Fabrication of nanofiber ribbons and sheets
Fabricating a nanofiber ribbon or sheet with a process that includes providing a primary assembly by arranging carbon nanotube nanofibers in aligned arrays, the arrays having a degree of inter-fiber connectivity, drawing the carbon nanotube nanofibers from the primary assembly into a sheet or ribbon, and depositing the sheet or ribbon on a substrate.
1. A process comprising:
(a) providing a primary assembly by arranging carbon nanotube nanofibers in aligned arrays, wherein
(i) the carbon nanotube nanofibers comprise carbon nanotubes that are multiwalled carbon nanotubes, and
(ii) the arrays having a degree of inter-fiber connectivity and a density of at least 20 billion nanotubes/cm 2 at a base of the array;
(b) drawing said carbon nanotube nanofibers from the primary assembly into a sheet or ribbon; and
(c) depositing said sheet or ribbon on a substrate.
2. The process of claim 1 , wherein the carbon nanotube nanofibers have a maximum thickness of less than 500 nm.
3. The process of claim 1 , wherein the carbon nanotube nanofibers have a minimum length-to-thickness ratio of at least 100.
4. The process of claim 1 , wherein the carbon nanotube nanofibers are produced by chemical vapor deposition of carbon nanotube forests.
5. The process of claim 1 , wherein the carbon nanotube nanofibers comprise, scrolled nanotubes, coiled nanofibers, functionalized nanofibers, or crimped nanofibers.
6. The process of claim 1 , wherein inter-fiber connectivity is formed through inter-fibril mechanical coupling.
7. The process of claim 4 , wherein the carbon nanotube nanofibers are drawn into sheets or ribbons that comprise an interconnected fibril network.
8. The process of claim 6 , wherein the carbon nanotube nanofibers are branched throughout the ribbon or sheet and form a laterally-extended interconnected nanofiber network.
9. The process of claim 1 , wherein the length of the carbon nanotube nanofibers is more than 10,000 times their thickness.
10. The process of claim 4 , wherein the forests have a height of from 50 to 300 microns.
11. The process of claim 1 , wherein drawing occurs at greater than 5 m/minute.
12. The process of claim 4 further comprising bundling of nanotubes within the forest.
13. The process of claim 1 , wherein the carbon nanotube nanofibers have different dimensions.
14. The process of claim 7 , further comprising infiltrating the sheet or ribbon with a liquid and subsequently evaporating the liquid from the ribbon or sheet, wherein the infiltration and evaporation at least partially densifies the ribbon or sheet and forms a densified ribbon or sheet.
15. The process of claim 14 , wherein said infiltration with the liquid comprises a method selected from the group consisting of vapor condensation, imbibing a liquid, exposure to an aerosol of a liquid, and combinations thereof.
16. The process of claim 1 , further comprising modifying the properties of the primary assembly through oxidation, reduction or substitution with functional groups.
17. The process of claim 16 , wherein the modifying promotes at least one of (a) covalently binding molecular, polymeric, or ionic species to the nanotubes, (b) forming non-covalent binding via van der Waals or charge-transfer binding, (c) covalently or non-covalently binding species capable of hydrogen bonding, and (d) physically over coating with a polymer, a metal, a metal alloy or a ceramic.
18. The process of claim 1 , wherein inter-fiber connectivity provides at least one of (a) high strength, (b) high toughness, and (c) dense packing of the sheet or ribbon.
19. The process of claim 18 , wherein the inter-fiber connectivity is a function of van der Waals interactions between carbon nanotube nanofibers.
20. The process of claim 1 , wherein
(a) the substrate is a spindle, and
(b) the step of depositing comprises wrapping said sheet or ribbon on the spindle.