Dielectrophoretic and Electrothermal Effects at Alternating Current Heated Disk Microelectrodes

When a disk microelectrode is polarized with an alternating potential of very high frequency (0.1−2 GHz) and a high amplitude (up to 2.8 Vrms), the electrode is heated up, and at the same time, a very intense electric field is created around the electrode (>106 V/m for electrodes 1 μm in radius). This strong electric field gives rise to positive or negative dielectrophoretic effects. Positive dielectrophoretic effects can be used to assemble nanowires from nanoparticles at the electrode edge. On the other hand, a negative dielectrophoretic effect is probably responsible for “jet boiling” observed at overheated microelectrodes. In addition, a combination of a high temperature gradient and a high potential gradient generates an intense electrothermal flow of solution which very strongly enhances the mass transport and is responsible for intense convection in such systems. The electrothermal flow and dielectrophoretic forces can be generated directly on a microelectrode employed in electrochemical detection because the high frequency ac polarization of the electrode does not interfere with the acquisition of analytical signals.