Memory-Induced Transition from a Persistent Random Walk to Circular Motion for Achiral Microswimmers

Area of Science:

• Soft Matter Physics
• Fluid Dynamics
• Colloidal Science

Background:

• Active Brownian motion describes self-propelled particles.
• Viscoelastic fluids exhibit both viscous and elastic properties.
• Microswimmer behavior deviates in non-Newtonian fluids.

Purpose of the Study:

• Investigate microswimmer dynamics in viscoelastic fluids.
• Characterize the transition from diffusion to directed motion.
• Understand the role of fluid memory on active particle behavior.

Main Methods:

• Experimental study of light-activated colloidal microswimmers.
• Analysis of particle trajectories and rotational motion.
• Development of a non-Markovian Langevin model.

Main Results:

• Spherical microswimmers showed a transition to persistent rotation above a critical speed.
• Circular orbits spontaneously reversed direction.
• Angular velocity and radius of curvature showed nonlinear dependence on propulsion speed.

Conclusions:

• Non-Newtonian fluid memory induces novel nonequilibrium effects in microswimmer motion.
• Delayed fluid response, not particle chirality, drives observed rotational behavior.
• Findings offer insights into active matter dynamics in complex fluids.