The origin of the anomalous low value of the static dielectric constant (SDC) of nanoconfined water is addressed and a few issues resolved, by considering nano-enclosures of different shapes and sizes, and using properly formulated linear response theory. While the value of the SDC remains universally low for small systems, it is different for different dielectric boundaries. Also, the response becomes anisotropic for water under non-spherical confinements. A significant role is played by the “electrically dead layer” (EDL). As the observed dielectric constant is the harmonic mean of the grid-wise SDCs, the first layer, having the smallest SDC, makes a disproportionately large contribution. This enhanced contribution, in turn, arises from the orientationally ordered surface water molecules. They exhibit reduced fluctuations in collective dipole moment, as the molecules remained partly caged due to water-surface interactions. This phenomenon is found to be universal. In our quest to develop a microscopic understanding, we study the structure and dynamics of the water molecules in different layers. We demonstrate that while the EDL remains alive at a molecular level, with a finite residence time, it exhibits timescales not substantially different compared to the distant layers of water. We explore solvation dynamics in such nanoconfined systems.

Anomalous dielectric properties of nanoconfined water: From low dielectric constant to electrically dead surface layer

ACS Spring Meeting 2021

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