Water layer at hydrophobic surface: Electrically dead but dynamically alive?

Water confined between parallel graphene sheets exhibits several interesting anomalies. This work unravels the origin of the surprisingly low static dielectric constant of such systems by employing linear response theory, a mean-field capacitor model and computer simulations. We find that the interfacial water layer, with a substantially attenuated dielectric permittivity, makes a disproportionately large contribution to the effective value. This is partly because the observed dielectric constant is a harmonic mean of the grid-wise dielectric constants. In addition, we study the dynamics of water molecules at a microscopic level. We find that the water molecules residing in the so-called “electrically dead layer” become orientationally ordered yet dynamically active, with a finite residence time in the layer. While these water molecules display timescales not substantially different compared to the water molecules at the distant layers, their dipole moment fluctuations are quenched. Our study provides new insights into the dielectric anomaly of nanoconfined water, which has been a topic of great current interest.

REFERENCE: https://pubs.acs.org/doi/10.1021/acs.nanolett.0c04312

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