Quasi-stabilized hydration layers on muscovite mica under a thin water film grown from humid air

Toyoko Arai,Asuka Iida,Masahiko Tomitori,Kohei Sato

doi:10.1038/s41598-017-04376-3

Abstract

The interfaces between solids and water films in air play fundamental roles in physicochemical phenomena, biological functions, and nano-fabrication. Though the properties of the interfaces have been considered to be irrelevant to the water film thickness, we found distinctive mechanical features of the interface between a cleaved muscovite mica surface and a thin water film grown in humid air, dissimilar to those in bulk water, using frequency-modulation atomic force microscopy. The thin water film grew with quasi-stabilized hydration networks of water molecules, tightly bound each other at the interface, to a thickness of ~2 nm at near-saturating humidity. Consequently, defective structures of the hydration networks persisted vertically through the hydration layers at the interface, and K+ ions on the cleaved surface remained without dissolution into the water film. The results provide atomistic insights into thin water films in regard to epitaxial-like growth from vapour and the motion of water molecules and ions therein.

Highlights

Most solid surfaces are covered with a water film under ambient conditions[1,2,3,4]
On solid surfaces under water, the solid–water interface takes a central role for chemical reactivity, whereas the water layer dominantly acts as a supplier or a receiver for the mass transportation
Two-dimensional water islands grow at relative humidities (RH) of less than 50%13, and a monolayer of water molecules is formed in the range of RH of 50–75%1, 2, 5, 13–17

Summary

Introduction

Most solid surfaces are covered with a water film under ambient conditions[1,2,3,4]. The water film is divided into three parts: a solid–water interface, a water layer, and a water–vapour interface. On solid surfaces under water, the solid–water interface takes a central role for chemical reactivity, whereas the water layer dominantly acts as a supplier or a receiver for the mass transportation. For a thin water film on a solid surface in air, its water layer is very thin or none, and the water–vapour interface is very close or overlapped with the solid–water interface. Exploring the structure and properties of the solid–water interface in the thin water film in air is intriguing and challenging for basic science and its industrial applications. The behaviour of water layers in the films with thicknesses over three monolayers would be the same with those of bulk water, because the thermodynamic parameters of the water layers were calculated to be close to those of bulk water[5]

Methods

Results

Conclusion