Frequency Response of Induced-Charge Electrophoretic Metallic Janus Particles

Abstract

The ability to manipulate and control active microparticles is essential for designing microrobots for applications. This paper describes the use of electric and magnetic fields to control the direction and speed of induced-charge electrophoresis (ICEP) driven metallic Janus microrobots. A direct current (DC) magnetic field applied in the direction perpendicular to the electric field maintains the linear movement of particles in a 2D plane. Phoretic force spectroscopy (PFS), a phase-sensitive detection method to detect the motions of phoretic particles, is used to characterize the frequency-dependent phoretic mobility and drag coefficient of the phoretic force. When the electric field is scanned over a frequency range of 1 kHz–1 MHz, the Janus particles exhibit an ICEP direction reversal at a crossover frequency at ~30 kH., Below this crossover frequency, the particle moves in a direction towards the dielectric side of the particle, and above this frequency, the particle moves towards the metallic side. The ICEP phoretic drag coefficient measured by PFS is found to be similar to that of the Stokes drag. Further investigation is required to study microscopic interpretations of the frequency at which ICEP mobility switched signs and the reason why the magnitudes of the forward and reversed modes of ICEP are so different.

Synergistic Speed Enhancement of an Electric-Photochemical Hybrid Micromotor by Tilt Rectification

“…In both cases, the motors moved with the TiO 2 forward and in randomized, independent trajectories (Figure S2 and Video S1), indicating autonomous motion and minimal drifting caused by light or electric fields. Moreover, similar to earlier reports, the speeds and directionality of a TiO 2 –Pt micromotor can be modulated by varying the driving AC frequencies (Figure f): they move with TiO 2 forward via ICEP at ∼10 kHz, come to a stop at ∼100 kHz, and begin to move in the opposite direction toward Pt beyond ∼200 kHz. − The last regime of reverse motion is not explored in the current manuscript, even though switching a hybrid micromotor between a forward and reverse motion is useful …”

Biomedical Applications of Microfluidic Devices: A Review

“…Biomedical microdevices include integrated structures consisting of numerous micro- and nano-sized integrated devices, where many processes from particle manipulation to sensing take place in the platform. Although different types of microfluidic devices can perform similar tasks in biomedical applications, passive microfluidic systems are mainly used for particle manipulation [ 1 , 2 , 3 , 4 , 5 ] and mixing liquids [ 4 , 6 ], while active types contribute more to particle trapping [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ] and sensing [ 20 , 21 , 22 , 23 , 24 ]. Passive devices are governed by diffusion, inertial forces, secondary flows, and geometry-induced turbulence and particle manipulation; active microfluidic devices generate streams depending on external energy to disturb particles or fluids inside microfluidic devices.…”

Electrophoresis of metal-dielectric Janus particles with dipolar director symmetry in nematic liquid crystals

“…In nonlinear electrophoresis or so-called induced-charge electrophoresis, the motility of particles is independent of the polarity of applied electric field and the propelling velocity is proportional to the square of the electric field ( v ∝ E 2 ). 19–28…”