Conductive nanocomposites

Abstract

Conductive or semiconductive nanoparticles are modified with conductive ligands so as to be able to obtain conductive or semiconductive layers without requiring a thermal treatment for forming the structures upon application of the layers. A composition can include a matrix polymer for producing conductive composites.

Claims

1. A composition for producing conductive layers by wet coating, comprising: a) a plurality of conductive metallic nanostructures, b) a conductive polymer or oligomer based on thiophene; and c) at least one solvent, wherein the conductive polymer or oligomer has heteroatoms of the thiophene that form at least ten coordinate bonds to surfaces of the plurality of metallic nanostructures.

2. The composition as claimed in claim 1, wherein the nanostructures are nanorods having an aspect ratio of length to diameter of at least 2:1.

3. The composition as claimed in claim 1, wherein the composition further comprises a matrix polymer.

4. The composition as claimed in claim 3, wherein the matrix polymer is present as a solution in the composition.

5. The composition as claimed in claim 3, wherein the matrix polymer comprises polystyrene, polyacrylate, polyvinyl alcohol, or polyvinylpyrrolidone.

6. The composition as claimed in claim 1, wherein the at least one solvent comprises solvents or solvent mixtures of solvents having in each case a boiling point below 120° C.

7. A process for producing a conductive layer on a surface, comprising: a) applying a composition as claimed in claim 1 to a surface; and b) removing the at least one solvent.

8. The process as claimed in claim 7, wherein the process does not comprise any treatment of the coating at temperatures above 60° C. after application to the surface.

9. A composite material, comprising: a composition as claimed in claim 1; and at least one matrix polymer.

10. A process for producing a composition as claimed in claim 1, comprising: a) providing a dispersion of conductive metallic nanostructures, with the dispersion being stabilized by at least one first ligand; b) adding the conductive polymer or oligomer; and c) replacing at least part of the first ligand by the conductive polymer or oligomer.

11. A display comprising the composite material as claimed in claim 9.

12. A conductor track comprising the composite material as claimed in claim 9.

13. A circuit comprising the composite material as claimed in claim 9.

14. A capacitor comprising the composite material as claimed in claim 9.

15. A solar cell comprising the composite material as claimed in claim 9.

16. The composition as claimed in claim 1, wherein the conductive polymer or oligomer comprises ethylene-3,4-dioxythiophene, 2-(3-thienyl)ethoxy-4-butylsulfonate, poly(ethylene-3,4-dioxythiophene), or poly(2-(3-thienyl)ethoxy-4-butylsulfonate).

17. The composition as claimed in claim 1, wherein the conductive polymer or oligomer has a side chain having at least one polar side group.

18. The composition as claimed in claim 1, wherein the metallic nanostructures comprise a metal, mixture of two or more metals, or an alloy of two or more metals.

19. The composition as claimed in claim 1, wherein the metallic nanostructures comprise gold, silver, copper, platinum, palladium, nickel, ruthenium, indium or rhodium.

20. The composition as claimed in claim 1, wherein the at conductive polymer or oligomer adsorbs on the nanostructure via its conjugated pi system or directly via a functionality in or in the direct vicinity of the conductive polymer backbone.

21. The composition as claimed in claim 1, wherein the at conductive polymer or oligomer has a molecular mass of at least 5 kDa.

22. The composition as claimed in claim 1, wherein the nanostructures are present in at least 10% by weight, based on the composition without solvent.

23. The composition as claimed in claim 1, wherein a degree of coverage of a nanostructure with the conductive polymer or oligomer is at least one monolayer on the total nanostructure surface.

24. A composition, comprising: a plurality of metallic nanorods; a conductive polymer or oligomer comprising a thiophene, wherein heteroatoms of the thiophene form at least ten coordinate bonds to a surface of the metallic nanorods; and at least one solvent comprising water, an alcohol, a ketone, an ether, or mixtures thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematic depiction of a structure according to the invention; A: nanostructure; B: conductive ligand; C: air or matrix;

(2) FIG. 2 schematic depiction of an embodiment of the conductive ligand (B1: conductive polymer backbone; B2: side chain covalently bound to the polymer backbone);

(3) FIG. 3 a) transmission electron micrographs of gold nanorods with CTAB (AuNR@CTAB), scale bars: top: 400 nm; bottom: 100 nm; b) transmission electron micrographs showing gold nanorods with ligands according to the invention, scale bars: top: 200 nm; bottom: 50 nm;

(4) FIG. 4 UV-VIS spectra of the nanostructures and the ligands; wavelength is plotted against absorbance (A: pure ligand; B: gold nanostructure with CTAB as ligand; C: gold nanostructure with ligand according to the invention);

(5) FIG. 5 IR spectra of the nanostructures and the ligands; the wave number is plotted against the intensity (A: pure ligand; B: gold nanostructure with CTAB as ligand; C: gold nanostructure with ligand according to the invention);

(6) FIG. 6 Raman spectra of the nanostructures in each case before and after ligand exchange; the Raman shift is plotted against the normalized intensity (B: gold nanostructure with CTAB as ligand; C: gold nanostructure with ligand according to the invention);

(7) FIG. 7 absorbance of dispersions of AuNR@CTAB in various solvents (A: water; B: water/methanol (25/75; v/v); C: water/acetone (25/75; v/v); the wavelength is plotted against the absorbance;

(8) FIG. 8 absorbance of dispersions of gold nanorods with ligands according to the invention in various solvents (A: water; B: water/methanol (25/75; v/v); C: water/acetone (25/75; v/v); the wavelength is plotted against the absorbance;

(9) FIG. 9 current/voltage graph for various coatings (C1: gold nanorods modified by means of PEG-SH; C2: gold nanorods modified by means of PEG-SH after O.sub.2 plasma treatment (resistance R=2.7Ω); C3: gold nanorods with ligands according to the invention (resistance R=11.5Ω); the voltage is plotted against the current;

(10) FIG. 10 scanning electron micrographs of coatings produced ((a) gold nanorods with ligands according to the invention; (b) gold nanorods modified by means of PEG-SH; (c) gold nanorods modified by means of PEG-SH after O.sub.2 plasma treatment;

(11) FIG. 11 scanning electron micrographs of composites.

DETAILED DESCRIPTION OF INVENTION

(12) FIG. 1 shows a schematic depiction of the composition according to the invention comprising nanorods. On the surface (type I) or in a matrix (type II), the nanorods adjoin one another in such a way that they form a conductive linear structure. The conductivity is increased by the significantly smaller number of interfaces along this structure.

(13) FIG. 2 shows a schematic depiction of a ligand according to the invention with polymer backbone and side chains.

(14) FIG. 3 shows that the structure of the gold nanorods and the ligand shell is retained on exchange of the ligands.

(15) FIG. 4 shows UV-VIS spectra in water of the particles with CTAB (B), the pure ligand (A) and gold nanorods with ligands according to the invention (C). It can be seen that the replacement of the ligands shifts the absorption maximum at 900 nm slightly. The smaller graph shows a section from the subtraction of the spectra of the two modified nanostructures (C-B). The maximum of the ligand at 410 nm can then clearly be discerned from the subtraction.

(16) FIG. 5 shows the IR spectra of the gold nanorods with CTAB (AuNR@CTAB, B), the pure ligand (A) and gold nanorods with ligands according to the invention (C). The characteristic bands of the ligand (A) can be seen in the case of the modified gold nanorods (C). These are missing in the case of the CTAB-modified gold nanorods. This indicates that the ligand has been adsorbed on the surface of the particles.

(17) FIG. 6 shows the Raman spectra (785 nm laser) of the gold nanorods with CTAB (AuNR@CTAB, B) and the gold nanorods with ligands according to the invention (C). In the case of the gold nanorods which have been modified according to the invention, the band at 278 cm.sup.−1 of an Au—S band can be seen, while the band at 182 cm.sup.−1 typical of an Au—Br bond is not to be seen. This shows that an interaction of the thiophene backbone with the surface of the gold nanorods occurs. Control experiments using thiophene on gold surfaces showed a similar pattern as the polythiophene ligand.

(18) FIGS. 7 and 8 show the stability of the dispersions in various solvents. These solvents are pure water (A), methanol/water (75/25, v/v) (B) and acetone/water (75/25, v/v). While the dispersions with ligands according to the invention were in all cases stable for at least six months and displayed virtually no change in the absorbance, the CTAB-modified gold nanorods are stable only in water. Even small amounts of other solvents lead to agglomeration and a large change in the absorption spectrum.

(19) FIG. 9 shows current-voltage graphs for coatings obtained. The coatings composed of gold nanorods modified by means of PEG-SH (25 kDa) displayed no conductivity (C1). When these coatings were treated by means of an oxygen plasma for 30 minutes, they became conductive (C2). Raman measurements, however, show that the PEG-SH ligand is also removed thereby, as a result of which direct metal-metal contact is established.

(20) The layers composed of the gold nanorods with ligands according to the invention are conductive immediately after drying without any further treatment.

(21) FIG. 10 shows scanning electron micrographs of surfaces of the various modified gold nanorods.

(22) FIG. 11 shows scanning electron micrographs of a conductive composite type II (this is gold nanorods with a conductive polymer as ligand, embedded in a PMMA matrix; the composite was produced by drop casting of an ink comprising these components in a solvent mixture of acetone and water 95.5/2.5 (v/v).

(23) The composite shown is conductive and displays a resistance of 45Ω.

(24) The matrix polymer can, for example, serve as “protective layer” or as insulating layer between a plurality of conductive layers. The nanostructure of the particle is also fixed by the matrix polymer and is thus more mechanically stable.

(25) Numerous modifications and developments of the working examples described can be realized.

LITERATURE CITED

(26) Kanehara et al. Angew. Chem. Int. Ed. 2008, 47, 307-310; Abe et al. Organic Electronics 2014, 15, 3465-3470; Minari et al. Adv. Funct. Mater. 2014, 24, 4886-4892 US 2013/0001479 A1 US 2007/0057255 A1 Englebienne et al. J. Coll. Interface Sci. 2005, 292, 445-454; U.S. Pat. No. 7,686,983 Ye et al. Nano Lett. 2013, 13, 765-771; Liu et al. Nanoscale 2013, 5, 7936-7941; Zhang et al. Adv. Mater. 2012, 24, 82-87; Colle et al. Phys. Status Solidi B 2011, 248, 1360-1368.