Nonequilibrium depletion interactions in active microrheology.

Area of Science:

• Soft Matter Physics
• Colloid Science
• Statistical Mechanics

Background:

• Entropic depletion forces are key interactions in systems with large and small particles, like colloid-polymer mixtures.
• These forces arise from excluded volume effects and drive self-assembly and phase behavior.
• Understanding these forces is crucial for designing novel materials and controlling colloidal systems.

Purpose of the Study:

• To calculate nonequilibrium forces between two colloidal particles in a bath of smaller depletants.
• To assess the accuracy of the dynamical superposition approximation (DSA) for these forces.
• To investigate the colloidal microstructure around a driven colloidal probe.

Main Methods:

• Theoretical calculation of inter-colloidal forces using the dynamical superposition approximation (DSA).
• Development of a theoretical framework for driven colloidal systems in a depletant bath.
• Validation of theoretical results through extensive Brownian dynamics (BD) simulations.

Main Results:

• The dynamical superposition approximation (DSA) provides a quantitative description of entropic depletion forces.
• The study elucidates the colloidal microstructure around a driven colloidal probe.
• Theoretical predictions for forces and microstructure are corroborated by Brownian dynamics simulations.

Conclusions:

• The dynamical superposition approximation (DSA) is a reliable method for studying nonequilibrium forces in colloidal suspensions.
• The findings offer insights into the behavior of driven colloidal particles and their interactions.
• This work contributes to the fundamental understanding of entropic depletion phenomena in complex fluids.