Structural and dynamical aspects of water in contact with a hydrophobic surface

Abstract

By means of molecular dynamics simulations we study the structure and dynamics of water molecules in contact with a model hydrophobic surface: a planar graphene-like layer. The analysis of the distributions of a local structural index indicates that the water molecules proximal to the graphene layer are considerably more structured than the rest and, thus, than the bulk. This structuring effect is lost in a few angstroms and is basically independent of temperature for a range studied comprising parts of both the normal liquid and supercooled states (240K to 320K). In turn, such structured water molecules present a dynamics that is slower than the bulk, as a consequence of their improved interactions with their first neighbors.

Hydrophobicity and geometry: Water at curved graphitic-like surfaces and within model pores in self-assembled monolayers

“…• , that is, they tend to orient with a vertex of the tetrahedron (an electron lone pair), an orientation consistent with that of the basal plane of ice Ih [32,10,31]. Such orientational tendency changes little when we go from the graphene sheet to a low radius carbon nanotube, which speaks of the fact that the a change in curvature for these convex surfaces does not produce significant alterations in the orientational ordering of the hydrating molecules.…”

“…Previous works have determined that water molecules around graphiticlike surfaces (within the first layers of the normal density plot) display a preferential orientational ordering resembling the structure of hexagonal ice (ice Ih) [10,31,32]. Thus, the water molecules closest to the surface sacrifice the lowest hydrogen bond (HB) coordination by orienting a vertex of the tetrahedron towards the surface, but contrary to the water-air [32,33] or water-vacuum [34] interfaces, they do not orient an H atom towards the surface but an electron lone pair [10,31].…”

“…Thus, the water molecules closest to the surface sacrifice the lowest hydrogen bond (HB) coordination by orienting a vertex of the tetrahedron towards the surface, but contrary to the water-air [32,33] or water-vacuum [34] interfaces, they do not orient an H atom towards the surface but an electron lone pair [10,31]. Thus, they lose one hydrogen-bond coordination water partner due to the presence of the surface.…”

“…2 ) with terminations in hydrogen atoms solvated with 11,644 TIP3P water molecules in an orthogonal cubic box with periodic boundaries [10]. The surface was centered in the middle of the box A c c e p t e d M a n u s c r i p t and parallel to the XY plane.…”

“…A complete knowledge of the behavior of water at interfaces and under nanoconfinement is expected to open new roads of both academic and technological relevance in fields ranging from biology to materials science A c c e p t e d M a n u s c r i p t [1,2,3,4,5,6,7,8,9,10,11,12]. Both in biological organization and in the supramolecular self-assembly of materials, the nanoconfinement that arises upon the interaction of the different assembling units affects the thermodynamic properties of the hydration water, which usually must be removed for the process to take place [7].…”