Groove-Assisted Global Spontaneous Alignment of Carbon Nanotubes in Vacuum Filtration

Recently, He and coworkers have developed a method for fabricating films of aligned single-wall carbon nanotubes (SWNCTs) using slow vacuum filtration [1]. Their fabricated SWCNT films are wafer-scale (centimeter size), highly packed (~ 1 nanotube per cross-sectional area of 1 nm2) and have nearly perfect alignment (nematic order parameter S ~ 1). However, the mechanism driving the aligned structures to grow into monodomains of macroscopic size has not been fully understood. In particular, what dictates the direction of SWNCT alignment has been under discussion. Here, we first examine a model suggested by He et al., where SWCNTs interact with each other and result in global alignment in a potential energy minimum near the surface [1]. We show experimental data that invalidates this model, suggesting that there must be a characteristic of the entire membrane that determines the alignment direction. We found a large number of parallel grooves that exist on most commercial filter membranes used for vacuum filtration, and show experimental results demonstrating that the grooves determine the direction of SWCNT alignment. Furthermore, when we eliminated the grooves by heating treatment, we observed multidomain alignment instead of monodomain alignment. Finally, we introduced intentionally created grooves on the filter membrane by an imprinting method, which successfully controlled the alignment direction. This procedure, groove-assisted CVF, provides a simple and reproducible way to align CNTs in a desired direction. Reference: [1] He, X.; Gao, W.; Xie, L.; Li, B.; Zhang, Q.; Lei, S.; Robinson, J. M.; Hároz, E. H.; Doorn, S. K.; Wang, W.; Vajtai, R.; Ajayan, P. M.; Adams, W. W.; Hauge, R. H.; Kono, J. Nat. Nanotechnol. 2016, 11, 633–638.