Abstract
The structure and the role of the interfacial water in mediating the interactions of extended hydrophobic surfaces are not well understood. Two-dimensional materials provide a variety of large and atomically flat hydrophobic surfaces to facilitate our understanding of hydrophobic interactions. The angstrom resolution capabilities of three-dimensional AFM are exploited to image the interfacial water organization on graphene, few-layer MoS2 and few-layer WSe2. Those interfaces are characterized by the existence of a 2 nm thick region above the solid surface where the liquid density oscillates. The distances between adjacent layers for graphene, few-layer MoS2 and WSe2 are ~0.50 nm. This value is larger than the one predicted and measured for water density oscillations (~0.30 nm). The experiments indicate that on extended hydrophobic surfaces water molecules are expelled from the vicinity of the surface and replaced by several molecular-size hydrophobic layers.
Highlights
The structure and the role of the interfacial water in mediating the interactions of extended hydrophobic surfaces are not well understood
These findings enable us to propose that on mildly-to-highly hydrophobic 2D materials surfaces immersed in water, the water molecules are expelled from the vicinity of the surface and replaced by two to three hydrophobic layers
Three-dimensional AFM reveals that the interfacial structure of a 2D materials–water interface is characterized by a layered structure formed by hydrophobic layers
Summary
The structure and the role of the interfacial water in mediating the interactions of extended hydrophobic surfaces are not well understood. The angstrom resolution capabilities of three-dimensional AFM are exploited to image the interfacial water organization on graphene, few-layer MoS2 and fewlayer WSe2 Those interfaces are characterized by the existence of a 2 nm thick region above the solid surface where the liquid density oscillates. The understanding the interfacial water structure on 2D materials could lead to more efficient 2D materials-based sensors Macroscopic measurements such as water contact angle measurements show that the hydrophobicity of graphene, few-layer MoS2, and WSe2 increases with time due to the adsorption of airborne hydrocarbon contaminants[17,18,19]. These findings enable us to propose that on mildly-to-highly hydrophobic 2D materials surfaces immersed in water, the water molecules are expelled from the vicinity of the surface and replaced by two to three hydrophobic layers
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