The manipulation of small particles (droplets, capsules, macromolecules, or living cells) by electric fields underlies many important technologies for particle separations, electronic displays, cell sorting, and DNA sequencing to name just a few. Most commonly, charged particles are actuated by spatially uniform electric fields through electrophoresis (EP); electrically polarizable particles are actuated by electric field gradients via dielectrophoresis (DEP). Recently, a new type of electrophoretic transport has been observed – termed contact charge electrophoresis (CCEP) – in which a conductive particle or droplet is first charged by contact with an electrode surface in the presence of an electric field and then actuated by that field via electrophoresis. In contrast to traditional EP and DEP, contact charge electrophoresis allows for rapid, sustained particle motion (>10 cm/s) driven by low power DC voltages (~1 nW). Our work aims to develop the fundamental understanding of CCEP and to apply it within mobile (i.e., small, battery-powered) microfluidic technologies.
