Functionalization of Boron Nitride Nanotubes with Poly(acrylic acid) via Electron-Beam-Induced Graft Polymerization and Their Improved Dispersion Property

Boron nitride nanotubes (BNNTs) are promising materials for next-generation technologies owing to their exceptional physicochemical properties, including outstanding chemical and thermal stabilities, and their neutron absorption capability derived from boron. However, dispersion is essential for the effective utilization of BNNTs. BNNTs have hydrophobic surfaces and strong van der Waals interactions, hindering their dispersion in water and various organic solvents. Dispersion techniques rely on strong physical and chemical treatments, which may damage the material and degrade its properties. Herein, we investigate a graft polymerization technique using electron-beam irradiation to functionalize BNNTs under various conditions of acrylic acid (AAc) concentration, Mohr’s salt concentration, and absorbed dose. We analyze the correlations between these conditions and their effects on the grafting yield. Subsequently, we employ X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy to elucidate the grafting mechanism of pristine BNNTs and poly(acrylic acid) (PAAc)-grafted BNNTs (PAAc-g-BNNTs). Furthermore, we evaluate the improved dispersibility and dispersion stability of the grafted BNNTs in water using ultraviolet-visible spectroscopy and zeta potential measurements. Additionally, we assess the dispersion behaviors of the pristine BNNTs and PAAc-g-BNNTs in 15 different solvents. We estimate the solubility range using the Hansen solubility parameter to confirm enhanced dispersion in various solvents. We believe our approach has high potential for applications such as the heatsink polymer composite, catalyst support, piezoelectric sensor in aerospace, electronics, and biotechnology fields.