Rotational Analysis of Spherical, Optically Anisotropic Janus Particles by Dynamic Microscopy

Area of Science:

• Colloidal science
• Soft matter physics
• Nanotechnology

Background:

• Janus particles, with distinct hemispherical caps (silica and Au/Pd), exhibit optical anisotropy dependent on orientation.
• The metal cap acts as a catalyst for hydrogen peroxide breakdown, enabling chemical activation.
• Particles are partially tethered, allowing rotation while restricting translational movement.

Purpose of the Study:

• To analyze the rotational dynamics of spherical colloidal Janus particles.
• To investigate rotational diffusion and constant rotation in tethered single Janus microspheres.
• To study the rotary motion of chemically activated Janus dimers.

Main Methods:

• Bright-field optical microscopy to observe particle orientation.
• Individual particle tracking for motion analysis.
• Differential dynamic microscopy (DDM) for analyzing both experimental and simulation data.

Main Results:

• DDM can effectively probe rotational diffusion and constant rotation even for single entities when translational motion is suppressed.
• Analysis of both experimental microscopy and computer-generated simulations provided insights into particle dynamics.
• Coupled Janus dimers exhibit stable rotary motion around a mutual center when chemically activated.

Conclusions:

• The orientation-dependent refractive index of Janus particles allows for optical tracking of their rotational dynamics.
• DDM is a powerful technique for studying rotational dynamics in colloidal systems, particularly when translation is limited.
• Chemically activated Janus particles offer tunable rotary motion for potential applications.