WO2007080323A2

WO2007080323A2 - Stable aqueous suspension of carbon nanotubes

Info

Publication number: WO2007080323A2
Application number: PCT/FR2007/000049
Authority: WO
Inventors: Frédérick ROUSSEL; Roch Chan Yu King
Original assignee: Universite Du Littoral Cote D'opale; Centre National De La Recherche Scientifique (Cnrs)
Priority date: 2006-01-11
Filing date: 2007-01-11
Publication date: 2007-07-19
Also published as: WO2007080323A3; FR2895987B1; FR2895987A1

Abstract

The present invention relates to a stable aqueous suspension of carbon nanotubes comprising, in addition, at least one non-ionic detergent of alkylphenol alkoxylate type and an alcohol, a polyol or mixture thereof.

Description

STABLE AQUEOUS SUSPENSION OF CARBON NANOTUBES

The present invention relates generally to the field of nanotechnology. More particularly, it relates to a stable aqueous suspension of carbon nanotubes and its implementation for the production of conductive devices intended, inter alia, for the manufacture of conductive electrodes forming part of rigid or flexible display devices.

Display technologies are currently experiencing a boom, related to the development of many consumer communication systems such as mobile phone screens, laptops, electronic diaries, television, etc. In addition, the realization of flexible and lightweight substrates electrodes is an important technological challenge for future applications in display technologies, such as for electronic books and newspapers, but also for the production of "all-plastic" components. For electronics.

Generally, known displays include glass slides coated with a thin layer of conductive oxide deposited under vacuum and at high temperature. This deposit technology has a high energy cost. Moreover, it is problematic for the production of large displays. The conductive oxides used as the electrode, in particular indium tin oxide (ITO), are also fragile when they are deposited on flexible substrates, leading to cracks and delamination during mechanical deformations.

To overcome these drawbacks, solutions have been proposed consisting of the use of new flexible conductive electrodes. Due to their mechanical, electrical and physical properties, carbon nanotubes are potential candidates for replacement of UO electrodes. However, carbon nanotubes, like all other members of the family of carbon-based materials, are insoluble regardless of the nature of the solvent used or form agglomerates, making their thin film deposition on a substrate complex.

Current methods for suspending carbon nanotubes involve chemical treatments to covalently attach atoms or groups of atoms to their walls (Smalley E, et al., Chem Phys Lett.

310, p. 367, 1999; H. Kuzmany et al., Synth. Metals, 141, p. 113, 2004). These functionalization processes require long processing times and use dangerous reagents such as fluorine (V. N. Khabasheska et al., Ace.

Chem. Research 35, p. 1087, 2002), free radical initiators (Y. Ying et al., Org Lett, 5, 1471, 2003, CA Dyke et al., J. Am Chem Soc, 125, 1156).

2003) or oxidizing agents (ZH Yu et al., J. Phys. Chem. A _1104, p. 10995,

2000).

Simple alternatives for solubilizing carbon nanotubes are to physically wrap them with different host materials: peptides (I. Musselman et al., J. Am Chem Soc 126, p.7222, 2004), oligosaccharides (G. Chambers et al., Nano Lett 3, pp. 843, 2003), surfactants (B. Li et al., Chemistry Letters p.598, 2001, RE Smalley et al., Science

280, p. 1253, 1998) or polymers such as polystyrene sulfonate (RE Smalley et al., Chemical Physics Letters 342, pp. 265, 2001), polyvinylpyrrolidone (PE Pehrsson et al., J. Am Chem Soc 124, 12418). , 2002), polyvinyl alcohol (RE

Smalley et al., Nano Letters 3, p. 1285, 2003), amphiphilic polycations (N.A.

Kotov, J. Am. Chem. Soc. 127, p. 3463, 2005).

However, the films prepared from these solutions are very often too little conductor and / or too diffusive after evaporation of the dispersion solvent for the development of thin transparent conductive layers.

In addition, the solvents used for the preparation of the solutions are for the most part toxic, and / or require evaporation procedures under vacuum (cresol derivatives in particular).

The Applicant has sought to develop stable suspensions of carbon nanotubes, allowing the production of thin transparent and conductive films, and found that carbon nanotubes could be dispersed uniformly in an aqueous medium containing at least one Nonionic detergent member of the family of Triton and an alcohol, a polyalcohol or a mixture thereof, this leading to obtaining stable carbon nanotube suspensions for a long period of time. These suspensions use low amounts of carbon nanotubes and non-toxic components and can be prepared using a simple method and low energy cost.

The present invention therefore aims to provide a stable aqueous suspension based on carbon nanotubes comprising at least one nonionic detergent of alkylphenol alkoxylate type, member of the family of Triton and an alcohol, a polyol or a mixture thereof. The carbon nanotubes can be purified or in the raw state, of the monofeuillet or multiwall type, with or without pendant side chains.

The present invention also relates to a stable aqueous suspension composition based on carbon nanotubes. The present invention also relates to a process for preparing the stable aqueous suspension based on carbon nanotubes mentioned above.

The present invention also relates to a conductive device comprising a thin layer of the stable aqueous suspension of carbon nanotubes according to the invention, said layer forming a conductive transparent thin film arranged on a support.

The present invention further relates to a method of manufacturing conductive devices comprising a thin layer of the stable aqueous suspension of carbon nanotubes according to the invention.

The present invention further relates to display devices based on a dispersion of liquid crystals in a polymer matrix addressed by electrodes made on the basis of the conductive device according to the invention.

The invention will be better understood on reading the detailed description which follows, to which are appended the following figures:

FIG. 1 represents the image obtained by scanning electron microscopy of a film based on single-walled carbon nanotubes according to the invention deposited on a glass substrate; _ ^ _

- Figure 2 schematically shows the diagram of a liquid crystal display device according to the invention;

FIG. 3 represents the variation of the transmittance at 632.8 nm as a function of the intensity of the applied electric field (at 50 Hz) in a liquid crystal display device according to the invention;

FIG. 4 shows the measurements of the rise times and the descent times in a liquid crystal display device according to the invention in the case of a plastic substrate;

FIG. 5 illustrates the operation of a liquid crystal based flexible display device according to the invention before (a, b), during (c, d) and after (e, f) the bending phase.

FIG. 6 represents the image obtained by scanning electron microscopy of a film based on single-walled carbon nanotubes according to the invention deposited on a polyethylene terephthalate (PET) substrate; FIG. 7 represents the image obtained by scanning electron microscopy of a film based on multiwall carbon nanotubes according to the invention deposited on a glass substrate;

- Figure 8 shows the image obtained by scanning electron microscopy of a film based on multiwall carbon nanotubes according to the invention deposited on a polymeric substrate (PET).

According to a first aspect, the invention relates to stable aqueous suspensions based on carbon nanotubes also comprising at least one nonionic detergent of alkylphenol alkoxylate type, which is a member of the Triton family and an alcohol, a polyol or their mixed. In an alternative embodiment, the carbon nanotubes used in these suspensions are subjected to a prior purification, according to known techniques. The purification process may consist, for example, in the oxidation of crude carbon nanotubes in an acidic medium, followed by a treatment step with a solution of hydrogen peroxide, preferably at 35% by volume in water. . The purification process further comprises the steps of: diluting the material thus obtained in a large volume of demineralized water; filtration; washing with diluted sodium hydroxide and then with water; drying, _

leading finally to obtain purified nanotubes bearing on their walls carboxyl groups.

In another variant embodiment, the carbon nanotubes used in the suspensions according to the invention are used in the raw state, as provided commercially. In this case, the impurity content varies between 5 and 50% by weight.

The applicant has found that it is possible to put carbon nanotubes (purified or unprocessed) in suspension in water, in the presence of at least one non-ionic detergent of the alkylphenol alkoxylate type, which are members of the family Triton, and an alcohol, a polyol or their mixture. These suspensions remain stable at room temperature for long periods (at least 18 months), that is to say that no precipitation of carbon nanotubes or phase separation is observed during this time. The aqueous suspensions of carbon nanotubes according to the invention are therefore "ready to use" and keep this characteristic for long periods of time.

The concentration of carbon nanotubes in water is between 0.01 and 1% by weight, preferably between 0.2% and 0.5% by weight.

The presence of at least one alkylphenol alkoxylate nonionic detergent, such as a polyoxyethylene isoalkyl phenyl ether or a polyoxyethylene isoalkyl cyclohexyl ether, makes it possible to disperse the carbon nanotubes in a liquid medium (which is preferably water). ). The stable suspensions of carbon nanotubes being intended in particular to be used as conductive coatings of inert supports, the amount of said detergent must not exceed 3% by weight, preferably between 0.5 and 2.4% by weight. Indeed, it has been observed that concentrations greater than 3% of detergent lead to the production of non-conductive coatings.

Furthermore, the aqueous suspensions of carbon nanotubes according to the invention contain between 3 and 5% by weight of an alcohol, a polyol or their mixture, preferably about 4.5% by weight. Preferably, the suspension according to the invention comprises ethylene glycol. The presence of this additive is closely related to obtaining a reproducible way of _

- D - high quality coatings on inert substrates, giving them good wettability properties.

According to a second aspect, the invention relates to a method for preparing the stable aqueous suspension of carbon nanotubes described, said method comprising the following steps: a) adding carbon nanotubes, purified beforehand or in the raw state to a liquid medium comprising water and at least one alkylphenol alkoxylate nonionic detergent (particularly a member of the Triton family), to obtain a first mixture, b) applying to said first mixture ultrasound for a period of time. of minimum Ih, to obtain a second mixture, c) incorporating in said second mixture an alcohol, a polyol or their mixture, to obtain a third mixture, d) homogenizing said third mixture by stirring for at least 3 minutes, to obtain an aqueous suspension stable carbon nanotubes.

In one embodiment, said liquid medium of step a is subjected to ultrasound for a predetermined duration, prior to the addition of carbon nanotubes. The ultrasound application step b to said first mixture is preferably interrupted at a given moment to homogenize by agitation said first mixture for a period of about three minutes, before resuming the application of ultrasound.

According to a preferred variant embodiment, the method according to the invention also comprises a filtration or centrifugation step of the second mixture obtained after step b and before the addition of an alcohol, a polyol or their mixture.

According to a third aspect, the subject of the invention is a conductive device based on carbon nanotubes comprising a thin layer of the stable aqueous suspension of carbon nanotubes according to the invention, said layer forming a conductive transparent thin film arranged on a support . In an alternative embodiment, said support is transparent and inert, the conductive device being intended in particular to constitute an electrode in a display device based on a dispersion of liquid crystals in a polymer matrix. The inert transparent support is a transparent inorganic material or a flexible transparent polymeric material. Said inorganic material is chosen from the group: glass (in particular silica or borosilicate), metal, ceramic, glass having a metal coating. Said flexible transparent polymeric material is selected from the group: polyethylene terephthalate, poly methyl methacrylate, polyvinyl chloride, polyethylene, cellulose acetate derivatives, polyvinyl alcohol, polyvinyl acetate, MyIa type polyester, and the like.

These inert carriers may be colored or colorless, and their thickness may be variable. In general, said inert support is flat. However, supports having curvature or permanent folding can be used within the scope of the invention. In addition, the substrates coated with the conductive transparent thin film based on carbon nanotubes can be cut into various shapes (for example round, square or rectangular) which can then be used as conductive electrodes in the display devices.

According to another aspect, the invention relates to a method of manufacturing the aforementioned conductive device comprising a step of coating said support with a thin layer of the stable aqueous suspension of carbon nanotubes according to the invention, followed by drying; this coating is carried out at ambient temperature and at atmospheric pressure.

In a preferred manner, the coating of the support with a thin layer of the stable aqueous suspension of carbon nanotubes according to the invention is carried out with an adjustable micrometric slit film applicator (bar-coating), which can be easily implemented. in a repetitive and controlled manner over a large area of the substrate and for a desired thickness of the film. However, other coating methods can be used, such as: dip coating, flow coating, spin coating, spray coating, ink jet coating or brushing.

Once the suspension of carbon nanotubes is coated on its inert transparent support, it is allowed to air dry. When the film is completely dry, it is washed with an apolar organic solvent such as toluene for about 10 seconds, and then allowed to air dry.

The attached FIG. 1 shows the image of a film based on single-walled carbon nanotubes, coated on a glass support, according to the aforementioned method. The coating has a thickness of about 100 nm; it comprises beams formed of individual nanotubes, the diameter of each beam ranging from 10 to 30 nm.

The surface resistivity of the films according to the invention, measured according to the four-electrode method, varies in a range from 10 ² to 10 ⁶ Ω squared ^1. The transmittance of the films according to the invention was determined to be 632.8 nm using a photodiode by measuring the transmittance of a Neon Helium laser beam passing through the film at normal incidence The values obtained are at least 75%.

The conductive devices based on carbon nanotubes, described above, are particularly suitable for use as electrodes in a display device, flexible or rigid, based on a dispersion of liquid crystals in a polymer matrix. These electrodes are intended to replace the ITO electrodes used in conventional liquid crystal display devices. In general, these conventional display devices comprise low molecular weight liquid crystals dispersed in the form of droplets whose size is of the order of a micrometer (or nanometer) in a polymer matrix. These devices comprise a conductive and transparent lower substrate and an upper substrate, between which said liquid crystal dispersion is placed. Their operation consists of an alternation of diffusion and transparency phases, depending on the application of a sufficiently large electric field, which reorients the droplet direction field. according to the refractive index of the droplets and that of the polymeric matrix (PS Drzaic, Liquid Crystal Dispersions, World Scientific 1995, Doane et al US 4,688,900).

With reference to the appended FIG. 2, a display device based on liquid crystals according to the invention comprises: two substrates (a), each substrate comprising a conductive device described above. One of the two substrates may be metallic. The two substrates are separated by an interelectrode space (c) in which the faces (b) coated with the film according to the invention are opposite. The dispersion (d) of liquid crystals in a polymer matrix filling this interelectrode gap comes into direct contact with the carbon nanotube-based films or the contact is via a dielectric passivation layer. The device also includes lead wires (e) provided at one end of each substrate to allow voltage to be applied to said films. The device further comprises a voltage source (f) electrically connected to said films through said conductive wires.

Micro-or nano-dispersions of liquid crystals for use in display devices are prepared according to one of the following techniques: a method of phase separation induced by polymerization; temperature-induced phase separation method; solvent induced phase separation method; emulsification process; encapsulation process.

The molecules that can be used for the preparation of said liquid crystal dispersions have phases: nematic, cholesteric, smectic, discotic, etc., and include ferroelectric, antiferroelectric or lyotropic materials. The liquid crystals of a certain type of material may be used alone or in mixture with those of another type, including eutectic mixtures.

The monomers, prepolymers, polymers or combinations thereof for the preparation of said liquid crystal dispersions are selected from: acrylates, methacrylates, vinyl compounds, styrenic compounds, urethanes, imides, carbonates, epoxides, esters, amides, celluloses, carbohydrates, nucleotides and combinations thereof.

In a preferred embodiment, the liquid crystal dispersion is prepared according to a polymerization-induced phase separation method comprising the following steps:

preparing a homogeneous mixture containing a nematic liquid crystal compound (E7 eutectic mixture) and a UV curable prepolymer (Norland UV UV curable resin);

- Capillary filling said interelectrode space with said mixture; polymerizing said mixture under UV, to form a liquid crystal film dispersed in the polymer.

The electro-optical performances (transmission properties, switching voltage, switching time) of the display devices thus prepared have been studied by means of conventional methods. The intensity of the transmitted light was recorded as a function of the applied sinusoidal electric field. The appended FIG. 3 illustrates an electro-optical response of a liquid crystal screen according to the invention, comprising electrodes produced by coating the suspension based on single-walled carbon nanotubes according to the invention on a glass support, compared with a screen. comprising ITO electrodes. The representation of the relative transmittance as a function of the electric field applied at 50 Hz has a sigmoidal curve shape. ElO and E90 respectively represent the values of the electric field required for the film to change to 10% or 90% of the change in transmittance between the zero state ("off") and the maximum transmittance state ("on") . The results show that the performances of the liquid crystal screen according to the invention are at least equivalent to those of an ITO-based screen, manufactured to serve for purposes of comparison.

The switching times of the liquid crystal displays according to the invention were measured by means of sinusoidal voltage pulses applied at a given frequency. The rise time is defined as the time interval required for the device to achieve 90% transmittance from 10% transmittance. The descent time is the time required for _ _No _

device to achieve 10% transmittance from 90% transmittance. The appended FIG. 4 illustrates the measurement of the response time of the liquid crystal display according to the invention, comprising electrodes obtained by coating a suspension based on multiwall carbon nanotubes according to the invention on a polymeric support (polyethylene terephthalate).

Liquid crystal display devices addressed by electrodes based on carbon nanotubes according to the invention have remarkable flexibility and pliability properties. The attached FIG. 5 illustrates the operation of a liquid crystal-based display addressed by electrodes based on single-walled carbon nanotubes. The sequence of operations in chronological order is as follows:

- the display is placed on two solid 5 mm thick supports at a distance of 13 mm; the device changes from an opaque state ("off" position, Fig. 5a) to a transparent state ("on" position, Fig. 5b - the "copyright" symbol below the screen becomes visible);

the screen is folded vertically by means of a pointed tool (three-point folding) so that it adopts a curved geometry and forms a teta angle (θ) with the horizontal; following the application of an electric field, the folded screen changes from the opaque state (Figure 5c) to the transparent state (Figure 5d); - The screen returns to the initial unfolded position and passes, when an electric field is applied, a transparent state (Fig 5e) in opaque state

(Fig. 5f).

Advantageously, the tetra flexion angle varies from 0 ° to approximately 40 °. Liquid crystal display devices addressed by electrodes based on carbon nanotubes according to the invention are flat, flexible and can be manufactured in any size.

The description of the invention will be completed by the following nonlimiting exemplary embodiments.

Example 1: Preparation of a stable aqueous suspension containing purified single-walled carbon nanotubes.

Single-wall carbon nanotubes (purity 50%, average diameter of tubes 1.2-1.5 nm, length 2-5 μm) were provided by Aldrich. The Purification procedure conventionally consists in the acid oxidation of carbon nanotubes [W. Zhao et al., J. Am. Chem. Soc., 124, p. 12418 (2002)]. Firstly, 53 ml of concentrated nitric acid (65%) are placed in a one-liter flask containing a magnetic bar, the whole being immersed in a cooling bath composed of a mixture of water and ice. 158 ml of concentrated sulfuric acid (98%) are then added in successive portions to the flask. After complete dissipation of the release of heat resulting from the mixing of the two acids, 409 mg of impure single-walled carbon nanotubes are added. The mixture obtained is then placed in an ultrasonic bath for 2.5 hours and then slowly poured into successive portions in 500 ml of deionized water. The whole is then filtered under vacuum on a Millipore membrane (lμm). The carbon nanotubes collected on the membrane are transferred to a beaker containing 140 ml of concentrated sulfuric acid. To this mixture, placed in a cooling bath, 26 ml of a solution of 35% hydrogen peroxide are added slowly in successive fractions. The whole is subjected to mechanical stirring for 20 minutes under cold conditions before the sequential addition of 83 ml of concentrated sulfuric acid and 26 ml of a 35% hydrogen peroxide solution. The whole is stirred mechanically for 25 minutes and then subjected to an ultrasonic bath for 5 minutes before dilution into several small fractions in 700 ml of cooled deionized water. After filtration under vacuum on a Millipore membrane (lμm), the collected carbon nanotubes are washed firstly with a 10mM solution of NaOH and then 150ml of deionized water. The purified carbon nanotubes are finally dried under vacuum in a desiccator containing calcium chloride first at 60 degrees C for 3.5 hours and then at room temperature overnight.

A vial containing a mixture of 28.9mg of Triton X-100, 6ml of deionized water, and 10.8mg of purified carbon nanotubes is placed in the ultrasonic bath (100W, 35kHz) for 30 minutes (this mixture is therefore consisting of a mass fraction of 0.18% carbon nanotubes and 0.48% Triton X-100). The mixture obtained is then mechanically stirred at 7000 rpm with a Polytron homogenizer (Kinematica AG, Switzerland) and then subjected again to the ultrasonic bath for 4 hours before, or Acrodisc membrane filtration. - Lo ~

(lμm), or centrifugation at 2000 rpm for 30 seconds. To 2.815 g of the above filtered mixture, 137 mg of ethylene glycol are added (4.6% by weight). This mixture is finally subjected to mechanical stirring (1000 revolutions / minute, mixer IKA Vibramax VXR) before its use for the production of thin films on inert substrates. It is important to note that these suspensions of carbon nanotubes are stable until more than 18 months.

Similarly, stable suspensions of multi-walled carbon nanotubes (IManostructured and Amorphous Materials, Inc. (USA); characteristics: outer diameter: 8-15nm, internal diameter: 3-5nm, length: 0.5-200μm) were prepared.

EXAMPLE 2 Physical Properties of the Conductive Films Produced from the Suspensions of Carbon Nanotubes

The suspensions of carbon nanotubes produced according to the protocol described above were spread on microscope glass slides (thickness: 1 mm, transmittance at 632.8 nm: 96%) or PET polyethylene terephthalate films (thickness: 100 μm, transmittance at 632.8 nm: 95%). The coating method used implements a slit micrometric film applicator (Elcometer 3570) allowing a uniform and reproducible controlled thickness deposition of suspensions of carbon nanotubes on substrates of different nature. After coating, the films are dried under air (fume hood type hood) and then briefly washed by immersing in a toluene bath (10 seconds) before being dried again in air. Figures 6, 7 and 8 respectively show scanning electron microscopy images of a film of single-walled carbon nanotubes on one. PET substrate (Fig. 6) ,. a film of multi-walled carbon nanotubes on a glass substrate (FIG 7) and a film of multi-walled carbon nanotubes on a PET substrate (FIG 8).

Table 1 summarizes the surface resistivity (Rs) and transmittance (T) values measured at 632.8 nm for the different carbon nanotube electrodes produced.

Table 1

EXAMPLE 3 Electro-Optical Properties of Displays of the Liquid Crystal Dispersion Type Addressed by Electrodes Based on Carbon Nanotubes

Table 2 shows the electro-optical characteristics of light-cured dispersions based on Norland 65 and E7 in the ratio (35:65) (thickness 22 μm) addressed by electrodes based on carbon nanotubes (electric field applied at 50 Hz). ElO and E90 are respectively the threshold and saturation fields (uncertainty 5%). The response times of the dispersions during the application and the cutting of the field are also given. For comparison, the values obtained with conventional ITO-type electrodes have been added.

Table 2

Table 3 shows the electro-optical characteristics of Norland 65 and E7 light-cured dispersions in the ratio (35: 65)

(thickness 22μm) addressed by electrodes based on carbon nanotubes

(electric field applied at 100Hz). ElO and E90 are respectively the threshold and saturation fields (uncertainty 5%). The response times of the dispersions during the application and the cutting of the field are also given. By way of comparison, the values obtained with conventional electrodes of the type

ITO have been added.

Table 3

The present invention can also find other fields of application, namely for systems using conductive films. It is possible to distinguish two broad categories of applications.

The first concerns systems requiring transparent electrodes for optical technologies (diffraction gratings, phase shifters, Pockels cells, etc.) and visualization such as conventional liquid crystal displays (twisted or super twisted nematic, _

phase shifters, Pockels cells, etc.) and visualization such as conventional liquid crystal displays (twisted or super twisted, cholesteric, ferroelectric, etc.) or liquid crystal gels, light-emitting diodes, or screens cathodic type or plasmas. The second application relates to systems requiring electrodes for the application of a voltage but not necessarily transparent. These are, for example, components for "all plastic" electronics such as capacitors, field effect transistors, Schottky diodes, etc. or Leclanche batteries, rechargeable, or electrolysis cells.

Claims

1. A stable aqueous suspension of carbon nanotubes characterized in that it also comprises at least one nonionic detergent of alkylphenol alkoxylate type and an alcohol, a polyol or a mixture thereof.

2. Suspension according to claim 1 having, by weight, the following composition:

0.01 to 1% by weight of carbon nanotubes, preferably 0.2 to 0.5%;

- 3% or less, preferably from 0.5 to 2.4%, of a nonionic detergent of alkylphenol alkoxylate type;

from 3 to 5% of an alcohol, a polyol or their mixture, preferably about 4.5%.

3. Process for the preparation of a stable aqueous suspension of carbon nanotubes according to claim 1, comprising the steps of: a) adding carbon nanotubes, purified beforehand or in the raw state, to a liquid medium comprising water and at least one non-ionic detergent of the alkylphenol alkoxylate type, to obtain a first mixture, b) applying to said first mixture ultrasound for a determined period of time, to obtain a second mixture, c) incorporating in said second mixing an alcohol, a polyhydric alcohol or their combination, to obtain a third mixture, d) homogenizing said third mixture by stirring for a predetermined period, to obtain an aqueous suspension of carbon nanotubes.

4. The method of claim 3, wherein said liquid medium of step a is subjected to ultrasound for a predetermined period, prior to the addition of carbon nanotubes.

5. Process according to any one of claims 3 and 4 further comprising, after step b, a step of filtration or centrifugation of said second mixture.

6. Method according to any one of claims 3 to 5 wherein the step b of applying ultrasound is interrupted for a period of time determined for - Iy -

homogenize by stirring said first mixture, before resuming the application of ultrasound.

7. Conductive device based on carbon nanotubes characterized in that it comprises a thin layer of the stable aqueous suspension of carbon nanotubes according to any one of claims 1 and 2, said layer forming a transparent conductive thin film arranged on a support.

8. Device according to claim 7 wherein the support is transparent and inert, said device being intended in particular to constitute an electrode in a display device based on a dispersion of liquid crystals in a polymer matrix.

The device of claim 8 wherein said inert transparent support is a transparent inorganic material or a flexible transparent polymeric material.

10. Device according to claim 9 wherein the inorganic material is selected from the group: glass, metal, ceramic, glass having a metal coating.

11. Device according to claim 9 wherein the polymeric material is selected from the group: polyethylene terephthalate, poly methyl methacrylate, polyvinyl chloride, polyethylene, cellulose acetate derivatives, polyvinyl alcohol, polyvinyl acetate, polyester Mylar type .

12. A method of manufacturing the conductive device according to any one of claims 7 to 11 comprising a step of coating said support with a thin layer of the stable aqueous suspension of carbon nanotubes according to any one of claims 1 and 2, followed by drying.

13. The method of claim 12 characterized in that the coating is performed according to a technique chosen from: film applicators (slit, bearing, spiral), centrifugal applicators, dipping methods, flow, spray, brushing.

14. Method according to any one of claims 12 or 13 characterized in that it further comprises, after the coating step:

A first step of drying in air the stable aqueous suspension of carbon nanotubes coated on said support, A step of rapid washing with an apolar organic solvent,

• a second step of air drying.

A display device based on a liquid crystal dispersion in a polymer matrix comprising: two substrates each having a conductive device according to claim 8; the two substrates being separated by an interelectrode space in which the faces coated by said film are opposite; a dispersion of liquid crystals in a polymer matrix filling this interelectrode space; conductors son provided at one end of each substrate to allow application of a voltage to said films.

16. Optical component equipped with a conductive device according to one of claims 7 to 11.

17. Electronic component equipped with a conductive device according to one of claims 7 to 11.