Structural and dynamical characterization of water on the Au (100) and graphene surfaces: A molecular dynamics simulation approach

The positioning, adsorption, and movement of water on substrates is dependent upon the chemical nature and arrangement of the atoms of the surface. Therefore the behavior of water molecules on a substrate is a reflection of properties of the surface. Based on this premise, graphene and gold substrates were chosen to study this subject from a molecular perspective. In this work, the structural and dynamical behaviors of a water nanodroplet on Au (100) and the graphene interfaces have been studied by molecular dynamics simulation. The results have shown how the structural and dynamical behaviors of water molecules at the interface reflect the characteristics of these surfaces. The results have demonstrated that residence time and hydrogen bonds’ lifetime at the water-Au (100) interface are bigger than at the water-graphene interface. Energy contour map analysis indicates a more uniform surface energy on graphene than on the gold surface. The obtained results illustrate that water clusters on gold and graphene form tetramer and hexamer structures, respectively. Furthermore, the water molecules are more ordered on the gold surface than on graphene. The study of hydrogen bonds showed that the order, stability, and the number of hydrogen bonds is higher on the gold surface. The positioning pattern of water molecules is also similar to the arrangement of gold atoms while no regularity was observed on graphene. The study of dynamical behavior of water molecules revealed that the movement of water on gold is much less than on graphene which is in agreement with the strong water-gold interaction in comparison to the water-graphene interaction.

Figure 1

The final snapshots of the water nanodroplet on (a) Au (100), and (b) graphene surfaces. Red, white, yellow, and green represent oxygen, hydrogen, gold, and carbon, respectively.

Figure 2

Density profile of water molecules on Au (100) and graphene substrates.

Figure 3

Comparison of the contour map energy between one water molecule with (a) Au (100), and (b) graphene substrate. (c) Comparison of the interaction energy between a water molecule with Au (100) and graphene substrates along the $Z$ axis.

Figure 4

Distribution of the triple angle between water molecules on the interface of (a) Au (100), and (b) graphene.

Figure 5

(a) Frequency distribution of the ternary, tetramer, pentamer, and hexamer clusters at the interface of Au (100) and graphene; (b) Formation of the tetramer cluster at the interface of Au (100), and (c) the formation of the hexamer cluster at the interface of graphene.

Figure 6

Order parameter of water molecules along the $Z$ axis.

Figure 7

(a) Number of hydrogen bonding at the interface of Au (100) and graphene in the last 500 ps of the simulation, Snapshots of water molecules at the interface of (b) Au (100), and (c) graphene.

Figure 8

Stability of hydrogen bonding at interface of Au (100) and graphene.

Figure 9

Variations of center of mass of water molecules on (a) gold, and (b) graphene surfaces.

Figure 10

Variation of MSD of hydrogen and oxygen atoms of water molecules at the interface of (a) Au (100) and (b) graphene. Variation of MSD of water molecules at the interface (blue) and adjacent layer (orange) of (c) Au (100) and (d) graphene systems.

Figure 11

Residence time of water molecules at the interface of Au (100) and graphene.