Dynamics of Self-Propelled Janus Particles in Viscoelastic Fluids

Area of Science:

• Colloidal science
• Soft matter physics
• Polymer physics

Background:

• Janus colloidal particles are synthetic microswimmers capable of self-propulsion.
• Viscoelastic fluids exhibit both viscous and elastic properties, affecting particle dynamics.
• Understanding particle motion in complex fluids is crucial for micro-robotics and targeted drug delivery.

Purpose of the Study:

• To experimentally investigate the active motion of Janus colloidal particles in a viscoelastic fluid.
• To quantify the effect of particle velocity on rotational diffusion.
• To analyze the anisotropic response of microswimmers in viscoelastic media.

Main Methods:

• Utilized spherical Janus colloidal particles for experiments.
• Induced self-propulsion via laser illumination creating local concentration gradients in a critical polymer mixture.
• Measured rotational diffusion and particle velocity in the viscoelastic fluid.

Main Results:

• Observed a significant increase (up to 2 orders of magnitude) in rotational diffusion with increasing particle velocity.
• Found that this enhancement can be described by an effective rotational diffusion coefficient dependent on the Weissenberg number.
• Demonstrated a highly anisotropic response of microswimmers to external forces, dependent on particle orientation.

Conclusions:

• Particle velocity strongly influences rotational diffusion in viscoelastic fluids.
• The Weissenberg number effectively characterizes the observed phenomenon.
• Active Janus particles display orientation-dependent behavior in complex viscoelastic media, impacting their motility and response to stimuli.