Thermomechanical properties of carbon nanotube forest

A forest of oriented carbon nanotubes (CNTs) is considered under lateral loading and heating under planar deformation using the molecular dynamics method with a reduced number of degrees of freedom. It is shown that a CNT forest of a sufficiently large diameter has a negative coefficient of transverse thermal expansion. The thermal expansion coefficient weakly depends on temperature in the range up to 1500 K and practically does not depend on the volumetric compression deformation up to 0.06. This effect is explained by the elliptization of the CNT cross section and warping of the CNT walls by thermal vibrations. Elliptization, while maintaining the CNT cross-section length, leads to a decrease in the cross-sectional area of the CNT, and the warping of the CNT wall leads to a decrease in the effective diameter of the CNT.