Collisions between amorphous carbon nanoparticles: phase transformations

¹ Physics Department and Research Center OPTIMAS, University Kaiserslautern, Erwin-Schrödinger-Straße, 67663 Kaiserslautern, Germany
e-mail: urbassek@rhrk.uni-kl.de
² Centro de Investigación DAiTA Lab, Facultad de Estudios Interdisciplinarios, Universidad Mayor, Santiago, Chile
³ Center for the Development of Nanoscience and Nanotechnology CEDENNA, Avda. Ecuador 3493, Santiago 9170124, Chile
⁴ Centro de Nanotecnología Aplicada, Facultad de Ciencias, Universidad Mayor, Santiago 8580745, Chile
⁵ CONICET and Facultad de Ingeniería, Universidad de Mendoza, Mendoza 5500, Argentina

Received: 16 April 2020
Accepted: 29 July 2020

Abstract

Context. Collisions of nanoparticles (NPs) occur in dust clouds and protoplanetary disks.

Aims. Sticking collisions lead to the growth of NPs, in contrast to bouncing or even fragmentation events and we aim to explore these processes in amorphous carbon NPs.

Methods. Using molecular-dynamics simulations, we studied central collisions between amorphous carbon NPs that had radii in the range of 6.5–20 nm and velocities of 100–3000 m s⁻¹, and with varying sp³ content (20–55%).

Results. We find that the collisions are always sticking. The contact radius formed surpasses the estimate provided by the traditional Johnson-Kendall-Roberts model, pointing at the dominant influence of attractive forces between the NPs. Plasticity occurs via shear-transformation zones. In addition, we find bond rearrangements in the collision zone. Low-sp³ material (sp³ ≤ 40%) is compressed to sp³ > 50%. On the other hand, for the highest sp³ fraction, 55%, graphitization starts in the collision zone leading to low-density and even porous material.

Conclusions. Collisions of amorphous carbon NPs lead to an increased porosity, atomic surface roughness, and changed hybridization that affect the mechanical and optical properties of the collided NPs.