Optically-transparent epoxy polymer nanocomposites reinforced with aligned boron nitride nanotubes

Nanocomposites of aligned boron nitride nanotubes (A-BNNTs) are envisioned as next-generation multifunctional materials due to the exceptional mechanical, optical, and thermal properties of hexagonal BNNTs, among others. Here we present optically-transparent polymer nanocomposites (PNCs) reinforced with A-BNNTs, using two structural epoxy matrices that are both optically transparent, including synthesis and characterization. Fourier Transform Infrared (FTIR) and Raman spectra show no evidence of nanofiber-matrix chemical interactions, however differential scanning calorimetry (DSC) indicates that polymer T_g is altered for both epoxies. Small-angle (SAXS) and wide-angle (WAXS) x-ray scattering indicates a high degree of BNNT alignment in the PNCs per Herman's orientation parameter. The A-BNNT reinforcement provides enhanced hardness and modulus, with nanoindentation revealing mechanical anisotropy that correlates with measured BNNT texture. Optical measurements in the UV–Vis range indicate that BNNT reinforcement does not significantly alter the absorbance of the polymers as might be expected due to the polymer-BNNT interfaces. This work establishes the first structure-property relations for controlled-morphology polymer nanocomposites (PNCs) with A-BNNTs, and provides a platform for further investigation including other multifunctional properties (such as piezoelectricity) and BNNT PNC process-structure relations at higher BNNT loading.