Nonlinear response and emerging nonequilibrium microstructures for biased diffusion in confined crowded environments.

Area of Science:

• Soft Matter Physics
• Statistical Mechanics
• Non-equilibrium Systems

Background:

• Active microrheology experiments often involve driven particles in confined environments.
• Understanding particle dynamics in crowded molecular systems is crucial for various applications.
• Previous models often relied on linear-response approximations, limiting their applicability.

Purpose of the Study:

• To analytically study the dynamics and microstructural changes of a host medium caused by a driven tracer particle.
• To investigate particle behavior beyond the linear-response (Stokes) regime in confined molecular crowding.
• To determine the force-velocity relation and stationary density profiles for a driven tracer particle.

Main Methods:

• Analytical investigation using a decoupling scheme.
• Modeling a confined lattice system (2D striplike or 3D capillary-like).
• Incorporating stochastic dynamics for tracer and bath particles.
• Validation through extensive numerical simulations.

Main Results:

• The terminal velocity of the driven tracer particle shows non-monotonic behavior with force under certain conditions.
• Negative differential mobility is observed in specific parameter ranges.
• The driven particle induces a nonequilibrium steady state with an exponentially decaying stationary density profile past the tracer.

Conclusions:

• The study provides a theoretical framework for understanding driven particle dynamics in confined crowded environments.
• The findings reveal complex behaviors like negative differential mobility, not seen in simpler models.
• The exponential decay of the density profile highlights the system's departure from equilibrium and unbounded lattice behavior.