On the origin of negative Poisson’s ratio in buckypapers

Abstract Unprecedented sign change of Poisson’s ratio not only paves the way for diverse applications, but it provides a sense of deep understanding of ‘hidden’ mechanics, yet to be discovered. Stochastically distributed multi-walled carbon nanotubes in the form of buckypaper possess negative Poisson’s ratio, but the underlying design principles are still unclear. Herein, we explored analytical approaches, namely, energy minimization, structural modeling, and force-balance as a means to target negative Poisson’s ratio in the buckypaper. Though ‘zero’ Poisson’s ratio is still achievable, the controlling parameters could not be identified. Guided by a ‘keyed-brick’ structure, a simple geometrical model is then constructed to account for sliding effects in carbon nanotubes for contemporary understanding of auxetic behavior (negative Poisson’s ratio). The alignment of carbon nanotubes plays a prominent role in augmenting the magnitude of negative Poisson’s ratio.