Theoretical Studies Of Collective Behaviors In Active System With Anisotropic Interactions

Active systems are ubiquitous at all scales in nature,from animal flocks to bacteria colonies.Their constituent units could transduce energy supplied internally or externally into mechanical work to drive their motions.Due to the unique nature of active motion,dynamical properties of active system are quite different from those of equilibrium system,such as giant number fluctuation,super-diffusion and spontaneous flow.Understanding the physical origins of such dynamical properties is of great importance for revealing the mystery of living systems and further for manufacturing smart materials.Therefore,the studies on the nonequilibrium dynamics of active systems have attracted extensive attention and become the frontier domain of physics,chemistry,biology and other interdisciplinary fields.In many studies of active system,a lot of time has been spent to understand the mechanism of collective behaviors in active system."More is different",as P.W.Anderson wrote long ago.As a result,abundant interesting collective behaviors that cannot be manifested in equilibrium systems have been reported both experimentally and theoretically,such as motility-induced phase separation,dynamical self-assembly and large-scale vortices,to list just a few.And interparticle interaction has been found to play a key role in collective behaviors,especially anisotropic interaction.In the present paper,we use computer simulations to investigate the influence of anisotropic interaction on the collective behaviors of active system.Detailed summary is as follows:1.Assembled superlattice with dynamic chirality in a mixture of biased-active and passive particlesWe introduce a general model of biased-active particle(BAP)with anisotropic interaction,where the direction of the active force has a biased angle from the principal orientation of the anisotropic interaction between particles,and investigate the self-assembly behaviors of a mixture of BAPs with passive particles by using Langevin dynamics simulations.Remarkably,a highly ordered superlattice consisting of small hexagonal clusters with dynamic chirality emerges within a proper range of active force,given that the biased angle is not too small.In addition,there exists an optimal level of particle activity,being dependent on the biased angle,which is the most favorable for both the long-range order and global dynamic chirality of the system.Our results demonstrate that fascinating collective behaviors can be explored through a proper design of new active particle models.2.Emergent swarming states in active particles system with opposite anisotropic interactionsRecent studies showed the anisotropic interaction between the active particles plays a key role on the phase behaviors.Here we investigate the collective behaviors of active Janus particles that experience an anisotropic interaction of which the orientation is opposite to the direction of active force by using Langevin dynamics simulations in two-dimensional space.Interestingly,the system shows emergence of collective swarming states upon increasing the total area fraction of particles,which is not observed for systems without anisotropic interaction or activity.More interestingly,we could control the collective states when area fraction exceeds the critical value by simply tuning the activity and anisotropic interaction strength,which makes it feasible to tune the swarming states in an efficient way.The threshold value of area fraction decreases with particle activity or interaction strength.We have also performed basic kinetics analysis to reproduce the essential features of the simulation results.Our results demonstrate that anisotropic interactions at the individual level are sufficient to set homogeneous active populations into stable directed motion.