Carbon nanotubes (CNTs) represent one of the most potentially useful materials known to man, possessing incredible strength and hardness as well as distinctive thermal and electrical properties. Producing structures that take advantage of these properties is therefore an appealing prospect, and a challenge that has inspired many researchers.
Scientists at the University of Central Florida have recently made a step forward in their approach by synthesizing a new “frozen smoke” aerogel from multi-walled CNTs [Zou et al., ACS Nano (2010) 4, 7293]. A conventional gel is a substance composed of a liquid constrained by a cross-linked solid network. An aerogel is similar, but where the liquid component has been replaced with gas. The result is an incredibly light, porous substance that can retain the properties of the parent material.
Dr Zai and co-workers succeeded in producing an ultralight free-standing multi-walled CNT aerogel monolith after realizing that increasing the interaction potential between nanotubes was the key to creating the low-density material. The final result was a material with a density of just 4 mg/cm3; the lowest density recorded for a free-standing CNT aerogel.
The monolith was capable of being compressed to just 5 % of its volume, with little change in the uncompressed volume once it was allowed to re-expand. After cycling the compression, the aerogel was found to be incredibly resilient, with only a slight change in the compressive stress after 1000 cycles. However, Zai does point out that there is room for improvement, “Although, the aerogel is very strong and flexible upon compression, we are working on improving its mechanical properties upon elongation”.
The electrical conductivity was not as high as for pure MWCNTs, having reduced by approximately half. This was attributed to the presence of the insulating additive that was used to create the strong bonds between nanotubes. However, conductivity was found to be incredibly dependent on changes in pressure, indicating that CNT aerogels could be used to construct highly sensitive pressure sensors.
Other potential uses include energy conversion and storage, as well as catalyst support. The team is currently working on new aerogels composed of functionalized nanotubes, which will hopefully lead to even more applications.


Stewart Bland