(125d) Modeling the Size-Dependent Stacking Dynamics of Graphene Particles at a Water-Vapor Interface

The dynamics of particles trapped at a fluid-fluid interface can be markedly different than in a bulk fluid because the interfacially trapped particles are confined to translate in only two dimensions. This has important implications for platelet-like particles, such as graphene, MoS₂, or hexagonal boron nitride, which would prefer to interact in a face-to-face orientation when suspended in a bulk fluid, but are forced to interact in an edge-to-edge orientation when pinned to a fluid-fluid interface. Thus, fluid-fluid interfaces have been exploited to fabricate and deposit large area films of laterally aggregated 2D materials for use in thin-film devices. However, it is important to understand the conditions under which laterally aggregated 2D materials at fluid interfaces are capable of overcoming the edge-to-edge orientation and stacking in a face-to-face manner in order to reproducibly deposit films with controlled thickness. These conditions are not yet understood as deposited films demonstrate regions of laterally aggregated, non-stacked graphene particles but molecular dynamics (MD) simulations demonstrate spontaneous and complete stacking of graphene particles upon lateral aggregation, which points to the disparity between experiments and simulations being a result of the difference in length scales of the particles studied. In this work, we have investigated the size-dependent stacking dynamics of graphene particles at a water-vapor interface using MD simulations, experiments, and simple modeling. We will present the results from these MD simulations that suggest the energy barrier to particle stacking is proportional to the length of contact between two aggregated graphene particles and related to the surface energy penalty required to deform a fluid-fluid interface. We will also present experimental results that align with our MD simulations and proposed model.