Structure and Orientation of Water Molecules at Model Hydrophobic Surfaces with Curvature: from Graphite Sheets to Carbon Nanotubes and Fullerenes

L.M. ALARCÓN; D.C. MALASPINA; E.P. SCHULZ; M.A. FRECHERO; G.A. APPIGNANESI

CHEMICAL PHYSICS

ELSEVIER SCIENCE BV

Año: 2011 p. 47 - 56

0301-0104

We study the structure and orientation of water molecules at model hydrophobic surfaces by means ofmolecular dynamics. We focus here on the role of geometry in water hydration by comparing the situa-tion for a planar graphene sheet with convex surfaces with different curvature: the exterior surfaces ofcarbon nanotubes and fullerenes of different radii. In all cases, we find the first water hydration layerto be more structured than the bulk. Additionally, the first water layers are found to be well oriented withrespect to the surface normal in a way consistent with a local Ice Ih-like structuring, but differently formthe water?air interface (along the opposite direction with respect to ice Ih basal plane). We also showthat as the curvature of the surface gets more pronounced, the water molecules get less structuredand oriented. This monotonic loss of local structure for proximal water represents a smooth tendencywhenever we deal with an extended surface. However, when the surface becomes partially or completelynon-extended (within the sub-nanometric regime), the surface water layer becomes to quickly lose struc-turing and orientation.