Molecular dynamics simulations are used to study the dynamics of a single Al nanosphere (singlet) colliding with an aggregate of two Al nanospheres (doublet) with initial Ⅰ-shaped configuration. Depending on the initial impact velocity, there are four collision outcomes, namely bounce, adhesion, aggregation and melting. At a very low velocity, the repulsive force between the nanospheres leads the nanospheres to rebound without contact, and the critical velocity of bounce decreases with the increase of the diameter of the nanosphere. As the velocity increases, the nanospheres are sintered together due to adhesion between them and the formation of new bonds. The phase transformation and atomic diffusion during singlet-doublet collisions are quantitatively characterized by common neighbor analysis, dislocation analysis and mean square displacement to explore the underlying sintering mechanism. The critical impact velocity of singlet melting is obtained by monitoring the temperature of singlet with different diameters.

Molecular dynamics simulations have been performed to explore the underlying synergistic mechanism of pillared graphene or non-covalent connected graphene and carbon nanotubes (CNTs) on the mechanical properties of polyethylene (PE) nanocomposites. By constructing the pillared graphene model and CNTs/graphene model, the effect of the structure, arrangement and dispersion of hybrid fillers on the tensile mechanical properties of PE nanocomposites was studied. The results show that the pillared graphene/PE nanocomposites exhibit higher Young's modulus, tensile strength and elongation at break than non-covalent connected CNTs/graphene/PE nanocomposites. The pull-out simulations show that pillared graphene by CNTs has both large interfacial load and long displacement due to the mixed modes of shear separation and normal separation. Additionally, pillared graphene can not only inhibit agglomeration but also form a compact effective thickness (stiff layer), consistent with the adsorption behavior and improved interfacial energy between pillared graphene and PE matrix.