Janus Colloids Actively Rotating on the Surface of Water

Area of Science:

• Colloid science
• Soft matter physics
• Active matter physics

Background:

• Microswimmers exhibit diverse trajectories like rectilinear, circular, or spiral motion.
• Janus particles are synthetic microswimmers with distinct properties on different hemispheres.
• The air-water interface provides a 2D environment for studying microswimmer dynamics.

Purpose of the Study:

• To investigate the motion of active Janus colloids at the air-water interface.
• To understand the factors contributing to observed circular trajectories.
• To analyze the influence of particle properties and wetting on motion persistence and diffusion.

Main Methods:

• Fabrication of Janus colloids with asymmetric and nonuniform surface properties.
• Observation and analysis of particle trajectories at the air-water interface.
• Characterization of motion persistence and rotational diffusion (in-plane and out-of-plane).

Main Results:

• Active Janus colloids were observed to follow circular trajectories.
• Asymmetric surface properties resulting from fabrication were identified as the cause of circular motion.
• Partial wetting of Janus particles enhanced motion persistence in their 2D movement.
• Slowing down of both in-plane and out-of-plane rotational diffusions was observed and discussed.

Conclusions:

• Fabrication-induced asymmetry in Janus colloids leads to predictable circular motion.
• The interplay between particle properties, wetting, and the 2D interface governs microswimmer dynamics.
• Understanding these dynamics is crucial for designing and controlling artificial microswimmers.