Molecular Dynamics Study of Wetting on Brushlike Nanopillar and Wavelike Nanorough Surfaces

Abstract

A Molecular Dynamics technique is proposed to simulate the motion of water nano-droplets on brushlike nanopillar and wavelike nanorough surfaces. Firstly, a brushlike nanopillar structure is obtained by deposition of a hexagonal packing of alkyl linear chains CnH2n+1 (n = 1–18) on a (0001) type flat surface, consisted of hexagonal packed carbon atoms. Distance between the grafted alkyl chains is selected in the 0.5–1.4 nm range, and the distance between the carbon atoms of the base surface is set to 0.1421nm. Next, the (0001) type flat surface is folded in order to obtain a wavelike nano-roughness. Water cluster is consisted of 729–2197 molecules, and after 25ps it reaches a diameter of 3–5 nm, which corresponds to a liquid phase of 1g/cm3 density, at an equilibrium temperature of 293K. Lennard-Jones potential is used to describe all the interactions into the considered system. By the appropriate input of the Lennard-Jones parameters one controls the hydrophilic level of the base surface. Influences of the intermolecular distance and the length of the grafted alkyls, as well as the influences of the nano-wavelength and the hydrophilic level of the base surface on the contact angle are illustrated. Such results are useful for the appropriate design of ultrahydrophobic nano-surfaces, and for the optimal design of nanoporous materials, able to produce surface dissipation of the mechanical energy.