Tracer diffusion in crowded solutions of sticky polymers

Area of Science:

• Soft matter physics
• Biophysics
• Computational physics

Background:

• Macromolecular diffusion in confined and crowded systems remains a complex, unresolved area.
• Understanding tracer behavior is crucial for biological and materials science applications.
• Existing models often simplify interactions, neglecting combined effects of excluded volume and attractions.

Purpose of the Study:

• To investigate how excluded-volume and attractive crowder-tracer interactions influence tracer diffusion.
• To compare diffusion and structural properties of standard hard-core (WCA) and core-softened (CS) tracers.
• To analyze the impact of tracer-polymer affinity and system density on transport phenomena.

Main Methods:

• Employed large-scale Langevin dynamics simulations.
• Simulated two tracer species: Weeks-Chandler-Andersen (WCA) and core-softened (CS) particles.
• Studied tracer diffusion and structure in a polymer-crowded environment at varying densities.

Main Results:

• WCA and CS tracers exhibited similar diffusion properties across densities.
• CS particles showed reduced propensity for structural ordering in crowded environments.
• WCA tracers displayed a nonmonotonic diffusion trend with increasing density at high tracer-polymer affinity, a 'waterlike anomaly'.

Conclusions:

• The competition between excluded-volume and affinity effects significantly impacts tracer diffusion, especially for WCA tracers.
• Core-softened particles are less prone to structural ordering under crowding.
• The observed 'waterlike anomaly' in WCA tracer diffusion highlights complex transport behaviors in crowded soft matter systems.