A theoretical evaluation of the effects of carbon nanotube entanglement and bundling on the structural and mechanical properties of buckypaper

Structural formation mechanisms of carbon nanotube (CNT) buckypaper and their effects on its mechanical properties are studied with numerical simulations. A bond swap algorithm, resulting from coupling the molecular dynamics and Monte Carlo methods, has been developed to equilibrate initial structures of buckypaper, generated by a random walk approach. Entanglement and bundling mechanisms are found to affect major structural features of buckypaper. Both mechanisms are evaluated quantitatively by calculating the entanglement network and pore size of buckypaper. Compared with (8,8)-(12,12) double-walled CNT, the structure of (5,5) single-walled CNT buckypaper is mainly dominated by entanglement, due to its smaller adhesion energy. We show that the pore size of modeled buckypaper, containing both types of CNTs, can be tuned from 7nm to 50nm by increasing the double-walled CNT content from 0wt% to 100wt%, due to the transformation from entanglement-dominated to bundling-dominated structures. Such an observation agrees exceptionally well with experimental results. Both entanglement and bundling mechanisms are also found to play important roles in the mechanical properties of buckypaper. The findings open a way to tailor both structural and mechanical properties of buckypaper, such as Young’s modulus or Poisson’s ratio, by using different CNTs and their mixtures.