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 or semiconductive layers by wet coating, comprising: a) at least one type of conductive or semiconductive nanostructures, wherein at least one conductive ligand is arranged on a surface of the nanostructures; and b) at least one solvent.

2. The composition as claimed in claim 1, wherein the ligand is a conductive polymer or oligomer based on thiophene.

3. 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.

4. The composition as claimed in claim 1, wherein the at least one conductive ligand comprises a polymer or oligomer having at least ten bonding positions which make coordinate bonding to the surface of the nanostructure possible.

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

6. The composition as claimed in claim 5, wherein the matrix polymer is present as a solution in the composition.

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

8. The composition as claimed in claim 1, wherein the nanostructure is a metallic nanostructure.

9. 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.

10. A process for producing a conductive or semiconductive layer on a surface, comprising: a) application of a composition as claimed in claim 1 to a surface; b) removal of the at least one solvent.

11. The process as claimed in claim 10, wherein the process does not comprise any treatment of the coating at temperatures above 60? C. after application to the surface.

12. A conductive or semiconductive structure obtained by the process as claimed in claim 10.

13. A composite material, comprising: a conductive or semiconductive nanostructure, at least one conductive ligand, and at least one matrix polymer.

14. (canceled)

15. A process for producing a composition as claimed in claim 1, comprising: a) provision of a dispersion of conductive or semiconductive nanostructures, with the dispersion being stabilized by at least one first ligand; b) addition of at least one conductive ligand; c) replacement of at least part of the first ligand by the at least one conductive ligand.

16. A display comprising the composite material as claimed in claim 13.

17. A conductor track comprising the composite material as claimed in claim 13.

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

19. A capacitor comprising the composite material as claimed in claim 13.

20. A solar cell comprising the composite material as claimed in claim 13.

Description

[0122] The working examples are schematically depicted in the figures. Identical reference symbols in the individual figures denote identical elements or elements which have the same function or correspond to one another in respect of their functions. In detail, the figures show:

[0123] FIG. 1 schematic depiction of a structure according to the invention; A: nanostructure; B: conductive ligand; C: air or matrix;

[0124] FIG. 2 schematic depiction of an embodiment of the conductive ligand (B1: conductive polymer backbone; B2: side chain covalently bound to the polymer backbone);

[0125] 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;

[0126] 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);

[0127] 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);

[0128] 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);

[0129] 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;

[0130] 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;

[0131] 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=2.7?); C3: gold nanorods with ligands according to the invention (resistance R=11.5?); the voltage is plotted against the current;

[0132] 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;

[0133] FIG. 11 scanning electron micrographs of composites.

[0134] 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.

[0135] FIG. 2 shows a schematic depiction of a ligand according to the invention with polymer backbone and side chains.

[0136] FIG. 3 shows that the structure of the gold nanorods and the ligand shell is retained on exchange of the ligands.

[0137] 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.

[0138] 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.

[0139] 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 AuS band can be seen, while the band at 182 cm.sup.?1 typical of an AuBr 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.

[0140] 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.

[0141] 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.

[0142] The layers composed of the gold nanorods with ligands according to the invention are conductive immediately after drying without any further treatment.

[0143] FIG. 10 shows scanning electron micrographs of surfaces of the various modified gold nanorods.

[0144] 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).

[0145] The composite shown is conductive and displays a resistance of 45?.

[0146] 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.

[0147] Numerous modifications and developments of the working examples described can be realized.

LITERATURE CITED

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