WO2009101231A1

WO2009101231A1 - Composition of polymers and carbon nanotubes, method for producing same and the uses thereof

Info

Publication number: WO2009101231A1
Application number: PCT/ES2009/070021
Authority: WO
Inventors: Ana Benito Moraleja; Pablo Jimenez Manero; Maria Teresa Martinez Fernandez De Landa; Wolfgang Maser
Original assignee: Consejo Superior De Investigaciones Científicas
Priority date: 2008-02-13
Filing date: 2009-02-12
Publication date: 2009-08-20
Also published as: ES2324810B1; ES2324810A1

Abstract

Composition of carbon nanotubes and polymer that can be obtained by means of a method that comprises: sonication of a dispersion of carbon nanotubes in an acid solvent; the addition of monomers to the nanotube dispersion; and the rapid addition of a radical initiator to the previous dispersion of nanotubes and monomer, the resulting mixture being maintained at a temperature of between 0ºC and 40ºC. The method is implemented with continuous sonication. Not only said composition but also the dispersion thereof in water are useful as components in paints, dyes, printing processes, electronic devices or circuits or in bioapplications.

Description

COMPOSITION OF CARBON POLYMERS AND NANOTUBES,

PROCEDURE OF OBTAINING AND ITS USES

The present invention relates to a process of in situ polymerization of monomers, more preferably aniline, in the presence of carbon nanotubes. In addition, it refers to the composition obtained by said process, which comprises a polymer, preferably fibrillary polyaniline, and carbon nanotubes, and its different uses. This composition is soluble and stable in water.

STATE OF THE PREVIOUS TECHNIQUE

Intrinsic conductive polymers (PCs), also called electroactive polymers or synthetic metals, have long been known. Examples of these PCs are polyacetylene, polypyrrole, poly (paraphenylene), polythiophene and its derivatives. PCs have electrical, magnetic and optical properties of a metal while they have mechanical properties usually associated with conventional polymers. They have a great potential of applications for the development of plastic electronics (flexible circuits, transistors, sensors, organic light emitting diodes, photovoltaic cells, actuators, etc.), as well as in applications of protection against corrosion and in functional textile materials . Its conductive properties are due to the doped form of the polymer, and this doping can be performed chemically or electrochemically. In their conductive form, these materials have limited use for technological applications, since they are often chemically unstable, and virtually intractable, being hardly processable in solution or in melt.

Among the PCs, polyaniline (PANI) has a special relevance. It is chemically stable and electrically conductive in protonated form. In addition, in recent years, ways of solubilizing it in conventional solvents have been described, which offers the possibility of being used using usual techniques to form coatings, films, fibers, printed patterns, etc.

The polyaniline polymer can be presented in various general forms, including the so-called reduced form (leuco-emeraldine base), Ia partially oxidized called the base form emeraldine and the pernigraniline form, completely oxidized. Each oxidation state can be presented in the form of its base or in protonated form (salt) by means of treating the base with an acid. The electrical and optical properties of PANI vary with different oxidation states, and different forms.

The emeraldine form of PANI is of great interest for the aforementioned applications, especially because of its conversion properties of the insulating form emeraldine base soluble to the emeraldine salt, conductive and not soluble. There are several chemical synthesis routes described in the literature, the majority based on acid doped. The non-conductive form of PANI, emeraldine base, is soluble in strong polar solvents such as N-methyl pyrrolidone (NMP), while the conductive form of PANI, emeraldine salt, is soluble only in very strong acids.

Recently, a process for obtaining PANI in fibrillar form by rapid addition of the polymerizing oxidizing agent to the aniline monomer in a single stage has been described (Huang J., et al., 2006, Chem. Commun. Vol. 4 pp. 367-376 ). The fibrillar character also improves the solubility of the emeraldine resulting in aqueous solutions.

There is a remarkable interest in finding a way to improve the conductivity of PANI while retaining its thermal stability and processability. It is also known in the literature that the combination of PANI with certain carbonaceous materials such as carbon nanotubes is possible.

Carbon nanotubes (CNTs) are relatively new nanoscale objects, composed of one or more sheets of graphene rolled forming cylindrical structures to give rise to what is called single-walled nanotubes (SWNT). multi-walled nanotubes (MWNT of English multiwalled carbon nanotubes). CNTs have unique structural, mechanical, thermal, electronic, and optical properties and are of great interest in applications in several fields of high technological interest such as nanoelectronics, field emission, nanoelectromechanical devices, sensors, composite materials or functional plastics. For many applications, especially for the manufacture of functional plastic composite materials, it is desirable to be able to disperse the CNTs and maintain such dispersions to achieve good product homogeneity, minimize processing problems and improve their quality.

There are composite materials with PANI and CNT that were obtained by means of CNT / PANI dispersion methods applying the appropriate treatment to the CNTs and their use in insulating polymers. The process is based on a mixture of the two constituents CNTs and PANI through an ex situ approach. This type of material could be used in electronic circuit printing.

On the other hand, in 2001 a process of in-situ polymerization of aniline in nanotubes was described, in order to obtain the first PANI / CNTs composite material, and the process of load transfer between nanotubes and polyaniline through selective interactions. These procedures were carried out at temperatures of about -3 ⁰ C (Cochet, M. et al., 2001, Chem. Commun., Vol. 16, pp. 1450-1451).

Subsequently, the manufacture of a highly functional CNT / PANI soluble composite material at temperatures below ⁰ ° C was described (In het Panhuis M., et al., 2005, J. Phvs. Chem. B, vol. 109, pp. 22725-22729). This composite, consisting of polyaniline in its base form and carbon nanotubes, was soluble in NMP (N-methyl-2-pyrrolidinone). The composite material, PANI / CNTs, in powder had conductivity in both its base and salt form, giving conductivity values at room temperature of approximately 1 S / cm, conductivity that was determined by the percolation network of the nanotubes in the composite material . EXPLANATION OF THE INVENTION

The present invention describes an in-situ polymerization process of monomers, preferably aniline, on carbon nanotubes, obtaining a composite material (fibrillar polyaniline salt in its conductive form (emeraldine) and carbon nanotubes) with nanotube contents of up to even more. 50% by weight (up to 70% by weight), which is highly dispersible and stable in aqueous solutions. In addition, Ia The invention relates to aqueous dispersions of this composition. Likewise, the material obtained is an electrical conductor, has better thermal stability than the polyaniline salt without nanotubes and is fluorescent.

In the production of these materials a combination of reaction conditions is involved, such as the irradiation by ultrasound of the dispersions, the temperature controlled in an in situ polymerization of aniline in the presence of nanotubes, the rapid addition of the oxidant, in addition, the nanometric size of these nanotube structures also allows the compositions of the present invention to be highly dispersible and stable in water, even with a high content of nanotubes.

In addition, the new nanostructured nanocomposite has high stability against detonation compared to the polymer only, due to the interaction of nanotubes with the polymer itself.

This synthesis process is allowed to transfer to other polyaniline derivatives and other types of conductive polymers, such as polythiophene, polypyrrole, poly (phenylene sulfide) or their possible mixtures.

Therefore, one aspect of the present invention relates to a process (from now on the process of the invention) for obtaining a composition of carbon and polymer nanotubes, comprising: a. sonication of a dispersion of carbon nanotubes in an acid solvent; b. addition of monomers in the dispersion of step (a); C. rapid addition of a radical initiator to the dispersion of step (b) maintaining the mixture obtained at a temperature of between O ⁰ C and 4O ⁰ C, preferably between 15 and 25 ⁰ C, for a time which can be between 30min and 24 hours.

Stirring by ultrasound irradiation (sonication) continues in steps (b) and (c).

By "quick addition" is meant the addition of once, not drop by drop, the radical initiator. The sonication can be carried out at an irradiation power of between 5-3,000W, the preferred range being 10-100W.

The polymer of the present invention is an electrically conductive material selected from the group comprising polyaniline or its derivatives, polythiophene or its derivatives, polypyrrole or its derivatives, poly (phenyl sulfide) or its derivatives, or any of their mixtures. By "mixtures", in this specific case, it is meant more than one polymer and / or a derivative of any polymer.

Preferably the polymer is polyaniline, and consequently its monomer is aniline, or its derivatives.

In the prior art, surfactants are usually used either to disperse carbon nanotubes in water or to produce PANI nanofibers. However, the process of the invention is carried out in the absence of surfactant, by means of said process achieving that the polyaniline nanostructures and carbon nanotubes are well dispersed in the matrix without surfactant.

A preferred embodiment of the process of the invention also comprises: d. filter, wash and dry the carbon and polymer nanotube compound, preferably polyaniline, obtained in step (c).

The acid solvent is a water soluble protic inorganic acid that is selected from the group comprising: hydrochloric acid (HCI), sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO3), phosphoric acid (H ₃ PO ₄ ), acid boric (HBO3), hydrofluoric acid (HF), hydrobromic acid (HBr), iodhydric acid (Hl), perchloric acid (HCIO ₄ ), periodic acid (HIO ₄ ), tetrafluoroboric acid (HBF ₄ ) or any combination thereof. Preferably, the acid is HCI.

Preferably the concentration of acid solvent is between 0.001 M to 5M.

Carbon nanotubes can be single layer carbon nanotubes

(SWNTs) or multi-layer (MWNTs), produced by electric arc discharge, chemical vapor deposition (CVD) - (including

HiPCO), laser ablation or any combination of them. Preferably the nanotubes that are used in the process of the invention are multilayer.

The amount of carbon nanotubes in the dispersion can be up to 60-70% by weight with respect to the polymer, preferably polyaniline. Despite its high concentration of nanotubes, the assembly continues to disperse without agglomerates.

Normally, in the state of the art such compositions are described with percentages of nanotubes below 5% with respect to the polymer, because from higher concentrations they immediately agglomerate and do not disperse well in the matrix.

Preferably the amount of carbon nanotubes is between 0.001% and 60% by weight with respect to the initial monomer, preferably to the initial aniline.

The aniline used in the process of the invention can be substituted or unsubstituted aniline, with a concentration range that can be between 0.001 g / ml and 0.2g / ml with respect to the dispersion of step (a).

The radical initiators are water soluble oxidizing inorganic salts, where the oxidant is selected from the group comprising peroxod ammonium sulfate ((NH ₄ J ₂ S ₂ Os, 2eq.redox (number of redox equivalents per mole of oxidant)), peroxod potassium sulfate (K ₂ S ₂ O ₈ , 2eq. redox), iron trichloride (FeCU, 1eq. redox), cobalt trichloride (C0CI ₃ , 1eq. redox), hydrogen peroxide (H ₂ O ₂ , 2eq. redox), copper sulfate (CuSO ₄ , 2eq. redox), copper chloride (CuCI ₂ , 2eq. redox), potassium permanganate (KMnO ₄ , 3eq. redox), potassium chlorate (KCIO ₃ , 6eq. redox), chlorate sodium (NaCIO ₃ , 6eq. redox), potassium dichromate (K ₂ Cr ₂ O ₇ , 6eq. redox), ammonium dichromate ((NhU) ₂ Cr ₂ O ₇ , 6eq. redox), sodium periodate (NH ₄ IO ₄ , 8eq. Redox), ammonium periodate (NaIO ₄ , 8eq. Redox) or any combination thereof. Preferably the oxidants are peroxod ammonium sulfate, iron trichloride, copper sulfate or ammonium periodate, and more preferably ammonium peroxodisulfate.

The concentration of initiators can be between 0.001 g / ml and 0.2g / ml with respect to the total dispersion. In this dispersion the number of equivalents redox oxidant, per mole of monomer, can be between 0.05 and 4 redox equivalents per mole.

A second aspect of the present invention refers to a composition obtainable by the process of the invention (from now on the composition of the invention).

The composition of the invention is much more dispersible than the nanotubes themselves, preferably MWNTs, so that the polymer, and more particularly PANI, acts here as an efficient vector for the dispersion of MWNTs. This makes the composition of the invention a good material for improving the processing of carbon nanotubes, with the advantage of preserving the properties and functionality of conductive polymers.

In these polyaniline-carbon nanotubes nanocompositions obtained by the process of the invention, the polyaniline is in the form of emeraldine salt (its conductive form) and in turn has nanostructured morphology.

A third aspect of the present invention refers to an aqueous dispersion comprising the composition of the invention.

In this invention, the synthesis of a PANI composite with CNTs is presented for the first time, in which the polyaniline preserves a nanometric scale morphology, and which is also dispersible in aqueous solutions. This allows improvements in the processing of said composite that can be used in various applications in fields such as textiles, inks and functional additives, electronics with plastics, biomaterials, etc.

In a more generic way, it is demonstrated that the process of the invention is an efficient way to obtain stable water dispersions of the carbon nanotubes themselves, which already constitutes a great advance in the processing and purification of said material.

For many applications, it is highly desirable to have compositions of a conductive polymer and CNT, preferably PANI / CNT, soluble in water, homogeneous and stable. And as a consequence of this dispersibility in water, there are:

-New opportunities to process nanocomposite polymer-nanotubes in films, fibers, or as an additive in various matrices such as polymers, paints, inks, and printing processes for electronic circuits / devices, textile impregnation processes, bioapplications, among others.

-New opportunities for the use of carbon nanotubes in aqueous systems such as paints, inks, printing processes, electronic circuits / devices and bioapplications.

Thus, a fourth aspect of the present invention refers to the use of the composition of the invention or of the dispersion of the invention, in paints, inks and dyes, printing processes, electronic circuits or devices or in bioapplications.

Thus, the composition of the invention can be easily used to prepare functional additives for paints, inks and dyes, to prepare films and fibers for special use in plastic electronics and optoelectronic devices, to prepare anticorrosive coatings.

Throughout the description and the claims, the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and characteristics of the invention will emerge partly from the description and partly from the practice of the invention. The following examples and drawings are provided by way of illustration, and are not intended to be limiting of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1.- They show the images by scanning electron microscopy (SEM) of the powder composites of: FIG.1A and FIG.1 B: PANI; FIG.1C and FIG.1 D: PANI / 5M; FIG. 1 E and FIG. 1 F: PANI / 10M; FIG. 1 G and FIG. 1 H: PANI / 30M; FIG. 11 and FIG. U: PANI / 50M.

FIG. 2.- They show the images by transmission electron microscopy (TEM) of the powdered composites of: FIG.2A: PANI; FIG. 2B: PANI / 5M; FIG. 2C: PANI / 10M; FIG. 2D: PANI / 30M.

FIG. 3.- They show the data obtained by infrared spectrometry of the powder composites of: FIG.3A: PANI; FIG. 3B: PANI / 10M; FIG. 3C: PANI / 30M; FIG. 3D: PANI / 50M.

FIG. 4.- They show the data obtained by Raman spectrometry of the powder composites of: FIG. 4A: PANI; FIG. 4B: MWNT; FIG. 4C: PANI / 50M; FIG. 4D: The previous three.

FIG. 5.- They show the data obtained by visible ultraviolet absorption spectrometry of composites dispersed in water and 0.001 M HCI of: FIG. 5A: PANI; FIG. 5B: PANI / 5M; FIG. 5C: PANI / 30M.

EXAMPLES

Next, the invention will be illustrated by tests carried out by the inventors, which shows the specificity and effectiveness of the process of the invention and the composition obtained by said process.

EXAMPLE 1

Multi-layer carbon nanotubes (MWNTs) were prepared by the electric arc discharge method. Pure graphite rods were sublimed at a voltage of 25V maintaining a current intensity of 6OA under a Helium atmosphere of 66kPa. The internal part of the cathodic deposit was collected and used without any further purification, this material was formed almost exclusively by MWNTs with lengths of several microns and diameters between 20 and 50nm.

15mg of MWNTs were dispersed by sonication in 2OmI of 1M aqueous HCI solution for 10 minutes. 0.3ml distilled aniline was added

(99.5%, Scharlau Chemie, Spain) and were dispersed by sonication for another 10 minutes at 15 ⁰ C. 2OmI of a rapidly added 0.32g solution of ammonium peroxodisulfate (APS, 98%, Sigma-Aldrich) in 1 M HCI. The reaction mixture thereafter was maintained under sonication of 5OW power ultrasound, at a temperature within the range of 15 to 2O ⁰ C for 2 hours.

After that time the mixture was filtered and the dark green precipitate was washed repeatedly with 1 M HCI and acetone. Finally the product was dried under vacuum at room temperature for 24 hours.

The material obtained can be easily dispersed in varying amounts of water by a short period (around 3 minutes) of sonication. The stability of these dispersions depends on the proportion of MWNTs in the composite material.

EXAMPLE 2

90mg of multilayer carbon nanotubes (MWNTs) produced according to the method detailed in EXAMPLE 1 were dispersed in 10ml of 0.5M HCI aqueous solution together with 0.3ml of aniline for 20 minutes at room temperature. The temperature of this dispersion was adjusted to 15 ⁰ C by means of a thermostated ultrasonic bath. 10ml of a 0.5g solution of FeCU hexahydrate in 0.5M HCI was added once. The reaction was maintained at a constant temperature within the range 15 to 25 ⁰ C and under sonication 6OW power for 1 hour.

After that time the mixture was filtered and the dark green precipitate was washed repeatedly with 0.5M HCI until completely removing the remains of oxidant and then with acetone. Finally the product was dried under vacuum at room temperature for 24 hours.

The material obtained was easily dispersed in varying amounts of water by a short period (around 3 minutes) of sonication. The stability of these dispersions depends on the proportion of MWNTs in the composite material.

EXAMPLE 3 Elemental analyzes of the products were performed on a Thermo Flash EA 1112 analyzer and thermogravimetric analyzes were performed on a Setaram TG-DTA 92 thermobalance, burning 10mg samples under an air flow of 5OmI per minute with a heating ramp of 3 ⁰ C per minute. Table 1 shows the results of the elementary analyzes of C, H, N and O, the weight loss corresponding to nanotubes obtained by TGA and the polymerization performance with respect to the aniline.

The nomenclature of the samples refers to the proportion by weight of MWNTs with respect to the amount of aniline initially used in the polymerization, so PANI does not contain nanotubes, PANI / 5M contains 5% of nanotubes, PANI / 10M 10%, PANI / 30M 30% and PANI / 50M 50%.

Table 1

The presence of nanotubes in the polymerization seems to affect its performance, as can be observed in Table 1. The increase in the amount of MWNTs induces a slight increase in the amount of PANI obtained. It is noteworthy that the same method that leads to the formation of PANI nanofibers produces homogeneous composites with a high content in MWNTs (up to 62%).

The thermogravimetries carried out with these materials showed the typical decomposition pattern associated with polycycline doped with HCI, with a loss of water up to 100 ⁰ C and a decomposition of the polyaniline chains between 280 and 620 ⁰ C. The composite materials presented oxidation of the MWNTs that happened at lower temperatures than in the case of the samples of pure MWNTs, as shown in Table 1. This phenomenon indicates the interaction between the PANI and the MWNTs, showing the good dispersion of the latter in the polymer matrix.

Powder samples of the products were observed by scanning electron microscopy (SEM) using a Hitachi S3400N microscope and by transmission electron microscopy (TEM) with a JEOL JSM-6400. Raman spectrometry was performed on a Horiba Jovin-Yvon brand equipment. Infrared spectrometry was performed by incorporating the powder material into KBr pads.

The SEM images (FIG. 1) clearly illustrate the nanometric morphology of these compositions. The MWNTs were presented in a wide range of diameters and lengths, although in all cases they kept the structure straight and without defects of the nanotubes produced by electric arc discharge. In the case of polyaniline, small elongated particles of about 100 nm in diameter were observed, as can be seen in FIG. 1A and 1 B and in FIG. 2A that corresponds to a TEM image. This morphology is that corresponding to the nanofibrillar PANI, which has been synthesized and characterized repeatedly, although the nanofibers shown here show a much less elongated appearance and greater homogeneity in terms of particle sizes. The nanometric size certainly favors the dispersibility of these materials. The composites present a new type of nanostructure that coexists with PANI nanofibers, in which the MWNTs are partially covered by PANI forming cylindrical structures of about 300nm in diameter (FIG. 1C). As can be seen in the TEM images (FIG. 2B, 2C and 2D), these cylinders usually house more than a single nanotube, oriented in parallel. These images allow to appreciate the homogeneity of the composite materials, which are capable of forming stable dispersions for contents of up to 50% in CNT. The presence of these nanostructures explains the vector role for the dispersion of CNTs exerted by the polyaniline in the composites, since the nanotubes are difficult to disperse coated by a layer of hydrophilic polyaniline.

The infrared spectrum obtained from solid samples of nanostructured PANI composites corresponds well with the PANI own spectrum in the state of emeraldine salt, as seen in Figures 3A-3D. Here the nanotubes do not produce any change in the intensities or frequencies of the infrared absorptions, since the MWNTs themselves do not have any characteristic absorption in that area. The spectra have the characteristic 'Fano' effect of doped polyanilines.

Raman spectra for MWNTs show the typical bands for well-graffiti arc MWNTs, as shown in FIG. 4B. The relative intensity of the band G located at 1582cm ^"1 in relation to the band D located at 1353cm ^{" 1} has a value of 7.88, which indicates the high graphitization of the nanotubes produced. For the nanostructured PANI, the Raman spectrum is typical of the polyaniline in the emeraldine salt state, with the most intense absorptions at 1168, 1488 and 1583cm ^"1 , this last absorption coincides with that of greater intensity in the case of the MWNTs. This makes that the presence of MWNTs in composites can only be detected in materials with a higher proportion of MWNTs, as seen in FIG. 4C, the presence of nanotubes is made evident by the appearance of the band around 2700cm ^"1 and an increase in the relative intensity of the peak around 1580cm ^"1 .

EXAMPLE 4

Aqueous dispersions of the materials were achieved by simple sonication of the products obtained in powder in water or aqueous solutions of 1mM HCI for 5 min. These dispersions were analyzed by UV-Vis absorption spectrometry. The stability of these dispersions was evaluated by leaving them at rest, taking aliquots of the upper part of the dispersions from time to time and analyzing them by UV-Vis absorption spectrometry and elemental analysis.

The stability of the aqueous dispersions of nanostructured PANI and its composites with MWNTs is remarkably high. A few minutes of sonication were sufficient to achieve homogeneous dipersions with sufficient stability to be processed and characterized by UV-Vis absorption spectrometry. The absorption spectra of both PANI and composites match the spectra found in PANI nanoparticle dispersion literature, as can be seen in Figures 5A, 5B and 5C. In dispersions made in distilled water a phenomenon of detonation of polyaniline was observed, so that to obtain the PANI spectrum in its protonated state, the dispersions must be carried out in an acid medium. In this case a concentration of 1 mM HCI was sufficient, these dispersions being stable for days and even weeks.

The effect of detonation of PANI and its composites depends on the concentration of the sample, thus the low concentration dispersions are quickly transformed into base emeraldine. The spectra obtained from these dispersions of emeraldine base do not differ much from those of the solutions of pure emeraldine base, with absorption maxima located at 351 and 696nm. The wider aspect of the absorption bands in the spectra of the composites is indicative of the lower homogeneity of these dispersions. In fact, the stability of the aqueous dispersions in the base emeraldine form is markedly lower than the dispersions in the form of the emeraldine salt. The MWNTs present in the composites affect the kinetics of the detonation reaction, this being slower for higher proportions of nanotubes in the dispersed material. The deprotonated materials, that is, in the form of emeraldine base, are soluble in NMP as are the composite materials with MWNTs synthesized by other methods.

Claims

1. Process for obtaining a composition of carbon and polymer nanotubes, comprising: a. sonication of a dispersion of carbon nanotubes in an acid solvent; b. addition of monomers in the dispersion of step (a); and c. rapid addition of a radical initiator to the dispersion of step (b) maintaining the mixture obtained at a temperature of between ⁰ C and 4O O ⁰ C, continuing Ia sonication in steps (b) and (c).

2. Method according to claim 1, further comprising: d. filter, wash and dry the carbon nanotube composition and the polymer obtained in step (c).

3. A method according to any one of claims 1 or 2, wherein the polymer is an electrical conductor selected from the group comprising polyaniline or its derivatives, polythiophene or its derivatives, polypyrrole or its derivatives, poly (phenyl sulfide) or its derivatives, or Any of your mixtures.

4. Process according to any one of claims 1 to 3, wherein the polymer is polyaniline (and its aniline monomer) or its derivatives.

5. Method according to any of claims 1 to 4, wherein the temperature of the reaction in step (c) is between 15 and 25 ' ⁰ C.

Method according to any one of claims 1 to 5, wherein the acid solvent is selected from the group comprising: hydrochloric acid (HCI), sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO ₃ ), phosphoric acid (H ₃ PO ₄ ), boric acid (HBO ₃ ), hydrofluoric acid (HF), hydrobromic acid (HBr), iodhydric acid (Hl), perchloric acid (HCIO ₄ ), periodic acid (HIO ₄ ), tetrafluoroboric acid (HBF ₄ ) or Any of your combinations.

7. Method according to any of claims 1 to 6, wherein the concentration of acid solvent is between 0.001 M to 5M.

A method according to any one of claims 1 to 7, wherein the carbon nanotubes are selected from among single-layer carbon (SWNTs) or multi-layer (MWNTs) nanotubes.

9. Method according to any one of claims 1 to 8, wherein the carbon nanotubes are multi-layered.

10. Method according to any of claims 1 to 9, wherein the carbon nanotubes are produced by the methods of electric arc discharge, chemical vapor deposition (CVD) - (including HiPCO), laser ablation or any combination of they.

11. Method according to any of claims 1 to 10, wherein the amount of carbon nanotubes is up to 70% by weight with respect to the initial aniline.

12. Method according to any of claims 1 to 11, wherein the amount of carbon nanotubes is between 0.001% and 60% by weight with respect to the initial aniline.

13. Method according to claim 4, wherein the polyaniline is in the form of emeraldine salt and nanostructured.

14. A method according to any one of claims 1 to 13, wherein the radical initiator is an oxidant selected from the group comprising ammonium peroxodulfate ((NH ₄ J ₂ S ₂ Os), potassium peroxodisulfate (K ₂ S ₂ O ₈ ) , iron trichloride (FeCI ₃ ), cobalt trichloride (CoCI ₃ ), hydrogen peroxide (H ₂ O ₂ ), copper sulfate (CuSO ₄ ), copper chloride (CuCI ₂ ), potassium permanganate (KMnO ₄ ), chlorate potassium (KCIO ₃ ), sodium chlorate (NaCIO ₃ ), potassium dichromate (K ₂ Cr ₂ O ₇ ), ammonium dichromate ((NH ₄ J ₂ Cr ₂ O ₇ ), sodium periodate (NH ₄ IO ₄ ), ammonium periodate ( NaIO ₄ ) or any of its combinations.

15. Method according to any of claims 1 to 14, wherein the concentration of initiators is between 0.001 g / ml and 0.2g / ml with respect to the total dispersion.

16. Composition obtainable by the process according to any of claims 1 to 15.

17. Aqueous dispersion comprising the composition according to claim 16.

18. Use of the composition according to claim 16 or of the dispersion according to claim 17, in paints, inks, printing processes, electronic circuits or devices or in bioapplications.