Nonequilibrium dynamics of star polymer in an active brownian particle bath
Active matter systems exhibit unique nonequilibrium phenomena that bridge the fields of soft condensed matter and biological physics. In this study, we investigate the structural and dynamical behaviors of a six-armed star copolymer immersed in a dense bath of active Brownian particles (ABPs) via Langevin dynamics simulations. Our results reveal a universal scaling relation for rotational dynamics: ω ∼ Pe1.2, which is independent of the copolymer's bending rigidity κ, thereby confirming the Péclet number (Pe) as the key variable governing nonequilibrium kinetics. Through a torque balance analysis to rotational dissipation, we derive theoretical bounds on the scaling exponent and relate the observed value n ≈ 1.2 to the weakly nonlinear regime where activity-driven accumulation competes with self-propelled escape. We find that interaction potential parameters finely tune the system's behavior: stronger and longer-range interactions promote compact conformations at low ABP densities, while enhancing rotational dynamics. At higher ABP densities, crowding effects dominate, leading to non-monotonic structural and dynamical responses. The effective diffusivity follows Deff/D0 ∼ 1 + αPe2 at moderate Pe and transitions to a different scaling regime (Pe1.3) at high Pe. Our analysis reveals that rotational motion is a finite-range phenomenon: for short arm lengths, the polymer arms sustain bent conformations enabling ABP collection and persistent rotation; other active-particle-induced arm collapse causes rotation to cease. These findings provide a theoretical framework for the quantitative design of active polymer composites and have important implications for intelligent soft materials and micro-nano robotics.