Boron nitride nanotubes (BNNTs), structural analogs of carbon nanotubes (CNTs), have attracted considerable interest due to their unique combination of mechanical robustness, chemical stability, high thermal conductivity, and electrical insulation. Composed of alternating boron and nitrogen atoms arranged in an hexagonal lattice, BNNTs display many of the desirable properties of CNTs, while exhibiting distinct behavior arising from their polar B–N bonds and wide electronic bandgap. Previous experimental studies
[1] have revealed unexpectedly large and radius-dependent surface slippage in CNTs, but negligible slippage in BNNTs. Due to their dipolar nature, water molecules can generate strong local electric fields that significantly polarize the charge distribution in nearby materials. While the impact of water-induced polarization on nanoscale transport in CNTs has been investigated previously by Misra et al.,
[2,3] the implications of electronic polarization effects on the thermodynamics and transport properties of water confined within BNNTs remain largely unexplored.
In this work, we utilize a recently introduced theoretical framework capable of accurately modeling many-body polarization interactions at 1D [2,3] and 2D nanomaterial surfaces [4–7] to develop all-atom polarizable force fields for BNNTs. Our model explicitly accounts for the anisotropic polarizability tensors of BNNTs, including components along both the transverse (radial) and longitudinal (axial) directions. We first demonstrate that our model can self-consistently describe the water–BN polarization interactions for water confined within BNNTs of various diameters and chiralities. Using molecular dynamics simulations, we investigate water transport in BNNTs with diameters ranging from 0.8 nm to 2.3 nm, observing a transition from single-file water structure in the narrowest tubes to bulk-like behavior in wider BNNTs.
Furthermore, we show that in narrow BNNTs (diameter < 1.5 nm), the friction coefficient exhibits a strong curvature dependence. In contrast, for BNNTs with larger diameters, this dependence becomes less pronounced. Our analysis reveals that electronic polarization influences the friction coefficient primarily by modulating the orientation of the OH bonds in the interfacial water molecules. Additionally, we find that the friction coefficients in zigzag BNNTs are significantly larger than those in armchair BNNTs of comparable diameters. This difference stems from the distinct electrostatic water–nanotube interactions associated with each chirality and their resulting effects on the dynamic behavior of confined water.
References
- Secchi, E., Marbach, S., Niguès, A., Stein, D., Siria, A. & Bocquet, L. Massive radius-dependent flow slippage in carbon nanotubes. Nature 2016, 537, 210.
- Li, Z.; Misra, R. P.; Li, Y.; Yao, Y. C.; Zhao, S.; Zhang, Y.; Chen, Y.; Blankschtein, D.; Noy, A. Breakdown of the Nernst-Einstein Relation in Carbon Nanotube Porins. Nanotechnol. 2023, 18 (2), 177-183.
- Li, Y.; Li, Z.; Misra, R. P.; Liang, C.; Gillen, A. J.; Zhao, S.; Abdullah, J.; Laurence, T.; Fagan, J. A.; Aluru, N.; Blankschtein, D.; Noy, A. Molecular Transport Enhancement in Pure Metallic Carbon Nanotube Porins. Mater. 2024, 23 (8), 1123–1130.
- Misra, R. P.; Blankschtein, D. Insights on the Role of Many-Body Polarization Effects in the Wetting of Graphitic Surfaces by Water. Phys. Chem. C 2017, 121 (50), 28166–28179.
- Misra, R. P.; Blankschtein, D. Ion Adsorption at Solid/Water Interfaces: Establishing the Coupled Nature of Ion–Solid and Water–Solid Interactions. Phys. Chem. C 2021, 125 (4), 2666–2679.
- Misra, R. P.; Blankschtein, D. Uncovering a Universal Molecular Mechanism of Salt Ion Adsorption at Solid/Water Interfaces. Langmuir 2021, 37 (2), 722–733.
- Luo, S.; Misra R. P.; Blankschtein D. Water Electric Field Induced Modulation of the Wetting of Hexagonal Boron Nitride: Insights from Multiscale Modeling of Many-Body Polarization. ACS Nano 2024, 18, 1629−1646.
