Molecular Dynamics: A Study on Slip, Drops, and Graphene

Molecular dynamics (MD) is a computational tool used to study physical systems by modeling the atomic-scale interactions between atoms. MD can accurately predict the properties of materials where models are well developed. For new materials, models may be in their early stages and may lack the ability to produce accurate results; however, MD can still provide insight into the physical properties of these new materials. This thesis will use MD to study two different systems. First, the Lennard-Jones (L-J) liquid is used to study how the intrinsic slip lengths of atomic sized surfaces add to produce an effective slip of a larger surface made up of these atomic constituents. The results show that the effective slip of a surface is dominated by its smallest slip, and these results show good agreement with a theory that predicts effective slip given the intrinsic slip and roughness of a surface. The L-J model is also used to investigate the rolling and sliding motion of viscous drops on super-hydrophobic surfaces. The effects of drop size, slip length, and gravity on drop velocities are investigated, and a model that predicts drop speed given the characteristics of a drop and a surface is proposed. The model shows good agreement with simulation results, especially for certain regimes. Second, graphene is studied with MD using various atomistic models. The energies of layers of graphene are reproduced using an Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential, and the energies required to exfoliate graphene from crystal graphite and nickel nano-particles are calculated. The calculations from MD show good agreement with literature and experiment, and these results demonstrate how simple models in MD can produce useful results to aid research and experiment. Finally, the formation of nano-bubbles in graphene grown on platinum is studied using the AIREBO and L-J potentials. The basic formation of graphene nano-bubbles is demonstrated by compressing the edges of graphene  flakes. The simulations highlight the importance of proper boundary conditions, such as atom pinning, in order to produce tall, smooth nano-bubbles. The results also suggest that accurate models will be required to effectively demonstrate bubble formation.</p