WO2008055311A1

WO2008055311A1 - Polymeric nanocomposites

Info

Publication number: WO2008055311A1
Application number: PCT/AU2007/001720
Authority: WO
Inventors: Gordon George Wallace; Peter Helena Hubertus In Het Panhuis; Peter Charles Innis
Original assignee: University Of Wollongong
Priority date: 2006-11-10
Filing date: 2007-11-09
Publication date: 2008-05-15

Abstract

The present invention provides an electrically conducting polymeric nanocomposite comprising a first electrically conducting polymer and a second electrically conducting polymer which acts as a dopant of the first electrically conducting polymer. The present invention also provides a method for preparing the polymeric nanocomposite and its use in optical and electrochemical devices including electrochromic devices. For example, the polymeric nanocomposite may be in the form of a nanodispersion which may be printed using an inkjet printer enabling fabrication of electroactive and electrochromic devices using roll-to-roll processing methods.

Description

POLYMERIC NANOCOMPOSITES

FIELD

The invention relates to polymeric nanocomposites that are electrically conducting. The use of such composites in optical and electrochemical devices including electrochemic devices are of particular interest.

PRIORITY DOCUMENTS The present application claims priority from:

Australian Provisional Patent Application No. 2006906284 entitled "Polymeric nanocomposites" and filed on 10 November 2006; and Australian Provisional Patent Application No. 2007904799 entitled "Polymeric nanocomposites" and filed on 4 September 2007. The entire^j content of each of these applications is hereby incorporated by reference .

BACKGROUND One key property distinguishing classical polymers from metals is their low electrical conductivity. Recently, a class of organic polymers capable of conducting electricity has been developed. These polymers become conductive upon partial oxidation or reduction, a process commonly referred to as doping.

The use of conductive polymers in the chemicals and electronics industry is opening up entirely new dimensions for polymeric materials. The major drawback of existing conductive polymers has been their modest environmental stability and/or intractability, which makes it difficult to process them into meaningful end products using conventional processing methods.

SUMMARY

According to a first aspect of the invention, there is provided an electrically conducting polymeric nanocomposite comprising a first electrically conducting polymer and a second electrically conducting polymer which acts as a dopant of the first electrically conducting polymer.

The second electrically conducting polymer may act as stabiliser for the first electrically conducting polymer.

Preferably, one or both polymers in the polymeric nanocomposite are electroactive and/or electrochromic, resulting in a conducting electroactive and/or electrochromic polymeric nanocomposite.

Preferably the electrically conducting polymeric nanocomposite is selected from the group consisting of Polyaniline (PAn) / poly (2-methoxyaniline-5-sulfonic acid) (PMAS), Polypyrrole (PPy)/ PMAS, Polythiophene (PTh) /PMAS, PAn / polypyrrole- sulphonic acid, PPy/ polypyrrole- sulphonic acid, Polythiophene (PTh) / polypyrrole- sulphonic acid, PAn / polythiophene- sulphonic acid, PPy / polythiophene- sulphonic acid, PTh / polythiophene- sulphonic acid, PPy or PAn or PTh/methoxyaniline (POMA) , and PPy or PAn or PTh /alkylcarboxy pyrrole diethoxy.

Preferably the ratio of the first polymer to the second polymer is 1:0.05-20.0, more preferably 1:1.5

The polymeric nanocomposite may further include nanotubes, and the second polymer may also act as a stabliser for the nanotubes. Preferably the nanotubes are multi walled carbon nanotubes (MWNT) . Preferably the amount of nanotubes in the nanocomposite is less than 32%w/v, more preferably in the range of 10%w/v to 32%w/v.

Preferably the nanocomposite is PAn/PMAS/MWNT in a ratio of 1:2.2:1.35. The nanocomposite may include nanofibres with diameters in the range of 30 to 50nm and lengths in the range of 100 to 50,000nm, preferably in the range 100 to 5000nm; and nanoparticles with diameters in the range of 20 to lOOnm.

The polymeric nanocomposite may be in the form of a nanodispersion, wherein the nanocomposite is dispersed in an aqueous solution, preferably in the range of 0.1%w/v to 15%w/v and more preferably in the range of 0.1%w/v to 1.0%w/v.

According to a second aspect of the invention there is provided a method for preparing an electrically conducting polymeric nanocomposite, comprising polymerisation of the constituent monomer (s) of a first electrically conducting polymer in the presence of the second electrically conducting polymer which acts as a dopant of the first electrically conducting polymer.

The method may also include the step of dispersing nanotubes in the second electrically conducting polymer. The second electrically conducting polymer may act as a stabiliser for the nanotubes.

According to a third aspect of the invention there is provided a device which is wholly or partly composed of the nanocomposite defined above.

The device may be an optical or electrochemical device including an electrochromic device .

According to a fourth aspect of the invention there is provided an electrochromic device comprising, (a) a first electrically conducting substrate;

(b) a second electrically conducting substrate spaced apart from said first substrate,- (c) a first electrically conducting electrochromic polymeric nanocoraposite layer deposited on surface of the first substrate layer facing the second substrate layer; (d) a second electrochromic polymer layer deposited onto the surface of said second substrate facing said first substrate; and

(f) an electrical power supply for applying a voltage between said first substrate and said second substrate, wherein the first electrochromic polymeric nanocomposite comprises a first electrically conducting polymer and a second electrically conducting polymer which acts as a dopant of the first electrically conducting polymer.

The first electrochromic polymer nanocomposite may further include nanotubes .

Preferably the polymeric nanocomposite is selected from the group consisting of polyaniline (PAn) / poly (2- methoxyaniline-5-sulfonic acid) (PMAS) , polypyrrole (PPy) / PMAS, polythiophene (PTh) /PMAS, PAn / polypyrrole- sulphonic acid, PPy/ polypyrrole- sulphonic acid, polythiophene (PTh) / polypyrrole- sulphonic acid, PAn / polythiophene- sulphonic acid, PPy / polythiophene- sulphonic acid, PTh / polythiophene- sulphonic acid, PPy or PAn or PTh/methoxyaniline (POMA) , PPy or PAn or PTh /alkylcarboxy pyrrole diethoxy, and PAn/PMAS/multi-walled Carbon nanotubes (MWNT) .

More preferably the nanocomposite is PAn/PMAS/MWNT and the amount of MWNT in the nanocomposite layer is less than 30%w/v, most preferably in the range of 10%w/v to 32%w/v.

Preferably each polymeric nanocomposite layer is deposited using inkjet printing or air brush spraying of a nanodispersion containing the polymeric nanocomposite .

The device may further include an electrolyte located between the first and second electrochromic layers.

One of the substrate layers in the device may also be reflective or include a reflective layer.

Preferably the second electrochromic polymer is a polymeric nanocomposite.

According to a fifth aspect of the invention there is provided a method for constructing an electrochromic device comprising at least one electrochromic nanocomposite layer which comprises the steps of:

(a) applying a first conductive material to a first substrate so as to form a first electrode layer;

(b) applying a nanodispersion containing an electrically conducting electrochromic nanocomposite comprising electrically conducting polymer which acts as a dopant of the first electrically conducting polymer to the first electrode layer so as to form a first electrochromic layer;

(c) applying a second electrochromic polymer to the first electrochromic layer so as to form a second electrochromic layer;

(d) applying a second conductive material to the second electrochromic layer so as to form a counter electrode layer; (e) applying a protective layer to the counter electrode layer, thereby forming a substantially transparent electrochromic device, the device having an optical transparency that varies with voltage applied between the electrodes.

The second electrochromic polymer may be a second polymeric nanocomposite and the layer is formed by applying a nanodispersion containing the second polymeric nanocomposite to the first electrochromic layer.

The method may further include the step of laying a reflective layer between the first substrate and the first electrode. Alternatively the first substrate may have a reflective surface.

Preferably the nanodispersion is applied using an inkjet printer or airbrush sprayer.

Preferably the polymeric nanocomposite is selected from the group consisting of polyaniline (PAn) / poly (2- methoxyaniline-5 -sulfonic acid) (PMAS), polypyrrole (PPy)/ PMAS, polythiophene (PTh) /PMAS, PAn / polypyrrole- sulphonic acid, PPy/ polypyrrole- sulphonic acid, polythiophene (PTh)/ polypyrrole- sulphonic acid, PAn / polythiophene- sulphonic acid, PPy / polythiophene- sulphonic acid, PTh / polythiophene- sulphonic acid, PPy or PAn or PTh/methoxyaniline (POMA) , PPy or PAn or PTh

/alkylcarboxy pyrrole diethoxy, and PAn/PMAS/multi-walled carbon nanotubes (MWNT) .

More preferably the nanocomposite is PAn/PMAS/MWNT.

The first substrate may be stored on a first roll, and the end of the first roll is fed onto a second roll, and an electrochromic device is printed onto the substrate exposed between the first and second rolls.

According to a sixth aspect of the invention, there is provided a method for printing an electrically conducting nanocomposite stratum comprising using an inkjet printer to apply one or more electrically conducting nanocomposite layers onto a substrate layer, wherein the inkjet printer prints a nanodispersion containing an electrically conducting nanocomposite comprising a first electrically conducting polymer and a second electrically conducting polymer which acts as a dopant of the first electrically conducting polymer.

The nanocomposite may be electroactive and/or electrochromic .

DESCRIPTION OF THE FIGURES

Figure 1 shows UV-vis spectra of (a) PAn/HCl, (b) PMAS and (c) PAn/PMAS (an embodiment of the invention) dispersions (0.0025% w/v) in (A) water and (B) 0.1 M NaOH (pH 13). These spectra are discussed below in the Examples section under the heading "Structure" .

Figure 2 depicts the cyclic voltamograms of PAn/HCl and an embodiment of the invention, PAn/PMAS, drop coated onto a glassy carbon electrode (250 μg/cm2) in 0.1 M HCl, scan rate 50 mV/sec. Redox couples labels are discussed in the section "Electroactivity" properties below.

Figure 3A provides transmission electron microscopy (TEM) images of PAn/HCl (scale bar 500 nm) .

Figure 3B provide TEM images of PAn/PMAS (scale bar 2000 nm) .

Figure 4 shows the stability of PAn/HCl and PAn/PMAS aqueous dispersions (0.005 % w/v) after 3 days.

Figure 5 depicts the rheological properties of PAni-PMAS dispersions .

Figure 6 shows the surface tension properties of PAni-PMAS dispersions

Figure 7 depicts the cyclic voltammograms obtained for sprayed ( ) and printed (—) PAn/PMAS dispersion on Shedahl-200 Ω.

Figure 8 provides visible absorption spectra obtained for PAn-PMAS dispersions sprayed on ITO coated plastic. Spectra for oxidized/reduced spectra clearly shows the electrochromic effect .

Figure 9A and Figure 9B provides photographs of ITO electrodes coated with PAn-PMAS dispersion in the oxidized (more opaque; Figure 9A) and reduced (more transparent; Figure 9B) form.

Figure 1OA is a TEM image of MWNTs in the composite of PAn/PMAS/MWNT (1 Pan :2.2 PMAS : 1.7 MWNT).

Figure 1OB is a graph showing the sheet resistance as a function of MWNT loading fraction in free standing composite films. [Insets: photographs of composite dispersions with increasing MWNT loading (top) and a free standing film (bottom)].

Figure 11 shows UV-visible absorption spectra (normalised) of PAn/PMAS/MWNT dispersions. Arrows indicate the effect of increasing MWNT loading, e.g. decrease in 450 nm band, increase in absorbance above 500 nm.

Figure 12 shows a thermogravimetrie analysis spectrum of starting materials (A) and carbon nanotube composite materials (B) . The number in B indicates the MWNT loading fraction.

Figure 13A shows a graph of sheet resistance (squares) and optical transparency (triangles) as a function of printed composite (10 mm x 35 mm, MWNT loading fraction 17.5%) layers on PET substrate at drop spacing 15 μm. Inset: photograph of printed film with T « 50%. - S -

Figure 13B a printed photographic image (15 mm x 15 mm, MWNT loading fraction 32 %) .

Figure 13C is a printed test pattern (25 mm x 45 mm, MWNT loading fraction 32%) .

Figure 14 (A) is a Cyclic voltammogram of a composite film (MWNT loading fraction 17.5 %) prepared by cast onto glassy electrode (0.535 mg/cm2) in 0.1 M HCl, scan rate 50 mV/s. (B) Cyclic voltammogram of a composite film (MWNT loading fraction 3.4%) prepared by printing onto Au-PVDF in 1 M HCl, scan rate 500 mV/s. Numbers indicate redox couples as discussed in the text. Figures 14V show photographs of printed film on Au-PVDF switched to yellow (-0.20 V; (C)) and blue (0.80 V; (D)).

Figure 15 shows cyclic voltammogram of composite film PAn/PMAS/MNTW (loading fraction 3.4%) printed onto Pt- ITO in 1 M HCl, scan rate 500m V/s.

Figure 16 shows transmission spectra of PAn/PMAS/CNT vs ProDOT (A) , PAn/PMAS vs ProDOT (B) , PMAS vs ProDOT (C) and PMAS/Prussian Blue vs ProDOT (D) .

Figure 17 shows various electrochromic devices constructed using one or more electrochromic layers comprised of a electrochromic nanocomposite. Figure 17a shows the layers forming an electrochromic device, Figure 17b illustrates construction using two elements, Figure 17c shows an electrochromic device with a reflective layer and Figure 17d illustrates an electrochromic device in which electrochromic layers also function as electrodes .

Figure 18 shows a digital display element constructed from electrochromic segments.

Figure 19 shows the polymerisation of aniline monomers to polyaniline (PAn) in the presence of poly (2- methoxyaniline-5-sulfonic acid) (PMAS) .

Figure 20 is a flowchart of the method for preparing a nanocomposite of the present invention.

Figure 21 is a flowchart for constructing an electrochromic device using a nanocomposite of the present invention.

DETAILED DESCRIPTION

Nanomaterials and Nanocomposites

Nanomaterials are materials which have structural features of nanometre (nm) scale in at least one dimension. Nanometre scale typically refers to feature sizes of around 1 to several hundred nanometres, but often extends outside of this, including up to micron or more. One dimensional nanomaterials include layers, thin films, surface coatings; two dimensional nanomaterials includes nanowires, nanofibres and nanotubes, and three dimensional nanomaterials include nanoparticles, nanorods, and quantum dots where the diameters or each dimension of the nanoparticle is less than a few hundred nanometres.

Nanoparticles may be substantially spherical, ellipsoidal, rodlike or irregularly shape and be of nanometre scale in two or three dimensions. Nanorods have aspect ratios (length to width) between about 3 and 5. However nanoparticle is sometime used interchangeably with nanomaterials to refer to particles with nanometre scale features or diameter on one, two or three dimensions.

Nanofibres may be coiled, elongated and/or rodlike.

Nanotubes are typically small cylinders made of organic or inorganic materials . Known types of nanotubes include carbon nanotubes (CNTs) , metal oxide nanotubes such as titanium dioxide nanotubes and peptidyl nanotubes .

CNTs are sheets of graphite that have been rolled up into cylindrical tubes. The basic repeating unit of the graphite sheet consists of hexagonal rings of carbon atoms, with a carbon-carbon bond length of about 1.45 A. Depending on how they are made, the nanotubes may be single-walled nanotubes (SWNTs) or multi-walled nanotubes (MWNTs) . A typical SWNT has a diameter of about 1.2 to 1.4nm.

The structural characteristics of nanotubes provide them with unique physical properties. Nanotubes may have up to 100 times the mechanical strength of steel and can be up to 2mm in length. They exhibit the electrical characteristics of either metals or semiconductors, depending on the degree of chirality or twist of the nanotube . Different chiral forms of nanotubes are known as armchair, zigzag and chiral nanotubes. The electronic properties of carbon nanotubes are determined in part by the diameter and length of the tube .

Typically the nanoscale features and high surface area to volume of nanomaterials confer some new or enhanced properties over the macroscale material (ie the same material, but with larger features) .

Nanocomposites are materials in which nanoparticles are added to, or embedded in, a matrix. Preferably the matrix is a polymer matrix. The nanoparticles are typically dispersed throughout the matrix and may only comprise a small percentage of the total weight of the nanocomposite.

Nanocomposites typically exhibit new or modified properties compared to the properties of one or more of the components. These properties may be physical, chemical, electrical, optical, electrochemical, electrochromic, etc. in nature.

The properties of nanocomposite materials depend not only on the properties of the components but also on the morphology and interfacial characteristics of the resulting nanocomposite. Hence whilst the properties of the resulting nanoncomposite may be influenced by the choice of the nanoparticle (s) and matrix the actual characteristics of the resulting nanocomposite arise through the interaction of the characteristics of the components, and thus may be substantially different.

Nanocomposite may also include other components which influence its properties such as nanotubes, metals, metal oxides and carbon e.g. bucky balls and graphene.

The polymeric nanocomposite of the present invention comprises at least two electrically conducting polymers . The nanocomposites possesses both optical and electrochemical properties. The electrical conductivity of each polymer may be the same or different, generally greater than 1 S/cm, preferably in the range of 10 mS/cm to 100 S/cm.

Examples of suitable classes of conducting polymers include polypyrroles, polythiophenes, polyanilines, polyphenylene vinylenes, biological polyelectrolytes and/or derivatives thereof.

It is envisaged that the choice of polymers will determine the properties of the resulting polymer nanocomposite. Thus the end product can be tailor made by effective choice of the polymeric components. For example, the properties of high conductivity can be found in the polyanilines (PAn) and polyaniline derivatives such as water soluble polyaniline, poly (2-methoxyaniline-5 sulfonic acid (PMAS) . The properties of biocompatibility and therefore suitability for medical applications can be found in the polymer class of polypyrroles and derivatives thereof .

The electronic properties of the polymer class of polythiophenes and derivatives thereof are suitable for polymer solar cells . The polymer class of polyphenylene vinylenes are also suitable for solar applications.

Biological polyelectrolytes such as DNA may function as semiconductors .

A combination of polymers with different properties may be combined for certain applications.

Derivatives of the conducting polymers may include optionally substituted and/or salts comprising of the conducting polymers or the constituent monomers.

The term "optionally substituted" refers to a group that may or may not be further substituted with one, two or more groups selected from negatively charged sulphonate groups, sulphonic acid, Ci_-6 alkyl, C₃.₆ cycloalkyl, C₂-₆ alkenyl, C₂.₆ alkynyl, aryl, heterocycylyl , halo, haloCχ. _salkyl, haloC₃-₆cycloalkyl, haloC₂-₆alkenyl, haloC₂__salkynyl, haloaryl, haloheterocycylyl , hydroxy, Ci-s alkoxy, C_2- ₆alkenyloxy, C₂.₆alkynyloxy, aryloxy, heterocyclyloxy, carboxy, haloC;L_₆alkoxy, haloC₂-₆alkenyloxy, haloC₂. 6alkynyloxy, haloaryloxy, nitro, nitroCi-_s, alkyl, nitroC₂. _salkenyl, nitroaryl, nitroheterocyclyl, azido, amino, C₁. ₆alkylamino, C₂.₆alkenylamino, C₂_₆alkynylamino, arylamino, heterocyclamino acyl, Ci-₆alkylacyl, C₂-₆alkenylacyl, C₂- ₆alkynylacyl , arylacyl, heterocycylylacyl, acylamino, acyloxy, aldehydo, Ci-₆alkylsulphonyl, arylsulphonyl, Ci_-6alkylsulphonylamino, arylsulphonylamino, Ci-₆alkylsulphonyloxy, arylsulphonyloxy, Ci__salkylsulphenyl, C₂-salklysulphenyl, arylsulphenyl, carboalkoxy, carboaryloxy, mercapto, Ci_₆alkylthio, arylthio, acylthio, cyano and the like. Preferably, the optional substituent is Cχ-₄ alkyl, halo Cχ-₄ alkyl, hydroxy, halo, Ci_₄ alkoxy or Ci-4 alkylacyl.

Suitable salts of the conducting polymers include anionic sufonates, anionic carboxylates, cationic ammonium and/or cationic anilinium salts .

Preferably, the optional substituent or salt is selected from Cχ-₄ alkoxy groups such as methoxy groups and/or ethoxy, sulphonate groups and sulphonic acid groups. It will be appreciated that more than one optional substituent and/or salt may be present on the conducting polymer or its constituent monomer (s) .

Preferably, the groups that may be used as optional substituents or salts, are charged species, making them more suitable in the present invention.

The nanocomposite may also include other components which influence its properties such as nanotubes, metals, metal oxides and carbon e.g. bucky balls and graphene. The use of nanotubes, for example SWNTs and/or MWNTs in the polymeric nanocomposite can result in better optical and electrical properties of the nanocomposite.

In one embodiment the nanotubes are SWNTs and/or MWNTs . Preferably, the nanotubes are MWNTs.

The amount of nanotubes present in the nanocomposite can alter the optical properties and conductivity. For example, changing the amount of nanotube in a nanocomposite deposited on transparent substrates (see example 13, MWNT loading fraction changed from 17.5% to 32%) resulted in changes in optical transmittance (30-70%) and sheet resistance (1000-5000 Ω/cm2) . This is further demonstrated in the examples below (see Figure 13 and Table 3) .

Where one of the conducting polymers is chosen from the list of suitable classes provided above, a second conducting polymer may be selected from derivatives of the polymers described above, including derivatives of the first polymer.

The ratio of the two conducting polymers in the polymeric composite depends on the choice of polymers. Generally, a range of 0.1 - 2 (first polymer) : 0.1 to 2 (second polymer) is envisaged (equivalently 1:0.05-20). In an embodiment including nanotubes, generally a range of 1 (first polymer) : 2.2 (second polymer) : 0.1 - 2.7 (nanotubes) is envisaged.

In one embodiment, a polymeric nanocomposite consisting of Polyaniline (PAn) and poly (2-methoxyaniline-5-sulfonic acid (PMAS) has a ratio range of 0.1 - 2 (Pan): 0.1 - 2 (PMAS) . One example of a Pan/PMAS composite has a ratio of l(Pan) : 1.5 (PMAS) . In an embodiment including nanotubes one example of a PAn/PMAS/CNT polymer nanocomposite has a ratio range of 1 (PAn) : 2.2 (PMAS) : 1.35 (CNT) .

Examples of suitable polymeric composites of the present invention include: Polyaniline / poly (2-methoxyaniline-5-sulfonic acid) ;

Polypyrrole (PPy)/ poly (2-methoxyaniline-5-sulfonic acid);

Polythiophene (PTh)/ poly (2-methoxyaniline-5-sulfonic acid) ;

Polyaniline / polypyrrole- sulphonic acid; Polypyrrole / polypyrrole- sulphonic acid;

Polythiophene / polypyrrole- sulphonic acid;

Polyaniline / polythiophene- sulphonic acid; Polypyrrole / polythiophene- sulphonic acid; Polythiophene / polythiophene- sulphonic acid; PPy or PAn or PTh/methoxyaniline (POMA) ; PPy or PAn or PTh /alkylcarboxy pyrrole diethoxy,- and. Polyaniline / poly (2 -methoxyanilino-5 -sulfonic acid) /MWNT;

Nanocomposites of polyaniline / poly (2-τnethoxyaniline-S- sulfonic acid) (PAn/PMAS) and PAn/PMAS/MWNT are preferred.

The nanocomposite may contain nano-particles and nanofibres. The nano-particles may be spherical in shape. The nano-fibres may be coiled, elongated and/or rodlike. The diameter of the nano- fibres and/or nano-particles may be in the range of 1 and 500nm, preferably in the range of 5 to 300nm, more preferably in the range of 10 to 200nm, even more preferably in the range of 20 to lOOnm. The length of the nano-fibres may be greater than lOOnm to several micrometers, preferably greater than 500nm.

In one embodiment, the nanofibrillar structure of a

PAn/PMAS nanocomposite has a diameter of 50 to 80nm. In addition, spherical nano-particles of diameters in the range of 20 to lOOnm are present. The length of the nano fibres may range from 1000 to 5000nm.

In another embodiment, a PAn/PMAS nanocomposite contains nanofibres with a diameter of 30 to 50 nm and a length of 100 to 5000 nm. In a further embodiment, a PAn/PMAS/MWNT nanocomposite contains nanofibres with a diameter of 30 to 50 nm and a length of 100 to 50,000 nm.

The polymeric composite can be in the form of a nanodispersion. The term "nanodispersion" refers to the dispersion of the nanocomposite in an aqueous solution. the nanodispersions are stable at pH values of 9 or 10 without the aid of an additional stabiliser (steric or ionic) . The nanodispersions may contain up to 20% w/v of the nanocomposite in aqueous solution, 0.05 to 15% w/v, more preferably 0.1 to 1.0% w/v. When the nanocomposite includes nanotubes, the nanotubes may be present in an amount up to 32 % w/v.

It has been found that stable nanodispersion containing up to 0.8% w/v of a Pan/PMAS nanocomposite can be formed in aqueous solution. This nanodispersion has rheological

(Figure 5) and surface tension (Figure 6) characteristics. These properties make this nanodispersion suitable for ink-jet printing or for air brush spraying as well as other means of subsequent processing. Either ink jet printing or spray coating can result in uniform adherent coatings on a range of substrates including papers, polymers or polymer coated (e.g. ITO) substrates.

The 0.8 % w/v PAn/PMAS nanocomposite dispersion showed stability over a 3 to 6 month period and up to several years. This example also displayed conductivity of about 2.8cm/S. It is hypothesized that extended pH stability has been achieved via SO₃H functionality of the PMAS.

In a further example of a PAn/PMAS/MWNT nanocomposite dispersion (1 (PAn): 2.2 (PMAS) : 1.35 (MWNT) at a concentration of about 1.0 w/v in aqueous solution, the dispersion showed stability over a 8 month period. This example, in the form of a free standing film, also displayed sheet resistance and conductivity of 5 Ω/cm² and 51.3 S/cm respectively. The combination of conducting polymers with conducting nanotubes such as carbon nanotubes, has shown to have all the demanding characteristics needed for inkjet printing. These materials may be deposited onto substrates such as photo paper, PET, Pt-ITO and Au-PVDF. A sheet resistance of 500 Ω/cm² was attained for a single printed layer on photo paper .

The term "electroactive" generally refers to the ability of a material to be rapidly and reversibly switched between different oxidation states. This redox switching provides a facile mechanism for both the uptake (during oxidation) and release (during reduction) of a wide range of anions. In one embodiment of the present invention, the polymeric nanocomposite is electroactive. In addition, one or both of the polymers making up the polymeric composite may be separately electroactive. Thus in one embodiment, the polymers making up the polymeric composite are each electroactive and also result in a polymer composite that is electroactive.

In one embodiment of the invention, electroactivity was investigated. The example of the polymer nanocomposite Pan/PMAS was investigated and discussed in the examples section below. As is shown, both sprayed and coated surfaces displayed well defined electrochemical switching characteristics (Figure 7) . This is important for a range of applications including printable electrochromics, batteries or even switchable hydrophobic / hydrophilic surfaces. The switchable electrochromic properties of both printed and sprayed substrates are clearly illustrated in Figure 8 and Figure 9.

Method

The method for preparing an electrically conducting polymeric nanocomposite is outlined in Figure 20 and comprises the steps polymerising the monomers of a first first electrically conducting polymer in the presense of a second electrically conducting polymer (112) .

When the nanocomposite includes other components such as nanotubes (102; 104), the nanotubes may be dispersed in the second conducting polymer (106) . The constituent monomers of the first conducting polymer are then polymerised in the presence of the nanotubes dispersed in the second conducting polymer (108) .

The polymerisation may be performed using any suitable known technique, such as, the addition of an oxidant. The oxidation can be conducted electrochemically or via the addition of an oxidising agent. Examples of oxidants include ammonium persulphate (APS) , iron salts and/or cerium salts. Electrochemical oxidation can be conducted using any suitable known technique such as electrolysis, for example, bulk electrolysis or flow-by electrolysis apparatus .

The dispersion of the other components such as nanotubes, in the second conducting polymer can be achieved using ultrasonic treatment.

It is postulated that the process involves the templating of monomers of the first polymer on the second polymer to form a first monomer and second polymer complex.

The template of the second polymer forces its conformation on the first polymer due to interaction between the monomer (s) of the first polymer and the electrolytic moieties on the second polymer prior to polymerisation. Polymerisation of the first monomer such as by the addition of an oxidant results in a templated complex. The resultant composite may then be conformationally trapped, thereby attaining the spectral aspects of the second polymer. In the specific example of the process of preparing a nanocomposite of PAn/PMAS, this conformation arises from the anilinium ion of the monomer of PAn to be oxidised via ion-pairing with the sulfonate of the templating PMAS as illustrated in Figure 19. The second polymer then functions in a dual role as a molecular dopant and stabiliser resulting in the formation of nanoparticles .

In the case where other components are added to the nanocomposite, the second polymer is also an excellent stabiliser for the other components, in particular for CNTs, while continuing to function as the dopant in the polymerisation of the constituent monomer (s) of the first polymer.

It is preferred that the polymerisation be conducted at a rapid rate rather than slowly. Bulk addition of the constituent monomer (s) of the first polymer and the second polymer is preferred and the polymerisation proceeds to completion with no stirring.

A nanodispersion may be formed by dispersing the electrically conducting nanocomposite in an aqueous solution (114) which may then be applied to a substrate (116) such as with a inkjet printer.

Applications

Devices composed partly or wholly of the electrically conducting polymeric nanocomposites are suitable for use in optical and electrochemical applications including electrochromics, electromagnetic shielding and/or controlled drug release. These articles may include polymer actuators, polymer photovoltaics, polymer solar cells, rechargable polymeric batteries, anti-corrosion coatings, textile coatings, fuel cells, ink jet printing, bioconductors for controlled release or regeneration of mammalian cells. The nanocomposite can also be used as a dye to coat textile fibres rendering them conductive.

Devices composed partly or wholly of the electrically conducting polymeric nanocomposites has use in electrochromic mirrors, for altering the intensity of reflected light, incident upon the mirror. Mirrors which are capable of reversibly dimming may be used in the automotive industry. In addition, the arrangement could be used in electrochromic glazing where a change in colour or transmissivity of an assembly can provide a dimming condition to a window or other type of screen. This dimming can increase the level of privacy to an area as well as control the level of radiant heat that permeates an area. Electrochromic glazing may be used in many industries including the automotive industry, architectural, industrial and aeronautical industries, etc.

Electrochromic devices incorporating nanocomposites of the present invention may also have applications in visual displays for example, in projector light modulators which may improve upon current LCD projector technology. The visual displays incorporating the present invention could be used in advertising. Manipulation of electric fields may allow an advert to be displayed on an electronic billboard. The advert could be readily replaced by varying the electric potential thereby providing the ability to display a number of advertisements on one billboard. Furthermore the dimming of the electrochromic assembly may be advantageously used in the ophthalmics industry. The tint and colour of lenses could be manually or automatically adjusted in order to modify the amount of light transmitted to the eyes .

Any industry which benefits from colour and/or reflectivity changes in the visible spectrum may make use of this technology. Colour control may have applications in the fashion industry where flexible laminates or woven fibres comprising the present system may provide a multitude of different colours in fabrics, jewellery and make-ups. It is also an option that the changes in colour be used for internal furnishing, for example, wallpaper which can change colour upon application of an applied potential.

An electrochromic device may be constructed using nanocomposites of the present invention. A typical electrochromic device comprises two complimentary electrochromic materials and an electrolyte sandwiched between two electrodes .

A typical electrochromic device is presented in Figure 17a. Electrochromic materials forming electrochromic layers 12 and 14 are coloured according to the frequencies of light that are absorbed by the electrochrome. The electrochromes which form the electrochromic layers 12 and 14 are selected to have absorption spectrum which are complementary to one another so that electrochromic layer 12 is anodically colouring while electrochromic layer 14 is cathodically colouring (complimentary electrochromic) .

Note that only one electrochromic layer is required, but typically two complimentary electrochromic materials are preferred as they provide greater stability as electrons released by one material are taken up by the other, and greater contrast difference as they either both transparent or both coloured.

An electrolyte may be interposed between the electrochromic layers . The electrolyte may be in the form of a liquid including an ionic liquid, a liquid infused membrane or support matrix, a gel or solid. The electrolyte can be a combination of ionic liquids, an ionic liquid and a non-inherently liquid salt such as NaCl, or ionic liquid and solvent, or any combination of these mixtures. Furthermore, the electrolyte may be a polymer having anionic or cationic functionalities. Alternatively the electrolyte can be a salt having a supporting solvent. Examples include LiC10₄/acetonitrile, 1-ethyl-3-methyl imadozolium [BMIM] bistrifluoromethane sulfonimide or [BMIM] [BF₄] .

Alternatively if electrically conducting electrochromic materials are used, or electrochromic materials to which conducting additives such as CNTs are added, then no electrolyte layer may be required. That is the electrochromic layers (preferably complimentary in nature) may be in direct contact with each other and capable of ion or charge exchange .

In one embodiment the electrochromic layers 12 and 14 may be two electrically conducting electrochromic nanocomposite layers or an electrochromic nanocomposite layer and an electrochromic inherently conducting polymer (ICP) layer. Note that nanoparticles may also be added to an ICP layer. The nanocomposite may be selected from one of the polymeric nanocomposites discussed above such as PAn/PMAS or PAn/PMAS/CNT. The ICP layer may be selected from the group consisting of polythiophenes, polypyrroles, polyanilines, polyindoles, polycarbazoles, polyphenylene sulphide and polyparaphenylene and derivatives thereof . It is an option that the compounds chosen from these groups be substituted with at least one chemical functionality. Alternatively the ICP may comprise copolymers, block copolymers or graft copolymers each of which may include one or more different monomers or oligomers selected from the abovementioned groups. For example, there may be a sequence of thiophene units followed by a sequence of indole or pyrrole units, etc.

In one embodiment, electrochromic layer 12 is cathodically colouring and formed from polyethylenedioxy-thiophene (PEDOT) doped with polystyrene sulfonic acid (PSS) . PEDOT has a low redox potential, is stable to multiple redox switching and has a high conductivity. These properties are attributed to the high electron density of the molecular structure. Other cathodically colouring electrochromes which can be used include polypropylenedioxy-thiophenes (PRODOT) . Electrochromic layer 14 is anodically colouring and formed from a nanocomposite material. Preferably this is PAn/PMAS and even more preferably it is PAn/PMAS/CNT. Other examples are presented above.

The electrochromic layers are typically laid over the electrode layers . Multiple layers of the same electrochromic material may be laid. Referring to Figure

17a electrochromic layers 12 and 14 are sandwiched between electrode layers 22 and 24 respectively (24 being a counter electrode) . In one embodiment, electrodes 22 and 24 are transparent indium tin oxide (ITO) , however any suitable substantially transparent electrode could be used, for example, fluorine doped tin oxide (FTO), antimony doped tin oxide or other conductive metal oxides or thin metal films . However suitable electrochromic compositions may also act as electrodes, thereby avoiding the need for a specific electrode layer. For example a nanocomposite layer incorporating ITO nanoparticles may be suitable.

The electrochromic layers and electrode layers are sandwiched between subtrates 32 and 34 which provide mechanical support and protection for the electrochromic layers. Examples include poly (ethylene terephtalate) (PET), glass, plastics, metal foil, etc. Busbars may also be added wires attached using conductive epoxy resin. The device may be sealed using a suitable material such as an epoxy resin.

A method for constructing an electrochromic device is outlined in Figure 21 (200) . A first conductive material is applied to a substrate layer to form a first electrode layer (202) . A nanodispersion containing an electrically conducting electrochromic nanocomposite is applied to the first electrode layer so as to form a first electrochromic layer (204) . A second electrochromic polymer is applied to the first electrochromic layer so as to form a second electrochromic layer (206) . A second conductive material is applied to the second electrochromic layer so as to form a counter electrode layer (208) . A protective layer may then be applied to the electrode layer (210) . Busbars may also be added wires attached using conductive epoxy resin. The device may be sealed using a suitable material such as an epoxy resin.

An electrochromic device may be constructed by building up successive layers . For example a suitable substrate such as PET could be used (32) . Electrode layer 22 could be laid followed by electrochromic layers 12, then 14, followed by electrode layer 24 and protective layer 34. These layers could be produced using known printing methods such as ink-jet, roll/press printing, silk screening or airbrushing; contact methods such as dip coating or spin coating. Electrochromic layers 12 and/or

14 may comprise multiple layers of the same electrochromic material. Alternatively the device could be constructed in parts which are brought together to form the device. For example a first component comprising first substrate, electrode and electrochromic layers, and a second component comprising a second substrate, electrode and electrochromic layers could be separately manufactured and brought together (eg pressed together) at time of manufacture of the electrochromic device.

It is an option that performance additives be added to the nanocomposite or ICP layer (or to other parts of the assembly) to improve the deposition process of the electrochromic layer. For example, a wetting agent, such as a non-ionic surfactant, may be used to decrease the surface tension of the solution from which the nanocomposite or ICP layers are deposited, thereby increasing the adherence of the electrochromic layer to the target substrate. Other performance additives include-, preservation additives, rheological additives and/or antifoaming agents which can also be advantageously used to improve the adherence, UV stability, consistency, longevity, flexibility or deposition of the electrochromic layers .

Typically the electrodes abut the electrochromic layer (except where they are combined) and the electrochromic layer covers at least a part of the electrode.

Alternatively the electrodes and electrochromic layers may be deposited onto suitable supports such as first sheet 32 and second sheet 24 which may be formed from plastic (PET) or glass or the like (Figure 17b) . The supports can then be pressed together and sealed (eg using Epoxy Resin) to thereby form an electrochromic device of Figure 17a.

For use in a dimming mirror, the electrochromic device further requires the inclusion of a reflective surface. The electrochromic assembly can abut a reflective surface (eg 30 in Figure 17c) or the electrode 22 or substrate 32 may be a reflective surface.

Preferably at least one of the supports has a reflective surface 30. It is an option that reflective surface 30 serve as an electrode, for example, electrode 22. Incident light reflected by the assembly is shown by the arrow is shown in figure 17c. The electrochromic device is optically transparent, an optical transmission path being formed between the electrodes and the reflective surface. The arrow in Figure 17c shows that incident light which enters the electrochromic device passes through the optically transparent outer layer (34) , though counter- electrode layer 24 , then electrochromic layers 14 and 12 , and then through electrode layer 22 where it is reflected from reflective surface 30. For the purposes of Figure 17c it is assumed that the electrochromic layers are not substantially interfering with the light path.

In some cases it may be advantageous to add a conducting layer of particles, preferably, nanoparticles, between the electrochromic layers and electrode layers so as to enhance the electrical contact between them.

In another embodiment, the nanocomposite and/or ICP layers may act as electrodes, thereby negating the need for layers 22 and 24 as shown in Figure 17d. This could be achieved through choice of nanoparticles and nanocomposites, or through further addition of conducting additives, preferably nanoparticles

In many cases the materials from which electrochromic devices incorporating nanocomposites of the present invention are not hazardous to health or the environment . The distance between the electrodes in the present arrangement is uniformly maintained electrochromic layers disposed between the electrode. The present arrangement therefore does not suffer to the same extent from the problems faced in LCD displays since external and internal stresses in the present arrangement do not substantially effect the uniformity of the electric fields in the electrochromic device since the spacing between the electrodes cannot be substantially changed. The electrode and electrochromic layers are thin and can rely on the supporting nature of the substrate to support them, and therfore prevent distortion and loss of functionality from physical stress.

For safety purposes, a means may be provided for returning the electrochromic assembly to the non-dimming condition in the event of electrical failure. This means can be an electrical switch which applies the required voltage potential between the electrodes in order to provide a non-dimming condition. This safety feature is particularly- useful in vehicle mirror systems where it is preferable that the vehicle mirror be in the non-dimmed state by default.

Electrochromic devices incorporating the nanocomposites of the present invention may be produced which can be switched between highly transmissive and highly absorptive states as a function of applied voltage potential. The electrical and optical properties of such electrochromic devices will depend upon the choice of materials (including the nanocomposite) . The electrical and optical properties may be further controlled through choice of drop spacing and the number of (identical) electrochromic layers (containing nanocomposites of the present invention) printed (see Example 2, Table 3 and Figure 13) .

Various means can be provided for controlling the potential applied to electrochromic device so as to provide various dimming and non-dimming conditions. This is particularly advantageous in a vehicle rear-view mirror where activation is required when headlights cause glare in the mirror. For instance, a photoelectrical switching device in the form of a photodiode, phototransistor or photocell such as an LDR can be used as a control means input. When the photoelectric switch senses the headlights of a following vehicle, the control means can be activated to provide a potential across the electrodes . Photovoltaic cells and power storage devices such as batteries may also be employed, for instance to provide self-powered dimmable mirrors . Various other components and control means can also be used.

Complex electrochromic devices could also be constructed, for example a digital display element (100) comprising 7 individual strip elements in a figure ^ΛΛ8" arrangement as shown in figure 18. Seven strips of PRODOT (122, 124, 126, 128, 130, 132, 134) are first patterned on to a sheet of ITO coated substrate (eg glass) forming a cathode (140) . Seven identical strips of a nanocomposite of the present invention (102, 104, 106, 108, 110, 112, 114), preferably PAn/PMAS/CNT is printed onto a segmented second sheet of ITO coated substrate (eg glass) forming the anode (120) . The PAn/PMAS/CNT/ITO strips oppose the PRODOT strips (dotted lines in Figure 18) . Alternatively the PAn/PMAS/CNT layer is printed directly over the PRODOT layer and the second sheet of segmented ITO coated substrate is pressed onto this layer (the segmentation and strips opposing the PRODOT strips) .One electrical contact is made with the cathode, and seven electrical contacts, are made with the anode, one contact for each ITO-coated glass plate segment. The edges of the device are then sealed using epoxy resin. Joint electrical contact for PRODOT and independent electrical contacts for PAn/PMAS/CNT are made by attaching metal wires using silver paint.

Nanocomposites and/or nanocomposite dispersions may be directly printed onto polymer substrates. This enables construction of devices using lamination and roll-to-roll processes. Roll to roll processing involves providing two physically spaced rollers. A flexible substrate material is wound on the first roller, and the exposed end is then wound onto the second roller, thereby exposing a relatively short section of the substrate material. Further rollers or means are used to guide and maintain the tension of the exposed material so that it may be guided over region where material may be deposited by various means onto the substrate. Following the deposition process, the modified substrate is rolled onto the second reel for storage.

The roll of substrate may be several metres wide by many kilometre long. One example of a deposition means is an ink jet printer. Such a printer could be used to pattern an electronic or electrochromatic device onto the substrate which incorporates a polymeric nanocomposite of the present invention. Other suitable means are also possible. An inkjet printer, or other suitable means could be used for depositing other layers. For example an electrode layer could be printed onto a poly (ethylene terephtalate) (PET) substrate. A nanocomposite dispersion such as PAn/PMAS/CNT could then be printed over the PET substrate. Multiple layers, electrode layers or protective layers could then be printed over the top . Such devices could be sealed and then the patterned substrate rolled onto the second roller where it may be stored. This roll may then be transported or used in a large scale manufacturing of devices incorporating the electronic or electrochromic device. This type of storage method with its easy access to the patterned device offers a significant cost and time advantage from a manufacturing perspective since the rolls can be easily delivered and do not require substantial modification prior to use.

The roll could contain individual portions or complete devices, or laminar sheets. Portions of the patterned devices may be cut from the roll and used during manufacture. Portions of desired size and shape could be cut from laminar sheets and incorporated to make a desired device .

Roll-to-roll processing could be used to make components which are brought together at the time of manufacturing of the final device. For example rolls with the two components in figure 17b could be produced and stored separately and then pressed together at the time of manufacture.

The ability to print nanodispersions using inkjet printing more generally facilitates the production of a variety of electrical and electrochromic devices of varying sizes and shapes. Choice of a flexible substrate would for example allow production of a curved electrochromic dimming mirror.

EXAMPLES

The invention will now be described with reference to the following non-limiting examples.

Preparation of Polyaniline / poly(2-methoxyaniline-5- sulfonic acid)

Materials : Aniline was purchased from Aldrich and was distilled and stored at -4 "C (freezer) prior to use. Ammonium persulfate (APS) was purchased from Aldrich. All reagents used were of analytical grade purity and all solutions were prepared using Milli-Q water (18 MΩ/cm) . 2-methoxyaniline-5- sulfonic acid monomer (MAS) was provided by Mitsubishi Rayon, Japan and purified in-house by acid-base crystallization before polymerisation. Catalytic chemical vapour deposition produced multi-walled carbon nanotubes were obtained from Nanocyl SA (Belgium, batch no. NFL60) .

Instrumentation:

The pH of monomer and polymer solutions was measured using a TPS Instruments Model 900-P pH meter. The synthesised nanodispersed materials were separated from the synthesis solution using a Beckman (J2-MC, rotor JAlO) centrifuge.

Reverse phase HPLC with a Waters Bondapak C18 column and a Linear UVIS 200 UV recorder (λmax = 258 nm) was used to determine residual aniline. UV-vis spectra were recorded using a Shimadzu UV-1601 spectrophotometer. Cyclic voltammetry (CV) was carried out in a three electrode cell using a glassy carbon working electrode with platinum mesh auxiliary and Ag/AgCl (3M NaCl) reference electrodes using an E-Corder 401 interface and Potentiostat (EDAQ) . Conductivity measurements were performed on dried films of about 10 μm thickness drop cast onto glass slides from 5% w/v dispersion solutions using a JANDEL four-point probe resistivity system (model RM2) . Transmission electron microscopy using a Hitachi H7000 TEM at 75 keV was used to observe the morphology of samples . Elemental analyses were performed by the ANU (Australian National University) Microanalytical laboratory. The samples were heated to 50°C in a vacuum oven for 5 hrs prior to microanalysis .

Synthesis and Purification of PMAS:

PMAS was chemically synthesised by polymerisation of MAS in the presence of ammonium persulfate as oxidant. PMAS was synthesised under similar conditions reported previously2 using 0.025 mol (5g) MAS dissolved in 50 mL water, adding approximately 1.5 mL NH3 (28% w/w) slowly to pH 4. To this solution 0.031 mol (7.14 g) (NH4)₂S₂O₈ (APS), dissolved in 25 mL, water was added dropwise to the monomer solution over 30 min at 5-10 °C. The reaction mixture was stirred overnight at the same temperature to complete the reaction. The polymer was purified by a tangential flow diafiltration system using the procedure developed previously.²

Preparation of Polyaniline/poly (2-methoxyaniline-5- sulfonic acid) .

Synthesis and Purification of PAn/PMAS Composite: The procedure described by Huang and Kaner¹ was modified to enable synthesis of PAn/PMAS nanocomposites . A 200 μL solution of 1 M APS <_aq) in 1 M HCl (_aq) was added rapidly to a 10 mL aqueous solution consisting of 0.16 M aniline and 1% (w/v) PMAS in 1 M HCl _(aq) . This was stirred overnight at room temperature to complete the reaction. The final aniline to APS molar ratio was 4:1, resulting in a dark green dispersion (suspension) , and was employed to prevent secondary polymer growth that would result in nanofibre coagulation, as reported previously¹. The dispersion was diluted six times in water and purified using a centrifuge at 4100 rpm for 15 min. The precipitate was then redispersed in water. The centrifugation/redispersion cycle was repeated 3 times until a pH of about 4 was obtained in the supernatant. UV-vis spectra obtained for the supernatant after filtering (0.2μm) to remove any particulate interferences . PAn/HCl dispersion was prepared under identical conditions but in the absence of PMAS.

The resultant PAn/PMAS composite was insoluble in NMP, hence no molecular weight analysis of the composite was possible. The lack of solubility in these common PAn solvents was presumed to arise from the highly ionic nature of the materials produced.

Structure:

The UV-vis spectra of PAn/PMAS, PMAS and HCl doped polyaniline dispersions were obtained (Figure IA) . The spectrum of PAn/HCl exhibited broad bands at ca. 330-440 nm and a broad palaron peak centred at 755 nm, consistent with a compact coil-like conformation for polyaniline. The spectrum of PMAS showed a band at 330 nm, attributed to π- π* transitions, and a sharp peak at 474 nm assigned as the lower wavelength polaron band. The broad absorption at wavelengths longer than 700 nm have been attributed to a delocalized polaron transition, with the presence of the latter peak suggesting an extended coil- like conformation for PMAS.⁴ The composite material formed by polymerisation of aniline in the presence of PMAS presented peaks at 360- 370 nm and 445 nm indicative of the presence of PAn. The strong free carrier tail above 800 nm and the absence of a polaron band at ca. 750 nm indicated that the polyaniline adopted an extended coil-like conformation.

To provide further evidence for the presence of polyaniline and PMAS in the composite, the spectra were recorded in alkaline media (Figure IB) . The spectrum of PAn/PMAS in 0. IM NaOH (aq) had features of both polyaniline and PMAS. Under these conditions the polyaniline was partly converted into the deprotonated emeraldine base form with a characteristic band at 600 nm while PMAS adopted a characteristic compact coil-like conformation seen at 750 nm.⁴ More interestingly, the PAn/PMAS system had behaviour that strongly paralleled PMAS. In this case, it is hypothesised that the PMAS template forces its own backbone conformation on the nascent (forming) polyaniline due to the anilinium cation associating with the sulfonates moieties of the PMAS prior to polymerisation. Upon oxidative polymerisation the resultant material was conformationally trapped, thereby attaining the observed spectral aspects of PMAS .

Elemental Analysis :

For the PAn/HCl (C_I4H_HN₂CI dimer unit) , the elemental analysis was: C 58.4, H 5.0, N 11.0, Cl 5.5. Based on the analysed N/Cl ratio (5.0) , a low doping level of 0.2 was estimated for the PAn/HCl material. Elemental analysis of PAn/PMAS was: C 44.65, H 3.8, N 8.0, S 10.2, Cl 0.4. Based on the C/S ratio (11.7) in PAn/PMAS, the ratio of PMAS to PAn was estimated to be 1.5. This analysis assumes that no free SO₄ ^2" from the reduced APS was present in the purified composited after the repeated and rigerous washing and UV- vis analysis of the supernantant . The higher content of PMAS in the composite was as a consquence of the dual role of PMAS acting simultaneously to dope and stabilise the dispesrion. The Cl/S ratio was 0.03, indicating traces of chloride anions in the composite. This indicated that Cl^" is in competition with free sulfonate group of PMAS in doping polyaniline. Doping by the free sulfonate groups of PMAS predominates due to their vicinity to the nitrogen centres in the polyaniline backbone. Morphology and dispersion stability:

Nanofibres of polyaniline having diameters between 30 - 50 nm and lengths varying from 500 nm to several micrometers have been obtained from interfacial polymeriation or rapidly mixing the reagents ,^lι9t12 TEM images were obtained by drop casting PAn/HCl or PAn/PMAS onto grids from dilute dispersions, Figure 3. Nanofibrillar structures with diameters of 50-80 nm were obtained for both PAn/HCl and PAn/PMAS. However, the polymerisation of aniline in the presence of PMAS resulted in the additional formation of spherical nanoparticles having diameters between 20 and 100 nm.

A dilute aqueous dispersion of PAn/HCl nanofibres prepared by the above method was only stable for 3-5 hours.

However, for the PAn/PMAS dispersion no precipitation was observed after standing for 3 days (Figure 4) and was maintained for a few months thereafter. At lower PMAS concentrations the composite was observed to form aggregated structures resulting in non-stable dispersions.

Electroactivity properties :

Pan/HCl and Pan/PMAS composite were drop cast onto separate glassy carbon electrodes, forming insoluble coatings after air drying over a day. Cyclic voltammetry studies were then carried out on the resultant films (Figure 2) . Two typical redox couples [A₁ZA₁' and B_x/B"i) with anodic peaks at 0.37 V and 0.86 V (vs Ag/AgCl) were obtained for the Pan/HCl film. PMAS is a water-soluble derivative of polyaniline which itself shows electroactivity either in solution² or in composite films resulting from complexation with other materials.⁵'⁵'⁷ Two pH-dependent redox couples have been reported for PMAS- PVP^[13] and PMAS-PLL⁶'⁷ complexes which are similar to the redox couples of sulfonated polyaniline (SPAN)⁸ with the anodic peaks at -0.25V and -0.65 V in 0.1 M HCl electrolyte. Cyclic voltammograms obtained using cast films of the Pan/PMAS composite presented three redox couples with anodic peaks at 0.26, 0.64 and 0.76 V. The first redox pair (A₂/A'₂ ) was attributed to the interconversion between the leucoemeraldine and emeraldine states of both Pan and PMAS . The second redox couple (B₂/B'₂) was attributed to the interconversion of emeraldine to the pernigraniline state of PMAS. ^[15' ^1S] The third redox pair (C₂/C₂) was assigned to the transformation of the Pan emeraldine state to the pernigraniline form. Notably, when PMAS was present the observed redox couples were more clearly defined with respect to the ,Pan/HCl films prepared under equivalent conditions. It is hypothesised that this enhancement may be as a result of the more conductive nature of the nanocomposites , as discussed below.

Conductivity:

Incorporation of PMAS as a dopant resulted in a PAn/PMAS composite which was 10 time more conducting (2.8 S/cm) than PAn/HCl prepared with HCl as dopant using the same synthesis conditions. The conductivity of the PAn/HCl fibres produced here was similar data reported by Huang and Kaner, ⁹ who observed pressed pellet conductivities of up to 0.5 S/cm. PMAS itself is an electronically conducting polymer electrolyte with a conductivity of 0.4 S/cm when prepared under the conditions described above. Clearly the electronic interaction of the PMAS with the PAn component improves the overall conductivity of the nanocomposite, particulary when compared to the use of nonconducting polyelectrolyte dopants¹⁰ and molecular template dopants . ^lλ

Conclusion

Electroactive PAn/PMAS nanoparticles with very high dispersion stability and high conductivity have been prepared with well defined nanofibres and nanoparticles of diameters between 20 and 100 nm, as observed by TEM. The UV-vis spectra of the PAn/PMAS composite in water and in alkaline media confirm the presence of both PAn and PMAS in the nanocomposite. The high S/Cl molar ratio obtained from elemental analysis and the high conductivity of the composite indicate that PMAS is the dominant dopant. The ratio of PMAS to PAn is 1.5, indicating that there is sufficient PMAS to dope the PAn in the emeraldine state, with excess sulfonate groups providing a stabilising effect in the resultant dispersion.

Example 2

Synthesis and characterisation of PAn/PMAS/MWNT composite

The procedure described by Huang and Kaner¹ was modified to enable synthesis of PAn/PMAS/CNT nanocomposites .

MWNTs were dispersed in PMAS using ultrasonic treatment. Solution of PMAS at concentration ~ 1 mg/ml were sonicated with a Branson Digital Ultrasonic Sonifier 450 D (400 W, 3 mm tapered microtip) for 2, 5, 10, 30 and 60 mins at 16W in pulsed mode (2s on, Is off) .

Sonolysis of this duration did not significantly degrade PMAS. Table 1 below shows the effect of sonication time (in pulsed mode) on PMAS molecular weight.

Table 1

A 100 μL solution of 1 M ammonium persulfate (APS) in 1 M HCl was added rapidly to 5 mL aqueous dispersion of PMAS- MWNT and 0.08 M aniline in 1 M HCl. This was stirred for 5 hours at room temperature to complete the reaction.

The final aniline-to-APS molar ratio was 4:1, while the MWNT: aniline weight ratios were 0.1, 0.2, 0.4, 0.6, 1.35 and 2.7. (loading fractions of 3.4%, 6.6%, 12.4%, 17.5%, 32% and 64 % of MWNT in PMAS respectively) .

The dispersion was diluted six times in water and purified using a centrifuge at 4100 rpm for 15 min. The precipitate was then redispersed in water. The centrifugation/redispersion cycle was repeated 3 times until a pH of about 4 was obtained in the supernatant.

PMAS functions in a dual role as a nanotube stabilizer and as a molecular dopant during aniline polymerisation which results in the formation of PAn/PMAS-MWNT composites.

Loading fraction

Stable dispersions were obtained for MWNT: aniline ratio ≤ 1.35, corresponding to 32% MWNT loading fraction. Higher MWNT loading fractions resulted in settling out of nanotube material, indicating the nanotube stabilization limit of PMAS. UV-visible absorption spectra (Figure 11) showed that with increasing nanotube content the intensity of the band at 450nm (assigned to polymer) decreases, while absorbance above 600 nm (assigned to nanotubes) increases .

The MWNT loading fraction is calculated as follows . Carbon nanotubes are stabilized in 80 mg PMAS for MWNT: aniline weight ratios 0.1, 0.2, 0.4, 0.6, 1.35 and 2.7. Hence a MWNT: aniline weight ratio of 0.1 corresponds to a MWNT loading fraction of 3.4%, e.g. 3.75 mg MWNT in ~110 mg polymeric material. (It was found that 70% of aniline starting amount (37mg) is consumed during polymerisation. ) Structure

A TEM image of an evaporated dispersion of a Pan/PMAS-MWNT dispersion is shown in Figure 10. 1 (PAn) : 2.2 (PMAS) : 1.7 (CNT) ] .

It can be seen that MWNT are evenly covered by the polymer [PAn/PMAS] indicating excellent wetting of the nanotubes surface.

Electroactivity properties

Sheet resistance and electrical conductivity: Film thickness of free standing films prepared by drop casting was determined by Mitutoyo digital micrometer. Conductivity measurements (Table 2) were carried out using a JANDEL four-point probe resistivity system (model RM2) .

Free-standing films (Figure 10) were easily prepared by evaporative casting onto a plastic substrate. After drying a stand alone film could be readily removed. Figure 10 shows that the sheet resistance [R₃) decreased by almost two orders of magnitude from 230.4 Ω/cm² for PAn/PMAS to 5.0 Ω/cm² (conductivity 51.3 S/cm) for polymeric nanocomposite with 32% MWNT loading fraction (see table 2) .

Table 2

Sheet resistance and electrical conductivity of free standing films as a function of MWNT loading fraction.

Thermogravimetrix analysis TGA

Thermogravimetrix analysis (see Figure 12) shows that the polymers decomposition pattern is augmented by a nanotube decomposition step, which increases with loading fraction.

The optical and electrical properties of highly conducting but light absorbing materials such as carbon nanotube are affected by the amount of nanotubes deposited as demonstrated using line patterning. Increasing the concentration reduces both R₃ (more electrical pathways) and transmittance [T, more light absorbed) . This is demonstrated by increasing the number of printed layers, the MWNT loading fraction and spacing between deposited drops. Figure 13 shows that increasing the number of prints to 3 improves the electrical sheet resistance by a factor 2.5, at a cost of 20% in optical transparency.

Increasing the MWNT loading fraction reduces R₃ and T by 50% and 13%, respectively (see Figure 13 and Table 3) . Changing the spacing between the drops ejected from the printer head results in the opposite effect, with both R₃ and T increasing significantly (see Table 3) .

Table 3

Sheet resistance (Rs) and transmittance (T) of inkjet printed films (1 layer, MWNT loading fraction 32%) on various substrates.

Nanotube dispersions (concentration 10mg/ml, temperature 25⁰C, viscosity 5.5 CP, and surface tension 72 mN/m) were inkjet printed using a Dimatrix materials deposition system (Fuji film Dimatrix) . Patterns were deposited onto flexible transparent poly (ethylene terephtalate) (PET) , Hewlett-Packard glossy photo paper, Platinized indium tin oxide coated glass (Pt-ITO) , and gold coated poly (vinylidene fluoride) (Au-PVDF) (see Figure 13) for examples .

Electrode

A PAn/PMAS/CNT electrode was tested with a standard ProDOT coating on the opposing electrode in an electrochromic device. For comparison, PAn/PMAS vs ProDOT, PMAS and PMAS/Prussian Blue electrodes were also produced and tested. The transmissitivity of the electrode combinations were studied in the forward and reverse potential states .

The PMAS based electrodes were deposited by spin-coating, with the aim to deposit approximately enough materials to produce an initial absorbance of circa 70% T for the PMAS electrode by itself. Panels A through D of Figure 16 illustrate the difference in transmissitivity (T) as a function of wavelength of each electrode combination when in the forward and reverse potential states.

The PAn/PMAS/CNT electrode (with a 6% loading of CNT used in combination with a ProDOT electrode produced highly desirable spectral qualities, dipping in transmission around the 550nm region on darkening, where the human eye is most sensitive (Panel A of Figure 16) .For the

PAn/PMAS/CNT the change in transmittance range at 550nm was approximately 47% (67% down to 20%) . This is compared to a 42% change in transmittance for PAn/PMAS (Panel B) , 38% for PMAS (Panel C) and 20% for PMAS/Prussian Blue (Panel D) . REFERENCES

1. J. X. Huang, and R. B. Kaner, Angewandte Chemie- International Edition, 2004, 43, 5817. 2. F. Masdarolomoor, P. C. Innis, S. Ashraf, G. G. Wallace, Synthetic Metals, 2005, 153,181.

3. W. Liu, A. L. Cholli, R. Nagarajan, J. Kumar, S. Tripathy, F. F. Bruno, L. Samuelson, J. Am. Chem. Soc . , 1999, 121 (49) , 11345. 4. E.V. Strounina, L. A. P. Kane-Maguire, G. G. Wallace , Synthetic Metals, 2003, 135-136, 289.

5. D. E. Tallman, G. G. Wallace, Synthetic Metals, 1997, 90, 13.

6. T. Tatsuma, T.O., R. Sato, N. Oyama, J. Electroanal. Chem., 2001, 501, 180.

7. O. Ngamna, A. Morrin, S. E. Moulton, A. J. Killard, M. R. Smyth, and G. G. Wallace, Synthetic Metals, 2005, 153(1-3), 185.

8. C. Barbero, M. C. Miras, B. Schnyder, 0. Hass, R. Kδtz, J. Mater. Chem., 1994, 4(12), 1775.

9. J.X. Huang, R.B. Kaner, Journal of the American Chemical Society, 2004, 126, 851.

10. J. Stejskal, M. Omastova, S. Fedorova, J. Prokes, M. Trchova, Polymer, 2003, 44, 1353. 11. G. L. Yuan, N. Kuramoto, S.J. Su, Synthetic Metals, 2002. 129(2), 173.

12. D. Li, R. B. Kaner, Chemical Communications, 2005, 3286. Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and ^λΛinclude" and variations such as "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers . The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications in its scope .

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. An electrically conducting polymeric nanocomposite including a first electrically conducting polymer and a second electrically conducting polymer which acts as a dopant of the first electrically conducting polymer.

2. The polymeric nanocomposite as claimed in claim 1 wherein the second electrically conducting polymer acts as stabiliser for the first electrically conducting polymer.

3. The polymeric nanocomposite as claimed in claim 1 or 2 wherein one or both of the polymers are electroactive and/or electrochromic and the nanocomposite is electroactive and/or electrochromic.

4. The polymeric nanocomposite according to any one of claims 1 to 3 wherein the polymeric nanocomposite is selected from the group consisting of polyaniline (PAn) / poly (2-methoxyaniline-5-sulfonic acid) (PMAS) , polypyrrole (PPy)/ PMAS, polythiophene (PTh) /PMAS, PAn / polypyrrole- sulphonic acid, PPy/ polypyrrole- sulphonic acid, polythiophene (PTh)/ polypyrrole- sulphonic acid, PAn / polythiophene- sulphonic acid, PPy / polythiophene- sulphonic acid, PTh / polythiophene- sulphonic acid, PPy or PAn or PTh/methoxyaniline (POMA) , and PPy or PAn or PTh /alkylcarboxy pyrrole diethoxy.

5. The polymeric nanocomposite according to any one of claims 1 to 4 wherein the ratio of the first polymer to the second polymer is in the range of 1:0.05-20.0.

6. The polymeric nanocomposite according to claim 5 wherein the ratio of the first polymer to the second polymer is 1:1.5.

7. The polymeric nanocomposite according to any one of claims 1 to 6 further comprising nanotubes .

8. The polymeric nanocomposite according to claim 7 wherein the second conducting polymer acts as a stabiliser for the nanotubes .

9. The polymeric nanocomposite according to claim 7 or 8 wherein the nanotubes are multi walled carbon nanotubes (MWNT) .

10. The polymeric nanocomposite according to claim 9 wherein the amount of nanotubes is less than 32%w/v.

11. The polymeric nanocomposite according to claim 10 wherein the amount of nanotubes is in the range of 10% w/v to 32%w/v.

12. The polymeric nanocomposite according to claim 9 wherein the polymeric nanocomposite is PAn/PMAS/MWNT.

13. The polymeric nanocomposite of claim 12 wherein the ratio of PAn/PMAS/MWNT is 1:2.2:1.35.

14. The polymeric nanocomposite according to any one of claims 1 to 13 wherein the nanocomposite comprises nanofibres with diameters in the range of 30 to 50nm and lengths in the range of 100 to 50,000nm and nanoparticles with diameters in the range of 20 to lOOnm.

15. The polymeric nanocomposite according to claim 14 wherein the lengths of nanofibres are in the range of 100 to 5000nm.

16. The polymeric nanocomposite according to any one of claims 1 to 15 which is in the form of a nanodispersion wherein the nanocomposite is dispersed in an aqueous solution .

17. The polymeric nanocomposite according to claim 16 wherein the amount of nanocomposite in the nanodispersion is in the range of 0.1 to 15%w/v.

18. The polymeric nanocomposite according to claim 17 wherein the amount of nanocomposite in the nanodispersion is in the range of 0.1 to 1.0%w/v.

19. A method for preparing an electrically conducting polymeric nanocomposite comprising polymerisation of the constituent monomer (s) of a first electrically conducting polymer in the presence of the second electrically conducting polymer which acts as a dopant of the first electrically conducting polymer.

20. The method according to claim 19 further comprising dispersing nanotubes in the second electrically conducting polymer.

21. The method according to claim 20 or 21 wherein the second electrically conducting polymer acts as a stabiliser for the nanotubes.

22. The method according to any one of claims 19 to 21, wherein the polymerisation of the first polymer is performed using oxidation.

23. A device which is composed wholly or partly of the polymeric nanocomposite according to any one of claims 1 to 18.

24. The device according to claim 23 which is an optical or electrochemical device.

25. The device according to claim 24 wherein the electrochemical device is an electrochromic device .

26. An electrochromic device, comprising:

(a) a first electrically conducting substrate; (b) a second electrically conducting substrate spaced apart from said first substrate;

(c) a first electrically conducting electrochromic polymeric nanocomposite layer deposited on surface of the first substrate layer facing the second substrate layer,-

(d) a second electrochromic polymer layer deposited onto the surface of said second substrate facing said first substrate, and

27. The device according to claim 26, wherein the polymeric nanocomposite is selected from the group consisting of polyaniline (PAn) / poly (2-methoxyaniline-5- sulfonic acid) (PMAS), Polypyrrole (PPy)/ PMAS, polythiophene (PTh) /PMAS, PAn / polypyrrole- sulphonic acid, PPy/ polypyrrole- sulphonic acid, polythiophene (PTh) / polypyrrole- sulphonic acid, PAn / polythiophene- sulphonic acid, PPy / polythiophene- sulphonic acid, PTh / polythiophene- sulphonic acid, PPy or PAn or PTh/methoxyaniline (POMA) , PPy or PAn or PTh /alkylcarboxy pyrrole diethoxy, and PAn/PMAS/multi-walled carbon nanotubes (MWNT) .

28. The device according to claim 26 or 27 further comprising an electrolyte located between the first and second electrochromic layers.

29. The device according to claim 26 or 27 wherein one of the substrate layers is reflective or includes a reflective layer.

30. The device according to claim 27 wherein the nanocomposite is PAn/PMAS/MWNT.

31. The device according to claim 30 wherein the amount of MWT in the nanocomposite layer is less than 32%w/v.

32. The device according to claim 31 wherein the amount of nanotubes in the nanocomposite layer is in the range of 20%w/v to 32%w/v.

33. The device according to claim 26 or 27 wherein the second electrochromic polymer is a second polymeric nanocomposite.

34. A method for constructing an electrochromic device, comprising at least one electrochromic nanocomposite layer which comprises the steps of: (a) applying a first conductive material to a first substrate so as to form a first electrode layer;

(d) applying a second conductive material to the second electrochromic layer so as to form a counter electrode layer;

(e) applying a protective layer to the counter electrode layer, thereby forming a substantially transparent electrochromic device, the device having an optical transparency that varies with voltage applied between the electrodes.

35. The method according to claim 34 wherein the second electrochromic polymer is a second polymeric nanocomposite and the layer is formed by applying a nanodispersion containing the second polymeric nanocomposite to the first electrochromic layer.

36. The method according to claim 33 or 34 further including the step of laying a reflective layer between the first substrate and the first electrode.

37. The method according to claim 33 or 34 wherein the first substrate has a reflective surface.

38. The method according to claim 33 or 34 wherein the nanodispersion is applied using an inkjet printer or airbrush sprayer.

39. The method according to claim 33 or 34 wherein the polymeric nanocomposite is selected from the group consisting of polyaniline (PAn) / poly (2-methoxyaniline-5- sulfonic acid) (PMAS), polypyrrole (PPy)/ PMAS, polythiophene (PTh) /PMAS, PAn / polypyrrole- sulphonic acid, PPy/ polypyrrole- sulphonic acid, polythiophene

(PTh)/ polypyrrole- sulphonic acid, PAn / polythiophene- sulphonic acid, PPy / polythiophene- sulphonic acid, PTh / polythiophene- sulphonic acid, PPy or PAn or PTh/methoxyaniline (POMA) , PPy or PAn or PTh /alkylcarboxy pyrrole diethoxy, and PAn/PMAS/multi-walled carbon nanotubes (MWNT) .

40. The method according to claim 39 wherein the nanocomposite is PAn/PMAS/MWNT.

41. The method according to claim 33 or 34 wherein the first substrate is stored on a first roll, and end of the first roll is fed onto a second roll and an electrochromic device is printed onto the substrate exposed between the first and second rolls.

42. A method for printing an electrically conducting nanocomposite stratum using an inkjet printer to apply one or more electrically conducting nanocomposite layers onto a substrate layer; wherein the inkjet printer prints a nanodispersion containing an electrically conducting nanocomposite comprising a first electrically conducting polymer and a second electrically conducting polymer which acts as a dopant of the first electrically conducting polymer.

43. The method according to claim 42 wherein the electrically conducting nanocomposite is electrochromic.

44. The method according to claim 42 wherein the electrically conducting nanocomposite is electroactive .