Frit compression

Frit compression is the technique used to fabricate buckypaper, buckydiscs, buckyprisms or buckycolumns from a suspension of carbon nanotubes in a solvent. This is a quick, efficient method over surfactant-casting or acid oxidation filtration of carbon nanotubes.

Background

Traditional methods of buckypaper production involves the use of surfactants to disperse carbon nanotubes into aqueous solutions [Rinzler AG, Liu J, Dai H, Nikolaev P, Huffman CB, Rodriguez-Macias FJ, et al. “Large scale purification of single-wall carbon nanotubes: process, product, and characterization.” Appl Phys A 1998;67(1):29-37] [Sun J, Gao L. “Development of a dispersion process for carbon nanotubes in ceramic matrix by heterocoagulation.” Carbon 2003;41(5):1063-8] . It was found that filtering this suspension allowed the nanotubes to pack together in a paper-like mat, thus coining the term “buckypaper” (bucky being the reference to the buckyminster fullerene molecule). The problem was the difficulty in removing the surfactant afterwards [Ausman KD, Piner R, Lourie O, Ruoff RS, Korobov M. Organic solvent dispersions of single-walled carbon nanotubes: Toward solutions of pristine nanotubes. J Phys Chem B 2000;104(38):8911–5] , where the surfactant has been linked with cell lysis and tissue inflammation [Cornett JB and Shockman GD. "Cellular lysis of Streptococcus faecalis induced with Triton X-100". J Bacteriol 1978;135(1):153–60] .

Acid oxidation [K Esumi K, Ishigami M, Nakajima A, Sawada K, Honda H. “Chemical treatment of carbon nanotubes.” Carbon 1996;34(2):279-81] of carbon nanotubes can also be used in filtration to form buckypaper, but requires a high degree of surface acidic groups in order to obtain efficient dispersal in aqueous solution [Leng T, Huie P, Bilbao KV, Blumenkranz MS, Loftus DJ, Fishman HA. “Carbon nanotube bucky paper as an artificial support membrane and Bruch's membrane patch in subretinal RPE and IPE transplantation.” Invest Ophth Vis Sci 2003;44(U97):481] .

Synthesis

) developed an alternative casting method to produce buckypaper that did not require the use of surfactants or the acid oxidation of carbon nanotubes in order to obtain high-purity buckypaper for biomedical applications [Whitby RLD, Fukuda T, Maekawa T, James SL, Mikhalovsky SV, "Geometric control and tuneable pore size distribution of buckypaper and buckydiscs". Carbon 2008;46(6):949-956] .

The frit-compression system was adapted from a Solid phase extraction (SPE) column, where a suspension of carbon nanotubes is squeezed between two polypropylene frits (70 micrometre pore diameter) inside a syringe column. The pore structure of the frit allows a rapid exit of the solvent leaving the carbon nanotubes to be pressed together. The presence of the solvent controls the interaction between the tubes allowing the formation of tube-tube junctions; its surface tension directly affects the overlap of adjoining nanotubes thus gaining control over the porosity and pore diameter distribution of buckypaper. The distribution of carbon nanotubes in solvent does not have to be a stable suspension, rather a general dispersion serves much easier to keep the nanotubes between the frits rather than pass through them.

Once the system is compressed, the frit-carbon nanotube sandwich is removed from the syringe housing and allowed to dry. The frits can then be removed to leave in tact buckypaper. This methodology rapidly speeds up the casting process, avoids use of surfactants and acid oxidation, and the solvent can be fully recovered.

Variety

The cross-sectional geometry of the syringe housing will determine the final structure of the buckypaper and the amount of carbon nanotubes added to the column will affect the height of the carbon nanotube mat. Although there is currently no formal classification for paper, discs and columns, it was deemed necessary to differentiate between the different structures obtained for research purposes.

Buckypaper

Typically, cylindrical columns are used with a few milligrams of carbon nanotubes in a solvent. This generates buckypaper with a circular cross-section and film heights of a few hundred micrometres. Buckypaper is usually a class of carbon nanotube mats with depths from 1 to 500 micrometres.

Buckydiscs

For buckypaper with heights larger than 500 micrometres are termed buckydiscs, being thicker than buckypaper and un-paperlike. Moreover, when casting in water (72.80 mN m-1), the edges of the film can lift due to surface tension effects of the remaining solvent in the system that can pull carbon nanotubes closer together [ Futaba DN, Hata K, Yamada T, Hiraoka T, Hayamizu Y, Kakudate Y, et al. “Shape engineerable and highly densely packed single-walled carbon nanotubes and their application as super-capacitor electrodes.” Nat Mater 2006;5(12):987-94] .

Buckycolumns

If the height of the carbon nanotube mat is greater than 1mm (1000 micrometres) they are classed as buckycolumns.

Buckyprism

It is possible to use square housing to generate square cross sections, known as buckyprisms.

References

See also

*Buckypaper
*Nanotechnology
*Carbon nanotube
*Graphene Oxide Paper