Accurate dielectrophoretic positioning of a floating liquid marble with a two-electrode configuration

Manipulation of a floating liquid marble (LM) plays an important role in LM-based digital microfluidics for three-dimensional cell culture. Dielectrophoretic (DEP) actuation is a simple yet versatile manipulation technique that enables small droplets to be delivered across an open liquid surface. This paper reports the concept of accurately positioning a floating LM using a pair of electrodes. The experimental scheme consists of a small LM floating on an open water surface with two identical electrodes suspended above it. High voltages applied to each electrode generated a non-uniform electric field, which attracted the floating LM towards the corresponding electrode by a DEP force. The combined DEP forces caused by the electrode pair effectively trapped the floating LM between the two electrodes. By controlling the voltages of two individual electrodes respectively, the DEP forces could be tuned to accurately position the floating LM. We also studied the effects of electrode arrangements on positioning capability by measuring the relative position of the LM to the electrodes at different voltage ratios. We formulated an analytical model to describe the DEP force and obtained a governing equation that determines the LM position for various electrode configurations. In addition, we determined the effective working range of this setup and discussed future work with three or more electrodes for positioning a floating LM in two dimensions. This manipulation technique uses a simple and inexpensive setup without moving parts, which fills the gap in knowledge about controlled manipulation of LMs.