Electrostabilized homogeneous dispersion of boron nitride nanotubes in wide-range of solvents achieved by surface polarity modulation through pyridine attachment

Abstract

Boron nitride nanotubes (BNNTs) show exceptional physical properties including high mechanical strength and thermal conductivity; however, their applications have been restricted due to limited dispersibility in processing solvents. Here, a novel BNNT dispersion method with exceptional dispersibility in a wide range of solvents has been demonstrated by surface polarity modulation through short-molecule pyridine attachment. Nitrogen atoms in pyridine are selectively bonded to electron-deficient boron atoms of the BNNT surface through Lewis acid-base reaction, which changes the surface polarity of BNNTs from neutral to negative. Re-dispersing pyridine-attached BNNTs (Py-BNNTs) create a thick and stable electronic double layer (EDL), resulting in uniform dispersion of BNNTs in solvents with an exceptional solubility parameter range of 18.5-48 MPa1/2. The uniform dispersion of BNNTs is maintained even after the mixing with diverse polymers. Finally, composites incorporating uniformly-distributed BNNTs have been realized, and extraordinary property enhancements have been observed. The thermal conductivity of 20 wt.% Py-BNNT/epoxy composite has been significantly improved by 69.6% and the tensile strength of 2 wt.% Py-BNNT/PVA has been dramatically improved by 75.3%. Our work demonstrates a simple and facile route to dispersing BNNTs in diverse solvents, consequently leading to selective utilization of BNNT dispersed solvents in various application fields.