Thermal fluctuations, stress relaxation, and actuation in carbon nanotube networks

Do carbon nanotubes behave like polymers? The answer appears to be—some do and some do not, depending on the number of walls. Analyzing the behavior of carbon nanotube networks, as found in sheets of “bucky paper,” provides an intriguing insight into the characteristics of nanotubes, noninvasively deducing the fundamental response of individual tubes from the average characteristics of the collective. We report stress relaxation experiments on singleand multiwalled carbon nanotube networks and also present their reversible photomechanical actuation response. Experimental similarities between multiwalled nanotube networks and a “sticky” granular system are observed, while single-walled tubes display entropic behavior akin to a polymer network. In both cases, photostimulated actuation is orders of magnitude larger than thermal expansion predictions. The analogy between single-walled tubes and entropically driven polymer chains, and between multiwalled tubes and granular networks, suggests a paradigm for theoretical and experimental analysis.