Theoretical Studies Of Nonequilibrium Dynamics Of Active System

In recent years,theoretical studies of non-equilibrium dynamics of active particle systems have gained a lot of attentions,and become the frontier domain of chemistry,physics,biology and other inter-disciplinary sciences.Active particles can conserve ambient free energy into consistent,direct motion.Due to this unique property,the dynamic properties of active particle system are notably different from the ones of equilibrium system.Thus the research of active particle system can help us to reveal the physics of non-equilibrium and design and manufacture biological intelligent devices or materials.When study and explore active particle system,scientific researchers have spent lots of time to solve the following two difficulties:one is how to understand mechanism of emergence of the complex collective motion in active system,another is how to understand how active environment composed of active particles affect the dynamic behavior of passive ones.In the present paper,we use computer simulation to study the influence of inter-particle interaction on phase separation of active system and the influence of active environment on the translocation of polymer through an nanopore.Reentrance phase separation of active particle system with anisotropic interactionIn recent years,many experimental and theoretical works focus on phase separation of active particle systems,while we mainly study how the anisotropic interaction,such as Janus interaction,will affect the phase separation.Simulation results show that Janus interaction tends to bring particles together with attractive sides staying together and repulsive staying away from each other.When the volume fraction is small,phase separation does not occur for active system without Janus interaction.With increasing the strength of Janus interaction intensity,reentrant phase separation occurs:the system stays disordered for both too weak and too strong Janus interaction,while a moderate one will lead the system to be phase separated.When volume fraction is large,phase separation has already occurred obviously.Adding up Janus interaction in active system will lead the phase separation to be more pronounced,while a large one also destroys the clusters and leads the system to be a disordered one.By analyzing static structure factor and size of maximum cluster,we believe that competition between the self-propulsion and the Janus interaction leads to the reentrance behavior:While self-propulsion can lead to clustering of the active particles,the Janus interaction favors the formation of states with attractive sides close to each other and repulsive sides staying apart.Translocation of polymer through an nanopore into active bathTranslocation of polymer through nanopore or channel has gained extensive attentions and indepth studies.On one hand,studying polymer translocation can help us to understand may key progresses in real biology systems,such as rapid transcription of DNA.On the other hand,it has long-term application value for realizing artificial controlling based on understanding the physics of polymer translocation.Considering that most of works about translocation are as to passive system,we focus on the influence of active bath on polymer translocation in the present paper.For a fixed volume fraction,the average translocation time shows a nontrivial dependence on activity:there exists a moderate value that makes the translocation slowest.While for a large fixed activity,the average translocation time also shows a nontrivial variance with increasing volume fraction:there exist an optimal value that is most favorable for translocation.By calculating waiting times and accumulative waiting times,we find that the active bath plays a two-fold role on the translocation:active particles tend to accumulate near the nanopore and decelerate the translocation,while active particles also aggregate near the polymer and accelerate the translocation by bringing the polymer moving together.The competition of these two effects lead to the nontrivial behavior.Further studies show that the average translocation time shows a good power-law scaling behavior of polymer length,while the exponent decreases monotonically with activity and volume fraction.