Study of active Brownian particle diffusion in polymer solutions.

Area of Science:

• Soft Matter Physics
• Polymer Science
• Statistical Mechanics

Background:

• Active Brownian particles (ABPs) are model systems for self-propelled objects.
• Polymer solutions present complex environments with length-scale-dependent properties.
• Understanding particle dynamics in such media is crucial for various applications.

Purpose of the Study:

• To investigate the diffusion behavior of an active Brownian particle (ABP) in polymer solutions.
• To explore the influence of particle size and active force on diffusion coefficients.
• To elucidate the underlying mechanisms governing non-trivial diffusion phenomena.

Main Methods:

• Langevin dynamics simulations were employed to model particle motion.
• Analysis of both long-time and short-time diffusion dynamics.
• Phenomenological introduction and analysis of effective viscosity experienced by the ABP.

Main Results:

• A non-monotonic dependence of the long-time diffusion coefficient (D) on particle size (R) was observed for sufficiently large active forces (Fa).
• Larger particles can diffuse faster than smaller ones, a counterintuitive finding.
• Effective viscosity (ηeff) experienced by the ABP is larger than the passive case and depends significantly on R and Fa.
• Diffusion coefficient (D) shows power-law scaling with propelling force (Fa) at fixed R, with scaling factors varying non-monotonically with R.

Conclusions:

• The counterintuitive diffusion behavior arises from the interplay between the ABP's persistent motion and the polymer solution's length-scale-dependent effective viscosity.
• Active processes introduce subtle but significant effects on nanoparticle diffusion in complex solutions.
• The study provides a deeper understanding of active particle dynamics in viscoelastic media.