| Spinning nanotube fibers:
"conventional wet spinning" vs. "direct
spinning from CVD synthesis"
03 Sept 2004
Since their
discovery, carbon nanotubes have attracted intense attention due to their
exceptional properties. Applications involving nanotubes on the micrometer
and nanometer domains are progressing rapidly. A lot of efforts have also
been taken to port the impressive properties of nanotubes from the
microscopic to the macroscopic. Among these, the research on spinning carbon
nanotube fibers is quite intensive in the recent couple of years.
In the journal Science, two new methods were reported this year on spinning
continuous nanotube fibers without any supporting surfactant or polymer
structure. One is "direct spinning from CVD synthesis" method developed by Windle
group at the Univ. of Cambrige [1]. The other is "conventional wet spinning"
method developed by Smalley group at Rice Univ. [2].
In the table below, we highlight
the advantages and disadvantages of these two methods. We also comment on
the quality of their final products. A lot of advances can be expected in
the near future for ultra-strong, highly conductive nanotube fibers.
| |
Direct
spinning from CVD synthesis |
Conventional
wet spinning |
|
Method descriptions |
Fibers and
ribbons of carbon nanotubes are directly spun from the chemical vapor
deposition synthesis zone of a furnace using a liquid source of carbon
and an iron nanocatalyst. |
Purified SWNTs
are dispersed in fuming sulfuric acid at high concentration (8wt%) and
extruded via solution spinning into continuous fibers. |
|
Devices (credit: Science) |
 |
 |
|
Industrial scalability |
Possible but
limited |
No limit |
|
Final products |
SEM images
(credit: Science) |
 |
 |
| Type of
nanotubes |
Mixture of
single-walled and mutiwall carbon nanotubes |
Single-walled
carbon nanotubes |
| Impurities |
High level
(5-10% iron) |
Very low
content |
| Nanotube
alignment |
Fairly good |
Very good |
| Mass density |
Low |
High (~1.1
g/cm3) |
| Electrical
conductivity |
8.3*105
Olm-1m-1 |
5*105
Olm-1m-1 |
| Thermal
conductivity |
|
21 W/K·m |
| Tensile
strength |
0.1-1.0 GPa |
2.6 GPa |
| Young's
modulus |
|
138 GPa |
|
Advantages |
Synthesis
process is very smart and simple. The nanotubes in the fiber are
as-grown thus might be very long and free of defects. The electrical and thermal
conductivity could be very high if the mass density of the fiber can be further
improved. |
Synthesis
method is flexible and controllable. It can be scaled up in industry
easily. The starting materials are purified nanotubes. In the future,
fibers which only contains metallic nanotubes would be of great
interest. |
|
Disadvantages |
The quality of
the final product is difficult to control. Particularly, it seems to be very
difficult to get rid of the catalyst impurities from the final product
if not impossible. The fibril stuff coming out directly from the CVD
furnace is usually fluffy thus the nanotube rope -rope packing within
the fiber might be rather loose. |
The nanotubes
were processed in super-acid for fiber-spinning. Acid-treatment is known
to introduce a lot of structural defects to nanotubes. Post-synthesis
annealing in vacuum might be helpful.
The nanotubes in these fibers
are typically less than 1 micron. Thus the transport properties of the
fiber is not exceptional for now. This can be improved in the future if
the source nanotubes contain only metallic species. |
|
|
References:
[1] Y. Li, I. A. Kinloch, A. H.
Windle, Sicence 304, 276 (2004).
[2] L. M. Ericson, H. Fan, H. Peng, V. A.
Davis, W. Zhou, J. Sulpizio, Y. Wang, R. Booker, J.
Vavro, C. Guthy, A. N. G. Parra-Vasquez, M. J. Kim, S.
Ramesh, R. K. Saini, C. Kittrell, G. Lavin, H. Schmidt, W. W.
Adams, W. E. Billups, M. Pasquali, W. Hwang, R. H. Hauge, J. E. Fischer, R. E.
Smalley, Science, 305, 1447 (2004).Related links:
Rice researchers make
continuous neat nanotube fibers
Direct spinning of carbon nanotube fibers from CVD synthesis
Rice engineers make first
pure nanotube fibers
|