Nanotube Yarn Actuators: Actuators are used to convert heat, light, or electricity into a twisting or tensile motion, and are often described as artificial muscles. Most materials that show actuation either provide larger forces with small-amplitude motions, such as the alloy NiTi, or provide larger motions with much less force, such as polymeric materials. Other problems with such actuators can include slow response times and short lifetimes. Lima et al. (p. 928 , see the Perspective by Schulz ) show that a range of guest-filled, twist-spun carbon nanotube yarns can be used for linear or torsional actuation, can solve the problems of speed and lifetime, and do not require electrolytes for operation.

Composite stretchable conducting wires: Think how useful a stretchable electronic “skin” could be. For example you could place it over an aircraft fuselage or a body to create a network of sensors, processors, energy stores, or artificial muscles. But it is difficult to make electronic interconnects and strain sensors that can stretch over such surfaces. Liu et al. created superelastic conducting fibers by depositing carbon nanotube sheets onto a prestretched rubber core (see the Perspective by Ghosh). The nanotubes buckled on relaxation of the core, but continued to coat it fully and could stretch enormously, with relatively little change in resistance. Science , this issue p. 400 ; see also p. 382

Recently, Zheng and Jiang [Phys. Rev. Lett. 88, 045503 (2002)] have proposed that multiwalled carbon nanotubes could be the basis for a new generation of nano-oscillators in the several gigahertz range. In this Letter, we present the first molecular dynamics simulation for these systems. Different nanotube types were considered in order to verify the reliability of such devices as gigahertz oscillators. Our results show that these nano-oscillators are dynamically stable when the radii difference values between inner and outer tubes are of $\sim 3.4\AA$. Frequencies as large as 38 GHz were observed, and the calculated force values are in good agreement with recent experimental investigations.

Most materials shrink laterally like a rubber band when stretched, so their Poisson's ratios are positive. Likewise, most materials contract in all directions when hydrostatically compressed and decrease density when stretched, so they have positive linear compressibilities. We found that the in-plane Poisson's ratio of carbon nanotube sheets (buckypaper) can be tuned from positive to negative by mixing single-walled and multiwalled nanotubes. Density-normalized sheet toughness, strength, and modulus were substantially increased by this mixing. A simple model predicts the sign and magnitude of Poisson's ratio for buckypaper from the relative ease of nanofiber bending and stretch, and explains why the Poisson's ratios of ordinary writing paper are positive and much larger. Theory also explains why the negative in-plane Poisson's ratio is associated with a large positive Poisson's ratio for the sheet thickness, and predicts that hydrostatic compression can produce biaxial sheet expansion. This tunability of Poisson's ratio can be exploited in the design of sheet-derived composites, artificial muscles, gaskets, and chemical and mechanical sensors.

Graphane is a two-dimensional system consisting of a single layer of fully saturated (sp(3) hybridization) carbon atoms. In an ideal graphane structure C-H bonds exhibit an alternating pattern (up and down with relation to the plane defined by the carbon atoms). In this work we have investigated, using ab initio and reactive molecular dynamics simulations, the role of H frustration (breaking the H atoms' up and down alternating pattern) in graphane-like structures. Our results show that a significant percentage of uncorrelated H frustrated domains are formed in the early stages of the hydrogenation process leading to membrane shrinkage and extensive membrane corrugations. These results also suggest that large domains of perfect graphane-like structures are unlikely to be formed, as H frustrated domains are always present.