Active Janus colloids at chemically structured surfaces.

Area of Science:

• Colloid science
• Chemical engineering
• Theoretical physics

Background:

• Janus particles exhibit self-propulsion due to catalytic activity creating chemical gradients.
• These gradients induce self-phoretic motion and chemiosmosis near confining surfaces.
• Understanding active colloid dynamics near patterned surfaces is crucial for designing micro-machines.

Purpose of the Study:

• To theoretically analyze the dynamics of active colloids near chemically patterned walls.
• To investigate the influence of pattern geometry and chemical contrast on particle trajectories.
• To explore changes in phase portrait topology with varying chemical contrast and stripe width.

Main Methods:

• Utilized a point-particle approximation for theoretical analysis.
• Employed multipole expansion to model particle-surface interactions.
• Simulated particle dynamics near planar walls with chemical steps and stripes.

Main Results:

• Demonstrated that chemical gradients drive self-propulsion via phoresis and chemiosmosis.
• Showcased the impact of chemical pattern geometry and contrast on particle trajectories.
• Identified topological changes in phase portraits correlating with pattern variations.

Conclusions:

• Chemically patterned walls significantly influence active colloid dynamics.
• The interplay between particle activity, wall chemistry, and geometry dictates self-motility.
• Theoretical framework provides insights into controlling active matter behavior near surfaces.