Methods and devices for electrophoretic deposition of a uniform carbon nanotube composite film

• US 20090078914A1
• Filed: 09/20/2007
• Published: 03/26/2009
• Est. Priority Date: 09/20/2007
• Status: Active Grant

• Current Assignee: NuRay Technology Co., Ltd.
• Original Assignee: Xintek, Inc.
• Inventors: Liu, Jie, Gao, Bo, Geng, Huaizhi, Lu, Mei
• Granted Patent: US 7,850,874 B2
• Time in Patent Office: Days
• US Class Current: 252/502
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: B82Y 40/00 Manufacture or treatment of nanostructures
• CPC Class Codes: C01B 2202/28 Solid content in solvents
• CPC Class Codes: C01B 32/174 Derivatisation; Solubilisation; Dispersion in solvents
• CPC Class Codes: C25D 13/02 with inorganic material
• CPC Class Codes: H01J 1/304 Field-emissive cathodes
• CPC Class Codes: H01J 2201/30469 Carbon nanotubes (CNTs)
• CPC Class Codes: H01J 9/025 of field emission cathodes
• CPC Class Codes: Y10S 977/742 Carbon nanotubes, CNTs
• CPC Class Codes: Y10S 977/745 having a modified surface
• CPC Class Codes: Y10S 977/746 Modified with biological, organic, or hydrocarbon material
• CPC Class Codes: Y10S 977/748 Modified with atoms or molecules bonded to the surface
• CPC Class Codes: Y10S 977/749 Modified with dissimilar atoms or molecules substituted for carbon atoms of the cnt, e.g. impurity doping or compositional substitution

Abstract

Methods and devices are provided relating to the homogeneous deposition of a composite film of carbon nanotubes by electrophoresis. The methods comprise linking carbon nanotubes to matrix particles prior to electrophoretic deposition. The methods improve the adhesion of the composite film to the substrate and reduce the surface roughness. Carbon nanotube films and electron field emission cathodes fabricated by this process demonstrate enhanced electron field emission characteristics.

Claims

1. A method of preparing a carbon nanotube-matrix particle complex, comprising:

providing at least one carbon nanotube;

providing at least one matrix particle; and

providing at least one linker molecule having at least two functional groups, wherein a first functional group binds to the surface of the at least one matrix particle and a second functional group binds to the at least one carbon nanotube to thereby form a carbon nanotube-matrix particle complex.

2. The method of claim 1, further comprising dispersing the at least one carbon nanotube, matrix particle and linker molecule in a liquid medium, wherein at least one linker molecule links at least one carbon nanotube to the at least one matrix particle through the at least two functional groups to form a carbon nanotube-matrix particle complex.

3. The method of claim 1, wherein the matrix particle is a glass particle.

4. The method of claim 3, wherein the glass particle has a diameter of 300 nm to 3 μ

m.

5. The method of claim 1, wherein the linker molecule is an aminosilane molecule.

6. The method of claim 5, wherein the aminosilane molecule is selected from the group consisting of (3-aminopropyl) triethoxysilane (APS), (3-aminopropyl) trimethoxysilane, (3-aminopropyl) methyldiethoxysilane, (3-aminopropyl) methyldimethoxysilane, (2-aminoethyl-3-aminopropyl) triethoxysilane, (2-aminoethyl-3-aminopropyl) trimethoxysilane, and (2-aminoethyl-3-aminopropyl) methyldimethoxysilane.

7. The method of claim 5, wherein the binding of the first functional group of the aminosilane molecule to the surface of the matrix particle is through a chemical reaction between one or more alkoxy groups of the aminosilane molecule and one or more hydroxyl groups of the matrix particle.

8. The method of claim 7, wherein the matrix particle is a glass particle.

9. The method of claim 5, wherein the binding of the second functional group of the aminosilane molecule to the carbon nanotube is through an electrostatic interaction between an amino group of the aminosilane molecule and one or more oxygen-containing groups of the carbon nanotube.

10. The method of claim 1, further comprising adding dispersant to the liquid medium, wherein the dispersant is selected from the group consisting of polyvinyl pyrrolidone (PVP), polyvinyl butyral (PVB) and ethyl cellulose.

11. The method of claim 2, further comprising treating the at least one carbon nanotube with acid prior to dispersion into the liquid medium.

12. A carbon nanotube-matrix particle complex made from the method of claim 1.

13. A method of preparing a carbon nanotube-matrix particle complex, comprising:

providing at least one carbon nanotube;

providing at least one matrix particle;

providing at least one linker molecule having at least two functional groups, wherein a first functional group binds to the surface of the at least one matrix particle and a second functional group binds to the at least one carbon nanotube;

forming at least one functionalized matrix particle by dispersing the at least one linker molecule and the at least one matrix particle in an alcohol solution; and

dispersing the at least one functionalized matrix particle and the at least one carbon nanotube in a liquid medium, wherein the at least one functionalized matrix particle binds the at least one carbon nanotube to form a carbon nanotube-matrix particle complex.

14. The method of claim 13, further comprising sonicating or stirring the alcohol solution comprising the at least one linker molecule and the at least one matrix particle to form the at least one functionalized matrix particle.

15. The method of claim 13, further comprising cross-linking the at least one functionalized matrix particle by applying heat.

16. The method of claim 13, wherein the at least one matrix particle is a glass particle.

17. The method of claim 16, wherein the glass particle has a diameter of 300 nm to 3 μ

m.

18. The method of claim 13, wherein the at least one linker molecule is an aminosilane molecule.

19. The method of claim 18, wherein the aminosilane molecule is selected from the group consisting of (3-aminopropyl) triethoxysilane (APS), (3-aminopropyl) trimethoxysilane, (3-aminopropyl)methyldiethoxysilane, (3-aminopropyl) methyldimethoxysilane, (2-aminoethyl-3-aminopropyl) triethoxysilane, (2-aminoethyl-3-aminopropyl) trimethoxysilane, and (2-aminoethyl-3-aminopropyl) methyldimethoxysilane.

20. The method of claim 18, wherein the binding of the first functional group of the aminosilane molecule to the surface of the at least one matrix particle is through a chemical reaction between one or more alkoxy groups of the aminosiloxane molecule and one or more hydroxyl groups of the matrix particle.

21. The method of claim 20, wherein the at least one matrix particle is a glass particle.

22. The method of claim 18, wherein the binding of the second functional group of the aminosilane molecule to the at least one carbon nanotube is through an electrostatic interaction between an amino group of the aminosiloxane molecule and one or more oxygen-containing groups of the carbon nanotube.

23. The method of claim 13, further comprising adding dispersant to the liquid medium, wherein the dispersant is selected from the group consisting of polyvinyl pyrrolidone (PVP), polyvinyl butyral (PVB) and ethyl cellulose.

24. The method of claim 13, further comprising treating the carbon nanotubes with acid prior to dispersion into the liquid medium.

25. A carbon nanotube-matrix particle complex made from the method of claim 13.

26. A method of fabricating a uniform carbon nanotube composite film by electrophoretic deposition, comprising:

providing carbon nanotube-matrix particle complexes, wherein said complexes comprise a carbon nanotube attached to a matrix particle;

electrophoretically depositing said complexes onto a substrate surface, comprising;

immersing electrodes into a liquid medium containing the carbon nanotube-matrix particle complexes, wherein at least one of the electrodes comprises the substrate; and

applying a direct or alternating current to the immersed electrodes thereby creating an electrical field therebetween,

wherein the carbon nanotube-matrix particle complexes migrate toward and bind to the substrate surface.

27. The method of claim 26, further comprising annealing said substrate to form a uniform carbon nanotube composite film, wherein the carbon nanotubes and matrix particles are intimately mixed.

28. The method of claim 27, further comprising activation after annealing, wherein the activation comprises removing a layer of excess matrix particles from a surface of the carbon nanotube composite film to expose the carbon nanotubes, whereby the carbon nanotubes protrude from the underlying layer of matrix particles.

29. The method of claim 26, wherein the carbon nanotube-matrix particle complexes are formed by dispersing carbon nanotubes, matrix particles and linker molecules in the liquid medium, wherein at least one linker molecule links at least one carbon nanotube to each matrix particle.

30. The method of claim 26, wherein the carbon nanotube-matrix particle complexes are formed by first forming functionalized matrix particles by dispersing linker molecules and matrix particles in an alcohol solution, and subsequently dispersing the functionalized matrix particles and carbon nanotubes in the liquid medium, wherein the functionalized matrix particles bind to the carbon nanotubes to form carbon nanotube-matrix particle complexes.

31. The method of either of claims 29 or 30, wherein the matrix particles are glass particles.

32. The method of claim 31, wherein the glass particles have a diameter of 300 nm to 3 μ

m.

33. The method of either of claims 29 or 30, wherein the linker molecules are aminosilane molecules.

34. The method of claim 33, wherein the aminosilane molecules are selected from the group consisting of (3-aminopropyl) triethoxysilane (APS), (3-aminopropyl) trimethoxysilane, (3-aminopropyl) methyldiethoxysilane, (3-aminopropyl) methyldimethoxysilane, (2-aminoethyl-3-aminopropyl) triethoxysilane, (2-aminoethyl-3-aminopropyl) trimethoxysilane, and (2-aminoethyl-3-aminopropyl) methyldimethoxysilane.

35. The method of claim 33, wherein the binding of the first functional group of the aminosilane molecules to the surface of the matrix particles is through a chemical reaction between one or more alkoxy groups of the aminosilane molecules and one or more hydroxyl groups of the matrix particles.

36. The method of claim 35, wherein the matrix particles are glass particles.

37. The method of claim 33, wherein the binding of the second functional group of the aminosilane molecules to the carbon nanotubes is through an electrostatic interaction between an amino group of the aminosiloxane molecules and one or more oxygen-containing groups of the carbon nanotubes.

38. The method of claim 26, further comprising adding dispersant to the liquid medium, wherein the dispersant is selected from the group consisting of polyvinyl pyrrolidone (PVP), polyvinyl butyral (PVB) and ethyl cellulose.

39. The method of claim 26, wherein the material of the substrate is selected from the group consisting of stainless steel, molybdenum, tungsten, and indium tin oxide.

40. The method of either of claims 29 or 30, further comprising treating the carbon nanotubes with acid prior to dispersion into the liquid medium.

41. The method of claim 26, wherein the composite film is substantially smoother and more homogenous than a carbon nanotube composite film fabricated without linker molecules.

42. The method of claim 41, wherein the fluctuation of the composite film thickness is less than 500 kÅ

.

43. The method of claim 26, wherein depositing carbon nanotube-matrix particle complexes substantially improves the adhesion of the carbon nanotubes to the substrate.

44. A carbon nanotube composite film made from the method of claim 26.

45. The carbon nanotube composite film of claim 44, wherein the composite film is substantially smoother and more homogenous than a carbon nanotube composite film fabricated without linker molecules.

46. The carbon nanotube composite film of claim 45, wherein the fluctuation of the composite film thickness is less than 500 kÅ

.

47. A carbon nanotube electron field emission cathode comprising:

a substrate; and

a composite film adherent to the surface of the substrate, wherein the composite film comprises a matrix layer, the matrix layer being an intimate mix of matrix particles, carbon nanotubes, and linker molecules.

48. The cathode of claim 47, wherein the carbon nanotubes protrude out from the matrix layer with the longitudinal axes of the carbon nanotubes substantially perpendicular to the substrate surface with one end of each carbon nanotube embedded in the matrix layer and linked to the matrix particles by the linker molecules.

49. The cathode of claim 48, wherein the carbon nanotubes protrude from the substrate surface by between about 1 microns and about 10 microns.

50. The cathode of claim 48, wherein the spacing between each of the carbon nanotubes attached to the substrate surface is between about 0.5 microns and about 10 microns.

51. The cathode of claim 48, wherein the matrix particles are glass particles.

52. The cathode of claim 47, wherein the linker molecules are aminosilane molecules.

53. The cathode of claim 52, wherein the aminosilane molecules are selected from the group consisting of (3-aminopropyl)triethoxysilane (APS), (3-aminopropyl) trimethoxysilane, (3-aminopropyl) methyldiethoxysilane, (3-aminopropyl) methyldimethoxysilane, (2-aminoethyl-3-aminopropyl) triethoxysilane, (2-aminoethyl-3-aminopropyl) trimethoxysilane, and (2-aminoethyl-3-aminopropyl) methyldimethoxysilane.

54. The cathode of claim 47, wherein the substrate comprises a material selected from the group consisting of stainless steel, molybdenum, tungsten, and indium tin oxide.