Flow fields around pinned self-thermophoretic microswimmers under confinement

Area of Science:

• Colloidal science
• Soft matter physics
• Fluid dynamics

Background:

• Phoretic swimmers, like Janus particles, generate flows due to self-thermophoresis.
• Particle behavior in confined geometries is crucial for understanding microfluidic devices and biological systems.
• Substrate interactions can significantly alter flow fields around active particles.

Purpose of the Study:

• To measure and characterize the flow field around a self-thermophoretic Janus particle confined in slit pores of varying widths.
• To investigate the influence of slit width on the generated flow patterns.
• To identify the mechanisms responsible for observed flow behaviors, particularly thermo-osmotic effects.

Main Methods:

• Utilized micrometer-sized Janus particles that exhibit self-thermophoresis.
• Employed thermophoretically inactive gold nanoparticles as tracers to visualize the flow field.
• Confined the Janus particle within slit pores of different controlled widths.
• Analyzed the movement of gold nanoparticles to map the surrounding flow field.

Main Results:

• Observed significant alterations in the flow field as the slit pore width decreased.
• Identified distinct features indicative of thermo-osmotic flows generated by temperature gradients along the confining glass surfaces.
• Demonstrated that these substrate-induced flows are a key factor in the measured flow fields.

Conclusions:

• The study reveals that thermo-osmotic creep flows at substrate boundaries significantly impact the hydrodynamics around self-thermophoretic Janus particles in confined geometries.
• These findings suggest that substrate-induced osmotic flows may play a crucial role in phenomena like particle clustering observed around phoretic swimmers.
• Highlights the importance of considering boundary effects in studies of active matter in confined environments.