Contact Charge Electrophoresis: Fundamentals and Microfluidic Applications

Abstract

Contact charge electrophoresis (CCEP) uses steady electric fields to drive the oscillatory motion of conductive particles and droplets between two or more electrodes. In contrast to traditional forms of electrophoresis and dielectrophoresis, CCEP allows for rapid and sustained particle motions driven by low-power dc voltages. These attributes make CCEP a promising mechanism for powering active components for mobile microfluidic technologies. This Feature Article describes our current understanding of CCEP as well as recent strategies to harness it for applications in microfluidics and beyond.

Controllable High‐Speed Electrostatic Manipulation of Water Droplets on a Superhydrophobic Surface

“…Schematic images in Figure b,c present the arrangement of charges in droplet and substrate. The density of field lines reflects the intensity of the electrostatic field . Influenced by the positively charged glass rod, negative charges rearrange on the superhydrophobic substrate with a high package at the rod side, and a low package at the further side.…”

Multiresponsive Wettability Switching on Polymer Surface: Effect of Surface Chemistry and/or Morphology Tuning

“…Finally, it must be noted that present multistimuli switchable surface is advantageous for its simplicity and flexibility in potential droplet manipulations. In particular, multiswitchable surface properties can be employed at the nano‐ or macro‐scale levels where the application of EF triggering (within 1 V µm −1 range) in combination with temperature and/or pH triggering can solve several key questions in the fields of microfluidic, on‐line drop manipulation, and smart electrophoresis devices …”

Emergence of traveling waves in linear arrays of electromechanical oscillators

“…Each track contained a single particle, which was free to move back and forth between the two electrodes. Application of a constant voltage (typically, V = 10 kV to 20 kV) caused the particles to oscillate continuously between the electrodes via CCEP 13,14 . The conductive particles acquired an electrostatic charge on contact with the biased electrodes and moved under the influence of the applied field.…”

“…To achieve scalable mechanisms of pattern formation, the processes that drive oscillations should scale in the same way as those used to couple neighboring oscillators. In this context, electromechanical oscillators based on contact charge electrophoresis (CCEP) 13,14 can provide a useful model on length scales spanning millimeters 15 to microns 16 (perhaps even nanometers 17,18 ).…”

“…Moreover, the charge acquired by the particle and the forces driving its motion are well described by classical electrostatics, which is invariant to changes in scale. The discovery of new CCEP motions at the macroscale is therefore transferable to emerging applications at the microscale 13 .…”