EP2945733A2 - Reinforced gel capsules, and reinforced lyophilized gel capsules, containing nano-objects and processes for preparing same - Google Patents

Abstract

Reinforced gel capsule comprising a solvent, in which are uniformly distributed nano-objects and/or nanostructures and/or submicronic objects, coated with macromolecules of polysaccharide(s), said macromolecules forming, in at least one part of the capsule, a gel by crosslinking with cations of at least one element, and in which the external surface of the capsule is covered with crystals of hydroxide of said element. Process for preparing said reinforced gel capsule. Reinforced gel lyophilized capsule prepared by lyophilization and then exposure, to a gas containing carbon dioxide, of said reinforced gel capsule and process for preparing same.

Description

 GELIFIED CAPSULES, AND LYOPHILIZED, REINFORCED CAPSULES CONTAINING NANO-OBJECTS AND PREPARATION METHODS THEREFOR.

DESCRIPTION

TECHNICAL AREA

The present invention relates to gelled, reinforced capsules containing nano-objects.

 More specifically, the present invention relates to gelled, reinforced capsules containing nano-objects such as carbon nanotubes or silicon nanoparticles, and / or submicron objects and / or nanostructures.

 The present invention also relates to the reinforced lyophilized gelled capsules obtained by lyophilization of said gelled capsules.

 By "reinforced" is meant capsules that are less fragile than known capsules.

 The present invention further relates to polymeric matrix nanocomposite materials comprising these reinforced gelled capsules, or gelled, lyophilized capsules, and reinforced or prepared from these gelled capsules.

 The invention also relates to a process for the preparation of these capsules and to a process for preparing these nanocomposite materials with a polymer matrix from these capsules.

 Finally, the invention relates to uses of these capsules.

STATE OF THE PRIOR ART

The technical field of the invention can, in general, be considered as that of the inclusion, the incorporation, the confinement, for various purposes of nano-objects such as nanoparticles or submicron objects in materials, such as polymers. Thus, according to a first aspect of the invention, the technical field of the invention can more precisely be defined as that of the protection, confinement of nanoparticles and nano-objects for their manipulation.

 It should also be noted that the invisible nature of these nano-objects due to their small size and the lack of knowledge about their impacts on the biological and living world also requires containment and encapsulation to control the spread and to satisfy the precautionary principle.

 The technical field of the invention may, more precisely in another aspect, be defined as that of composite materials, more specifically nanocomposite materials and in particular nanocomposite materials with a polymer matrix.

 The nanocomposite polymer matrix materials are multiphasic materials, in particular two-phase materials, which comprise a polymer matrix forming a first phase in which nano-objects such as nanoparticles forming at least a second phase, which are generally known as reinforcement or load.

 The nanocomposites are so called because at least one of the dimensions of the objects such as particles forming the reinforcing phase or charge is at the nanoscale, namely generally less than or equal to 100 nm, for example of the order of one nanometer at one or a few tens of nanometers, in particular from 1 to 100 nm. As a result, these objects and particles are called nano-objects or nanoparticles.

 Document FR-A1-2 934 600 discloses agglomerates or capsules comprising a solvent, in which nano-objects or nanostructures coated with macromolecules of polysaccharide are homogeneously distributed, said macromolecules forming in at least a part of the agglomerate a gel by crosslinking with positive ions.

The document WO-A1-2010 / 012813 describes lyophilized capsules or agglomerates which are prepared by lyophilization of the capsules or gelled agglomerates described in the document FR-A1-2 934 600. It is stated in these documents that the capsules described therein make it possible, in particular, to prepare nanocomposite materials with a polymer matrix in which nano-objects or nanostructures are dispersed, distributed, organized in a homogeneous manner, in particular at a low concentration.

 These capsules can also act as chemical microreactors.

According to these documents, these capsules also ensure the containment of nano-objects and control their dissemination in the environment.

 It can be considered that the capsules of FR-A1-2 934 600, comprise an outer polysaccharide membrane, for example alginate which surrounds the capsule and confines the nano-objects or nanostructures.

 However, this membrane composed essentially of polysaccharide macromolecules, for example stacked macromolecules of alginate, proves to be fragile at the time of lyophilization.

 In FIG. 1, the tear that occurs in the outer membrane of the gelled capsules during the freeze-drying of these capsules is clearly observed according to the process described in the document WO-A1-2010 / 012813.

 In the same way, the outer membrane of the lyophilized capsules of document WO-A1-2010 / 012813 can tear as shown in FIG. 2.

 In this Figure, it is possible to observe torn zones of the outer membrane of a freeze-dried capsule prepared according to the method of the document

WO-A1-2010 / 012813.

 The fragility of the gelled capsules described in document FR-A1-2 934 600, as well as the freeze-dried gelled capsules of document WO-A1-2010 / 012813, therefore pose extremely important problems with regard to "nano safety", in particular Indeed the capsules no longer play their role of confinement, nano-objects and nanostructures and all the contents of the capsules, escape and are disseminated in the environment.

In addition, as is the case of the capsule shown in FIG. 2, the lyophilized capsules can be used as a microreactor, for example as a microreactor for the chemical vapor deposition (CVD) technique (cf. FR-A-2 981 643), and the membrane must then in principle ensure the confinement of the reagents inside the capsule.

 The tearing of the membrane of FIG. 2 causes a rupture of the confinement and allows the reagents and reaction products to escape, thereby helping to reduce the yield of these reactions. To the problems related to the spread are then added those due to this loss of yield.

 There is therefore a need, in view of the above, to make the capsules prepared in FR-A1-2 934 600 and WO-A1-2010 / 012813 less fragile, to increase their mechanical strength, so that their function of containment is ensured and maintained, and so that their contents namely nano-objects, nanostructures is not widespread, disseminated in the environment, even when they are subject to constraints.

 There is also a need, when these capsules are used as microreactors, so that reagents and reaction products do not escape from the capsules causing reaction yield losses.

 The object of the present invention is, among others, to meet this need.

The object of the present invention is still to provide capsules which do not have the disadvantages, defects, limitations and disadvantages of the capsules prepared in the documents FR-A1-2 934 600 and WO-A1-2010 / 012813 and which solve the problems. capsules of these documents.

STATEMENT OF THE INVENTION

This and other objects are achieved, according to a first aspect of the invention, by providing a reinforced gelled capsule comprising a solvent, in which nano-objects and / or submicron objects are homogeneously distributed. and / or nanostructures, coated with macromolecules of polysaccharide (s), said macromolecules forming, in at least a part of the capsule, a gel by crosslinking with cations of at least one element, and in which the outer surface of the capsule is covered with hydroxide crystals of said element. Each macromolecule consists of a single polysaccharide and a single polysaccharide or polysaccharides may be used.

 The reinforced gelled capsule according to the invention differs fundamentally from the gelled capsules of document FR-A1-2 934 600 in that its external surface is covered with hydroxide crystals which are generally in the form of discrete islands.

 In other words, in the gelled, reinforced capsule according to the invention, a shell of hydroxide, for example calcium hydroxide, is produced, generally discontinuous in the thickness, and in the form of sheets in the plane, around gelled capsules of FR-A1-2 934 600.

 The outside of the gelled capsule is generally composed only of a layer of polysaccharide (s), such as a reticulated alginate, organized in sheets, with for example a number of sheets of 10 to 100. Each of the leaflets may have for example a thickness of 1 to 10 nm, which can give for example a total thickness of 100 nm to 1 μιη, in particular 100 nm. The outer surface of this layer of crosslinked polysaccharide (s) constitutes the outer surface of the gelled capsule.

 As a result, thanks to these hydroxide crystals, the reinforced gelled capsule according to the invention has an increased mechanical strength, and is much less fragile than the gelled capsules of document FR-A1-2 934 600, which is the reason for which this capsule is called "reinforced".

 The reinforced gelled capsule according to the invention fulfills its role of confining nano-objects, submicron objects, nanostructures, reagents and reaction products with much greater safety than the capsules of document FR-A1-2 934 600.

 This capsule can be called to simplify "gelled agglomerate", or

"Gelled capsule", or "first capsule", or "first agglomerate". Because the outer surface of the capsule is covered with hydroxide crystals, this capsule is referred to as "reinforced gelled capsule".

The layer, shell, of hydroxide generally has a thickness of 10 μιη to 500 μιη. The terms "capsule" and "agglomerate" are used interchangeably herein.

 By "homogeneously distributed" is generally meant that the nano-objects and / or submicron objects, and / or nanostructures are uniformly distributed regularly in the capsule and that their concentration is substantially the same throughout the capsule, in all parts of it.

 The gel may be formed in the entire capsule, or the gel may be formed only in a portion of the capsule, for example on the surface of the capsule, the interior of the capsule being in the liquid state. Preferably, however, the gel is formed in the entire capsule, in other words the capsule is gelled "heart".

 Advantageously, the concentration of nano-objects and / or submicron objects, and / or nanostructures (which is greater than 0% by mass) is less than or equal to 5% by mass, preferably it is less than or equal to 1% in bulk, more preferably it is from 10 ppm to 0.1% by weight of the total weight of the capsule.

 The solvent of the capsule may comprise in volume 50% water or more, preferably 70% water or more, more preferably 99% water or more, better 100% water (the solvent of the capsule is then constituted by water).

 The solvent of the capsule, when it does not comprise 100% water, may further comprise at least one other solvent compound generally chosen from alcohols, in particular aliphatic alcohols, such as ethanol; polar solvents, in particular ketones, such as acetone; and their mixtures.

 The nano-objects can be chosen from nanotubes, nanowires, nanofibers, nanoparticles, nanocrystals, and mixtures thereof; and submicron objects may be selected from submicron particles.

The material constituting the nano-objects, nanostructures, or submicron objects may be selected from carbon; sulfur ; metals such as tin; metal alloys; metalloids such as silicon; metalloid alloys; metal oxides such as rare earth oxides possibly doped; the metalloid oxides; ceramics; organic polymers; and materials comprising a plurality of these.

 Nano-objects and / or submicron objects, and / or nanostructures may include carbon nano-objects; and possibly nano-objects or submicron objects in at least one material other than carbon such as silicon.

 Advantageously, the carbon nano-objects are selected from carbon nanotubes ("CNT"), carbon nanowires, carbon nanofibers, carbon nanoparticles, carbon nanocrystals, carbon blacks, and mixtures thereof; and the nano-objects or submicron objects in at least one material other than carbon are selected from nanotubes, nanowires, nanofibers, nanoparticles, submicron particles, nanocrystals, in at least one material other than carbon such than silicon, and their mixtures. The material other than carbon may be chosen from the materials other than carbon mentioned above.

 The carbon nanotubes may be chosen from single-walled carbon nanotubes ("SWCNT") and multi-walled carbon nanotubes ("MWCNT") such as double-walled carbon nanotubes.

 The macromolecules of polysaccharide (s) may be chosen from pectins, alginates, alginic acid, and carrageenans.

 The alginates may be alginates extracted from brown seaweed Phaeophyceae, mainly Laminaria such as Laminaria hyperborea; and Macrocystis such as Macrocystis pyrifera.

 Advantageously, the polysaccharide macromolecule has a molecular weight of 80000 g / mol to 500000 g / mol, preferably 80000 g / mol to 450000 g / mol.

The gelled capsule, or agglomerate, especially in the case where it does not already comprise a polymer soluble in the solvent of the first capsule, may be impregnated with at least one polymer or monomer that is soluble in the solvent of the capsule, preferably a water-soluble polymer chosen for example from polyethylene glycol (PEG), poly (ethylene oxide), poly (acrylamide), poly (vinyl pyridines), (meth) acrylic polymers, chitosans, celluloses, PVAs and all other water-soluble polymers.

 The gelled capsule may be further crosslinked and / or polymerized.

Advantageously, said element is calcium, and the hydroxide is calcium hydroxide Ca (OH) ₂ .

 Generally, the gelled, reinforced capsule according to the invention has a spherical or spheroidal shape.

 Advantageously, the gelled, reinforced capsule according to the invention has a size, defined by its largest dimension, such as the diameter in the case of a spherical or spheroidal capsule of 100 μιη to 2 mm, preferably 500 μιη to 1 mm.

 The invention furthermore relates to a gelled, lyophilized, reinforced capsule prepared by freeze-drying and then exposed to a gas containing carbon dioxide, the gelled, reinforced capsule described above, in which the outer surface of the capsule is covered. a carbonate layer of said element.

 When exposed to a gas containing carbon dioxide, such as air, the hydroxide is converted to carbonate.

 The capsule prepared by lyophilization of the gelled capsule or first capsule may be called "lyophilized gelled capsule" or simply "freeze-dried capsule".

 Because the outer surface of the capsule is covered with a hardened carbonate layer or shell, this capsule is referred to as a "freeze-dried, enhanced gelled capsule".

 In the case where the element is calcium, the layer or shell is a layer or shell of calcium carbonate.

The reinforced freeze-dried gelled capsule according to the invention is fundamentally different from the lyophilized gelled capsules of document WO-Al-2010/012813 in that its outer surface is covered with a carbonate layer or shell, for example calcium carbonate CaCO _3. . In other words, in the gelled, freeze-dried, reinforced capsule, according to the invention, a layer, carbonate shell, for example calcium carbonate around the gelled, freeze-dried capsules of WO-Al-2010/012813 is manufactured.

 Therefore, thanks to this carbonate shell, the freeze-dried gelled capsule, reinforced, according to the invention has an increased mechanical strength, and is much less fragile than the gelled, freeze-dried capsules of WO-Al-2010/012813, c. is why this capsule is called "reinforced".

 The gelled, freeze-dried, reinforced capsule according to the invention fulfills its role of confining nano-objects, submicron objects, nanostructures, and reagents and reaction products, with much greater certainty than the capsules of document WO-A1. -2010/012813.

 The layer, carbonate shell is usually organized in layers.

The layer, shell, of carbonate is compact (at the level of the sheets), porous (between the sheets) discontinuous (because of the succession of the sheets), and resistant, and generally has a thickness of 10 μιη to 500 μιη.

 This carbonate layer makes it possible, when the gelled, lyophilized, reinforced capsules according to the invention are used as microreactors to confine the reagents and reaction products, to contain the pressure of the vaporized compounds and to limit the diffusion of the reagents and reaction products.

 The homogeneous distribution of nano-objects and / or submicron objects, and / or nanostructures is furthermore preserved in the freeze-dried capsule prepared from the first capsule.

The term "lyophilization" is a term well known to those skilled in the art. The lyophilization generally comprises a freezing step during which the solvent (liquid), for example the water of the first capsule is put into solid form, for example in the form of ice, and then a sublimation step during which, under the effect of vacuum, the solid solvent such as ice is transformed directly into steam, for example water vapor, which is recovered. Optionally, once all the liquid solvent, for example all ice, is removed, the capsules are cold-dried. During lyophilization, the solvent of the first capsule will be completely removed, replaced by the polymer or monomer, preferably water-soluble such as PEG impregnating the gelled agglomerate.

 Similarly during lyophilization, the solvent of the first capsule, or gelled capsule, can be completely removed and replaced by the polymer or monomer soluble in the solvent of the capsule and already present in the capsule.

 The freeze-dried capsule according to the invention generally contains from 1% to 90% by weight, preferably from 30% to 75% by weight, more preferably from 50% to 60% by weight, nano-objects and / or submicron objects. and / or nanostructures, and from 10% to 99% by weight, preferably from 25% to 70% by weight, more preferably from 40% to 50% by weight of polysaccharide (s).

 Advantageously, the lyophilized capsule according to the invention may also have undergone after lyophilization, a heat treatment or a treatment, enzymatic attack.

 This enzymatic attack can be carried out for example with an alginate degrading enzyme, such as an Alginate Lyase type enzyme, such as the enzyme EC 4.2.2.3, also called E-poly (-D-mannuronate) lyase.

 The heat treatment or the enzymatic treatment makes it possible to eliminate, at least partially, that is to say partially or totally, the polysaccharide (s) of the capsule having undergone lyophilization.

 Generally, the heat treatment makes it possible to eliminate at least part of the polysaccharide (s) whereas the enzymatic treatment generally makes it possible to totally eliminate the polysaccharide.

 The enzymatic attack can be carried out according to standard conditions within the reach of those skilled in the art, for example by aqueous dissolution of the lyophilized capsules and introduction of the enzyme into this solution.

After this thermal or enzymatic treatment, the freeze-dried capsule generally contains from 50% to 100% by weight, preferably from 80% to 100% by weight of nano-objects and / or submicron objects, and / or nanostructures. This thermal or enzymatic treatment therefore makes it possible to increase the content of nano-objects and / or submicron objects, and / or nanostructures, such as carbon nanotubes, without the structure of the agglomerates, capsules, being changed and without the homogeneous distribution of nano-objects and / or submicron objects, and / or nanostructures in the capsule is affected.

 The additional heat treatment stage, which could also be called the calcination stage of the capsules, lyophilized agglomerates, or the additional enzymatic treatment step, makes it possible to eliminate at least part of the polysaccharide (s) , for example alginate while retaining the organization obtained beforehand and in particular the homogeneous distribution of the nano-objects and / or submicron objects, and / or nanostructures present in the first capsules (gelled) and in the lyophilized capsules.

 The additional step of heat treatment or enzymatic treatment, carried out after freeze-drying, makes it possible to create agglomerates or capsules loaded with nano-objects and / or submicron objects, and / or nanostructures, in particular from 80 to 95% by weight of agglomerate.

 Such a high content is obtained even with a very low content of nano-objects and / or submicron objects, and / or nanostructures such as CNTs in gelled capsules, because the tubes, for example, are generally long with a length for example between 1 μιη and 100 μιη.

 Such a content is greater than all the contents of nano-objects and / or submicron objects, and / or nanostructures previously obtained in such agglomerates or capsules and without the homogeneous distribution of these nano-objects and / or submicron objects. , and / or nanostructures, their three-dimensional organization, already present both in the first gelled capsules and in the freeze-dried capsules is affected in the capsules after heat treatment that one could also call "calcined" capsules or in the capsules after treatment enzyme.

In other words, the heat treatment or calcination step, or the enzymatic treatment step, is intended to totally or partially eliminate the (s) polysaccharide (s) in the freeze-dried capsule. At the end of the heat treatment, calcination or enzymatic treatment step, carried out after lyophilization, structures which can be formed solely of nano-objects and / or submicron objects and / or nanostructures (when the polysaccharide such as alginate has been completely eliminated) such as CNTs, these structures being organized and porous, which is an advantage to integrate these structures in some polymers.

 The content of polysaccharide in the capsules after thermal or enzymatic treatment is generally from 1% to 50% by weight, preferably from 1% to 20% by weight, or even 0% by weight, in particular when an attack, treatment, enzyme.

 Advantageously, the gelled, freeze-dried, reinforced capsule according to the invention has a size, defined by its largest dimension, such as the diameter in the case of a spherical or spheroidal capsule 100 μιη at 2 mm, preferably 500 μηΐ. θ ΐ mm.

 The invention also relates to a solid nanocomposite material with a polymer or composite matrix comprising a reinforced gelled capsule, or a reinforced freeze-dried gel capsule according to the invention as described above, in which the nano-objects and / or submicron objects and / or nanostructures are distributed homogeneously.

 The polymer (s) of the matrix may be chosen from aliphatic and apolar polymers such as polyolefins, such as polyethylenes, and polypropylenes; polystyrenes; copolymers of cycloolefins; but also among polar polymers such as polyamides and poly (meth) acrylates such as PM MA; and mixtures thereof.

 The polymer of the matrix may also be chosen from polymers which melt or which are soluble in water.

The composite of the matrix may be chosen from composite materials comprising at least one polymer chosen, for example, from the polymers mentioned above for the matrix, and an inorganic filler. The invention furthermore relates to a method for preparing the gelled, reinforced capsule, as defined above, in which the following successive steps are carried out:

 a) is dispersed in a first solvent comprising mainly (50% at most) water, nano-objects, and / or nanostructures and / or submicron objects, and is dissolved in the first solvent macromolecules polysaccharide (s), and optionally, a soluble polymer or a salt soluble in the first solvent, whereby a first solution is obtained;

 b) a third solution is prepared by contacting the first solution with a second solution in a second solvent, comprising for the most part water, at least one salt (which is not a hydroxide) of at least a water-soluble element capable, capable of releasing cations from said element into the second solution, the concentration of said element in the second solution being such that it is greater than the concentration of said element which corresponds to the solubility limit hydroxide of said element in said second solution (i.e., the solubility limit is determined with respect to the second solution), whereby a gelled capsule is obtained;

 c) the gelled capsule is separated from the third solution and rinsed with deionized water;

 d) the gelled capsule is immersed in a hydroxide solution of said element, the hydroxide concentration of said element in said hydroxide solution being greater than the solubility limit of said hydroxide, and the concentration of the element within said hydroxide solution; the capsule being greater than the concentration of the element in the hydroxide solution, whereby the reinforced gelled capsule is obtained in which the outer surface of the capsule is covered with hydroxide crystals of said element;

e) the reinforced gelled capsule is separated from the hydroxide solution. The first solvent may comprise in volume 50% water or more, preferably 70% by volume of water or more, more preferably 99% by volume of water or more, and more preferably 100% by volume of water.

 Nano-objects, nanostructures, and submicron objects, and polysaccharides are advantageously such as has already been defined above.

 The first solvent when it does not comprise 100% water may also comprise at least one other solvent compound generally chosen from alcohols, in particular aliphatic alcohols such as ethanol; polar solvent compounds, in particular ketones such as acetone; and their mixtures.

 The dispersion of the nano-objects, and / or nanostructures and / or submicron objects, in the first solvent and the dissolving of the polysaccharide macromolecules (s) can be two simultaneous operations, or they can be two consecutive operations, the dispersion preceding dissolution, or vice versa.

 Advantageously, the ratio of the number of macromolecules to the number of nano-objects, and / or nanostructures and / or submicron objects, in the first solution may be from 1 to 10, preferably this ratio is equal to or close to 1.

 The content of nano-objects, and / or nanostructures and / or submicron objects, and the content of macromolecules of polysaccharide (s) (which are greater than 0% by weight) may advantageously be less than or equal to 5% by weight preferably less than or equal to 1% by weight, and more preferably 10 ppm to 0.1% by weight of the mass of the first solvent.

 The second solvent may comprise 50% by volume of water or more, preferably 70% by volume of water or more, more preferably 99% by volume of water or more, more preferably 100% by volume of water.

The second solvent may further comprise, when it does not comprise 100% water, at least one other solvent compound generally chosen from alcohols, in particular aliphatic alcohols such as ethanol; polar solvents, in particular ketones such as acetone; and their mixtures. Advantageously, the second solvent is identical to the first solvent and is preferably constituted by water.

Advantageously, the cations are chosen from monovalent cations, divalent cations, and trivalent cations, preferably divalent cations are chosen from Cd ²⁺ , Cu ²⁺ , Ca ²⁺ , Co ²⁺ , Mn ²⁺ , Fe ^{2 +} , Hg ²⁺ ; the monovalent cations are chosen from Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ , Ag ⁺ , Ti ⁺ , Au ⁺ ; and the trivalent cations are selected from Fe ³⁺ , and Al ³⁺ ; more preferably the cations are Ca ²⁺ cations.

 Advantageously, the second solution can comprise several salts so that a mixture of cations, preferably a mixture of cations comprising at least one monovalent cation, at least one divalent cation, and at least one trivalent cation can be released in the second solution. .

 Preferably, the second solution comprises a single salt which is a calcium salt and the hydroxide is calcium hydroxide.

 The process for preparing the gelled capsule is reversible and may optionally also comprise a step c1) (performed on the capsule obtained at the end of step c)), during which the first capsule is brought into contact with at least one chelating agent such as diethylene tetramine pentaacetic acid (DTPA), ethylene diamine tetraacetic acid, or trientine (triethylene tetramine, TETA) to trap and deactivate the role of the cations.

 At the end of step b) or of step c), the capsule obtained, and possibly separated for example by simple filtration, may be further impregnated with a solution of a polymer or monomer soluble in the first solvent , preferably by an aqueous solution of at least one water-soluble polymer or monomer chosen, for example, from polyethylene glycol (PEG), poly (ethylene oxide), poly (acrylamide), poly (vinyl pyridines), (meth) acrylic polymers, chitosans, celluloses,

PVAs and all other water-soluble polymers.

However, as already mentioned, a polymer or monomer may also be added during step a) so as to mechanically consolidate the solution of dispersed nano-objects with the polysaccharide, said polymer or monomer being then soluble in the solvent ("first solvent") used in step a). It can be in particular of a water-soluble monomer or polymer which may be selected from the polymers already mentioned above.

 The invention furthermore relates to a method for preparing the reinforced lyophilized gelled capsule as defined above in which a gelled capsule reinforced by the method described above is prepared, said reinforced gelled capsule is lyophilized, and said reinforced gelled capsule is exposed. to a gas containing carbon dioxide, whereby the hydroxide crystals of said element which cover the outer surface of the capsule are converted into a carbonate layer of said element.

 The freeze-drying can be carried out on the first capsule whether or not it comprises a polymer or monomer added during step a) and whether it has been impregnated or not with a solution of a polymer or monomer, for example by a aqueous solution of a water-soluble polymer or monomer at the end of step b) or of step c).

 Following lyophilization, and after exposure to a gas containing carbon dioxide, a thermal or enzymatic treatment of the freeze-dried gelled agglomerate is optionally carried out.

 The thermal or enzymatic treatment is intended to remove at least partly the polysaccharide (s) still present (s).

 Generally, at least 30% by weight of the polysaccharide present in the lyophilized capsules is removed by this heat treatment, for example from 30% to 45% by weight. It is even possible to completely eliminate the polysaccharide (s) with enzymatic attack.

 At the end of this thermal or enzymatic treatment, a capsule is obtained, generally comprising from 0% to 50% by weight, preferably from 0% to 20% by weight of polysaccharide, and from 50% to 100% by weight, preferably from 80% to 100% by weight of nano-objects, and / or nanostructures, and / or submicron objects.

The heat treatment must be carried out at a temperature such that it allows at least partial removal of the polysaccharide (s) lyophilized capsules. Advantageously, it is carried out at a temperature of from 400 ° C. to 600 ° C., preferably from 500 ° C. to 550 ° C., for a period of 1 to 5 hours, preferably from 1 to 3 hours, more preferably from 1 to 3 hours. at 2 hours, for example at a temperature of 300 ° C for one hour.

 The conditions of the enzymatic treatment, as already mentioned above, can be easily determined by those skilled in the art.

 The invention finally relates to a process for the preparation of a nano-composite material in which is carried out the incorporation of at least one gelled, lyophilized, reinforced, optionally heat-treated or enzymatically-treated capsule or at least one gelled capsule, reinforced, as defined in the foregoing in a polymer or composite matrix.

 In other words, it is possible to incorporate into the polymer or composite matrix a gelled, reinforced capsule, a gelled, lyophilized or reinforced capsule or a thermally treated, calcined capsule, or an enzymatically treated capsule.

 The polymer of the matrix has already been defined above.

 The incorporation of at least one gelled, lyophilized, reinforced, optionally heat-treated or enzymatically-treated capsule or at least one gelled, reinforced capsule into the polymer matrix may be carried out by a plastics processing process such as extrusion.

 Extrusion consists of melting n-materials and kneading them along a screw or twin-screw with optimized temperature profile and rotational speed for optimal mixing.

 At the end of this bi-screw or single-screw, is a die that shapes the mixture before complete solidification. The shape can be a ring, a film or have any type of profile.

The capsules according to the invention make it possible to keep in the final solid nano-composite material according to the invention the same organization, in particular the same homogeneous distribution of nano-objects, and / or nanostructures and / or submicron objects, as that which existed in the dispersion of these nano-objects, and / or nanostructures and / or submicron objects in a liquid medium. According to the invention, this organization is preserved in the first gelled capsule, reinforced, then in the gelled capsule, freeze-dried, reinforced, and in the capsule having undergone heat treatment or enzymatic.

 In fact, the gelled structure of the capsules according to the invention makes it possible to fix, fix, "freeze" stably the organization of nano-objects, and / or nanostructures and / or submicron objects, for example the distribution homogeneous, which was that of nano-objects, and / or nanostructures and / or submicron objects in the liquid dispersion and then retain it integrally in the final composite material.

 Thanks to the capsules according to the invention, it is possible to maintain the state of dispersion of the nano-objects, and / or nanostructures and / or submicron objects, which exists in the initial dispersion in the final nano-composite material which can then be processed, converted in a conventional manner by any process of plastics, for example by extrusion.

 In the final composite material, there is, for example, the same homogeneous distribution throughout the volume of the material of the nano-objects, and / or nanostructures and / or submicron objects, as in the initial dispersion.

 The nano-composite materials according to the invention are intrinsically different from the nano-composite materials of the prior art, in particular by the fact that they comprise the reinforced gelled capsules or the gelled, reinforced, lyophilized capsules according to the invention, which communicate with them. intrinsically new and unexpected properties vis-à-vis nano-composite materials of the prior art, particularly with regard to the homogeneity of the distribution of nano-objects, and / or nanostructures and / or objects submicron, at low levels, concentrations.

Indeed, this conservation of the state, which was that of nano-objects, and / or nanostructures and / or submicron objects in the starting dispersion, also in the final composite material is intimately linked to the implementation of the particular capsules according to the invention, and is in particular observed surprisingly, for a low concentration of nano-objects, and / or nanostructures and / or submicron objects, namely a concentration generally less than or equal to 5% by weight. mass, preferably less than or equal to 1% by weight, preferably from 10 ppm to 0.1% by weight in the composite material.

 But the invention can also be advantageously implemented for high concentrations of nano-objects, and / or nanostructures and / or submicron objects, for example a concentration of up to and around 20% by weight. . At these high concentrations, the method according to the invention makes it possible to control the organization, the arrangement and the level of entanglement.

 In general, the concentration of nano-objects, and / or nanostructures and / or submicron objects, will therefore be from 10 ppm to 20% by weight, preferably from 10 ppm to 5% by weight, more preferably from 10 ppm to 1 μm. % by weight and better still from 10 ppm to 0.1% by weight in the final composite material.

 Due to the homogeneous distribution of nano-objects, nanostructures obtained according to the invention at a low level, at a low concentration, namely generally less than or equal to 5% by weight, preferably less than or equal to 1% by weight, the improvement of the properties (mechanical, electrical, thermal, magnetic, etc.) due to these nano-objects, and / or nanostructures and / or submicronic objects, such as carbon nanotubes, is observed at lower concentrations . This results in a significant saving of materials which are often expensive on the one hand, and whose synthesis methods are not adapted to mass production, on the other hand.

 The shape, properties of the nano-objects, and / or nanostructures and / or submicron objects are not affected in the reinforced capsules according to the invention, and then in the composite materials according to the invention, they undergo no degradation as well. well in the capsules as in the composite material.

 The invention finally relates to the use of a reinforced gelled capsule as described above, or a reinforced lyophilized gelled capsule as described above, as a chemical microreactor within which chemical reactions are carried out, for example reactions for chemical vapor deposition (CVD).

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood on reading the detailed description which follows, made as illustrative and nonlimiting with reference to the accompanying drawings in which:

 FIG. 1 is a photograph, taken under a scanning electron microscope (M EB or "SEM"), which shows the tearing of the outer membrane of gelled capsules at the time of lyophilization of these capsules according to the process described in the document A1-2010 / 012813.

 The scale shown in FIG. 1 represents 20 μιη.

 Figure 2 is a photograph, taken under a scanning electron microscope (M EB or "SEM"), which shows torn zones of the outer membrane of lyophilized capsules prepared according to the method of WO-A1-2010 / 012813.

 The scale shown in FIG. 2 represents 1 μιη.

Figure 3 is a schematic sectional view of a reinforced lyophilized capsule according to the invention with an outer shell of carbonate, for example CaCO ₃ .

- Figure 4 is a photograph taken under a scanning electron microscope (M EB or "SEM"), which shows the outer shell CaC0 ₃ of a reinforced lyophilized capsule according to the invention.

 The scale shown in FIG. 4 represents 200 μιη.

FIG. 5A is a photograph, taken under a scanning electron microscope (M EB or "SEM"), of a reinforced lyophilized capsule according to the invention with its external CaCO ₃ shell.

 The scale shown in FIG. 5A represents 200 μιη.

Figure 5B is a scanning electron microscope (M EB or "SEM") photograph of the surface of the CaC0 ₃ outer shell of the lyophilized capsule of Figure 5B.

 The scale shown in FIG. 5B represents 100 μιη.

DETAILED DESCRIPTION

The following detailed description is rather made in connection with the process according to the invention for the preparation of "gelled" capsules, of freeze-dried capsules, and of nano-composite polymer matrix materials but it also contains teachings that apply to the capsules and materials according to the invention.

 As a preamble to this detailed description, we first clarify the definition of some of the terms used herein.

 By nano-objects, we generally mean any single object or related to a nanostructure of which at least one dimension is less than or equal to 500 nm, preferably less than or equal to 300 nm, more preferably less than or equal to 200 nm, and better still less or equal to 100 nm, for example is in the range of 1 to 500 nm, preferably 1 to 300 nm, more preferably 1 to 200 nm, more preferably 1 to 100 nm; more preferably 2 to 100 nm, or even 5 to 100 nm.

 These nano-objects may be, for example, nanoparticles, nanowires, nano-fibers, nano-crystals or nanotubes.

 By submicron object is generally meant any object whose size, such as the diameter in the case of a spherical or spheroidal object is less than 1 μιη, preferably 50 to 800 nm.

 By nanostructure, we generally mean an architecture consisting of an assembly of nano-objects and / or submicron objects that are organized with a functional logic and which are structured in a space ranging from cubic nanometer to cubic micrometer.

By polysaccharide is generally meant a polymeric organic macromolecule consisting of a chain of monosaccharide units. Such a macromolecule can be represented by a chemical formula of the form - [^ (Η ₂ 0) _γ ] _η -.

 By capsule (or agglomerate) is generally meant a system comprising, preferably composed of, a solvent, preferably a solvent comprising predominantly water or consisting of water; nano-objects and / or submicron objects, and / or nanostructures; macromolecules of polysaccharide (s); and positive ions acting as cross-linking nodes between two polysaccharide molecules.

The term meta-materials, in physics, in electromagnetism, generally refers to composites and nano-composites as a whole artificial that have electromagnetic properties that are not found in natural materials.

 A definition of polymeric matrix nano-composite materials has already been given above.

 In a first step, dispersing in a first solvent generally comprising mostly water, nano-objects and / or submicron objects, and / or nanostructures, and is dissolved in the first solvent at least one macromolecule belonging to the family of polysaccharides, whereby a first solution or dispersion is obtained in which the nano-objects and / or submicron objects, and / or nanostructures are dispersed.

 At this stage of the process, one can add to the first solution a polymer or monomer soluble in the first solvent, for example water-soluble, whose function will be to maintain the gelled structure when the first solvent such as water will be gone.

 By solvent comprising mostly water, it is generally meant that the solvent comprises 50% by volume or more of water, preferably 70% by volume or more of water, and more preferably more than 99% by volume of water. water, for example 100% water.

 The first solvent may comprise, in addition to water in the abovementioned proportions, at least one other solvent compound, generally chosen from alcohols, in particular aliphatic alcohols such as ethanol; polar solvents, in particular ketones such as acetone; and their mixtures.

 In addition to the abovementioned solvents, the first solution may, as specified above, also contain at least one polymer chosen from all the polymers that are soluble in the first solvent, in particular water-soluble polymers such as PEGs, poly (oxide ethylenes), polyacrylamides, poly (vinyl pyridines), (meth) acrylic polymers, celluloses, chitosans, PVAs, whose function is to effectively stabilize the dispersion of nano-objects and / or submicron objects, and / or nanostructures.

The nanostructures can be constructions, assemblies whose bricks are nano-objects and / or submicron objects. The nanostructures may be, for example, carbon nanotubes "decorated" with platinum, copper or gold nanoparticles; Silicon nanowires "decorated" with gold, nickel, platinum, etc.

 Among the nanostructures, mention may in particular be made of the ZnO-Ni nanostructure which is a three-dimensional structure of ZnO terminated by nickel nanospheres.

 The capsules may contain only one type of nano-object, submicron object, or nanostructure but they may contain both several types of nano-objects, and / or nanostructures, and / or submicron objects, which may differ in their shape and / or the material constituting them and / or their size.

 For example, a capsule may contain both nano-carbon objects, such as carbon nanotubes, and nanoparticles of metal such as copper; or both nano-carbon objects, such as carbon nanotubes, and nanoparticles or submicron silicon particles.

 There is no limitation on the polysaccharide macromolecule and all molecules belonging to the family of polysaccharides can be used in the process according to the invention. They may be natural or synthetic polysaccharides.

 The polysaccharide macromolecule may be selected from pectins, alginates, alginic acid, and carrageenans.

 By alginates is meant alginic acid as well as salts and derivatives thereof such as sodium alginate. Alginates and especially sodium alginate are extracted from various brown seaweed Phaeophyceae, mainly Laminaria such as Laminaria hyperborea; and Macrocystis such as Macrocystis pyrifera. Sodium alginate is the most common commercialized form of alginic acid.

Alginic acid is a natural polymer of the empirical formula (C ₆ H ₇ NaO ₆ ) n consisting of two monosaccharide units: D-mannuronic acid (M) and L-guluronic acid (G). The number of base units of the alginates is generally about 200. The proportion of mannuronic acid and guluronic acid varies from one species from one seaweed to another and the number of units M over the number of units G can range from 0.5 to 1.5, preferably from 1 to 1.5.

 The alginates are linear unbranched polymers and are not generally random copolymers but according to the alga from which they come, they consist of sequences of similar or alternating units, namely GGGGGGGGG sequences, M M M M M M M M, or G M G M G M G M.

 For example, the M / G ratio of alginate from Macrocystis pyrifera is about 1.6 while the M / G ratio of alginate from Laminaria hyperborea is about 0.45.

 Among the alginates polysaccharides derived from Laminaria hyperborea, mention may be made of Satialgine SG 500, among the alginates polysaccharides derived from Macrocystiis pyrifera of different lengths of molecule, mention may be made of the polysaccharides designated A7128, A2033 and A2158 which are generics of acids alginic.

 The polysaccharide macromolecule used according to the invention generally has a molecular weight of 80000 g / mol to 500000 g / mol, preferably 80000 g / mol to 450000 g / mol.

 The dispersion of the nano-objects and / or submicron objects, and / or nanostructures in the first solvent and the dissolution of the polysaccharides may be two simultaneous operations, or it may be two consecutive operations, the dispersion preceding the setting in solution, or vice versa.

The dispersion of nano-objects such as nanotubes, and / or submicron objects, and / or nanostructures, in the first solvent can be done by adding nano-objects and / or submicron objects, and / or nanostructures to the first solvent and subjecting the solvent to the action of ultrasound with an acoustic power density generally from 1 to 1000 W / cm ² , for example 90 W / cm ² , for a period of generally from 5 minutes to 24 hours, for example from 2 hours.

The dissolution of the polysaccharide (s) can be carried out by simple addition to the first solvent with stirring generally at a temperature of 25 ° C. to 80 ° C., for example 50 ° C., for a period generally of 5 minutes at 24 hours, for example two hours. The content of nano-objects and / or submicron objects, and / or nanostructures and the content of polysaccharide (s) depend on the quantity of nano-objects and / or submicron objects, and / or nanostructures to be coated with respect to the amount of polysaccharide molecules.

 The content of nano-objects and / or submicron objects, and / or nanostructures in the first capsule, or gelled capsule, as well as the polysaccharide content are generally less than or equal to 5% by weight, preferably less than or equal to 1% in mass, the mass of the solvent. The invention allows such "low" concentrations to achieve particularly advantageous effects. More preferably, the content of nano-objects and / or submicronic objects, and / or nanostructures and the content of polysaccharides are from 10 ppm to 5% by weight, more preferably from 10 ppm to 1% by weight, and more preferably 10 ppm to 0.1% by weight of the solvent mass in the gelled capsule.

 The ratio of the number, the quantity, of macromolecules to the number of nano-objects and / or submicron objects, and / or nanostructures in the first solution and consequently in the gelled capsules or agglomerates and then in the reinforced capsules (it There is no change in the ratio following the formation of the hydroxide shell, the ratio remains the same) is generally from 0.1 to 10, preferably equal to or close to 1.

 This ratio between the quantity, the number of macromolecules of polysaccharides and the quantity, the number of nano-objects and / or submicron objects, and / or nanostructures sets the dispersion level or dispersion factor and the average distance for the nanoparticles, or sets the basic network mesh for nanostructures, nanowires and nanotubes.

 The optimum of the mixture will always be when the ratio polysaccharide / nano-objects and / or submicron objects, and / or nanostructures (for example nanotubes) is close to 1. It is the concentration of species that determines the size of the mesh.

In one embodiment in which nano-objects in a first material are used, for example carbon nano-objects such as NTCs and nano-objects in a second material other than carbon such as nanoparticles. of silicon, the first step may advantageously be carried out according to the following successive steps:

 the nano-objects are brought into contact with at least one first material with water, and then the nano-objects are mixed in at least one first material with water using the succession, possibly repeated, of a mixing technique ultrasound then a high speed mixing technique, the mixture of nano-objects in at least a first material and water being circulated, for example by a pump such as a peristaltic pump, so as to avoid that the nano-objects in a first material do not agglomerate, whereby a dispersion consisting of nano-objects in at least a first material and water that is kept circulating.

 Indeed, this dispersion is an unstable mixture when the circulation stops, for example when the pump is stopped, such as a peristaltic pump which conveys the mixture of nano-objects and water from the apparatus for implementing the ultrasonic mixing technique, such as a disperser, mixer, ultrasonic, to the apparatus for implementing the mixture at high speed;

 without interrupting the circulation of the dispersion, the mixing is stopped by ultrasound and nano-objects or submicron objects are mixed in at least one second material with the dispersion consisting of the nano-objects in at least one first material and water using a high-speed mixing technique, whereby a dispersion consisting of nano-objects in at least one first material, nano-objects or submicron objects in at least a second material, and water is obtained it is kept in circulation;

without interrupting the circulation of the dispersion, at least one polysaccharide in the dispersion constituted by the nano-objects in at least one first material, the nano-objects or the submicron objects in at least one a second material, and water, and the macromolecules are mixed with the dispersion using a high-speed mixing technique, whereby a dispersion is obtained in which nanostructures each constituted by a three-dimensional network are homogeneously distributed. constituted by the nano-objects in at least a first material bonded and maintained by a hydrogel of the polysaccharide, the nano-objects or submicron objects in at least a second material being self-assembled around said network and being attached to the nano-objects in at least one first material by said polysaccharide hydrogel.

 The very specific structure or organization of the material thus obtained can be defined as a "grape bunch" structure or organization in which the nano-objects made of a first material, such as carbon, for example carbon nanotubes, form a network. three-dimensional or skeleton around which agglomerate, aggregate, self-assemble, the nano-objects into a second material, for example a material other than carbon, such as silicon nanoparticles.

 Nano-objects in a first material, for example nano-objects in carbon such as NTCs form the branch and peduncle of the cluster, while nano-objects in a second material, for example in a second material other that carbon (in the case where the first material is carbon), such as nanoparticles of silicon form the grapes.

 In a second step, gelled capsules (first capsules or agglomerates) are prepared by contacting the first solution or dispersion of nano-objects and / or submicron objects, and / or dispersed nanostructures prepared during the first step, described below. above, with a second solution called gelling solution or crosslinking.

 This second solution is a solution, in a second solvent comprising in majority water, at least one salt of a water-soluble element, capable of releasing into the second solution cations of said element, the concentration of said element in the second solution being such that it is greater than the concentration of said element which corresponds to the solubility limit of the hydroxide of said element in said second solution.

 This salt is not a hydroxide of said element.

Said cations are generally chosen from monovalent, divalent and trivalent cations. By solvent comprising mostly water, it is generally meant that the solvent of the second solution comprises 50% by volume or more of water, preferably 70% by volume or more of water, and more preferably more than 99% by weight. % by volume of water, for example 100% water.

 The solvent may comprise, in addition to water in the abovementioned proportions and when it does not comprise 100% water, at least one other solvent compound generally chosen from alcohols, in particular aliphatic alcohols such as ethanol; polar solvents such as ketones, for example acetone; and their mixtures.

The divalent cations can be selected from Cd ²⁺ , Cu ²⁺ , Ca ²⁺ , Co ²⁺ , Mn ²⁺ , Fe ²⁺ , and Hg ²⁺ .

The monovalent cations can be chosen from Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ , Ag ⁺ ,

Ti ⁺ , and Au ⁺ .

The trivalent cations may be selected from Fe ³⁺ , and Al ³⁺ .

 The anion of the salt or salts may be chosen from nitrate, sulfate, phosphate and halide ions such as chloride and bromide.

 The solution may comprise only one salt or it may comprise several salts.

 Advantageously, the solution comprises several salts so that a mixture of cations can be released in the second solution.

 The solution may comprise a mixture of salts that can release into the solution a mixture of cations comprising at least one monovalent cation, at least one divalent cation, and at least one trivalent cation.

A mixture of cations chosen from the three families of monovalent, divalent, and trivalent cations and preferably comprising at least one cation chosen from each of the families, makes it possible to control the quantity of crosslinking nodes of the system, and makes it possible in particular to make this quantity of minimal crosslinking nodes to thus ensure the structural stability of the gelled capsules and lyophilized capsules. Indeed, the amount of crosslinking nodes is a parameter that must be controlled according to the use that is made of the capsules and their applications.

Preferably, however, the second solution contains a single salt which is a calcium salt such as CaCl ₂ . The calcium concentration may for example be maintained at a higher value, even much higher, 1.3 10 ^"2 mol / L, preferably it is 2 to 20 ^{10" 2} mol / L, for example 9 10 ^{" 2} mol / L.

The minimum value of 1.3 × 10 ^-2 mol / L corresponds to the solubility limit of Ca (OH) ₂ calcium hydroxide.

 Contacting the first solution and the second solution is generally performed under the following conditions:

 In a first embodiment of this contacting, the solution of nano-objects and / or submicron objects, and / or dispersed nanostructures drops by drop in the second solution. In this case, the size of the tip is important since it determines the size of the gelled capsule. Too big, the freeze-drying, subsequent extraction for example of the water, happens moderately well and the withdrawal is more important therefore the dispersion less good.

 Too small, the capsules lyophilize perfectly, but the preparation time of these agglomerates is incredibly long. The optimum size of the nozzle is between 0.5 and 2 mm, ideally 1 m m.

 Depending on the conditions of the contacting and the nature of the nano-objects and / or submicron objects, and / or nanostructures, it is possible to manufacture spherical gelled capsules or filamentary gelled aggregates and stretched with controlled stretching ratios. .

 In a second embodiment of this contacting and unlike the drip technique, a continuous contact is made with the crosslinking solution by a nozzle directly placed in the crosslinking solution.

The shape and size of the nozzle, and in particular the ratio of the diameter of the inlet cylinder to the diameter of the outlet cylinder and the length thereof condition the draw ratio of nano-objects and / or submicron objects, and / or nanostructures such as carbon nanotubes.

 For example, an inlet and outlet diameter respectively of 2 mm and 50 μιη gives a draw ratio of 400%. By doubling the input diameter for the same output diameter, the draw ratio is multiplied by 4 to reach 1600%.

 This type of stretching makes it possible, if necessary, to align nano-objects and / or submicron objects, and / or nanostructures such as carbon nanotubes. If this nozzle is equipped with electrodes to generate an electric field, it allows to organize nano-objects and / or submicron objects, and / or nanostructures just before gelation.

 The spherical gelled capsules may have a size of 100 μιη to 5 mm and the filamentous gelled capsules may have a size of 10 μιη to 5 mm.

 It is therefore possible to control the orientation of nano-objects and / or submicron objects, and / or nanostructures in the gelled agglomerate, which are aligned in the case of maximum stretching, or which are oriented in a purely random manner but regularly distributed, homogeneously in the case of spherical capsules.

 Generally the capsules formed in the crosslinking solution are maintained for the time necessary for complete gelation and "up to heart" of the capsules. This time is generally 0.5 hours to 8 hours, for example one hour.

 It is also possible to form only a reticulated skin and to keep the inside of the first capsules in the liquid state. This can be achieved by spraying the cross-linking solution onto the forming liquid drop prior to its unhitching of the nozzle. It is thus possible to keep a great mobility of the nano-objects and / or submicron objects, and / or nanostructures inside the capsules.

In some areas, it is necessary to have high performance metamaterials, retaining high values of electrical or magnetic permittivity at very high frequencies. The mobility of charge carriers therefore remains maximal even at high frequencies, which is no longer the case in solid metamaterials. Retaining this mobility is a major asset. The second step can be reversible. The advantage of the reversible nature of this step is that, in the case of partially gelled capsules used as a chemical mini-reactor, it may be advantageous to recover the reaction products by degelling the skin of the reactor to thereby recover the new nanostructure formed. Thus, the first capsules, agglomerates can be destroyed, disassembled, putting them in contact with chelating agents, chelators.

 These chelating agents are chelating agents specific for the cations included in the capsule structure.

Thus one can choose the diethylene tetramine pentaacetic acid (DTPA) or the ethylene diamine tetraacetic acid for the Ca ²⁺ cations, or the trientine (Triethylene tetramine, TETA) for the Fe ³⁺ and Al ³⁺ cations.

In a third step, the first capsules, or gelled capsules, obtained at the end of the second step are separated, removed from the second solution or crosslinking solution by any suitable separation method, for example by filtration, and they are rinsed with water. deionized water to remove the ions from the salt of the second crosslinking solution, eg Ca ²⁺ and Cl ions ^"of the surface of the capsules.

 The gelled capsules, such as spheres obtained in the second step and then separated, may optionally be treated by impregnation, for example with polyethylene glycol or any other water-soluble polymer or monomer, in solution (for example for water, the optimum polyethylene glycol concentration is 20%). Examples of such polymers have already been given above.

 The separated gelled rinsed capsules are then immersed in a hydroxide solution of the same element as that of the salt of the second solution.

 Generally, the gelled capsules are immersed in the hydroxide solution directly after rinsing, and without waiting for them to be dry.

Preferably, this hydroxide is calcium hydroxide Ca (OH) ₂ . The hydroxide concentration of said element in said solution is greater than the solubility limit of said hydroxide. Preferably, the hydroxide concentration of said element in said solution is slightly greater than the solubility limit of said hydroxide. By "slightly higher" is generally meant that this concentration is at most 20% higher than the solubility limit of the hydroxide in said solution.

 The concentration of the element inside the capsule is greater than the concentration of the element in the hydroxide solution, whereby the reinforced capsule is obtained in which the outer surface of the capsule is covered with hydroxide crystals. said element.

 It should be noted that in order for the concentration of the element inside the capsule to be greater than the concentration of the element in the hydroxide solution, it is possible to use a crosslinking solution whose concentration of element such as Ca is very high. significantly higher than that of the hydroxide solution, for example at least twice as much.

Indeed, since the concentration of the element such as calcium inside the capsule is greater than the concentration of the element in the hydroxide solution, for example calcium hydroxide, the cations, such as the Ca ²⁺ cations, therefore diffuse through the polysaccharide membrane, for example gelled alginate. The gelled membrane has the property of selective permeation with the cations, it thus leaves only the cations. When the cations, for example Ca ²⁺ cations have passed through the membrane, they come into contact with the hydroxide solution, and there is nucleation of a hydroxide precipitate, for example Ca (OH) ₂ .

The process is generally continued for a period of 5 to 60 minutes, for example 15 minutes, and the surface of the capsules is covered with hydroxide crystals, for example Ca (OH) ₂ .

 These crystals are generally in the form of discrete islands, leaflets (as described above), on the surface.

 These gelled capsules coated with hydroxide crystals are the reinforced gelled capsules according to the invention.

The reinforced gelled capsules are separated, removed from the hydroxide solution by any suitable separation method, for example by filtration. These reinforced gelled capsules are frozen for example by being immersed in liquid nitrogen. Instant solidification minimizes the release of the solvent, such as water, from capsules maintaining maximum dispersion. This solidification, freezing, is in fact the first part of the lyophilization treatment. The frozen capsules may optionally be stored in a freezer prior to sublimation and subsequent treatments.

 This solidification, freezing of the optionally impregnated capsules, is followed by a sublimation step which constitutes the second part of the freeze-drying treatment. During this sublimation step, under the effect of vacuum, the frozen solvent, such as ice, is removed inside the capsules and the polymer, such as polyethylene glycol, is optionally crystallized.

The capsules can therefore be placed for example in a chamber cooled to -20 ° C at a minimum and under a high vacuum (10 ^{~ 3} -10 ^{~ 7} mbar) to sublimate the frozen solvent such as ice and optionally crystallize the polymer present such than polyethylene glycol.

 Optionally, the lyophilization treatment may comprise a third part during which the agglomerates are cold-dried.

 Lyophilization can be carried out whatever the solvent of the gelled capsules, whether it is water or any other solvent or mixture of solvents. Generally, however, it is necessary that the solvent gelled capsules contain mostly water and is even constituted by water.

 At the end of lyophilization, there is no longer substantially solvent in the lyophilized capsules. The solvent content is generally less than 0.01% by weight.

 If the solvent of the gelled agglomerates consists of water, the water content of the lyophilized capsules is generally less than 0.01% by mass.

 Reinforced gelled capsules retain their shape and usually 90% of their volume after lyophilization.

The organization of nano-objects, such as CNTs, is stored in freeze-dried capsules. Optionally, in order to at least partially remove the polysaccharide from the freeze-dried capsules, these lyophilized capsules are subjected to heat treatment or enzymatic treatment.

 The heat treatment should generally be performed at a temperature and for a time sufficient to at least partially remove the polysaccharide such as alginate.

 It can also be carried out at a temperature of 400 to 600 ° C, preferably 500 to 550 ° C for a period of 1 to 5 hours, preferably 1 to 3 hours, more preferably 1 to 2 hours.

 For example, it will be possible to achieve a slow rise at a rate of 1 ° C / minute from room temperature up to 500 ° C, maintain the temperature at 500 ° C for 1 hour, then go down at a rate of 1 ° C / minute from 500 ° C to room temperature.

 The conditions of the enzymatic treatment can be easily determined by those skilled in the art. Examples of these conditions have already been given above.

 The lyophilized capsules are then exposed to a gas containing carbon dioxide, whereby the hydroxide crystals of an element which cover the outer surface of the capsule are converted into a carbonate layer of said element.

 Said layer generally has a thickness of 10 μιη to 100 μιη. For example, calcium hydroxide crystals can be converted to calcium carbonate crystals.

 The gas containing carbon dioxide generally contains from 1% to 100% carbon dioxide and may be simply air.

 The duration of the exposure of the capsules to the gas containing carbon dioxide such as air is generally from 2 hours to 48 hours, for example 24 hours.

 Hardening of the shell occurs according to the following chemical reaction in the case of calcium hydroxide:

Ca (OH) ₂ + C0 ₂ -> CaCO ₃ + H ₂ 0 The reaction of Ca (OH) ₂ with the CO ₂ of the air produces water which locally dissolves the Ca (OH) ₂ crystals and finally forms a continuous CaC0 ₃ shell after curing.

FIG. 3 shows a gelled, freeze-dried, reinforced capsule according to the invention with, for example, inside the capsule nanostructures of CNTs and silicon nanoparticles (1), a membrane polysaccharide (2), for example alginate, and a carbonate shell (3), for example CaCO ₃ .

In fact, the carbonate shell, such as CaCO ₃ , comprises a stack or "mille-feuilles" consisting of an alternation of carbonate layers with a thickness of 1 nm to 10 nm, and layers of polysaccharide of a thickness from 50 nm to 100 nm.

 The total number of layers is 10 to 100 and the upper layer of the stack is a polysaccharide layer.

 The total thickness of the carbonate shell is from 10 μιη to 500 μιη.

 The reinforced gelled capsules, or the lyophilized and optionally heat-treated or enzymatically-treated and reinforced capsules can then be mixed directly by mechanical action with the granules of polymers or composites, that is to say mixtures of polymers and inorganic fillers. such as glass fibers, particles of talc, mica and other elements conventionally used in the composite medium.

 This mechanical action may include one or more operation (s). For example, one can only perform extrusion; or we can achieve a simple mechanical mixing, optionally followed by drying of the mixture, followed by extrusion of the mixture in an extruder.

 The organization of nano-objects and / or submicron objects, and / or nanostructures, such as CNTs, is preserved after mixing the capsules with a polymer such as PMMA.

The invention will now be described with reference to the following example, given for illustrative and non-limiting purposes: EXAMPLE:

 In this example according to the invention, there is described the preparation of reinforced gelled capsules containing both carbon nanotubes and silicon nanoparticles, and lyophilization of these reinforced gelled capsules to obtain reinforced lyophilized gelled capsules.

 The manufacture of the gelled capsule can be carried out for example by following the procedure described in the application FR-Al-2 934 600 or in the application WO-A1-2010 / 012813 to the description of which we can refer.

 Preferably, the following successive steps are carried out:

 the carbon nanotubes are brought into contact with water, then the carbon nanotubes are mixed with the water using the succession, possibly repeated, of an ultrasonic mixing technique and then of a high-speed mixing technique the mixture of carbon nanotubes and water being kept in circulation, for example by a pump such as a peristaltic pump, so as to prevent the carbon nanotubes from agglomerating, whereby a dispersion consisting of Carbon and water nanotubes that are kept in circulation.

 Indeed, this dispersion is an unstable mixture when the circulation stops, for example when the pump is stopped, such as a peristaltic pump which conveys the mixture of carbon nanotubes and water from the apparatus for implementing the ultrasonic mixing technique, such as a disperser, mixer, ultrasonic, to the apparatus for implementing the mixture at high speed;

 without interrupting the circulation of the dispersion, the mixture is stopped by ultrasound and the silicon nanoparticles are mixed with the dispersion consisting of carbon nanotubes and water, using a high-speed mixing technique, whereby a dispersion consisting of carbon nanotubes, silicon nanoparticles, and water which is kept in circulation;

without interrupting the circulation of the dispersion, at least one polysaccharide in the dispersion is added at constant speed, and is gradually dissolved consisting of carbon nanotubes, silicon nanoparticles and water, and the macromolecules are mixed with the dispersion using a high-speed mixing technique, whereby a dispersion is obtained in which homogeneous nanostructures are homogeneously distributed. each by a three-dimensional network constituted by the carbon nanotubes bonded and maintained by a hydrogel of the polysaccharide, the silicon nanoparticles being self-assembled around said network and being fixed to the carbon nanotubes by said hydrogel of the polysaccharide.

The dispersion thus prepared falls into a CaCl ₂ solution whose calcium concentration is maintained above 1.3 × 10 ^-2 mol / l, ideally maintained at 9 × 10 ^-2 mol / l.

The minimum value of 1.3 × 10 ^-2 mol / l corresponds to the solubility limit of the calcium hydroxide Ca (OH) ₂ therefore the solubility constant is 8.10 ^-6 mol / l.

 Capsules are thus obtained which begin to gel.

The capsules are maintained in the crosslinking solution of CaCl ₂ for the time necessary for complete gelation and to the core.

For IL of alginate solution containing the NTCs and the silicon particles, one needs 2L of CaCl ₂ solution at a concentration of 9.10 ^-2 mol / L. The time of the crosslinking is about 1 hour.

 The gelled capsules have a diameter of 0.5 μm to 2 μm, ideally 1 mm. The gelled capsules are composed of water, alginate crosslinked by calcium and contain the nanostructure of carbon nanotubes and silicon nanoparticles.

 The outside of the capsule is composed solely of a layer of crosslinked alginate, organized in sheets, with a total thickness of 100 nm.

 In the capsule, the alginate concentration is 15 g / liter, that of the nanotubes is 2.5 g / l. and that of silicon is 8.75 g / l. The calcium concentration is 0.09 mol / L.

Then a solution of Ca (OH) ₂ is prepared by mixing 2.2 g of Ca (OH) ₂ in 2L of demineralised water, which makes a concentration of 1.5.10 ^-2 mol / L., Just above the solubility limit of calcium hydroxide. There remains some crystals of calcium hydroxide undissolved in the solution.

The gelled capsules are removed from the crosslinking solution and rinsed with deionized DI water to remove ^{Ca2 +} and CI ^"ions from the surface of the capsules. Without waiting drying, the capsules are immersed directly in the hydroxide solution calcium.

Since the calcium concentration inside the capsules is greater than the calcium concentration in the calcium hydroxide solution, the Ca ²⁺ cations thus diffuse through the gelled alginate membrane.

 The gelled membrane has the property of selective permeation with the cations, it thus leaves only the cations.

When the Ca ²⁺ ions have passed through the membrane, they come into contact with the calcium hydroxide solution and there is nucleation of a precipitate of Ca (OH) ₂ . The process is continued for 15 minutes and the surface of the capsules is covered with crystals of Ca (OH) ₂ which form discrete islands on the surface.

 After 15 minutes, the capsules are removed from the calcium hydroxide solution and immersed in liquid nitrogen to undergo rapid freezing to form micrometric ice crystals.

 These capsules are then lyophilized.

 For this, they are placed in a lyophilization chamber at -77 ° C. under a vacuum of 0.002 mbar.

 The ice is thus sublimed and at the end of the process, the lyophilization chamber is returned to the open air for 24 hours to achieve the hardening of the shell according to the following chemical reaction:

Ca (OH) ₂ + C0 ₂ -> CaCO ₃ + H ₂ 0

The reaction of Ca (OH) ₂ with the CO ₂ of the air produces water which locally dissolves the Ca (OH) ₂ crystals and finally after curing a continuous CaCO ₃ shell (Figure 4).

The capsules have a size between 0.5mm and 2mm, ideally 1 mm. The structure of a capsule is divided into two parts.

 The first part is the heart of the capsule, consisting of a nanostructure which generally has a so-called "grape bunch" structure. This nanostructure consists of carbon nanotubes and silicon nanoparticles (silicon nanoparticles make up more than 90% of the volume), linked by alginate.

 The second part of the capsule is an outer layer constituted by a composite structure comprising a multi-layer stack of crosslinked alginate layers, and calcium carbonate layers representing less than 10% of the volume of the capsule (this percentage by volume refers to the multi-layer stack).

 Each sheet has a thickness of 1 nm to 10 nm (the thickness of the carbonate sheets and alginate sheets is the same). Depending on the manufacturing time, the outer layer may consist of 10 to 100 sheets and the total thickness of the outer layer may be delO μιη to 100 μιη.

 Macroscopically, the capsule according to the invention thus prepared is as in Figure 5A which is a photograph showing such a capsule with its outer shell.

In Figure 5B which is an enlarged view of the surface of the capsule of Figure 5A, one can observe the stratification of the CaCO ₃ layer produced by the nanoscale organization of the gelled alginate.

 It is notably the crack at the bottom of the image that shows the stratification of the

CaCO ₃ by the gelled alginate, specific to the invention.

This stratification is characteristic of the process for preparing a freeze-dried gelled capsule reinforced with a CaCO ₃ shell of the invention.

Claims

1. Reinforced gelled capsule comprising a solvent, in which nano-objects, and / or nanostructures, and / or submicron objects, coated with macromolecules of polysaccharide (s), are homogeneously distributed, said macromolecules forming, in at least a portion of the capsule, a gel by crosslinking with cations of at least one element, and wherein the outer surface of the capsule is covered with hydroxide crystals of said element.

The reinforced gelled capsule according to claim 1, wherein the gel is formed in the entire capsule.

3. reinforced gelled capsule according to claim 1, wherein the concentration of nano-objects, and / or nanostructures and / or submicron objects is less than or equal to 5% by mass, preferably less than or equal to 1% by weight; more preferably it is from 10 ppm to 0.1% by weight of the total weight of the capsule.

4. Reinforced gelled capsule according to any one of the preceding claims, wherein the solvent comprises by volume 50% or more water, preferably 70% water or more, more preferably 99% water or more, better 100% water.

The reinforced gelled capsule according to claim 4, wherein the solvent of the capsule, when it does not comprise 100% water, further comprises at least one other solvent compound chosen from alcohols, in particular aliphatic alcohols such as ethanol; polar solvents, in particular ketones such as acetone; and their mixtures.

The reinforced gelled capsule according to any one of the preceding claims, wherein the nano-objects are selected from nanotubes, nanowires, nanofibers, nanoparticles, nanocrystals, and mixtures thereof; and submicron objects are selected from submicron particles.

7. reinforced gelled capsule according to any one of the preceding claims, wherein the material constituting the nano-objects, nanostructures, or submicron objects is selected from carbon; sulfur ; metals such as tin; metal alloys; metalloids such as silicon; metalloid alloys; metal oxides such as rare earth oxides possibly doped; metalloid oxides; ceramics; organic polymers; and materials comprising a plurality of these.

The reinforced gelled capsule according to any one of the preceding claims, wherein the nano-objects and / or submicronic objects, and / or nanostructures comprise carbon nano-objects; and possibly nano-objects or submicron objects in at least one material other than carbon such as silicon.

The reinforced gelled capsule according to claim 8, wherein the carbon nano-objects are selected from carbon nanotubes ("CNT"), carbon nanowires, carbon nanofibers, carbon nanoparticles, carbon nanocrystals. carbon blacks and mixtures thereof; and the nano-objects or submicron objects in at least one material other than carbon are selected from nanotubes, nanowires, nanofibers, nanoparticles, submicron particles, nanocrystals, in at least one material other than carbon such than silicon, and their mixtures.

The reinforced gelled capsule according to any one of the preceding claims, wherein the polysaccharide macromolecules (s) are selected from pectins, alginates, alginic acid, and carrageenans.

11. Reinforced gelled capsule according to any one of the preceding claims, wherein the polysaccharide macromolecule has a molecular weight of 80000 g / mol to 500000 g / mol, preferably 80000 g / mol to 450000 g / mol.

The reinforced gelled capsule according to any one of the preceding claims, wherein said element is calcium.

13. Freeze-dried, reinforced gelled capsule, prepared by lyophilization, then exposure to a gas containing carbon dioxide, of the gelled, reinforced capsule, according to any one of claims 1 to 12, wherein the outer surface of the capsule is covered with a carbonate layer of said element.

A solid nanocomposite material with a polymer or composite matrix comprising a reinforced gelled capsule according to any one of claims 1 to 12, or a reinforced freeze-dried gelled capsule according to claim 13, wherein the nano-objects, and / or nanostructures, and / or submicron objects are distributed homogeneously.

15. Nanocomposite material according to claim 14, wherein the polymer of the matrix is chosen from aliphatic and apolar polymers such as polyolefins such as polyethylenes, and polypropylenes; copolymers of cycloolefins; polystyrenes; polar polymers such as polyamides and poly (meth) acrylates such as PMMA; and mixtures thereof; as well as among polymers that melt or are soluble in water; and the matrix composite is selected from composite materials comprising at least one polymer and an inorganic filler.

16. Process for preparing the reinforced gelled capsule according to any one of claims 1 to 12, in which the following successive steps are carried out:

 a) is dispersed in a first solvent comprising in the majority water, nano-objects, and / or nanostructures and / or submicron objects, and is dissolved in the first solvent polysaccharide macromolecules (s), and optionally, a soluble polymer or a salt soluble in the first solvent, whereby a first solution is obtained;

 b) a third solution is prepared by contacting the first solution with a second solution in a second solvent, mainly comprising water, at least one salt of at least one water-soluble element, capable of to release in the second solution cations of said element, the concentration of said element in the second solution being such that it is greater than the concentration of said element which corresponds to the solubility limit of the hydroxide of said element in said second solution, by means of what is obtained a gelled capsule;

 c) the gelled capsule is separated from the third solution and rinsed with deionized water;

 d) the gelled capsule is immersed in a hydroxide solution of said element, the hydroxide concentration of said element in said hydroxide solution being greater than the solubility limit of said hydroxide, and the concentration of the element within said hydroxide solution; the capsule being greater than the concentration of the element in the hydroxide solution, whereby the reinforced gelled capsule is obtained in which the outer surface of the capsule is covered with hydroxide crystals of said element.

 e) the reinforced gelled capsule is separated from the hydroxide solution.

17. The method of claim 16, wherein the dispersion of nano-objects, and / or nanostructures and / or submicron objects in the first solvent and the dissolving of polysaccharide macromolecules (s) are two operations. simultaneous, or two consecutive operations, the dispersion preceding dissolution, or vice versa.

18. A method according to any one of claims 16 and 17, wherein the ratio of the number of macromolecules to the number of nano-objects, and / or nanostructures and / or submicron objects in the first solution is from 1 to 10 , preferably equal to or close to 1.

19. A method according to any one of claims 16 to 18, wherein the content of nano-objects, and / or nanostructures and / or submicron objects, and the content of macromolecules of polysaccharide (s) are less than or equal to 5% by weight, preferably less than or equal to 1% by weight, more preferably 10 ppm to 0.1% by weight of the mass of the first solvent.

20. Process according to any one of claims 16 to 19, wherein the cations are chosen from monovalent cations, divalent cations, and trivalent cations, preferably the divalent cations are chosen from Cd ²⁺ , Cu ²⁺ , Ca ²⁺ , Co ²⁺ , Mn ²⁺ , Fe ²⁺ , Hg ²⁺ ; the monovalent cations are chosen from Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ , Ag ⁺ , Ti ⁺ , Au ⁺ ; and the trivalent cations are selected from Fe ³⁺ , and Al ³⁺ .

21. Process for the preparation of the reinforced lyophilized gelled capsule according to claim 13, in which a gelled capsule reinforced by the method according to any one of claims 16 to 20 is prepared, said capsule is lyophilized, and said capsule is exposed to a carbon dioxide-containing gas, whereby the hydroxide crystals of said element which cover the outer surface of the capsule are converted into a carbonate layer of said element.

22. Process for the preparation of a nanocomposite material according to any one of claims 14 and 15, wherein the incorporation of at least one reinforced gelled capsule according to any one of claims 1 to 12, or at least one reinforced lyophilized gelled capsule according to claim 13 in a polymer or composite matrix.

23. Use of a reinforced gelled capsule according to any one of claims 1 to 12, or a reinforced lyophilized gelled capsule according to claim 13 as a chemical microreactor within which chemical reactions are carried out, for example reactions for chemical vapor deposition (CVD).