Boron Nitride Nanotubes: Force Field Parameterization, Epoxy Interactions, and Comparison with Carbon Nanotubes for High-Performance Composite Materials

Boron nitride nanotubes (BNNTs) are a very promising
reinforcement
for future high-performance composites because of their excellent
thermo-mechanical properties. To take full advantage of BNNTs in composite
materials, it is necessary to have a comprehensive understanding of
the wetting characteristics of various high-performance resins. Molecular
dynamics (MD) simulations provide an accurate and efficient approach
to establish the contact angle values of engineering polymers on reinforcement
surfaces, which offers a measure for the interaction between the polymer
and reinforcement. In this research, MD simulations and experiments
are used to determine the wettability of various epoxy systems on
BNNT surfaces. The reactive interface force field (IFF-R) is parameterized
and utilized in the simulations to accurately describe the interaction
of the epoxy monomers with the BNNT surface. The effect of the epoxy
monomer type, hardener type, local atomic charges, and temperature
on the contact angle is established. The results show that contact
angles decrease with increases in temperature for all the epoxy/hardener
systems. The bisphenol-A-based epoxy system demonstrates better wettability
with the BNNT surface than the bisphenol-F based epoxy system. Furthermore,
the MD predictions demonstrate that these observations are validated
with experimental results, wherein the same contact angle trends are
observed for macroscopic epoxy drops on nonwoven nanotube papers.
As wetting properties drive the resin infusion in the reinforcement
materials, these results are important for the future manufacturing
of high-quality BNNT/epoxy nanocomposites for high-performance applications
such as aerospace and aeronautical vehicles.