Unpassivated edges as gateways to collision-driven topological transformations in finite graphene nanoflakes

Finite graphene nanoflakes occupy a unique position in the carbon allotrope landscape. Near equilibrium, these systems exhibit pronounced structural robustness, indicating that large-scale allotropic transformations require strongly non-equilibrium energy deposition. In this work, we investigate how unpassivated graphene edges act as chemically active gateways for collision-driven topological transformations in finite graphene systems. Using reactive molecular dynamics simulations, we model energetic collisions involving a C₆₀ fullerene projectile and a finite C₂₉₆ graphene nanoflake across a broad parameter space of collision energies, incidence angles, and edge orientations. The structural response is analysed through statistical transformation maps that quantify the probability of nanoflake bending, edge stitching, and the formation of nanotube-like structures. We identify a regime of collision energies and oblique incidence angles under which localised energy deposition at unpassivated edges promotes bond rearrangement, cooperative bending, and covalent stitching between opposing edges. Furthermore, we find that armchair-directed impacts align opposing zigzag edges and promote efficient edge-to-edge stitching over a broader parameter range. In contrast, zigzag-directed impacts are associated with a higher probability for atom ejection and bring opposing armchair edges into contact, which is less favourable for seam propagation, resulting in a narrower parameter window for nanotube-like structure formation. These results establish a non-equilibrium framework linking local edge chemistry and collision-induced energy deposition to topological evolution in finite graphene systems. The results demonstrate collision-driven self-organisation as a viable pathway for the emergence of tubular nanostructures without reliance on catalytic surfaces or sustained thermal annealing.