Multi-scale analysis of the interaction in ultra-long carbon nanotubes and bundles

•The inter-wall/inter-tube interaction in double-walled carbon nanotube (DWCNT)/carbon nanotube bundle (CNTB) is firstly in-situ measured under optical microscope.•The multi-scale model, where the dynamic friction is included specially, is developed to illustrate the interaction in the ultra-long DWCNT/CNTB.•The force to pull out the inner/core tube consists of three parts, including the boundary effect, the configuration force and the dynamic friction.•Results from the multi-scale model are verified by the atomic simulation and can explain the physical mechanism behind the experimental phenomena.