Active and passive particles: modeling beads in a bacterial bath.

Area of Science:

• Physics
• Soft Matter Physics
• Statistical Mechanics

Background:

• Understanding particle dynamics in complex fluids is crucial.
• Active matter systems, like bacteria, exhibit unique self-propulsion behaviors.
• Previous studies on passive particle diffusion in active baths lacked a unifying theoretical framework.

Purpose of the Study:

• To introduce a simple theoretical model for passive particle motion in an active bath.
• To provide a framework for interpreting experimental results on particle diffusion in bacterial suspensions.
• To predict the emergence of superdiffusive behavior in active matter systems.

Main Methods:

• Development of a simplified theoretical model for particle dynamics.
• Analysis of particle trajectories in a two-dimensional fluid film.
• Comparison of model predictions with experimental data from polystyrene beads displaced by bacteria.

Main Results:

• The proposed model successfully describes the motion of passive particles in an active bath.
• The model framework aligns with experimental observations of diffusive properties.
• Superdiffusive behavior is predicted in the transition region of collective motion onset.

Conclusions:

• The introduced model offers a correct framework for studying passive particle dynamics in active media.
• Experimental results on polystyrene beads and bacteria are well-explained by this model.
• Superdiffusion is a generic phenomenon expected at the onset of collective motion in active systems.