(481e) Polymer Depletion-Based Length Separation of Boron Nitride and Carbon Nanotubes

Partitioning rod-like particles by shape and critical dimension yields a rich platform for investigating fundamental colloidal interactions, establishing rigorous metrological standards for emerging materials, and advancing technological frontiers. In this talk, I will present new investigations of entropically driven polymer-induced precipitation of highly purified single-wall carbon nanotubes (SWCNTs) and boron nitride nanotubes (BNNTs) for large scale and tunable length separation of these materials. For demonstration I will present results from four distinct nanotube populations with increasing average diameter and stiffness produced by different synthesis methods. In detail, aqueous, ionic surfactant-stabilized dispersions of each nanotube population were subjected to multistage fractionation at successively lower polymer concentrations of 6 kDa poly-methacrylic acid, from 40 to 5 g/L, progressively isolating longer nanotube length distributions in the “reverse sequential” separation scheme [1,2]. We characterize the resulting populations through analytical ultracentrifugation, optical spectroscopy and atomic force microscopy, enabling cross-comparison of length separation fidelity and distributions from different measurement methods, and across diameter/material space for the applied polymer concentrations during precipitation. In all cases, very strong fractionation by length was achieved with distinct populations, achieving mass-weighted average lengths from 200 nm up through 1 micron. Kinetic parameters were, however, empirically determined to be significant, especially for reducing contamination of longer nanotubes in shorter populations. As such, we introduced an additional settling/precipitation step at each stage that significantly improves mass propagation to later separation stages. Comparing across materials, a clear trend of increasing mean length with decreasing diameter was observed for the same nominal PMAA concentration, indicating differences in effective exclusion yielded by the polymer that are suspected to arise from the diameter dependence in nanotube persistence length. For BNNT materials, the precipitation is furthermore found to yield shape selection, significantly removing non-tube mass from the dispersion in the earliest fractions. Details of these results and of additional intercomparisons and relationship to the phenomenon of the depletion-mediated separation will be discussed.

[1] Khripin, C. Y., Arnold-Medabalimi, N., & Zheng, M. (2011). Molecular-crowding-induced clustering of DNA-wrapped carbon nanotubes for facile length fractionation. ACS Nano, 5(10), 8258–8266.

[2] Gui, H., Chen, H., Khripin, C. Y., Liu, B., Fagan, J. A., Zhou, C., & Zheng, M. (2016). A facile and low-cost length sorting of single-wall carbon nanotubes by precipitation and applications for thin-film transistors. Nanoscale, 8, 3467.