Aspect-ratio-dependent void formation in active rhomboidal and elliptical particle systems

We execute a numerical simulation on active nematics with particles interacting by excluded volume effect. The system with rhomboidal particles and that with elliptical particles are considered in order to investigate the effect of the direct contact of particles. In our simulation, the void regions, where the local number density is almost zero, appear in both the systems when aspect ratio of the particles is high. We focused on the relationship between the void regions and the particle orientation of the bulk. The particle number density, particle orientation, topological defects, and void regions are analyzed for different aspect ratios in both the systems. The systems with rhomboidal particles have a characteristic void size, which increases with an increase in the aspect ratio. In contrast, the distribution of the void-region size in the systems with elliptical particles is broad. The present results suggest that the void size in the system with rhomboidal particles is determined by the correlation length of the particle orientational field around the void regions, while that in the system with elliptical particles might be determined by the system size.