Shear properties of the liquid bridge between two graphene films using a refined molecular kinetics theory and molecular dynamics simulations

Abstract

At the micro/nano-scale, the friction arising from capillary-condensed liquid bridges has a large effect on the friction performance between two sliding surfaces, where the shear field in the vicinity of the moving contact line (MCL) is sufficiently intense. In this study, we develop a refined molecular-kinetic theory (MKT) of dynamic wetting by considering the effect of both the liquid-solid and liquid-solid-vapour interfaces on the shear stress. The capillary shearing process of liquid bridges between two graphene films is studied using large-scale molecular dynamics (MD) simulations. Our MD results show that the shear stress at the liquid-solid-vapour interface is of the same order of magnitude as that at the liquid-solid interface. The stronger depth of the Lennard-Jones (LJ) potential between the liquid and solid molecules results in smaller static/dynamic contact angles and larger friction coefficients and interfacial adhesion energies. The total shear stress of three-dimensional (3D) liquid bridges increases as the velocity of the graphene film increases within a certain range. The sizes of liquid bridges strongly affect the shear stress of the liquid bridges, but hardly affect the static/dynamic contact angles. The present refined MKT has higher accuracy than the other available theoretical models as the velocity of graphene films increases, in comparison with that of the MD simulations. Our results will be of great help for understanding the dynamic wetting at the molecular level and the friction in micro/nano-fluidics and micro/nano-electromechanical systems (M/NEMS).