Spontaneous Alignment of Boron Nitride Nanotubes into Polycrystalline Film Arrays for Enhanced Piezoelectric Nanogeneration

Abstract

1D nanomaterials feature distinct physical properties owing to their characteristic anisotropy and size-induced quantization; yet, creating an ordered ensemble of the nanomaterials is nontrivial, marking it as a grand challenge in materials science. Herein, the spontaneous alignment of a model 1D nanomaterial, boron nitride nanotube (BNNT), into a highly ordered multidomain film is presented. A conventional, benchtop gravity filtration is employed, during which thickening of the BNNT dispersion leads to a formation of the liquid crystal (LC) phase that is readily isolatable. The spontaneity of the phase separation excludes notoriously persisting synthetic impurities to a degree >99%, from ？50% of the initial material purity. The LC-based thin film features an aligned multidomain with an exceptionally low angular deviation of <2.5° and a domain size of >50？μm. A piezoelectric nanogenerator based on the thin film records a 1000-fold increase in the piezocurrent compared to its random analog. This work demonstrates the first example of the spontaneous alignment of an unconventional nanotube system and the realization of the macroscopic properties therefrom, which can be readily expanded to 1D materials in general.