Sunday, August 29, 2010

Sidewall Derivatized Single-Wall Carbon Nanotubes Using Fluorine

Rice University (Houston, TX) earned United States Patent 7,780,939 for sidewall derivatized carbon nanotubes.  Rice inventors developed a high yield, single step method for producing large quantities of continuous macroscopic carbon fiber from single-wall carbon nanotubes using inexpensive carbon feedstocks at moderate temperatures. 

This invention is directed to chemical derivatives of carbon nanotubes wherein the carbon nanotubes have a diameter up to 3 nm. In one embodiment, Rice scientists developed a method for preparing carbon nanotubes having substituents attached to the side wall of the nanotube by reacting single-wall carbon nanotubes with fluorine gas and recovering fluorine derivatized carbon nanotubes, then reacting fluorine derivatized carbon nanotubes with a nucleophile. Some of the fluorine substituents are replaced by nucleophilic substitution.

If desired, the remaining fluorine can be completely or partially eliminated to produce carbon nanotubes having substituents attached to the side wall of the nanotube. The substituents are dependent on the nucleophile, and preferred nucleophiles include alkyl lithium species such as methyl lithium, according to inventors John L Margrave, Edward T. Mickelson, Robert Hauge, Peter Boul, Chad Huffman, Richard E. Smalley, Ken Smith.   Fluorine may be fully or partially removed from fluorine derivatized carbon nanotubes by reacting the fluorine derivatized carbon nanotubes with various amounts of hydrazine, substituted hydrazine or alkyl amine.
  
Carbon has from its very essence not only the propensity to self-assemble from a high temperature vapor to form perfect spheroidal closed cages (of which C60 is prototypical), but also (with the aid of a transition metal catalyst) to assemble into perfect single-wall cylindrical tubes which may be sealed perfectly at both ends with a semifullerene dome. These tubes, which may be thought of as one-dimensional single crystals of carbon, are true fullerene molecules.

Single-wall carbon nanotubes are much more likely to be free of defects than multi-wall carbon nanotubes. Defects in single-wall carbon nanotubes are less likely than defects in multi-walled carbon nanotubes because the latter have neighboring walls that provide for easily-formed defect sites via bridges between unsaturated carbon valances in adjacent tube walls. Since single-wall carbon nanotubes have fewer defects, they are stronger, more conductive, and therefore more useful than multi-wall carbon nanotubes of similar diameter.

Carbon nanotubes, and in particular the single-wall carbon nanotubes, are useful for making electrical connectors in micro devices such as integrated circuits or in semiconductor chips used in computers because of the electrical conductivity and small size of the carbon nanotube. The carbon nanotubes are useful as antennas at optical frequencies, and as probes for scanning probe microscopy such as are used in scanning tunneling microscopes (STM) and atomic force microscopes (AFM). The carbon nanotubes may be used in place of or in conjunction with carbon black in tires for motor vehicles. The carbon nanotubes are also useful as supports for catalysts used in industrial and chemical processes such as hydrogenation, reforming and cracking catalysts.

Ropes of single-wall carbon nanotubes will conduct electrical charges with a relatively low resistance. Ropes are useful in any application where an electrical conductor is needed, for example as an additive in electrically conductive paints or in polymer coatings or as the probing tip of an STM. 

FIG. 1. A) TEM image of pure, unreacted SWNT B) TEM of SWNT after being fluorinated at 325.degree. C. C) TEM of SWNT after being fluorinated at 500.degree. C. 


Not unexpectedly, the electronic properties of the fluorinated tubes differ dramatically from those of their unfluorinated counterparts. While the untreated SWNT are good conductors (10-15.OMEGA. two probe resistance across the length of the .about.10.times.3 mm.times.30 .mu.m bucky paper samples), the tubes fluorinated at temperatures of 250.degree. C. and above are insulators (two probe resistance >20 M.OMEGA.). 



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