Physical adsorption of block copolymers to SWNT and MWNT: A nonwrapping mechanism

A detailed study of the interaction mechanism between carbon nanotubes and physically adsorbed block copolymers is presented. The combination of experimental observations, computer simulations and theory suggests that while the solvophobic blocks adsorb to the nanotubes by a nonwrapping mechanism, the dangling (solvophilic) blocks provide a steric barrier that leads to the formation of stable dispersions of individual single walled carbon nanotubes (SWNT) and multiwalled carbon nanotubes (MWNT) above a threshold concentration of the polymer. The observed threshold concentration depends on the length of the solvophobic blocks, and it is higher for MWNT as compared to SWNT. Theory suggests that the latter is a consequence of dimensional considerations. Spectroscopic characterization of the dispersions indicate that the dispersing block polymers do not alter the electronic structure of the well dispersed individual SWNT, supporting the model of nonspecific adsorption of the polymer to the tube driven by van der walls type interactions. The study presented here offers a generic scheme for optimization of the structure and composition of block copolymers used for dispersion of CNT in different media.