Spinning microrods in a rotating electric field with tunable hodograph

Area of Science:

• Colloidal science
• Soft matter physics
• Microfluidics

Background:

• Rod-like colloidal particles exhibit polarization in external electric fields.
• A temporal delay in polarization generates torque, influencing particle rotation.
• The electric field's hodograph dictates particle rotational dynamics.

Purpose of the Study:

• To investigate the control of rotational dynamics of rod-like colloidal particles using external high-frequency rotational electric fields.
• To explore the relationship between electric field hodograph and particle rotational behavior.
• To demonstrate tunable rotational behaviors in microparticles.

Main Methods:

• Experiments utilized synthesized monodisperse silica microrods (3.29×1.12×1.12μm³) in deionized water.
• An 8-electrode system generated a 30 kHz rotating electric field with an elliptical hodograph.
• Optical microscopy with a CCD camera and Fiji software were used for data acquisition and processing.

Main Results:

• Controlled imposition of three distinct rotational dynamics: asynchronous continuous rotation (tunable spinners).
• Oscillatory motion with sporadic flips (rotational jumpers) leading to enhanced directional ordering.
• A regime of 'arrested' particle orientation along the principal axes of field anisotropy.

Conclusions:

• High-frequency rotational electric fields offer precise control over microparticle rotational dynamics.
• The electric field's hodograph is a key parameter for manipulating particle behavior.
• Demonstrated potential for applications in micro-manipulation and self-assembly.