Origin of the anisotropic dielectric response of nanoconfined water · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

Title
Origin of the anisotropic dielectric response of nanoconfined water
Plain
Water squeezed into a gap about a nanometer wide barely responds to an electric field across the gap, as if it were oil, yet it responds enormously to a field along the gap. A single microscopic explanation of both facts is missing.
Precise · changed · core
Revision 1: For water in slits of height h between atomically flat graphite or hBN walls, the perpendicular dielectric constant falls to epsilon_perp ~ 2 for $h \sim 1\ \mathrm{nm}$ (2018 measurement), while a 2025 measurement found the in-plane constant $\epsilon_{\mathrm{par}}$ of about 1000 at few-layer thickness with superionic-level conductivity. Determine whether a model of interfacial layers with an anisotropic local dielectric tensor reproduces both epsilon_perp(h) and epsilon_par(h), or whether nonlocal correlated polarization and proton transport are required. An answer is a first-principles or simulation prediction of epsilon_perp(h), epsilon_par(h) and conductivity that matches both data sets.
Revision 2: For water in slits of height h between atomically flat graphite or hBN walls, the perpendicular dielectric constant falls to $\epsilon_{\mathrm{perp}} \sim 2$ for $h \sim 1\ \mathrm{nm}$ (2018 measurement), while a 2025 measurement found the in-plane constant $\epsilon_{\mathrm{par}}$ of about 1000 at few-layer thickness with superionic-level conductivity. Determine whether a model of interfacial layers with an anisotropic local dielectric tensor reproduces both $\epsilon_{\mathrm{perp}}(h)$ and $\epsilon_{\mathrm{par}}(h)$, or whether nonlocal correlated polarization and proton transport are required. An answer is a first-principles or simulation prediction of $\epsilon_{\mathrm{perp}}(h)$, $\epsilon_{\mathrm{par}}(h)$ and conductivity that matches both data sets.
Settled by
Ab initio or validated force-field simulations of the measured geometries reproducing both dielectric components and the conductivity versus h, with the controlling molecular feature identified.
Kind
phenomenon
Answer type
mechanism
References
(empty)
Literature status
open
Status note
The 2025 Nature in-plane measurement attributed the enhancement to disordered hydrogen bonding and fast proton exchange; the low out-of-plane value is broadly reproduced by simulations of interfacial ordering.
Posed since
2018

Decisions