and a molar concentration of NaOH [NaOH]=0.15 mol/L.

(6) The reaction mixture thereby obtained is then heated to 170 C., under mechanical stirring, for 30 min, after which time a black coloured solution is obtained.

(7) The CoNi nanoparticles are next collected and washed, three times, with ethanol by centrifugation for 5 min and at 8000 rpm, before being dried in an oven.

(8) With reference to FIG. 1, which corresponds to the SEM image of the nanoparticles thereby prepared, it is observed that the nanoparticles obtained by the implementation of the preparation method described above are in the form of nanoparticles which are agglomerated with each other. These agglomerates have a size comprised between 30 nm and 60 nm, it being noted that, by complementary analysis, it has been determined that the nanoparticles themselves have a size of 2 nm to 3 nm.

(9) It is thus easily understood that a composite material that would be obtained from a formulation comprising the nanoparticles prepared in accordance with the protocol that has just been described cannot have a homogeneous distribution of the nanoparticles within the polymeric matrix. This has the consequence that an electric current is capable of being established, at least within said composite material, or even with other materials with which it could come into contact, making it lose its dielectric properties to said composite material.

(10) 2. Preparation of CoNi Nanoparticles Coated According to the Method of the Invention

(11) The CoNi nanoparticles were prepared from cobalt acetate tetrahydrate, Co(CH.sub.3COO).sub.2, 4H.sub.2O, and nickel acetate tetrahydrate Ni(CH.sub.3COO).sub.2, 4H.sub.2O.

(12) As in the preceding example 1, 1.59 g of cobalt acetate tetrahydrate and 0.398 g of nickel acetate tetrahydrate were dissolved in 100 mL of butane-1,2-diol, in a Co/Ni molar ratio of 80/20. To the mixture thereby obtained are next successively added 600 mg of sodium hydroxide pellets, so as to reach a molar concentration of NaOH, in the solution, of 0.15 mol/L, and 52 mg of ruthenium trichloride RuCl.sub.3. The resulting solution A has the following characteristics: a molar concentration of cobalt-nickel [Co+Ni]=0.08 mol/L, a [Ru]/[Co+Ni] molar ratio=2.5%, and a molar concentration of NaOH [NaOH]=0.15 mol/L.

(13) Two solutions B were prepared, each comprising styrene and benzoyl peroxide (Luperox) in tetrahydrofuran THF under argon at 25 C., the monomer/Luperox ratio being above 100 and below 400.

(14) To characterise the polymer that will form the polymeric layer of the CoNi nanoparticles, the Inventors have examined the reaction product such as obtained in situ from one of the two solutions B: it is a polystyrene having a number average molar mass Mn, such as measured by exclusion chromatography, of 35000 g/mol.

(15) The other solution B is added to the solution A. The reaction mixture thereby obtained is then heated to 170 C., under mechanical stirring, for 30 min, at the end of which a black coloured solution is obtained.

(16) The coated metal nanoparticles thereby obtained are next collected and washed, three times, with ethanol by centrifugation for 5 min and at 8000 rpm, before being dried in an oven.

(17) With reference to FIG. 2, it may be observed that the SEM image shows that the coated metal nanoparticles such as obtained by the implementation of the preparation method according to the invention are in the form of individualised rods, of an average length of 200 nm.

(18) This length of the coated metal nanoparticles is directly linked to the reaction time of the reaction mixture. Indeed, if a reaction time of 30 min makes it possible to obtain an average length of 200 nm, experience shows that a reaction time of 10 h enables average lengths of coated metal nanoparticles of 10 m to be reached.

(19) It is thus possible, without any difficulty, to adapt the reaction time to the average length of the coated metal nanoparticles that it is sought to obtain.

(20) The coated metal nanoparticles such as obtained by the method according to the invention may then be introduced into a polymeric matrix. The formulation thereby obtained may be deposited on a surface in the form of a layer in which the nanoparticles are spread out in a regular manner and along a same direction. The polymeric coating of the nanoparticles makes it possible to ensure that no short circuit forms in the composite material obtained after heat treatment, even in the hypothesis where some of the nanoparticles could come into contact with each other. The composite material thus has concurrently magnetic and dielectric properties.

BIBLIOGRAPHY

(21) [1] WO 2007/106771 A2