The physics of carbon nanotubes (CNTs) has rapidly evolved into a research field since their discovery by Iijima in 1991. Since then, theoretical and experimental studies in various fields such as electronics, biotechnology, optic, and mechanics have focused on both the fundamental physical properties and on their potential applications of CNTs. Recently, collaborative efforts of K. Hata and colleagues from the Technology Research Association for Single Wall Carbon Nanotubes (TASC), Nanotube Research Center, Institute of Advanced Industrial Science and Technology (AIST), and Japan Science and Technology Agency in Kawaguchi, Japan realized viscoelastic behavior in CNTs. The researchers assembled the material from a random network of long interconnected carbon nanotubes that exhibited an operational temperature ranging from −196°C to 1000°C.
As reported in the December 3rd, 2010 issue of Science (DOI: 10.1126/science.1194865; p. 6009), the researchers synthesized transverse long CNTs with a very high density of intermittent physical interconnections using a combination of reactive ion etching, water-assisted chemical vapor deposition (CVD), and compression. These CNTs produced contained ~68% double-walled CNTs, ~22% single-walled CNTs, and ~10% triple-walled CNTs of 0.009 g/cm3, 4.5 mm in height and 99.9% carbon purity. The researchers observed an intertube structure where CNTs transverse laterally, making interconnections with other CNTs using a scanning electron microscope (SEM) (see Figure). The researchers observed a 100% strain from a shear-mode dynamic mechanical analysis (DMA) with high nonlinearity.
After further looking into the mechanism of viscoelasticty of these tubes, the group concluded that the strain was absorbed at low level by reversible unfolding of the traversing CNTs and 100% strain by an irreversible process of straightening, slipping, and bundling of CNTs. They also observed a closed hysteresis without abrupt changes which is typical for viscoelastic energy dissipative and highly deformable materials such as rubber. The CNT material synthesized had a similar stiffness (storage modulus = 1 MPa), high dissipation ability (loss modulus = 0.3 MPa), and damping ratio (0.3) than silicon rubber at room temperature. These viscoelastic properties were measured over a wide range of temperature from −196°C to 1000°C. Further analysis at this temperature range demonstrated temperature-invariant frequency stability, and the same level of reversible deformation and fatigue resistance.
Flexible intertube carbon nanotube material, with scanning electron micrograph (inset). Reproduced with permission from Science 330 (6009) (2010) DOI: 10.1126/science.1194865; p. 1364. © 2010 AAAS.
The CNT material not only demonstrates thermal stability, but also provides temperature-invariant viscoelasticity and thus can be used as building blocks of thermally stable and viscoelastic materials in various applications, from human tissues, shoe soles, ear plugs, and mattresses to vibration isolators.
