Nanotube formation from a self-curling nanofilm driven by surface stress: a core-surface model.

A continuum theoretical model for describing nanotube formation from a self-bending (self-curling) nanofilm driven by surface stress was established in this paper. Surface stress, surface elasticity and anisotropic deformation were considered. A nanofilm was cured along tangential direction to form a nanotube. The other in-plane direction (cylindrical direction) maintains straight state. Isotropic surface stress no longer induces an isotropic bent under this condition. Therefore, isotropic Stoney theory should be modified and the anisotropic deformation should be reckoned in. Curling structure affects radius as well as elongation strain of nanotubes obviously. Film stiffness instead of biaxial modulus in the curling equation means the difference between our theory and Stoney formula (as well as its modified form). If surface elasticity is balance, elongation strain holds isotropic despite the anisotropic curling structure of nanotubes. Since residual strain and stress influence the physical properties within nanotube wall, the residual strain and stress were also analyzed in this paper. [ABSTRACT FROM AUTHOR]