Title of Invention: NANOCOMPOSITE CASTING COMPOSITION

Technical Field

[1] The present invention relates to nanocomposite casting composition and method for casting, particularly for sensing electrode applications.

Background Art

[2] Conducting polymers are typically prepared by polymerizing pyrrole, aniline and thiophene monomers. The three monomers incorporate different heteroatoms into its structures - nitrogen atom is within the 5-membered ring of pyrrole and sulfur is part of the thiophene ring structure. While all the monomers are aromatically stabilized, pyrrole and thiophene needs to lose one of its six-electron aromatic system during oxidative polymerization, whereas, aniline loses its amine lone pair electron (Scheme 1). The oxidation potentials of the monomers also reveals that it is much more difficult to remove an electron from thiophene (oxidation potential of 1.7V versus SCE) compared to that of pyrrole (oxidation potential of 0.8V versus SCE). The implication of the high energy required to oxidize thiophene is the inefficiency of typical po- tentiostat setup to directly polymerized thiophene onto electrode surface such as screen printed carbon.

[3] [Chem. l]

[5] Scheme 1 : Oxidation potentials for un-substituted pyrrole, aniline and thiophene monomers

[6] US 6, 621, 099 disclosed an electronic device containing a polythiophene of Formula

(I)

[Chem.2]

[7] wherein R and R' are side chains; A is a divalent linkage; x and y represent the

number of unsubstituted thienylene units; z is 0 or 1, and wherein the sum of x and y is greater than about zero; m represents the number of segments; and n represents the degree of polymerization.

[8] US 2007/0117961 A 1 disclosed polythiophene may be processed using a method including providing a composition including the polythiophene and a liquid including at least one hydrocarbon having at least 6 carbon atoms; heating the composition to a temperature of at least about 50.degree. C; and separating solid polythiophene from the heated composition. Alternatively, the method may include providing a composition including polythiophene and an organic liquid; heating the composition to dissolve a portion of the polythiophene in the organic liquid; and separating solid polythiophene from the heated composition.

[9] US7,972,537 B2 disclosed a carbon nanotube-conductive polymer composite

includes a plurality of CNTs and conductive polymer fibers. The CNTs are connected with each other to form a network. The conductive polymer fibers adhere to surfaces of the CNTs and/or tube walls of the CNTs.

[10] US 7,691,533 disclosed the invention provides an electrode comprising a collector with electron conductivity and an electrode active material-containing layer with electron conductivity formed on the collector, wherein the electrode active material- containing layer includes conductive polymer-covered carbon nanotubes.

[11] High oxidation potential of thiophene and the tendency of the electrodes to short when miniaturized electrodes are immersed in monomer electrolytes are major setback in the utilization of thiophene for sensing electrode application. Therefore, there is a need to provide a casting composition and an improved method for casting thiophene for sensing electrode.

Disclosure of Invention

Technical Problem

Summary

[12] According to a first aspect of the invention, there is provided a doped polythiophene nanocomposite casting composition comprising; conductive polythiophene, dopant; organic binder; crosslinker; carbon nanotubes; and chemical diluents. The provision of the doped polythiophene nanocomposite casting composition is advantageous as the composition improves efficiency of polymerizing thiophene onto an electrode.

[13] Accordingly, the organic binder is selected from acrylate copolymer or

polysaccharide.

[14] Accordingly, the conducting polythiophene comprises at least one or combination of the following monomers; thiophene, bithiophene, 3-hexyl thiophene, 3-octyl thiophene.

[ 15] Accordingly, the conducting polythiophene having the following structure: [Ch

[16] or

[Ch

[17] Accordingly, the doped polythiophene nanocomposite comprises 0.1 to 20% polythiophene, 0.1 to 20% dopant, 40 to 90% binder and 0.1 to 20% carbon nanotubes, all by weight.

[18] Accordingly, the dopant is at least one or combination of the following dopants; chloride, tetrafluoroborate, iodide, para-toluene sulfonate, trifluoromethane sulfonate, camphor sulfonate, poly styrene sulfonate, nafion, hexafluorophosphate.

[19] Accordingly, the polysaccharide is at least one or combination of the following polysaccharides; cellulose acetate, ethyl cellulose, cellulose, chitosan, starch, gum arabic, dextrin, maltodextrin, beta-glucan, chitin, mannan, galactan, fructan.

[20] Accordingly, the acrylate copolymer comprises at least one or combination of the following monomers; tetrahydrofurfuryl acrylate, dodecyl acrylate, decyl acrylate, n- butyl acrylate, methyl methacrylate, glycidyl acrylate.

[21] Accordingly, the polysaccharide functions as a second binder and assists in passage of current.

[22] Accordingly, the chemical diluent is at least one or combination of the following polar solvents; tetrahydrofuran, dichloromethane, diethyl ether, chloroform, acetone, ethanol, iso-propanol, propanol, dimethyl formamide, dimethyl sulfoxide, N-methyl pyrrolidone.

[23] According to a second aspect of the invention, there is provided a method of

preparing the doped polythiophene nanocomposite casting composition comprising the steps of;

[24] (a) dispersing carbon nanotubes in a solvent;

[25] (b) mixing binder with dispersed CNT;

[26] (c) mixing dopant with homogenous CNT-binder;

[27] (d) mixing thiophene monomers with CNT solution; and

[28] (e) polymerizing thiophene by chemical or electrochemical method.

[29] Accordingly, step (e) further comprises the steps of; adding catalytic amount of oxidizing agent into the homogenous mixture of step (d); and heating the homogenous mixture. [30] Preferably, the oxidizing agent to afford polymerization of thiophene monomers comprises is selected from at least one or combination of the following chemicals; ferric chloride, hydrogen peroxide, sodium persulfate, chlorine, nitric acid, sulphuric acid, persulfuric acid, chlorite, osmium tetroxide, permanganate, hypochlorite, chlorate, dichromate.

[31] Accordingly, the preparation of doped polythiophene nanocomposite casting composition is applicable for application such as in electrical transducer for sub-ppm chemical sensor, membrane-less chemical sensors for aquaculture and environmental monitoring, printable organic transistor, solar cells, or super capacitor.

[32] Advantageously, the polythiophene nanocomposites casting composition dispense onto electrode surface improves adhesion when dried to withstand harsh environmental conditions and high acidity or alkalinity upon application.

Brief Description of Drawings

[33] The embodiments of the invention will now be described, by way of example only, with reference to the accompanying figure in which:

[34] Figure 1: illustrated doped (bottom) and de-doped (top) polythiophene.

[35] Figure 2: illustrates doped polythiophene nanocomposite with aery late binder.

[36] Figure 3: illustrates doped polythiophene nanocomposite with polysaccharide

binder.

[37] Figure 4: illustrates self-doped polythiophene co-polymer used in the conductive nanocomposite.

[38] Figure 5: illustrates chart for preparation of polythiophene nanocomposite casting composition.

[39] Figure 6: illustrates freshly prepared homogenous polythiophene nanocomposite solution.

[40] Figure 7: illustrates cyclic voltammetry plot of cast polythiophene nanocomposite on screen printed carbon electrode in 0.1 M KC1 solution.

[41] Figure 8: illustrates SEM picture of polythiophene nanocomposite on screen printed carbon electrode.

Best Mode for Carrying out the Invention

Detailed Description of The Preferred Embodiment

[42] Polythiophene has two major forms, the doped and de-doped forms, as illustrated in Figure 1. Figure.l.a illustrates polythiophene in doped form and Figure.l.b illustrates polythiophene in de-doped form. In one embodiment of the present invention, a doped polythiophene nanocomposite casting composition comprises homogenously dispersed carbon nanotubes for casting or printing applications. The doped polythiophene nanocomposite casting composition comprising conductive polythiophene, dopant; organic binder; crosslinker; carbon nanotubes; and chemical diluents; wherein the conductive polythiophene is able of self-doping.

[43] In one preferred embodiment as illustrated in Figure. 2, the polythiophene nanocomposite casting composition comprises; conductive polythiophene; a dopant; acrylate copolymer, heat curable binder; diamine crosslinker; carbon nanotubes and chemical diluents.

[44] In another preferred embodiment; the polythiophene nanocomposite casting composition illustrated in Figure. 3 comprises; self-doped conductive polythiophene; dopant; uncharged polysaccharide as a binder; charged polysaccharides for stabilizing negative charge of dopant anions and allow passage of current, carbon nanotube as conducting material for electrical current and substrate for growing polythiophene; chemical diluents as solvents to dilute the nanocomposites.

[45] The self-doped conductive polythiophene provides electrochemical transduction for sensor functionality. Organic binder preferably low impedance acrylate copolymer functions to bind all components together and allow passage of current, crosslinker molecules to cross link between strands of heat curable polymers, whereas ionizable polysaccharide function to bind all components together and allow passage of current, the carbon nanotubes functions as conducting material for electrical current, substrate for growing polythiophene and the chemical diluents functions as solvents to dilute the nanocomposites in order to achieve desired viscosity of the composition.

[46] In a preferred embodiment the polythiophene is polymerized onto carbon nanotubes surface, wherein the nanotubes are homogeneously dispersed in organic solvent. The polythiophene-CNT nanocomposite should remain homogenously dispersed after the polymerization. In another preferred embodiment low impedance and heat curable organic binder and crosslinker are homogenously blended in the polythiophene-CNT solution with the selected solvents. Polysaccharides are also used as binder and in preferred embodiment the polysaccharide reacts with sulfonic acid dopant to produce charged polysaccharide and organic sulfonate dopant. In yet another preferred embodiment the dopant is negatively charged species and functions as counter-ion to the positively charged conductive polythiophene, and the dopants form homogenous blend with the rest of the nanocomposite components.

[47] The polythiophene nanocomposite solution comprises doped polythiophene, grown on carbon nanotubes, well dispersed in organic solvent. In a preferred embodiment the whole mixture of the nanocomposite components are homogenously dissolved and dispersed in water-free or all-organic solvent system. Sulfonated polythiophene copolymer is polymerized onto carbon nanotubes, well dispersed in suitable all-organic solvent system as illustrated in Figure. 4.

[48] Figure.5 illustrates flow chart for method of preparing doped polythiophene

nanocomposite casting composition. In general, a method of preparing doped polythiophene nanocomposite casting composition comprising the steps of; (a) dispersing carbon nanotubes in a solvent; (b) mixing binder with dispersed CNT; (c) mixing dopant with homogenous CNT-binder; (d) mixing thiophene monomers with CNT solution; and(e) polymerizing thiophene by chemical or electrochemical method. Step (e) further comprises the steps of; adding catalytic amount of oxidizing agent into the homogenous mixture of step (d); and heating the homogenous mixture.

[49] In a more detailed example, the method of preparing doped polythiophene

nanocomposite casting solution involves five main steps. In the first step, carbon nanotubes are dispersed in organic solvent to produce homogenous CNT solution. In the second step, organic binder such as heat curable acrylate copolymer or cellulose acetate is added to the CNT solution to produce homogenous blend of binder and CNT in organic solvent or mixture of solvent system. It is critical to ensure at this stage that the CNT-binder blend is fully dispersed and there are no floating particles, precipitate at the bottom or sticking materials at the wall of the container. If there are precipitates or floating or sticking particles, a different mixture of solvent is needed before polymerization can take place. In the fourth step, thiophene monomer or mixture of substituted monomers are added into the CNT-binder solution. Finally, the thiophene monomer or mixture of monomers is polymerized onto the dispersed carbon nanotubes to produce the nanocomposite solution.

[50] Preferably strong oxidizing agents is used to induce the oxidative polymerization.

[51] Alternatively electrochemical method can be used, but the monomer and the dopant should reduce the oxidation potential for polymerization. Again, it is crucial that all the components in the mixture remains homogenously blended together and fully dispersed in the solvent system. In the case of heat curable acrylate copolymer binder diamine crosslinker is added in the polythiophene solution, or alternatively it can be mixed together before application on electrode surface i.e. the crosslinker is stored separately from the polythiophene solution.

[52] Accordingly, the doped polythiophene nanocomposite casting composition

comprises at least one or combination of the following monomers; thiophene, bithiophene, 3-hexyl thiophene, 3-octyl thiophene.

[53] Accordingly, the conducting polythiophene having at least the following structure;

[Chem.5]

[54] or

[Chem.6]

[55] Accordingly, the doped polythiophene nanocomposite comprises 0.1 to 20% polythiophene, 0.1 to 20% dopant, 40 to 90% binder and 0.1 to 20% carbon nanotubes, all by weight. [56] Accordingly, the dopant is selected from at least one or combination of the following dopants; chloride, tetrafluoroborate, iodide, para-toluene sulfonate, trifluoromethane sulfonate, camphor sulfonate, poly styrene sulfonate, nafion, hexafluorophosphate.

[57] Accordingly, the polysaccharide is selected from at least one or combination of the following polysaccharides; cellulose acetate, ethyl cellulose, cellulose, chitosan, starch, gum arabic, dextrin, maltodextrin, beta-glucan, chitin, mannan, galactan, fructan. The selected polysaccharides also functions as a second binder and assist in passage of current.

[58] Accordingly, the chemical diluent is selected from at least one or combination of the following polar solvents; tetrahydrofuran, dichloromethane, diethyl ether, chloroform, acetone, ethanol, iso-propanol, propanol, dimethyl formamide, dimethyl sulfoxide, N- methyl pyrrolidone.

[59] Accordingly, the oxidizing agent to afford polymerization of thiophene monomers comprises at least one or combination of the following chemicals; ferric chloride, hydrogen peroxide, sodium persulfate, chlorine, nitric acid, sulphuric acid, persulfuric acid, chlorite, osmium tetroxide, permanganate, hypochlorite, chlorate, dichromate.

[60] The preparation of doped polythiophene nanocomposite casting composition is applicable for application such as in electrical transducer for sub-ppm chemical sensor, membrane-less chemical sensors for aquaculture and environmental monitoring, printable organic transistor, solar cells, or super capacitor.

[61] It is a requirement for the intended applications that the polythiophene

nanocomposites give good adhesion with the substrate. The cast polythiophene coat must be able to withstand harsh environmental conditions, high acidity or alkalinity from delamination or fouling. It is also required that the polythiophene composition remains homogenous in the selected solvents without precipitation at the bottom of the container or agglomeration of materials in the solution or floating on the surface of the solution. It is further required that none of the component in the polythiophene solution sticks to the wall of the container.

[62] Advantageously, the polythiophene nanocomposites casting composition of present invention improves efficiency of polymerizing thiophene onto an electrode.

[63] Advantageously, the polythiophene nanocomposites casting composition dispense onto electrode surface improves adhesion when dried to withstand harsh environmental conditions and high acidity or alkalinity upon application.

[64] Examples

[65] The invention is further described but not limited to the following examples.

[66] Example 1

[67] Preparation of Polythiophene Nanocomposite Casting Composition with

[68] Low Impedance Acrylate Copolymer Binder

[69] Polythiophene nanocomposite casting composition with low impedance acrylate copolymer binder was prepared by the following procedure: Single wall carbon nanotubes (1 weight percent) were dispersed in N-methyl pyrrolidone solution of poly (vinyl pyrrolidone). Homogenous dispersion is achieved by sonication for at least 30 minutes. Acrylate copolymer; methyl methacrylate, glycidyl methacrylate and tetrahy- drorurfuryl, in 1: 1 : 1 ratio, was prepared by bulk copolymerization in toluene with catalytic amount of benzoyl peroxide initiator. The unreacted monomers were removed by cleaning with acetone. The dried acrylate copolymer (3 weight percent) was dissolved in dichloromethane and mixed with dispersed nanotube solution until homogenous mixture was achieved. One monomer or mixture of monomers - thiophene, 3-alkyl thiophene and thiophene (3-alkyl sulfonic acid) were added into the ho- mogenously doped CNT-acrylate copolymer solution. One equivalent of ferric chloride in chloroform was added and the final mixture was transferred into a round bottom flask equipped with reflux condenser, addition funnel and nitrogen inlet. Catalytic amount of hydrogen peroxide was added to start oxidative polymerization of the monomers onto the CNT surface within the acrylate copolymer matrix. Diamine crosslmker (para-xylylene diamine, 1 weight percent) was added prior to casting of the composition onto printed carbon well.

[70] Example 2

[7 ] Preparation of Poly thiophene Nanocomposite Casting Composition

[72] with Polysaccharide Binder

[73] Polythiophene nanocomposite casting composition was prepared by the following procedure: Single wall carbon nanotubes (1 weight percent) were dispersed in N- methyl pyrrolidone solution of poly (vinyl pyrrolidone). Homogenous dispersion is achieved by sonication for at least 30 minutes. Cellulose acetate solution (3 weight percent) in tetrahydrofuran is added to the well dispersed CNT solution. Camphor sulfonic acid dopant is added to the CNT-binder solution to produce homogenous solution with 1 equivalent of sulfonic acid dopant to 4 equivalents of thiophene monomers. In case precipitation occurs ethanol is added to dissolve the precipitates and the remaining solid materials removed and the mixture sonicated for at least additional 30 minutes. One monomer or mixture of monomers - thiophene, 3-alkyl thiophene and thiophene (3-alkyl sulfonic acid) were added into the homogenously doped CNT-polysaccharide solution. One equivalent of ferric chloride in chloroform was added and the final mixture was transferred into a round bottom flask equipped with reflux condenser, addition funnel and nitrogen inlet. Catalytic amount of hydrogen peroxide was added to start oxidative polymerization of the monomers onto the CNT surface within the polysaccharide matrix. Figure. 6 illustrates freshly prepared homogenous polythiophene nanocomposite solution

[74] Example 3

[75] Fabrication and Characterization of Cast Polythiophene Nanocomposite

Electrode

[76] Silver paste (2 -4mm diameter) was screen printed on FR4 substrate. The printed silver was oven cured at 120 °C for 30 minutes to afford 100 micrometer thickness of dried silver. The process was repeated with carbon paste and it was screen printed on top of the dried silver paste, and cured gives 100 micrometer thickness of the printed carbon. The whole electrode surface was covered with screen printed epoxy or solder mask, only to expose the carbon electrode area and contact pins for electrical connections. Doped polythiophene nanocomposite solution prepared in Example 2 was cast (3 microliter) onto screen printed carbon electrode, cleaned with sonication. The dispensed polythiophene nanocomposite was dried under continuous flow of nitrogen gas for at least 1 hour. The dried surface was further cleaned with ethanol and deionized water before further electrochemical analysis. Figure. 7 illustrates cyclic voltammetry plot of cast polythiophene nanocomposite on screen printed carbon electrode in 0.1 M KC1 solution. Figure. 7 illustrates that the doped polythiophene electrode affords distinct oxidation and reduction peaks. Repeats of experiments prove that the redox peaks are reproducible. Scanning Electron Microscope analysis remarkably shows that the cast polythiophene nanocomposite electrode has homogenous film structure and smooth surface as illustrated in Figure. 8. Doped polythiophene nanocomposite solution prepared in Example 1 also undergoes similar fabrication method and the electrode exhibit similar characteristics.

While the preferred embodiment of the present invention has been describe, it should be understood that various changes, adaptation and modification may be made thereto. It should be understood, therefore, that the invention is not limited to details of the illustrated invention shown in the figure and that variation in such minor details will be apparent to a person skilled in the art.