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Nanodroplets Behavior on Graphdiyne Membranes Ygor M. Jaques and Douglas S. Galvão Applied Physics Department, University of Campinas, Campinas, SP 13081-970, Brazil

ABSTRACT In this work we have investigated, by fully atomistic reactive (force field ReaxFF) molecular dynamics simulations, some aspects of impact dynamics of water nanodroplets on graphdiyne-like membranes. We simulated graphdiyne-supported membranes impacted by nanodroplets at different velocities (from 100 up to 1500 m/s). The results show that due to the graphdiyne porous and elastic structure, the droplets present an impact dynamics very complex in relation to the ones observed for graphene membranes. Under impact the droplets spread over the surface with a maximum contact radius proportional to the impact velocity. Depending on the energy impact value, a number of water molecules were able to percolate the nanopore sheets. However, even in these cases the droplet shape is preserved and the main differences between the different impact velocities cases reside on the splashing pattern at the maximum spreading.

INTRODUCTION The materials science revolution created by the advent of graphene [1] has renewed the interest for other two-dimensional carbon allotropes, such as graphynes [2–5]. Graphyne is a generic name for a family of 2D carbon allotropes where acetylenic groups connect benzenoidlike rings, with the coexistence of sp and sp2 hybridized carbon atoms. Similarly to graphene, tubular structures can also exist [3,4]. Graphdiynes are graphyne-like structures with double acetylene linkages (Figure 1). Graphdiynes can exist in many different configurations, the most common are known as α, β, and γ-graphdiynes (see Figure 1 for an example of γ-graphdiyne). They constitute a family of interesting class of membranes with uniformly distributed nanopores [5–7] that can be exploited for a variety of applications. They are one of the most stable nonnatural carbon allotropes and some structures have been already experimentally realized [6]. In order to study the applicability of graphdiynes as selective membranes [8,9], it is important to known their wettability behavior on equilibrium and also on non-equilibrium conditions, such as like under high velocity impacts. Droplet splashing dynamics on surfaces is an important area in general science and industry [10–13], dealing with diverse aspects that a liquid could have (such as shapes and sizes) on impacting surfaces at different velocities. In this work, we have use fully atomistic molecular dynamics (MD) simulations to investiagate how water nanodroplets behave on impact at graphdyine membranes. Due to space limitations we restrict ourselves to the case of γ-graphdyines.

THEORY The MD simulations were carried out using the reactive force field ReaxFF [14], as implemented on LAMMPS package [15]. We considered structures (Figure 1) consisting of γ-

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