Mesoscopic clustering behavior of thermophoretic-type active particle suspension under quasi-one-dimensional...

Area of Science:

• Soft Matter Physics
• Mesoscopic Physics
• Microfluidics

Background:

• Active particle suspensions exhibit complex behaviors influenced by self-propulsion and interactions.
• Spatial confinement, such as in microchannels, can significantly alter these behaviors by modifying dissipation and geometry.
• Thermophoresis, the movement of particles in response to a temperature gradient, is a key force in active matter systems.

Purpose of the Study:

• To experimentally investigate the mesoscopic clustering behavior of thermophoretic-type active particle suspension.
• To explore these behaviors under quasi-one-dimensional spatial confinement within a high aspect ratio microchannel.
• To understand the role of thermophoretic forces and confinement in pattern formation.

Main Methods:

• Utilized a high aspect ratio microchannel to create quasi-one-dimensional confinement.
• Operated the active particle suspension in a subpropulsion regime by enhancing viscous dissipation.
• Varied excitation laser intensity to observe transitions in particle configurations.

Main Results:

• Observed a transition from homogeneous state to various clustering patterns with increasing laser intensity.
• Identified distinct patterns: sausage-like bundles, quasiperiodic isolated clusters, and aperiodic isolated clusters.
• Noted a final transition to propulsion-induced accumulation at the channel boundary.

Conclusions:

• The observed patterns arise from the interplay between outward-pointing thermophoretic forces and spatial confinement.
• The subpropulsion regime in confined geometries leads to rich, non-intuitive mesoscopic clustering.
• These findings suggest novel possibilities for particle manipulation at the mesoscopic scale.