WO2019073012A1 - Composition comprising silver nanowires and at least one fluorinated polymer - Google Patents

Abstract

The present invention relates to a composition comprising at least one fluorinated polymer and silver nanowires coated with at least one metal oxide and a process for preparing said composition. It also relates to films comprising said composition and processes for preparing these films.

Description

Composition comprising silver nanowires and at least one fluorinated polymer

This application claims priority to European application N°. 17306383.5 filed on October 12, 2017, the whole content of this application being incorporated herein by reference for all purposes.

The present invention concerns a composition comprising at least one fluorinated polymer and silver nanowires coated with at least one metal oxide and a process for preparing such composition. It also pertains to films comprising said composition and to processes for preparing these films.

Materials having high dielectric permittivity and low dielectric loss are highly desirable for the manufacture of devices having low electrical

consumption and/or having high electrical response to mechanical stimuli and/or having high mechanical response to electrical stimuli which are properties useful for electromechanical applications (e.g. sensors (in particular haptic sensors), actuators (in particular haptic actuators), energy harvesting devices...). On one hand, low electrical consumption is economically valuable because it spares resources and also because it increases the shelf life of the device by avoiding over-heating during operating. On the other hand, enhanced response to stimuli provides better sensitivity of the device.

Polymer composites having high dielectric permittivity can be useful in many applications such as capacitors, actuators, sensors or energy harvesting devices. Generally in composites, polymers are used as matrix where they bring excellent thermal and mechanical properties while fillers, which are dispersed in the polymer matrix, bring functionalities. Polymer matrix in composite is also responsible for high flexibility and high processability.

Thus, dispersing in a polymer matrix conductive nano-objects having low percolation threshold because of their high aspect ratio, is a strategy to achieve high dielectric permittivity materials. However the addition of conductive fillers such as metal nanowires can also increase dielectric loss and leakage current because of forming a conduction network.

The dielectric permittivity and dielectric loss of a material are related to each other by the dissipation factor tan δ also named dielectric loss tangent:

tan δ = ε"/ε' wherein ε" is the dielectric loss and ε' the dielectric permittivity. The lower the dielectric loss tangent the better is the performance of a dielectric material for example for charge storage application because it represents a good balance between low dielectric loss ε" and high dielectric permittivity ε'.

L.Wang et al. in Applied Physics A, 2015, vol. 118, n°. l, p. 243-248 propose high dielectric polyimide composite film filled with carbon-coated silver nanowires. The coating with carbon of silver nanowires avoids a detrimental increase of dielectric loss because the insulating shells of the core-shell structure protect the silver cores from connecting with each other. The preparation of the film is made under harsh conditions; for example curing at 250 °C is required. The glass transition of the film is over 260 °C which precludes good

electromechanical properties at room temperature. Moreover coating by carbon may be detrimental to breakdown voltage of the film.

A.Bruna da Silva et al. in Polymer, 2014, vol. 55, p. 226-234 describe composites of copper nanowires and polyvinylidene fluoride (PVDF) with high dielectric permittivity and low dielectric loss. The composite is prepared by mixing at room temperature a solution of PVDF in DMF with a dispersion of Cu nanowires in DMF. The dielectric loss of the composite significantly increases with the copper nanowires content and the dissipation factor tan δ is rather high. Moreover, dielectric permittivity values are very limited in some domains of frequency sweep.

C.Chen et al. in Composite Science and Technology, 2014, vol. 105, p. 80- 85 describe epoxy/silica coated silver nanowires composites and compare their dielectric properties with those of epoxy/ silver nanowires composites. They notice a slight decrease of dielectric constant value when comparing properties of composites comprising uncoated silver nanowires with those of composites comprising silica coated silver nanowires. No significant difference between properties of composites comprising silica coated or uncoated silver nanowires in term of dielectric loss tangent is observed. The resulting film is thermoset, which requires a long curing time (8h at 150°C) and prevents the film from being recycled. The glass transition of the film is over 135 °C which may be detrimental to electromechanical properties at room temperature.

X.Huang et al. describes in Polymer International, 2014, vol.63, p. 1324- 1331 titania coated silver micro-/nanowires composites with poly(arylene ether nitrile). The manufacturing of the composites is made by dispersing Ti0₂ coated silver micro-/nanowires in NMP and addition of the dispersion to a solution of poly(arylene ether nitrile) in NMP. Finally, composites are obtained after evaporation of the solvent at temperature up to 200°C. Increasing the content of titania coated silver micro-/nanowires in the composite induces only moderate increase of dielectric constant and an increase of the dielectric loss. Despite the increase of titania coated silver micro-/nanowires content in the composite, the dielectric constant is kept very low. The glass transition of the film is close to 220 °C which precludes good electromechanical properties at room temperature.

WO2014/028027 Al discloses the injection molding of polyphenylene sulfide with silica coated silver nanowires. Resulting composites have high thermal conductivity. Nothing is said about dielectric properties of the material.

According to all the above, the applicant has found some needs in the domain of high dielectric permittivity composites.

Materials having high dielectric permittivity and low dielectric loss are highly desirable for manufacturing devices having low electrical consumption and/or having high electrical response to mechanical stimuli and/or having high mechanical response to electrical stimuli e.g. for electromechanical applications. Among those devices one can cite for example sensors (in particular haptic sensors), actuators (in particular haptic actuators) and energy harvesting devices. Low electrical consumption is economically valuable because it spares resources and also because it increases the shelf life of the device by avoiding over-heating during operating.

Materials having high dielectric permittivity and low dielectric loss are also highly desirable for manufacturing energy storage devices such as capacitors.

There is a need for new compositions combining high dielectric permittivity and low dielectric loss, in other terms having simultaneously high dielectric permittivity ε' and a low dissipation factor or dielectric loss tangent: tan δ.

There is a need for such compositions showing also high breakdown voltage.

In addition, there is a need for compositions combining the properties above described having high thermal and chemical stability. There is also a need for high processability of such compositions.

Finally, there is a need for films combining high dielectric permittivity, low dielectric loss and high breakdown voltage with high mechanical properties such as flexibility and for processes for preparing and recycling such films. All these needs and others are fulfilled by a composition comprising at least one fluorinated polymer and silver nanowires coated with at least one metal oxide.

In the present invention, by the term fluorinated polymer is meant polymer comprising repeat units derived from at least one fluorinated monomer. By the term fluorinated monomer is meant ethylenically unsaturated monomer comprising at least one fluorine atom.

In certain embodiments, the fluorinated polymers suitable are chosen among vinylidene fluoride homopolymers or copolymers which provide advantageously high chemical resistance.

Vinylidene fluoride copolymers comprise generally at least 50 % by moles, very often at least 60 % by moles, preferably at least 75 % by moles, more preferably at least 85 % by moles and possibly at least 95 % by moles of repeat units derived from vinylidene fluoride.

Vinylidene fluoride copolymers comprise generally from 0 to 15 % by moles of repeat units derived from monomers selected from the list consisting of vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, hexafluoroisobutylene, pentafluoropropene, 3,3,3- trifluoropropene, perfluoromethylvinylether and mixtures thereof.

Vinylidene fluoride copolymers may also comprise repeat units derived from at least one (meth)acrylic monomer. (Meth)acrylic monomers include monomers having the formula (I) thereafter :

wherein:

Ri, R₂ and R₃ are equal to or different from each other, are independently selected from hydrogen atom and a C₁-C4 group, and

R4 is selected from hydrogen atom and Ci-Ci₂ group optionally comprising at least one heteroatom.

Non limitative examples of (meth)acrylic monomers are notably acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate,

hydroxypropyl(meth)acrylate; hydroxyethylhexyl(meth)acrylates.

The (meth)acrylic monomer is preferably selected among:

- hydroxyethylacrylate (HEA) of formula:

- 2-hydroxy propyl acrylate (HP A) of either of formulae:

- acrylic acid (AA) of formula:

- and mixtures thereof.

The repeat units derived from the (meth)acrylic monomer are comprised in the copolymer in an amount of preferably from 0% to 15 % by moles and more preferably from 0% to 10 % by moles.

Good results can be obtained with terpolymers VF₂-TrFE-CTFE, copolymers VF₂-HFP and copolymers VF₂-CTFE, wherein VF₂ is

vinylidenfluoride, TrFE is trifluoroethylene, CTFE is chlorotrifluoroethylene and HFP is hexafluoropropylene.

In some other embodiments, the suitable fluorinated polymer is a fluoropolymer [polymer (F)] comprising:

- recurring units derived from vinylidene fluoride (VDF);

- from 10% to 50% by moles of recurring units derived from

trifluoroethylene (TrFE); and

- from 0.01 % to 10% by moles of recurring units derived from at least one (meth)acrylic monomer [monomer (MA)] having formula (II) here below:

wherein:

- R'i, R'₂ and R'₃, equal to or different from each other, are independently selected from a hydrogen atom and a Ci-C₃ hydrocarbon group, and - R'OH represents a hydrogen atom or a Ci -C₅ hydrocarbon moiety comprising at least one hydroxy 1 group.

The polymer (F) of the invention comprises preferably from 15% to 48% by moles, more preferably from 16% to 45% by moles, even more preferably from 17% to 40% by moles of recurring units derived from trifluoroethylene (TrFE).

The (meth)acrylic monomer [monomer (MA)] preferably complies with formula (III) here below:

wherein:

- R"i and R"₂, equal to or different from each other, are independently selected from a hydrogen atom and a C1-C3 hydrocarbon group, preferably R"i and R"₂ being hydrogen atoms,

- R"₃ is a hydrogen atom, and

- R"OH represents a hydrogen atom or a C1-C5 hydrocarbon moiety comprising at least one hydroxy 1 group.

Non- limitative examples of (meth)acrylic monomers (MA) notably include acrylic acid, methacrylic acid, hydroxyethyl(meth)acrylate,

hydroxypropyl(meth)acrylate, hydroxyethylhexyl(meth)acrylate.

The monomer (MA) is more preferably selected from the folio wings:

- hydroxyethylacrylate (HEA) of formula:

- 2-hydroxypropyl acrylate (HP A) of either of formulae:

- acrylic acid (AA) of formula:

- and mixtures thereof.

The monomer (MA) is even more preferably acrylic acid (AA) or fry droxyethylacry late (HE A).

The polymer (F) of the invention may further comprise recurring units derived from one or more other fluorinated comonomers [comonomer (F)].

The term "fluorinated comonomer [comonomer (F)]" is hereby intended to denote an ethylenically unsaturated comonomer comprising at least one fluorine atom.

The comonomer (F) may further comprise one or more other halogen atoms such as chlorine, bromine and iodine atoms.

Non- limitative examples of suitable comonomers (F) notably include the folio wings:

(i) C₂-Cs perfluoroolefins such as tetrafluoroethylene (TFE) and hexafluoropropylene (HFP);

(ii) perfluoroalkylethylenes of formula CH₂=CH-R_fo, wherein Ra is a C₂- C₆ perfluoroalkyl group;

(iii) chloro- and/or bromo- and/or iodo-C₂-C₆ fluoroolefins such as chlorotrifluoroethylene (CTFE);

(iv) perfluoroalkylvinylethers of formula CF₂=CFOR_fi, wherein RA is a Ci-C₆ perfluoroalkyl group, such as perfluoromethylvinylether (PMVE) and perfluoropropylvinylether (PPVE);

(v) (per)fluorooxyalkylvinylethers of formula CF₂=CFOXo, wherein X₀ is a Ci-Ci₂ oxyalkyl group or a Ci-Ci₂ (per)f uorooxyalkyl group having one or more ether groups, e.g. perfluoro-2-propoxy-propyl group; (vi) (per)fluoroalkylvinylethers of formula CF₂=CFOCF₂ORc, wherein I½ is a Ci-C₆ (per)fluoroalkyl group, e.g. -CF₃, -C₂F₅, -C₃F₇, or a Ci-C₆

(per)fluorooxyalkyl group having one or more ether groups, e.g. -C₂F₅-0-CF₃;

(vii) functional (per)fluorooxyalkylvinylethers of formula CF₂=CFOYo, wherein Y₀ is selected from a Ci-Ci₂ alkyl group or (per)fluoroalkyl group, a Ci- C₁₂ oxyalkyl group and a Ci-Ci₂ (per)fluorooxyalkyl group having one or more ether groups, Yo comprising a carboxylic or sulfonic acid group, in its acid, acid halide or salt form;

(viii) fluorodioxoles, especially perfluorodioxoles.

The comonomer (F) is preferably free of hydrogen atoms.

Most preferred fluorinated comonomers (F) are chlorotrifluoroethylene (CTFE), perfluoromethylvinylether (PMVE), tetrafluoroethylene (TFE), hexafluoropropylene (H FP).

Should the fluorinated comonomer (F) be present, the polymer (F) of the invention comprises typically from 2% to 20% by moles, preferably from 3% to 18% by moles, more preferably from 4% to 15% by moles of recurring units derived from said fluorinated comonomer (F).

Good results were obtained using P(VDF-TrFE-CTFE) terpolymer Solvene® T provided by Solvay Specialty Polymers as the fluorinated polymer [polymer (F)].

The glass transition temperature of the fluorinated polymer is generally of at most 50 °C, preferably of at most 20 °C, more preferably of at most 0 °C and even preferably of at most -5 °C. Besides, the glass transition temperature of the fluorinated polymer is generally of at least -60 °C, preferably of at least -50 °C and more preferably of at least -40 °C.

Glass transition can be measured by differential scanning calorimetry (DSC) well known by the skilled person.

The silver nanowires comprised in the composition according to the invention are coated with at least one metal oxide.

Generally, the oxide is selected from the list consisting of titanium, zirconium, hafnium, vanadium, aluminum, gallium, indium, silicon, germanium and tin oxides and mixtures thereof.

The metal oxide is often selected from the list consisting of titanium, zirconium, aluminum and silicon oxides and mixtures thereof. It is preferably selected from the list consisting of silicon oxides and titanium oxides. It is more preferably silicon dioxide. In some embodiments, the metal oxide is selected from the list consisting of hafnium, vanadium, gallium, indium, germanium and tin oxides and mixtures thereof.

Generally, the metal oxide coating is obtained by a sol-gel process conducted in the presence of silver nanowires. However, any commercially available silver nanowires coated with at least one metal oxide can be used in the process.

The sol-gel process can be seen as the hydrolysis and the condensation of metal alkoxides giving a three dimensional network of metal oxides. Just for sake of example, sol-gel process steps are described by L.Hench et al. in

Chemical Review, 1990, vol.90, n°. l, 33-70.

The sol-gel process is generally conducted in a reaction medium

comprising at least one alcohol and water. It is conducted in a reaction medium comprising a volume ratio of alcohol and water generally of at most 10/1, preferably of at most 8/1, more preferably of at most 6/1 and even more preferably at most 5/1. Besides, the volume ratio of alcohol and water is generally of at least 1/5, preferably of at least 2/5, more preferably of a least 3/5 and even more preferably of at least 4/5.

Precursors for the metal oxides are generally titanium, zirconium, aluminum, or silicon alkoxides.

Precursors of silicon oxide can be but are not limited to

tetramethylorthosilicate (TMOS), Tetraethylorthosilicate (TEOS) or

tetraisopropylorthosilicate (TPOS).

Precursors of aluminum oxide can be but are not limited to aluminum- (isopropoxide) or aluminum-(2-butoxide).

Precursor of zirconium oxide can be but is not limited to zirconium- (isopropoxide) and precursors of titanium oxide can be but are not limited to titanium-(2-ethoxide) or titanium-(isopropoxide).

Some other precursors for the oxides are generally hafnium, vanadium, gallium, indium, germanium or tin alkoxides such as hafnium isopropoxide, vanadium (V) oxytriisopropoxide, tetraethyl orthogermanate, gallium (III) isopropoxide, indium ethoxide or tin tert-butoxide.

The synthesis of the metal oxide via the sol-gel process can be catalyzed by the use of an acid or a basic catalyst. For example, in the former case HC1 may be involved while in the latter case ammonia may be used. In a preferred embodiment, ammonia is used as basic catalyst. The sol-gel process can be performed by adding under stirring to a suspension of silver nanowires in a mixture comprising water and at least one alcohol, metal oxide precursors and catalyst, all these components being as previously described.

The sol-gel process can be conducted at room temperature. It is often conducted at a temperature of at least 40°C, possibly at a temperature of at least 60°C, sometimes at a temperature of at least 80°C and rarely at a temperature of at least 100°C.

In some other embodiments the sol-gel process is performed using inorganic precursors.

Inorganic precursors for the metal oxides are generally titanates, zirconates, aluminates or silicates. Inorganic precursors are generally alkali metal or earth alkaline metal titanates, zirconates, aluminates or silicates. They are preferably alkali metal, more preferably potassium or sodium and even more preferably sodium titanates, zirconates, aluminates or silicates.

Some other inorganic precursors for the metal oxides are generally vanadates, germanates or stannates such as potassium or sodium and preferably sodium vanadates, germanates or stannates.

The synthesis of the metal oxide via the sol-gel process involving inorganic precursors can be catalyzed by the use of an acid catalyst. In a preferred embodiment, HC1 is used as acid catalyst.

The sol-gel process can be performed by adding under stirring to a suspension of silver nanowires in a mixture comprising water and optionally an alcohol, inorganic metal oxide precursors and catalyst, all these components being as previously described.

After the sol-gel process the silver nanowires coated with metal oxide are generally recovered from the reaction mixture. For example, the silver nanowires coated with metal oxide can be recovered by sedimentation resulting from centrifugation. Thus, the alcohol/water supernatant can be removed and the coated nanowires isolated. The coated nanowires can also be isolated by vacuum- filtering the sedimented suspension.

The weight ratio of metal oxide with regard to the total weight of silver nanowires coated with at least one metal oxide is generally of at least 1 wt. %, often of at least 5 wt. % and possibly of at least 10 wt. %. The ratio is generally of at most 25 wt. %, often of at most 20 wt. % and possibly of at most 15 wt. %. The silver nanowires coated with at least one metal oxide suitable for the invention have generally an aspect ratio of at least 10, preferably of at least 15 and even preferably of at least 20. The silver nanowires coated with metal oxide have usually an aspect ratio of at most 5000, preferably of at most 1000, even more preferably of at most 500 and the most preferably at most 200.

The aspect ratio is the ratio of length to width of a particle (ISO, 1999). An average aspect ratio may be determined by image processing of TEM or SEM.

The coated nanowires can be further submitted to several dispersion- centrifugation cycles in a solvent to remove impurities. Among impurities one can consider species involved in the sol-gel process such as alcohol, acid or base catalyst or small metal oxide particles or any chemical which is not coated silver nanowires. Often, the coated silver nanowires are submitted to at least 2 dispersion-centrifugation cycles in the solvent, sometimes to at least 3 dispersion-centrifugation cycles, rarely to at least 4 dispersion-centrifugation cycles. The solvent may be the polar aprotic solvent suitable for the invention as will be described below.

The composition according to the invention comprises generally at least 50 wt. %, often at least 60 wt. %, sometimes at least 70 wt. % and rarely at least 80 wt. % of fluorinated polymer with regard to the total weight of the composition. Besides, the composition comprises generally at most 99.5 wt. %, often at most 99.0 wt. % and sometimes at most 98 wt. % of polymer.

The composition according to the invention comprises generally at least 0.5 wt. %, often at least 1 wt. % and sometimes at least 2 wt. % of silver nanowires coated by metal oxide with regard to the total weight of the composition. Besides, the composition comprises generally at most 50 wt. %, often at most 40 wt. %, sometimes at most 30 wt. % and rarely at most 20 wt. % of silver nanowires.

The composition according to the invention is generally free of any surfactant. This is a desirable situation when the composition is aimed to be used in very demanding applications. For example, it may be the case when the composition is intended to be used for preparing materials comprising silver nanowires coated with at least one metal oxide and fluorinated polymers for some electronic applications.

In certain embodiments, it is substantially free of any surfactant. In this case the weight ratio of surfactant with regard to Ag metal is generally of at most 0.01 wt. %, often of at most 0.005 wt. %. In other embodiments the composition comprises at least one surfactant. When the surfactant is present, the weight ratio of surfactant with regard to Ag metal is generally of at least 0.1 wt. %. It is preferably of at least 0.5 wt.% and more preferably of at least 1 wt.%.

Besides, the weight ratio of surfactant with regard to Ag metal is generally of at most 250 wt.%. It is often of at most 200 wt.% and more possibly of at most 150 wt.%.

According to IUPAC a surfactant is a substance which lowers the surface tension of the medium in which it is dissolved, and/or the interfacial tension with other phases, and, accordingly, is positively adsorbed at the liquid/ vapor and/or at other interfaces.

The surfactant that may be present in the composition according to the invention can be selected from the list consisting of anionic, cationic,

amphoteric, non- ionic surfactants and mixtures thereof.

Anionic surfactants suitable for the invention are generally chosen from the list consisting of phosphates, sulfonates, sulfates, carboxylates and mixtures thereof.

Cationic surfactants suitable for the invention are generally chosen from the list consisting of phosphonium, ammonium and pyridinium salts. Ammonium salts corresponding to the formula (1) are preferred : !-N- ₄ X

I

^R3 Formula (1)

wherein R_{l s} R₂, R₃ and R4, which may be the same or different represent H or a Ci-C₃o hydrocarbyl or heterohydrocarbyl group and,

wherein X is an halogen atom or an alkyl sulfate group.

The term "hydrocarbyl" as used herein refers to a group only containing carbon and hydrogen atoms. The hydrocarbyl group may be saturated or unsaturated, linear, branched or cyclic. If the hydrocarbyl is cyclic, the cyclic group may be an aromatic or non-aromatic group.

The term "heterohydrocarbyl" as used herein refers to a hydrocarbyl group wherein one or more of the carbon atom(s) is/are replaced by a heteroatom, such as Si, S, N or O. Included within this definition are heteroaromatic rings, i.e. wherein one or more carbon atom within the ring structure of an aromatic ring is replaced by a heteroatom. Distearyl dimethyl ammonium chloride, distearyl dimethyl ammonium bromide, lauryl trimethyl ammonium chloride, lauryl trimethyl ammonium bromide, cetyl trimethyl ammonium chloride, cetyl trimethyl ammonium bromide, alkyl dimethyl benzyl ammonium chloride, alkyl dimethyl benzyl ammonium bromide, cetyl pyridinium chloride, cetyl pyridinium bromide, didecyl dimethyl ammonium chloride and didecyl dimethyl ammonium bromide are examples of adequate quaternary ammonium surfactants.

In a preferred embodiment cetyl trimethyl ammonium bromide is advantageously used.

Amphoteric surfactants suitable for the invention are generally chosen from the list consisting of betaines, sulfobetaines and amine oxides.

Cocamidopropyl dimethyl betaine and lauramidopropyl betaine, coco hydroxypropyl sulphobetaine and dodecyl hydroxypropyl sulphobetaine, coco N, N - dimethylamine-N-oxide and N, N - dimethyldodecylamine-N-oxide are examples of respectively adequate betaines, sulfobetaines and amine oxides.

Non- ionic surfactants suitable for the invention are generally chosen from the list consisting of alkoxylates, pyrrolidinones, glycerides, glycosides and amines.

Lauryl alcohol ethoxylate, nonyl phenol ethoxylate, stearyl alcohol ethoxylate and cetostearyl alcohol ethoxylate are examples of appropriate alkoxylates .

Suitable amines correspond to the formula NR₅R₆R₇ wherein R5, and R₇, which may be the same or different represent H or a C1-C30 hydrocarbyl or heterohydrocarbyl group; n-dodecylamine is an example of appropriate amine. The inventors have found advantageous to use n-dodecylamine. Good results were obtained using Fentamine® A12 available from Solvay Novecare.

In some embodiments, suitable non-ionic surfactants are chosen from poly(alkylene oxide)s. Poly(alkylene oxide)s suitable for use in the present invention are polymers essentially all or all the repeating units of which comply with general formula -C_nH2_n-0- wherein -C_nH2_n- represents a divalent alkylene group with n ranging from 2 to 10. Such poly(alkylene oxide)s may be terminated by a hydroxyl group. Particularly suitable poly(alkylene oxide)s are those wherein n ranges from 2 to 4, preferably from 2 to 3, more preferably wherein n = 2. The poly(alkylene oxide)s may be either linear or branched.

Linear poly(alkylene oxides) are generally preferred. Specific examples of suitable poly(alkylene oxide)s include

polyoxyalkylene polyols, such as polyoxy ethylene glycol (also known as poly(ethylene glycol) or poly(ethylene oxide), polyoxyethylene triol, polyoxyethylene tetraol, polyoxypropylene glycol (also commonly referred to as poly(propylene glycol) or poly(propylene oxide), polyoxypropylene triol, polyoxypropylene tetraol, polyoxybutylene glycol, , polyoxypentane glycol, polyoxyhexane glycol, polyoxyheptane glycol, and polyoxyoctane glycol. These polymers may be used either individually or in combinations of two or more; for example, it can be cited random copolymers of ethylene oxide and propylene oxide, and poly(ethylene oxide)-poly(propylene oxide) block copolymers.

The hydroxyl end groups of the poly(alkylene oxide)s may according to a preferred embodiment be partly or fully substituted by alkoxide groups, preferably methoxy or alkoxy. Methods for converting hydroxyl groups of poly(alkylene oxide)s into alkoxy groups are known to the skilled man and described in the literature.

Certain suitable oxyalkylene-containing compounds suitable in the compositions in accordance with the instant invention are amine-terminated poly(alkylene oxide)s, in particular amine-terminated poly(ethylene oxide)s or amine-terminated poly(propylene oxide)s, including copolymers comprising both mentioned types of oxyalkylene units which are commercially available under the tradename Jeffamine® from Huntsman Chemical Corporation.

In certain cases poly(alkylene oxide)s having a number average or weight average molecular weight of at least 20,000, preferably at least 200,000 and even more preferably at least 1,000,000 are advantageous. In other cases average molecular weights of at most 20,000, preferably at most 10,000 and even more preferably at most 1000 are useful. The molecular weight of the poly(alkylene oxides) suitable may also be optimized. For example, a methoxy-terminated poly(ethylene oxide) having a number average or a weight average molecular weight of at most 2,000 may be used.

Copolymers comprising oxy ethylene and oxypropylene units in random or block distribution may also be suitable and respective products are commercially available under the tradename Pluronics® from BASF and Synperonics® from CRODA.

The composition according to the invention is generally free of any solvent. Often it is substantially free of any solvent. In this case a polar aprotic solvent can be present generally in an amount not exceeding 0.5 wt. %, often not exceeding 0.2 wt. % sometimes not exceeding 0.1 wt. % based on the total weight of the composition.

In other embodiments the fluorinated polymer is dissolved in at least one polar aprotic solvent. When the fluorinated polymer is dissolved in polar aprotic solvent, the composition contains generally at least 50 wt. %, preferably at least 60 wt. %, more preferably at least 70 wt. % of the solvent, based on the total weight of the composition. Besides, the composition contains generally at most 95 wt. %, preferably at most 90 wt. % of solvent, based on the total weight of the composition.

When the fluorinated polymer is dissolved in polar aprotic solvent, the composition contains at least 5 wt. % of the fluorinated polymer, often at least 10 wt. %. Besides, the composition contains generally at most 50 wt. % of the fluorinated polymer, often at most 40 wt. %, possibly at most 30 wt. %, based on the total weight of the composition.

Good results can be obtained with composition comprising from 10 to 30 wt. % of the fluorinated polymer and from 90 to 70 wt. % of the solvent, wherein the aforementioned wt. % are based on the total weight of the composition.

The Ag content in such a composition is generally of at least 50 ppm. It is often of at least 100 ppm.

The Ag content in the composition is generally of at most 200000 ppm. It is often of at most 50000 ppm and sometimes of at most 10000 ppm.

When surfactant is used, the molar ratio between Ag and the surfactant is generally of at least 0.05 and often of at least 0.1.

Besides, the molar ratio between Ag and the surfactant is generally of at most 1000. It is often of at most 500 and possibly of at most 250.

The weight ratio of surfactant with regard to Ag metal is generally of at least 0.1 wt. %. It is often of at least 0.5 wt.% and possibly of at least 1 wt.%.

Besides, the weight ratio of surfactant with regard to Ag metal is generally of at most 250 wt.%. It is often of at most 200 wt.% and possibly of at most 150 wt.%.

The solvent suitable for the composition according to the invention is chosen among polar aprotic solvents. According to IUPAC a polar aprotic solvent is a solvent with high dielectric constant and a sizable permanent dipole moment that cannot donate suitably labile hydrogen atoms to form strong hydrogen bonds.

Polar aprotic solvents suitable for the process according to the invention are solvents having a dielectric constant measured at 20 °C generally over 5. The dielectric constant of the polar aprotic solvent is preferably more than 10, more preferably more than 12 and even more preferably more than 15.

The dielectric constant of solvents can be determined using for example BI-870 Dielectric Constant Meter available from Brookhaven Instruments Corporation, following the recommendations of the provider.

Suitable polar aprotic solvents are solvents having a dipole moment generally over 0.5 Debye. The dipole moment of the polar aprotic solvent is preferably more than 1.0 Debye, more preferably more than 1.5 Debye and even more preferably more than 2.0 Debye.

It is advantageous to use a solvent having a relatively low boiling point when the suspension is aimed to be used in an application requiring removal of this solvent. Removal at lower temperature of low boiling point solvent is cost effective and may be useful when conducted in the presence of temperature sensitive compounds or materials.

Suitable polar aprotic solvents are solvents having a normal boiling point generally below 250°C, preferably below 200°C, more preferably below 150°C and even more preferably below 100°C.

Suitable polar aprotic solvents have a boiling point generally above 40 °C and preferably above 50°C.

Normal boiling point is measured at atmospheric pressure by any method well known by the skilled person.

Dielectric constant, dipole moment and boiling point of pure solvents can be found in the "Handbook of Organic Solvent Properties" edited by

I.M.Smallwood and published by Elsevier in 1996 (ISBN : 978-0-340-64578-9).

The solvent suitable for the process according to the invention is generally chosen in the list consisting of ketones, ethers, esters, amides, nitriles, sulfoxides and mixtures thereof.

In some embodiments, the solvent suitable for the process according to the invention is generally chosen in the list consisting of ketones, ethers, esters, amides, nitriles, sulfoxides, carbonates and mixtures thereof.

For sake of example, among amides, dimethylformamide,

dimethylacetamide and mixtures thereof may be used; among esters, ethylacetate, cyclohexyl acetate may be used; among ethers, 2- methyltetrahydrofuran, tetrahydrofuran and mixture thereof may be used; among nitriles, acetonitrile may be used; among sulfoxides, dimethylsulfoxide may be used and among carbonates dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, ethylmethyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate may be used.

Still for sake of example mixture of ethers with amides such as a mixture of 2-methyltetrahydrofurane with dimethylformamide may be used.

In some other embodiments, the solvent suitable for the process according to the invention can be chosen in the list consisting of ketones, ethers, esters, amides, nitriles, sulfoxides carbonates, of solvents which are mixtures consisting essentially of at least 80% by weight of H₃CO(0)C-CH(CH₃)-CH₂-CH₂- C(0)OCH₃ and H₃CO(0)C-CH(C₂H₅)-CH₂-C(0) OCH₃ such as

RHODIASOLV^® IRIS provided by Solvay, of solvents which are mixtures consisting essentially of at least 80% by weight of H₃CO(0)C-CH(CH₃)-CH₂- CH₂-C(0)N(CH₃)₂ and H₃CO(0)C-CH(C₂H₅)-CH₂-C(0) N(CH₃)₂ such as RHODIASOLV^® POLARCLEAN provided by Solvay , of solvents which are mixtures consisting essentially of at least 70%> by weight of H₃CO(0)C-(CH₂)₃- C(0)OCH₃ and H₃CO(0)C-(CH₂)₂-C(0)OCH₃ such as RHODIASOLV^®RPDE provided by Solvay, of solvents consisting essentially of (H₃C)₂HC-H₂C-0(0)C- (CH₂)4-C(0)0-CH₂-CH(CH₃)2, (H₃C)2HC-H₂CO(0)C-(CH₂)₃-C(0)0-CH2- CH(CH₃)₂ and (H₃C)₂HC-H₂C-0(0)C-(CH2)2-C(0)0-CH2-CH(CH2)2 such as RHODIASOLV^®DIB provided by Solvay and mixtures thereof.

In a preferred embodiment, the solvent is selected from ketones and mixtures thereof. Acetone, methylethyl ketone, diethyl ketone, cyclopentanone, cyclohexanone and mixtures thereof are advantageously used and methylethyl ketone may be preferred.

The composition according to the invention may additionally comprise at least one other ingredient; for example, it may comprise a stabilizer, a plasticizer or a processing aid. Good results can be obtained with compositions composed essentially of, or even composed of the silver nanowires coated with at least one metal oxide, optionally the surfactant, the fluorinated polymer and the polar aprotic solvent.

It is another object of the present invention to propose a process for preparing the composition as previously described.

In a first embodiment the process comprises the steps of: - dispersing silver nano wires coated with at least one metal oxide in a polar aprotic solvent optionally in the presence of at least one surfactant so as to obtain a suspension (a),

- preparing a solution (b) comprising at least one fluorinated polymer and at least one polar aprotic solvent,

- mixing the suspension (a) with the solution (b) so as to obtain a composition (c),

- optionally removing the solvent from the composition (c) so as to obtain a composition (d) substantially free of solvent i.e. generally comprising an amount not exceeding 0.5 wt. % of solvent based on the total weight of the composition (d), or even free of any solvent.

In a second embodiment the process comprises the steps of:

- dispersing silver nano wires coated with at least one metal oxide in a polar aprotic solvent optionally in the presence of at least one surfactant so as to obtain a suspension (e),

- solubilizing at least one fluorinated polymer in the suspension (e) so as to obtain a composition (f),

- optionally removing the solvent from the composition (f) so as to obtain a composition (g) substantially free of solvent i.e. generally comprising an amount not exceeding 0.5 wt. % of solvent based on the total weight of the composition (g), or even free of any solvent.

Compositions (f) and (g) have the same features as respectively

compositions (c) and (d).

In a third embodiment, the process comprises the steps of:

- preparing a solution (h) comprising at least one fluorinated polymer and at least one polar aprotic solvent,

- dispersing silver nano wires coated with at least one metal oxide in the solution (h), optionally in the presence of at least one surfactant, so as to obtain a composition (i),

- optionally removing the solvent from the composition (i) so as to obtain a composition (j) substantially free of solvent i.e. generally comprising an amount not exceeding 0.5 wt. % of solvent based on the total weight of the composition (j), or even free of any solvent.

Compositions (i) and (j) have the same features as respectively

compositions (c) and (d). Dispersing the silver nanowires coated with at least one metal oxide in a polar aprotic solvent so as to obtain the suspension (a) or (e) is generally conducted by sonication. However, any other mean of providing energy to the mixture may be used. Dispersing can be conducted, for example and not in a limitative way, by using vessels equipped with agitator and optionally baffles, static mixers or high shear dispersers.

Solutions (b) and (h) may be obtained by dissolving the fluorinated polymer in the polar aprotic solvent under stirring possibly accompanied by heating.

Just for sake of example, mixing the suspension (a) with the solution (b) can be performed by mechanical stirring of the mixture in a vessel. In some embodiment this mechanical stirring is accompanied by further sonication. The sonication may advantageously allow the homogeneous dispersion of the silver nanowires in the composition.

Compositions (c), (f) and (i) have all the features of the composition according to the invention wherein the fluorinated polymer is dissolved in at least one polar aprotic solvent as previously described.

Removal of the solvent can be obtained for example by spray drying of the compositions (c), (f) or (i) or by heating the composition (c), (f) or (i) in an oven under vacuum. However any other process well known by the skilled person can be used. When the solvent is removed by spray drying the composition is recovered as a powder.

All the steps of the process for preparing the composition are generally conducted under inert atmosphere which may be nitrogen or argon atmosphere.

After removal of the solvent, the composition is generally free of any solvent; often it is substantially free of any solvent. Thus, compositions (d), (g) and (j) have all the features of the composition according to the invention which is generally free of any solvent or often is substantially free of any solvent. In this later case composition (d), (g) or (j) comprises a polar aprotic solvent generally in an amount not exceeding 0.5 wt. %, often not exceeding 0.2 wt. % and sometimes not exceeding 0.1 wt. % based on the total weight of the composition.

It is also an object of the present invention to propose the use of the composition substantially free or even free of any solvent as previously described in an extrusion and/or in a molding process. Just for sake of example, the composition obtained as a powder after removal of the solvent by spray drying may be used in compression or injection molding. It may also be used in extrusion to prepare granules.

Still another object of the invention is to disclose a process for preparing a film comprising the steps of:

- casting the composition according to the invention wherein the fluorinated polymer is dissolved in at least one polar aprotic solvent as previously described on a substrate, so as to form a swollen film,

- removing the polar aprotic solvent from the swollen film so as to obtain the film.

Removal of the solvent can be obtained for example by heating the swollen film in an oven but any other process well known by the skilled person can be used.

The substrate can notably be a plate of a chemically inert material and casting can be performed using for example a doctor blade device. In a certain embodiment, the chemically inert material is glass. In some embodiment the film is recovered by dipping the substrate into a water bath.

After removal of the solvent, the film is generally free of any solvent; often it is substantially free of any solvent. In the latter case it comprises a solvent in an amount generally not exceeding 0.5 wt. %, often not exceeding 0.2 wt. % and sometimes not exceeding 0.1 wt. % based on the total weight of the film.

Another object of the invention is to disclose a film obtainable by the process as above described, said film having the same composition as the composition obtained by the process according to the invention after solvent removal as previously described.

As it is the case for the composition according to the invention, the film may additionally comprise at least one other ingredient; for example, it may comprise a stabilizing agent, a plasticizer or a processing aid.

The film obtained by the process according to the invention has generally an average thickness not exceeding 200 μιη, preferably not exceeding 100 μιη, more preferably not exceeding 50 μιη. The average thickness of the film according to the invention is at least 5 μιη, preferably at least 10 μιη, more preferably at least 15 μιη. In a most preferred embodiment, the average thickness of the film ranges froml5 μιη to 50 μιη.

The thickness may be measured using a digital micrometer onto the film recovered from the process described above. The value can be the average value of at least ten different measurements made along the film and distanced of at least 1 cm.

The silver nanowires dispersion in the film can be evaluated by scanning electron microscopy.

The content of silver in the film can be determined by inductively coupled plasma optical emission spectrometry (ICP-OES). For this purpose, the intensity of the emission measured for a sample diluted in nitric acid 5% aqueous solution at the silver specific wavelength (eg. 328.068 and 338.289 nm) is compared to a calibration curve in a similar range of concentration of silver standards obtained in similar analytical conditions.

Dielectric measurements can be performed onto films beforehand metallized using a sputtering coater such as Q150R S available from Quorum Technologies. For example, Modulab XM-MTS equipment from Solartron Analytical may be used following the recommendation of the provider. The dielectric permittivity and dielectric loss are plotted as function of frequency and the dissipation factor tan δ is calculated:

tan δ = ε"/ε'

wherein ε" is the dielectric loss and ε' the dielectric permittivity.

Breakdown voltage is the minimum voltage that causes the film to become electrically conductive. It can be measured onto films beforehand metallized by methods well known to those skilled in the art.

Another object of the invention is a film having the same composition as the composition according to the invention and having all the features of the film obtained by the process according to the invention.

Finally, the present invention relates to a device comprising such a film. For example, said device may be a sensor (in particular a haptic sensor), an actuator (in particular a haptic actuator), an energy harvesting or an energy storage device. The device can be used in haptic applications.

The dielectric properties of the film according to the invention have a direct influence onto the behavior of the device. Thus, an actuator comprising a film having a dielectric permittivity ε' and a low tan δ will give a larger deformation than an actuator having the same ε' but a higher tan δ at a given voltage V. Similarly, a sensor comprising a film having a dielectric permittivity ε' and a low tan δ will give a better electrical response to pressure than a sensor having the same ε' but a higher tan δ. Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

Examples

Preparation of the suspension of non-coated silver nanowires

Silver nanowires were synthesized using the classical polyol route in propylene glycol using PVP as directing agent. At the end of the synthesis the reaction was quenched with cold water. The resulting slurry was composed of silver nanowires and silver nanoparticles in a propylene glycol/water mixture.

To remove potential silver nanoparticles from the nanowiress the slurry obtained (1750g) was filtered using a nylon filter made of 5μιη pores. The resulting cake was then dispersed in 270g of water by sonication in a water bath using a Bransonic® 221 sonifier during 5 min. at 48 kHz and 50W.

The obtained concentrated suspension of silver nanowire was titrated by potentiometry using a solution of potassium iodine at 0.05M. The measurement was carried out after digestion of a sample in nitric acid 5% aqueous solution and further dilution in water. The content of the silver was 7585 ppm.

A volume of the suspension in water corresponding to lg of solid silver nanowires (AgNW) was transferred from water to methylethyl ketone (MEK) by 3 cycles of centrifugation (4500 rpm during 30min) /dispersion with a final dispersion of the AgNW into 12g of MEK.

Preparation of the suspension of silver nanowires coated with silica

lg of silver nanowires obtained by filtration were dispersed under 100 rpm stirring in 731.5 g of an ethanol/water mixture (5 / 1 vol. / vol.) and the suspension was heated at 40°C in an oil bath before 20 ml of a solution of ammonia 28 wt. % in water was added. Then 708 of tetraethylortho silicate (TEOS) was added dropwise to the solution under stirring and the reaction conducted during 90 min. The suspension was centrifugated at 4500 rpm during 30 min to remove the solvent, ammonia and unreacted TEOS and redispersed in ethanol before being centrifugated again for washing ammonia and unreacted TEOS. Silver nanowires coated with silica (AgNW@Si02) were then transferred in methylethyl ketone (MEK) by 2 cycles of centrifugation/dispersion with a final dispersion of the AgNW@Si0₂ into 12g of MEK. Films preparation by solvent casting

Flurinated polymer used to prepare the films was P(VDF-TrFE-CTFE) terpolymer Solvene^® T provided by Solvay Specialty Polymers.

Preparation of film 1 comprising AgNW@Si0₂

The dispersion comprising lg of AgNW@Si0₂ and 12 g of MEK was introduced in a polypropylene centrifugating tube. A vortex stirring was applied to the tube using Vortex 4 basic equipment provided by Ika to ensure dispersion of AgNW@Si0₂ and the obtained dispersion was poured in a Schott duran bottle. The centrifuging tube was rinsed with a little MEK to recover the totality of AgNW@Si0₂.

Ultrasonication was then performed using UP200ST ultrasonication system provided by Hieschler equipped with Sonotrode S2d7 operating at 40 watt for 15 min. under nitrogen without exceeding -4°C.

When temperature went upper -4°C, ultrasonication was stopped and revived when the temperature was lower than -15°C until reaching 15 min of effective ultrasonication.

After ultrasonication, the dispersion was stirred with a magnetic bar and 2.07 grams of terpolymer Solvene^® T were added.

The dispersion was then heated under stirring at 75°C in a bath of water so that the polymer dissolved and the MEK evaporated until the solid content reached 24,7 wt. % of MEK.

A glass plate was cleaned with a sponge using tap water and soap, then rinced in ethanol and wiped with a cloth (special white room Essuyeur specW7 provided by VWR).

The glass plate was then positioned on the 4340 automatic table from

Elcometer and cleaned with acetone. The adjustable applicator was also cleaned with acetone, as well as the 700μιη knife setting. The applicator was positioned on the glass plate, against the mobile cart the Elcometer table.

The dispersion to cast was then placed on the plate close to the applicator and the mobile cart of the Elcometer table was put in motion at speed 2 at room temperature.

Finally, the glass plate was put in the oven at 70 °C under vaccum for 3 hours to remove the solvent. Once dry and cooled, the film was removed from the substrate by dipping the glass plate in a tray of demineralized water. Preparation of film 2 comprising AgNW

The same procedure as for film 1 was used to prepare film comprising non- coated silver nanowires.

Preparation of film 3 of neat terpolymer Solvene^® T

The same procedure as for films 1 and 2 was used to prepare film comprising terpolymer only.

Silver content in the films

Content of silver element into the films was determined by ICP-OES performed on Agilent 5100 serie from Agilent Technologies.

0.1 g of the film sample was weighed with a precision of 0.1 mg in the

Platinum capsule. Then 10 ml of H₂SO₄ 96% were added and the capsule put on a heating plate at 300°C. After the sample was digested H₂SO₄ was evaporate until 1ml was left and 1ml of HNO₃ 65% was added. HNO₃ was added until obtaining a transparent solution. When the solution was colorless the capsule was weighted to determined the remaining quantity of H₂SO₄. Then, the content of the capsule was poured in the volumetric f ask of 50 ml, the capsule was rinsed several times and the flask was completed to 50 ml with distilled water and then further diluted x 50 for analysis.

The intensity measured on the Silver specific wavelength (eg. 328.068, 338.289 nm and 241.318nm) was compared to a calibration curve obtained in similar analytical conditions in order to determine the amount in the diluted solution. The amount in the solution was obtained by calculation using the dilution factor. The calibration curve was prepared using silver standards in the range of 0 to 15 mg/L comprising Sc as internal standard and the same amount of H2SO4 as the samples.

ICP-OES measurements carried out onto film 1 comprising AgNW coated with S1O₂ gave an amount of 18.4 wt. % of Ag compared to the total weight of the film while for film 2 comprising non coated AgNW an amount of 25.0 wt. % of Ag was obtained. These amounts were in same order of magnitude as the theoretical amounts which were 33.3 wt. % and revealed a good dispersion of the nanowires into the terpolymer matrix.

Dielectric measurements

The tests were carried out at room temperature onto dried films. One side of the film was metalized with gold using a sputtering coater such as Q150R S available from Quorum Technologies. The other side was partially metalized using the same apparatus on a central disk of 20 mm diameter in order to preserve a non-metalized ring which ensured the insulation between the 2 sides of the sample. The metalization was performed four times on each side, at 30mA for 120 seconds.

The samples were placed between 2 stainless steel electrodes of 20 mm diameter connected to the Modulab XM-MTS equipment from Solartron Analytical. The configuration corresponded to high impedance setup with reference capacitor. The applied voltage was 2.5 volts in amplitudes with an offset to 0 Volt. The frequency sweep was done from 1 MHz to 0.1 Hz through 10 measures by decades. The complex permittivity (ε", ε') was plotted in functions of frequency and the loss factor Tan δ = ε'7 ε' could be calculated The results of dielectric measurements are compiled in table 1.

Table 1 : dielectric properties of films comprising terpolymer

Advantageously, at these two frequencies, the addition of coated silver nano wires in the terpolymer led to an increase of the dielectric constant ε' from 47 to 124 while keeping tan δ at a very low value (see results of film 1 compared to those of film 3).

In the same conditions, the film containing non-coated silver nanowires presented also an increase of the dielectric constant ε' but accompagnied with prohibitive dielectric losses illustrated by a very high value of Tan δ (45.88 vs 0.007 see results of film 2 compared to those of film 3).

Claims

C L A I M S

1. A composition comprising at least one fluorinated polymer and silver nanowires coated with at least one metal oxide.

2. The composition according to claim 1, wherein the fluorinated polymer comprises repeat units derived from vinylidene fluoride, preferably in an amount of at least 50 mol. % of repeat units derived from vinylidene fluoride, more preferably in an amount of at least 60 mol. % of repeat units derived from vinylidene fluoride.

3. The composition according to claim 1 or 2, wherein the fluorinated polymer is a vinylidene fluoride copolymer.

4. The composition according to claim 3, wherein the vinylidene fluoride copolymer comprises repeat units derived from monomers selected from the list consisting of vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexaf uoropropylene, hexafluoroisobutylene,

pentafluoropropene, 3,3,3-trifluoropropene, perfluoromethylvinylether and mixtures thereof.

5. The composition according to claim 3 or 4, wherein the vinylidene fluoride copolymer comprises repeat units derived from at least one

(meth)acrylic monomer.

6. The composition according to any one of claims 1 to 5, wherein the metal oxide is selected from the list consisting of titanium, zirconium, aluminum, silicon oxides and mixtures thereof.

7. The composition according to any one of claims 1 to 6, which is substantially free of solvent or is even free of any solvent.

8. The composition according to any one of claims 1 to 7, wherein the fluorinated polymer is dissolved in at least one polar aprotic solvent.

9. A process for preparing the composition according to any one of the claims 1 to 8 comprising the steps of: - dispersing silver nano wires coated with at least one metal oxide in a polar aprotic solvent optionally in the presence of at least one surfactant so as to obtain a suspension (a),

- preparing a solution (b) comprising at least one fluorinated polymer and at least one polar aprotic solvent,

- mixing the suspension (a) with the solution (b) so as to obtain a composition (c),

- optionally removing the solvent from the composition (c) so as to obtain a composition (d) substantially free of solvent or even free of any solvent.

10. A process for preparing the composition according to any one of the claims 1 to 8 comprising the steps of:

- dispersing silver nano wires coated with at least one metal oxide in a polar aprotic solvent optionally in the presence of at least one surfactant so as to obtain a suspension (e), - solubilizing at least one fluorinated polymer in the suspension (e) so as to obtain a composition (f),

- optionally removing the solvent from the composition (f) so as to obtain a composition (g) substantially free of solvent or even free of any solvent.

11. A process for preparing the composition according to any one of the claims 1 to 8 comprising the step of:

- preparing a solution (h) comprising at least one fluorinated polymer and at least one polar aprotic solvent,

- dispersing silver nanowires coated with at least one metal oxide in the solution (h), optionally in the presence of at least one surfactant, so as to obtain a composition (i),

- optionally removing the solvent from the composition (i) so as to obtain a composition (j) substantially free of solvent or even free of any solvent.

12. A process for preparing a film comprising the steps of: - casting the composition according to claim 8 on a substrate, so as to form a swollen film,

- removing the polar aprotic solvent from the swollen film so as to obtain the film.

13. A film comprising the composition according to any one of claims 1 to

8.

14. A device comprising the film of claim 13.

15. The device according to claim 14, which is a sensor, an actuator, an energy harvesting or an energy storage device.

16. Use of the composition according to claim 7 in an extrusion and/or in a molding process.