2.

Characterization of thin-film assemblies of boron nitride nanotubes (BNNTs) after various degrees of centrifugation-based refinement, realized via SVF. (a) Cross-polarized optical microscopy images of thin films filtered from two BNNT dispersions: one from an only sonicated dispersion, and the second from its daughter dispersion after centrifugation, with the extent denoted by multiples of the gravitational acceleration constant, G (9.81 m/s²) (see Methods for details). Red arrows in the top panels denote the rotation of the films for maximum birefringence (vertical) and at 45° rotation. The film formed from the centrifuged dispersion displays greater global alignment and visually larger domains. (b) Average birefringent intensity of thin films formed from BNNTs with varying extents of centrifugation as a function of film rotation between crossed polarizers. The increasing fractional modulation observed for films from centrifuged dispersions indicates increased anisotropy. (c) Small-sample measurements of nanotube lengths from each processed material population, obtained by AFM, showing a mild narrowing of the length distribution with increasing applied centrifugation.