Structural and dynamical fingerprints of the anomalous dielectric properties of water under confinement
Iman Ahmadabadi, Ali Esfandiar, Ali Hassanali, Mohammad Reza Ejtehadi
Abstract
There is a long-standing question about the molecular configuration of interfacial water molecules in the proximity of solid surfaces, particularly carbon atoms, which plays a crucial role in electrochemistry and biology. In this study, the dielectric, structural, and dynamical properties of confined water placed between two parallel graphene walls at different interdistances from the angstrom scale to a few tens of nanometer have been investigated using molecular dynamics. For the dielectric properties of water, we show that the dielectric constant of the perpendicular component of water drastically decreases under sub-2-nm spatial confinement. The dielectric constant data obtained through linear response and fluctuation-dissipation theory are consistent with recent reported experimental results [L. Fumagalli et al., Science 360, 1339 (2018)]. By determining the charge density as well as fluctuations in the number of atoms, we provide a molecular rationale for the behavior of the perpendicular dielectric response function. We also interpret the behavior of the dielectric response in terms of the presence of dangling O-H bonds of water. By examining the residence time and lateral diffusion constant of water under confinement, we reveal that the water molecules tend to keep their hydrogen bond networks at the interface of water-graphene. We also found consistency between lateral diffusion and the $z$-component of variance in the center of mass of the system as a function of confinement.