2025 AIChE Annual Meeting

(412d) Unraveling Polarization-Driven Structure–Transport Coupling in Graphene Nanoconfined Water

Authors

Tom Frömbgen, UNIVERSITY OF BONN
Barbara Kirchner, UNIVERSITY OF BONN
Daniel Blankschtein, Massachusetts Institute of Technology
Understanding water behavior under nanoscale confinement is central to advancing desalination, molecular separations, and energy-harvesting technologies. While prior Molecular Dynamics (MD) simulation studies have largely utilized pairwise-additive (nonpolarizable) force fields involving Lennard-Jones potentials to model solid/fluid interactions, such models neglect many-body polarization effects, which have been shown to play an important role at solid-liquid interfaces.1-6 Because water is a polar liquid, its molecules generate strong local electric fields that can dynamically polarize the confining solid surfaces. This interplay between water’s intrinsic fields and the electronic response of the interface leads to polarization-induced charge redistribution — a phenomenon that is not accounted for in conventional force fields.

In this work, we use Grand Canonical Molecular Dynamics (GCMD) simulations to investigate how explicitly incorporating polarization effects influence the structure, dynamics, and transport properties of water confined between graphene layers with channel spacings ranging from 0.8 to 5 nm. Our simulations reveal that in a graphene nanochannel with 0.8 nm spacing, many-body polarization (i) weakens the confinement-induced structural ordering observed using nonpolarizable models, (ii) increases the occurrence of out-of-plane molecular orientations, and (iii) reduces the number of hydrogen bonds. Structure factor analysis shows that nonpolarizable systems promote solid-like water with long-range correlations, whereas polarizable systems suppress crystallization and contribute to faster force decorrelation. These structural modifications result in reduced water density and lower interfacial friction under strong confinement.

Extending the analysis to wider channels, we find that the water density increases monotonically with channel spacing, while the friction coefficient exhibits a nonmonotonic trend. Decomposition of friction into static and dynamic components reveals that molecular memory effects dominate in ultra-confined regimes, while bulk-like relaxation behavior emerges at larger spacings. At large graphene interlayer separations, we predict a slip length of ~20 nm, closely matching the experimental values (~16 nm)7 and resolving discrepancies previously observed using nonpolarizable simulations. These findings underscore the importance of incorporating polarization effects for accurately modeling nanoconfined water and offer insights for the design of high-performance nanofluidic membranes.

References

  1. Misra, R. P.; Blankschtein, D. Insights on the Role of Many-Body Polarization Effects in the Wetting of Graphitic Surfaces by Water. J. Phys. Chem. C 2017, 121 (50), 28166–28179.
  2. 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.
  3. Misra, R. P.; Blankschtein, D. Ion Adsorption at Solid/Water Interfaces: Establishing the Coupled Nature of Ion–Solid and Water–Solid Interactions. J. Phys. Chem. C 2021, 125 (4), 2666–2679.
  4. Misra, R. P.; Blankschtein, D. Uncovering a Universal Molecular Mechanism of Salt Ion Adsorption at Solid/Water Interfaces. Langmuir 2021, 37 (2), 722–733.
  5. 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. Nat. Nanotechnol. 2023, 18 (2), 177-183.
  6. 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. Nat. Mater. 2024, 23 (8), 1123–1130.
  7. Xie, Q.; Alibakhshi, M. A.; Jiao, S.; Xu, Z.; Hempel, M.; Kong, J.; Park, H. G.; Duan, C. Fast water transport in graphene nanofluidic channels. Nat. Nanotechnol. 2018, 13, 238–245.