(466g) Electronic Polarization As the Fundamental Mechanism for Pronounced Curvature Dependence of Water Slip Flow in Carbon Nanotubes

Carbon nanotubes (CNTs) hold immense promise for applications at the water-energy nexus, including seawater desalination, energy storage, and as chemical and flow sensors. This potential has, in turn, triggered tremendous interest in understanding how water molecules interact with CNTs on a fundamental level. Previous experimental studies have found that the CNT wall acts like a low-friction surface, contributing to large slip lengths of water inside 30-100 nm diameter CNTs [1] and inside sub-1nm diameter CNT porins, which exhibit enhanced water permeabilities compared to their biological counterparts [2]. Although water molecules due to their dipolar nature, can exert strong electric fields which can significantly polarize the charge distribution in CNTs, the role of the ensuing water-carbon polarization interactions in the different regimes of slip flow remains unknown.

In this work, we utilize a recently introduced theoretical framework which can accurately model the many-body polarization interactions at 1D and 2D nanomaterial surfaces [3-5] to investigate the diameter-dependent friction coefficients and slip lengths of water inside CNTs. To this end, we first demonstrate that our model can self-consistently describe the water-CNT polarization interactions in both metallic and semiconducting CNTs, and then utilize this model to uncover two different water transport regimes. Specifically, we show that for narrow CNTs with diameters less than 1.5 nm, the water-CNT polarization interactions have a pronounced effect on the water friction coefficients through an enhancement in the water density. On the other hand, for larger diameter CNTs, the water-CNT polarization interactions cause a strong curvature dependence of the friction coefficient by influencing the orientation of the interfacial water molecules near the CNT wall. In particular, for zigzag chirality CNTs, we show that the water-CNT polarization interactions contribute to a remarkable quadratic scaling of the water friction coefficient with the CNT diameter. In contrast, modeling the water-CNT interactions using a Lennard-Jones potential, which reflects the water-CNT London dispersion interactions, results instead in a weak, sub-linear diameter dependence of the water friction coefficient. Therefore, our study offers new insights into the significantly different contributions of water-nanopore dispersion and polarization interactions in governing water transport, paving the way for the rational design of CNTs and other 1-dimensional nanomaterials in membrane-based applications.

References

[1] Secchi, E., Marbach, S., Niguès, A., Stein, D., Siria, A. & Bocquet, L. Massive radius-dependent flow slippage in carbon nanotubes. Nature 537, 210 (2016).

[2] Tunuguntla, R., Henley, R., Yao, Y.-C., Pham, T. A., Wanunu, M. & Noy, A. Enhanced water permeability and tunable ion selectivity in sub-nanometer carbon nanotube porins. Science 357, 792–796 (2017).

[3] Misra, R. P. & Blankschtein, D. Insights on the Role of Many-Body Polarization Effects in the Wetting of Graphitic Surfaces by Water. The Journal of Physical Chemistry C 121, 28166-28179 (2017).

[4] 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. Nature Nanotechnology 18, 177-183 (2023).

[5] 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 18, 1629−1646 (2024).