Abstract
Water molecules at solid surfaces typically arrange in layers. The physical origin of the hydration layers is usually explained by two different reasons: (1) the attraction between the surface and water and (2) the water confinement due to the surface. While the attraction is specific to the particular solid, the confinement is a general property of surfaces; a differentiation between the two effects is, therefore, critical for research on interactions at aqueous interfaces. Here, we investigate the graphite-water interface, which is a widely used model system where the solid-water attraction is often considered to be negligible. Similar to previous studies, we observe hydration layers using three-dimensional atomic force microscopy at the graphite-water interface. We explain why the confinement could cause the formation of hydration layers even in the absence of attraction between surface and water by employing Monte Carlo simulations. Using additional molecular dynamics simulations, we continue to show that at ambient conditions, however, the confinement alone does not cause the formation of layers at the graphite-water interface. We thereby demonstrate that there is a significant graphite-water attraction.
Highlights
Hagen Söngen,1,* Ygor Morais Jaques,2 Lidija Zivanovic,2 Sebastian Seibert,1 Ralf Bechstein,1 Peter Spijker,2 Hiroshi Onishi,3 Adam S
It is desirable to differentiate between layering through attraction and layering through confinement: While the attraction results from the interaction between the liquid molecules and the surface, liquid confinement would be generally expected for any solid surface
We remove the attractive contribution from the carbon-water interaction within the molecular dynamics (MD) simulation [Fig. 5(a), red curve] to test whether the graphite-water attraction is necessary for the hydration layer formation or whether the confinement alone causes the formation of layers in this case
Summary
We performed 3D AFM experiments to map the hydration structure at the graphite-water interface. A representative vertical slice of a 3D data set in Fig. 1 shows the excitation frequency shift. [7], the local maxima in the excitation frequency shift are assigned to local maxima in the water density. These experimental results, along with the large number of research papers describing the observation of layers at interfaces, raise the fundamental question as to whether the observed solvation layers are caused solely by the confining nature of the surface or whether they appear because of attractive interactions between the graphite surface and water (or due to a combination of both)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
