Simulation Study Of Rod-like Particle Diffusion In Active Bath

The active system is one that drives itself away from equilibrium by consuming energy input from the outside world,which is widely distributed in nature,from the macroscopic fish and bird flocks to the microscopic intracellular microsystems.The study of dynamic behaviors of active particle systems has become a frontier scientific problem in the interdisciplinary fields of chemistry,physics and biology.A large num-ber of artificial active particles have also been synthesized in recent years.Most of these particles are coated with some catalytic materials on the surface and generate self-driving force by catalyzing chemical reactions in solution.The study of active sys-tems can helps us to understand some important biochemical processes in the body,and guide us to design and synthesize new intelligent devices and materials for transport,detection and artificial control of the synthesis process and other related processes.Ac-tive particles show a large number of collective behaviors,such as vortex movements,swarm motion,motility induced phase separation,which are impossible to occur in an equilibrium state.Among many questions about the active system,one important questions is how the environment composed of active particles affects the dynamic behavior of passive particles.For example,the diffusion behavior of an passive spherical particle in active bath such as a bacterial suspensions has been studied systematically,showing superdif-fusion in short time and normal diffusion in long time.Some work has also reported that the diffusion coefficient of spherical particles has a non-monotonic dependence on their sizes,i.e.big particles may move faster than a smaller one.However,most nat-ural particles are not perfectly spherical,and just a few studies so far have focused on diffusion of anisotropic particles such as rods or ellipsoids in active bath.Motivated by this,we use langevin dynamics to study the diffusion behavior of a passive rod-like particle in active bath in this thesis.We find that consistent with the pre-vious work,the rod-like particle exhibits superdiffusion behavior in both translational and rotational degrees of freedom in a short time and normal diffusion in a long time,and the effective diffusion coefficient in long time increases with the activity increase.It is also found that the effective translational diffusion coefficient and rotational dif-fusion coefficient have a non-monotonic dependence on the length when the particle activity is not too low,i.e.the diffusion coefficient increases at first and then decreases with the increase of the length.We also pay attention to the translation-rotation coupling of the rod-like particle and find that the rod-like particle has abnormal coupling mode with the increase of particle activity.It is also found that with the further increase of particle activity,the abnormal coupling disappears.We present a qualitative explanation for the competition of two mechanisms based on activity.