Fig. 3: Aligned films of BNNTs.

a Photograph of a BNNT film made from a ~1 wt% solution of highly purified BNNTs (HP-BNNTs) floating on water with its original structure intact. b Photograph of the same film as in a redeposited onto a new glass slide and held at an angle to observe the film more easily. c Photograph of the BNNT film from b on the glass slide laid over the Rice shield, demonstrating high transparency. d Polarized light microscopy (PLM) images of the BNNT film on a glass slide: unpolarized transmitted light image and polarized light images with polarizer/analyzer at fixed at 0°/90°. The film was rotated to 45° for the last polarized light image and the double-sided white arrows in the lower left corners of the PLM images indicate the orientation of the shear axis for the film. e Plot of HP-BNNT film birefringence intensity normalized by incident light intensity (circles) and film absorbance (squares) against stage rotation angle. Birefringence intensity and absorbance are both plotted with model fits with coefficients of determination (r²) of 0.996 and 0.991, respectively. f Scanning electron micrograph of the BNNT film on glass. The double-sided white arrow indicates the shear axis for the film on SEM micrograph.