METHOD FOR PRODUCING A COMPOSITE MATERIAL COMBINING A POLYMER AND NANOMATERIALS

Description

TECHNICAL FIELD

[0001] The present invention relates to the general field of composite materials comprising a polymer and nanomaterials, for example nanoparticles.

[0002] The invention relates to a method for manufacturing such a composite material.

[0003] The invention has applications in many industrial fields, including the manufacture of dielectrics for capacitors, the manufacture of magnetic materials for inductors, and the manufacture of surface coatings.

[0004] The invention is particularly interesting because it makes it possible to obtain homogeneous composite materials. PREVIOUS STATE OF THE ART

[0005] Currently, to form a composite material comprising a polymer and nanomaterials, for example nanoparticles, a first solution containing a first solvent and a polymer is prepared, as well as a second solution (dispersion) containing a second solvent and the nanoparticles. The two solutions are mixed, and then the resulting solution is deposited onto a substrate or injected into a mold.

[0006] The polymer concentration is a crucial parameter because it primarily determines the viscosity of the final solution. It therefore plays a vital role in the quality of the deposit.

[0007] However, when the second solution containing the nanomaterials is added to the solution containing the polymer, the polymer concentration is automatically reduced, which changes the viscosity of the solution. For example, if the polymer concentration is reduced by a factor of 2, this can decrease the viscosity by a factor of 10. It will then be difficult to properly deposit the composite material (too thin a layer, insufficient material, poor uniformity, etc.).

[0008] To address this drawback, several solutions could be considered.

[0009] The first solution involves adding nanomaterial powder directly to the solution containing the polymer. However, this most often leads to the formation of aggregates. Therefore, nanomaterials are dispersed in a suitable solvent before use.

[0010] Conversely, one could add polymer powder or granules directly to the nanomaterial dispersion in the correct proportion to achieve the desired viscosity. However, such an action most often leads to the nanoparticles settling at the bottom of the bottle before the polymer powder or granules have completely dissolved because the dissolution time of polymers (for example, several hours) is generally much longer than the sedimentation time of nanomaterials (for example, on the order of ten minutes for magnetic nanoparticles). Otherwise, the polymer would not be completely dissolved.

[0011] Another solution involves drying the nanomaterial dispersion by evaporating the solvent used to disperse it. The dried product can then be collected and added to the polymer solution. However, drying the nanoparticle dispersion generally leads to its re-agglomeration. Indeed, it is known that some solvents are more conducive to the dispersion of certain nanomaterials than others: the solvent used to dissolve the polymer (generally chosen according to the deposition technique and / or the intended application) is not necessarily a good solvent for the dry residue. The nanomaterials are then not dispersed homogeneously. The resulting mixture may, for example, have a supernatant on the surface or sediment at the bottom of the bottle.

[0012] Therefore, there is currently no satisfactory solution for preparing a homogeneous solution with the appropriate viscosity for manufacturing a composite material.

[0013] FR 3 074 495 A1 describes a process for manufacturing a composite comprising a first polymer and phosphors, the process comprising the following steps: providing a solution comprising a first solvent, a first polymer, phosphors and a second solvent, the boiling point of which is at least 30°C higher than the temperature of the first solvent; deposition of the solution in the cavities and evaporation of the solvents. DESCRIPTION OF THE INVENTION

[0014] One object of the present invention is to propose a method remedying the disadvantages of the prior art and, in particular, a method for forming a homogeneous composite material, the method being simple to implement.

[0015] To this end, the present invention proposes a method for manufacturing a composite material comprising a polymer and nanomaterials, the method comprising the following steps: a) dissolution of the polymer in a first solvent, thereby obtaining a first solution, b) dispersion of the nanomaterials in a second solvent different from the first solvent, thereby obtaining a second solution;c) mixing the two solutions, thereby obtaining a third solution; d) heating the third solution so as to evaporate at least 10% by volume of the second solvent, and preferably so as to evaporate the second solvent completely, thereby obtaining a final solution; e) deposition of the final solution onto a substrate or injection of the final solution into a mold and evaporation of the first solvent, and optionally evaporation of the volume fraction of the second solvent not evaporated in step d); the second solvent has a boiling point at least 30°C lower than the boiling point of the first solvent, and the viscosity of the final solution is equal to within 20% and, preferably, is equal to within 10% of the viscosity of the first solution.

[0016] The invention differs fundamentally from the prior art by using two distinct solvents with different boiling points. The solvent change is carried out while remaining in a liquid medium throughout, i.e., without an intermediate drying step, which ultimately ensures good dispersion of the nanomaterials in the final solution.

[0017] It is thus possible, initially, to easily dissolve the polymer in the first solution and to easily disperse the nanomaterials in the second solution, then, following the mixing of the two solutions and the preferential evaporation of the second solvent, to easily deposit the final solution, which has an adequate viscosity and good dispersion of the nanomaterials, which leads to the formation of a homogeneous composite material.

[0018] Advantageously, the second solvent has a boiling point at least 50°C lower than that of the first solvent.

[0019] Advantageously, the first solvent has a boiling point above 100°C and the second solvent has a boiling point below 90°C. Low-boiling-point solvents (below 90°C or even below 70°C) are generally not used as application solvents because they dry too quickly and do not allow for the proper deposition of a continuous film on a substrate or the complete filling of a mold. In practice, the solution dries before it is fully spread or dispensed, resulting in a poor-quality material. However, the use of such a solvent is particularly advantageous in the context of this invention.

[0020] Advantageously, the first solvent is chosen from among propylene glycol methyl ether acetates (PGMEA), ethyl lactates (EEP, ethyl 3-ethoxy propionate), xylene, anisole, and cyclopentanone. These solvents generally have high boiling points (130°C to 190°C).

[0021] Advantageously, the second solvent chosen is acetone, benzene, butadone, ethyl acetate, hexane, 2-propanol, chloroform, dichloroethane and dichloromethane.

[0022] Advantageously, the first solvent is PGMEA and the second solvent is a chlorinated solvent, such as chloroform.

[0023] Advantageously, the polymer is chosen from polystyrene, polyepoxide, poly(vinylidene fluoride), polymethacrylate and polyetherimide.

[0024] According to a first advantageous embodiment, the nanomaterials are chosen from nanoparticles.

[0025] Nanoparticles can be core-shell structure nanoparticles, for example, formed of a metallic core based on Cu, Ni, Co or Fe, coated by a layer of carbon.

[0026] Nanoparticles can be magnetic.

[0027] Nanoparticles can be ferroelectric.

[0028] Nanomaterials can be wide bandgap semiconductors.

[0029] According to another advantageous embodiment, the nanomaterials are chosen from hexagonal boron nitride (h-BN) nanosheets and nanodiamonds.

[0030] Advantageously, the second solvent is a chlorinated solvent, and the nanomaterials are nitrided or carbonized. The nanomaterials can be nitrided or carbonized throughout (core) or only on the surface (shell).

[0031] Advantageously, step b) is carried out using ultrasound. This results in a homogeneous mixture.

[0032] The process offers numerous advantages: Compared to prior art, there is no intermediate drying step, which simplifies the process and limits the risk of nanomaterial re-agglomeration during the intermediate drying stage. The viscosity of the final solution remains unchanged or similar to that of the initial solution. The nanomaterials are better dispersed within the polymer. The thickness, uniformity, and homogeneity of the deposited or molded material are better controlled. The physical properties of the deposited films are improved; for example, since dielectric and magnetic losses are dependent on the size of the aggregates, the quality factors of the materials obtained with this process are enhanced. It is thus possible to obtain high-performance components, such as capacitors and inductors.

[0033] Other features and advantages of the invention will become apparent from the supplementary description that follows.

[0034] It goes without saying that this additional description is given only as an illustration of the object of the invention and should in no way be interpreted as a limitation of this object. DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0035] The manufacturing process for a composite material comprising a polymer and nanomaterials involves the following steps: a) Dissolving the polymer in a first solvent, thereby obtaining a first solution; b) Dispersing the nanomaterials in a second solvent different from the first solvent, thereby obtaining a second solution (also called a dispersion), the second solvent having a boiling point at least 30°C lower than that of the first solvent; c) Mixing the two solutions, thereby obtaining a third solution; d) Heating the third solution so as to evaporate at least 10% by volume of the second solvent, and preferably so as to evaporate the second solvent completely, thereby obtaining a final solution, the viscosity of the final solution being equal to within 20% of the viscosity of the first solution, preferably to within 10% of the viscosity of the first solution, and even more preferably to within 5% of the viscosity of the first solution.e) deposition of the final solution onto a substrate or injection of the final solution into a mold and evaporation of the first solvent, and possibly of the portion of the second solvent not evaporated during step d).

[0036] By equal to within 10%, we mean that the viscosity value of the final solution does not vary by more than 10% from the viscosity value of the first solution.

[0037] In step a), a polymer is dissolved in a solvent.

[0038] The first solvent is preferably an organic solvent.

[0039] This includes, for example, solvents used with lithography resins or screen printing inks such as PGMEA, EEP, xylene, anisole, or cyclopentanone. For example, the density of PGMEA is 0.96 with a boiling point of 146°C.

[0040] Alternatively, the first solvent could be water.

[0041] The first solvent has a high boiling point (preferably greater than or equal to 100°C and even more preferably strictly greater than 100°C).

[0042] The solvent serves both to dissolve and dilute the polymer. The concentration of polymer in the first solvent determines the viscosity of the first solution.

[0043] The polymer can be a photosensitive or electroactive polymer.

[0044] The polymer is preferably chosen from polystyrenes (PS), polyepoxides, poly(vinylidene fluoride) (PVDF, P(VDF-TerFe), P(VDF-TerFe-CTFE or CFE), a polymethacrylate (PMMA) and a polyetherimide (PEI).

[0045] Several polymers can be used in mixtures.

[0046] The viscosity of the first solution is, for example, between 1000 and 10000 cP at 25°C.

[0047] In step b), the nanomaterials are dispersed in the second solvent. This step can be carried out using ultrasound.

[0048] The second solvent is an organic solvent.

[0049] The second solvent has a low boiling point (preferably strictly below 90°C).

[0050] The second solvent is, for example, acetone, benzene, butadone, ethyl acetate, hexane, 2-propanol, chloroform, dichloroethane and dichloromethane.

[0051] Chlorinated solvents such as chloroform, dichloroethane and dichloromethane are particularly interesting with carbon or nitride nanomaterials such as carbon nanotubes, carbon black, carbon-coated nanoparticles, boron nitride nanosheets, etc.

[0052] Advantageously, ultrasonication, used to disperse nanomaterials, causes partial decomposition of chloroform, releasing chlorine radicals that can attach, for example, to the surface of carbon nanotubes through non-covalent bonds. Since chlorine is a large molecule, it can attach to nanomaterials and generate steric hindrance (similar to surfactants), helping to separate them and thus keeping them in suspension for longer (increased sedimentation time).

[0053] Nanomaterials can be 1D, 2D, or 3D nanomaterials.

[0054] Nanomaterials are, for example, nanoparticles. These can be nanoparticles made of noble metals, non-noble metals, magnetic materials, semiconductor materials, metal oxides, ferroelectric materials, etc.

[0055] Preferably, core-shell nanoparticles should be chosen. The core, for example metallic, is coated by a layer of carbon or an oxide layer, particularly silica or alumina.

[0056] Preferably, the core is made of Cu, Ni, Co or Fe and the shell is made of carbon, notably composed of some graphene sheets. It can also be made of amorphous carbon or graphite.

[0057] Nanomaterials can also be hexagonal boron nitride (h-BN) nanosheets or even nanodiamonds.

[0058] Several types of nanomaterials can be used in mixtures.

[0059] The concentration of the nanomaterial suspension is advantageously between 0.01 and 0.2g / mL, for example 0.1 g / mL.

[0060] The concentration of nanomaterials suspended in the second solvent is chosen so as to have a final solution with the right ratio of quantity of nanomaterials / quantity of polymer to obtain the desired concentration of nanomaterials in the dry polymer (after evaporation of the solvents).

[0061] The presence of nanomaterials suspended in a solvent does not significantly alter its viscosity (it is considered to be unchanged).

[0062] In step c), the first solution and the second solution are mixed.

[0063] We obtain a nanocomposite solution formed from a suspension of nanomaterials in a liquid polymer matrix with a predetermined ratio of nanomaterial quantity to polymer quantity.

[0064] After mixing, the viscosity of the solution decreases due to the dilution of the polymer. The viscosity of the solution after mixing is, for example, between 1 and 10 cP at 25°C.

[0065] The first solvent and the second solvent are advantageously miscible.

[0066] Preferably, the first solvent is PGMEA and the second solvent is a chlorinated solvent. Chloroform is a denser solvent (1.48) than PGMEA, capable of keeping nanomaterials in suspension for longer, and has a significantly lower boiling point: PB = 61°C.

[0067] PGMEA and chloroform should be chosen as the preferred options.

[0068] In step d), the third solution is heated. This solution is heated to a temperature close to the boiling point of the second solvent and below the boiling point of the first solvent. By "close to" we mean ±20°C, and preferably ±10°C.

[0069] It can be heated above the boiling point of the second solvent.

[0070] It is also possible to heat from 0 to 20°C, and preferably from 0 to 10°C, below the boiling point of the second solvent to avoid the formation of bubbles

[0071] This causes partial or total evaporation of the second solvent. Partial evaporation means that at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% by volume is evaporated.

[0072] For illustrative purposes, the following table lists the viscosities of different solutions at the end of step d), as a function of the volume fraction of the second solvent that has been evaporated. Evaporation of the second solvent (% vol.) 0 20 50 100 Viscosity at 25°C (cP) 1-10 10-100 100-1000 1000-10000

[0073] All (100% by volume) or almost all (at least 95% by volume) of the first solvent is retained (residual evaporation is considered negligible). A few minutes are sufficient to evaporate the second solvent.

[0074] After evaporation, preferably complete, of the second solvent, a homogeneous nanocomposite solution is obtained. The final solution has the correct viscosity for deposition and to form a homogeneous composite material. The solvent in this solution is the first solvent, which is the application solvent.

[0075] In step e), the final nanocomposite solution is deposited onto a substrate. This nanocomposite solution can advantageously be used for film deposition, for example using a spinner, or for wafer molding, for example by hot pressing or injection molding. The film or wafer is then dried near the boiling point of the first solvent to remove it.

[0076] This results in a homogeneous composite material comprising a polymer and nanomaterials (1D, 2D or 3D).

[0077] Although this is by no means limiting, the invention finds particular applications in the field of capacitors (using as a dielectric a polymer with nanomaterials) and inductors (using as a magnetic material a polymer with magnetic nanoparticles).

[0078] The invention also has applications in the field of surface coatings (wear-resistant, hydrophobic, optical, etc.). Depending on the nanomaterials chosen, it is indeed possible to modify the hardness of a resin, or even the optical index of a coating.

Claims

1. Method for manufacturing a composite material comprising a polymer and nanomaterials, the method comprising the following steps: a) dissolution of the polymer in a first solvent, whereby a first solution is obtained, b) dispersion of the nanomaterials in a second solvent, different from the first solvent, whereby a second solution is obtained, c) mixing of the two solutions, whereby a third solution is obtained, d) heating of the third solution so as to evaporate at least 10% by volume of the second solvent and preferably so as to evaporate totally the second solvent, whereby a final solution is obtained, e) deposition of the final solution on a substrate or injection of the final solution into a mould and evaporation of the first solvent, and optionally evaporation of the volume fraction of the second solvent not evaporated during step d), wherein the second solvent has a boiling point lower by at least 30°C than that of the first solvent, and and wherein the viscosity of the final solution is equal to some 20% and preferably equal to some 10% of the viscosity of the first solution.

2. Method according to claim 1, wherein the second solvent has a boiling point lower by at least 50°C than that of the first solvent.

3. Method according to any one of claims 1 and 2, wherein the first solvent has a boiling point above 100°C and the second solvent has a boiling point below 90°C.

4. Method according to any one of the preceding claims, wherein the first solvent is chosen from among propylene glycol methyl ether acetates (PGMEA), ethyl lactates, xylene, anisole and cyclopentanone.

5. Method according to any one of the preceding claims, wherein the second solvent is chosen from among acetone, benzene, butanone, ethyl acetate, hexane, 2-propanol, chloroform, dichloroethane and dichloromethane.

6. Method according to claims 4 and 5, wherein the first solvent is PGMEA and the second solvent is chloroform.

7. Method according to any one of the preceding claims, wherein the polymer is chosen from among polystyrenes, polyepoxides, poly(vinylidene fluorides), polymethacrylates and polyetherimides.

8. Method according to any one of claims 1 to 7, wherein the nanomaterials are chosen from among nanoparticles, and preferably nanoparticles with core-shell structure, for example formed of a metal core based on Cu, Ni, Co or Fe, coated by a layer of carbon.

9. Method according to the preceding claim, wherein the nanoparticles are magnetic.

10. method according to any one of claims 1 to 7, wherein the nanomaterials are ferroelectric nanoparticles.

11. Method according to any one of claims 1 to 7, wherein the nanomaterials are wide gap semiconductors.

12. Method according to any one of claims 1 to 7, wherein the nanomaterials are chosen from among nanosheets of hexagonal boron nitride (h-BN) and nanodiamonds.

13. Method according to any one of the preceding claims, wherein the second solvent is a chlorinated solvent and the nanomaterials are nitride-containing or carbon-containing.

14. Method according to any one of the preceding claims, wherein step b) is carried out under ultrasounds.