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.

当磁盘微电极在极高频率（0.1−2 GHz）和较高幅度（高达2.8 Vrms）的交变电势下极化时，电极被加热，同时在其周围产生非常强烈的电场（电极半径为1 μm时，电场强度超过10^6 V/m）。此强电场引发了正或负的介电泳效应。正介电泳效应可被用于在电极边缘组装纳米线从纳米粒子。另一方面，负介电泳效应可能负责在过热微电极上观察到的‘喷射沸腾’现象。此外，高温梯度和高电势梯度的结合产生了强烈的电热流动，极大地增强了物质传输，并导致了此类系统中的强烈对流。电热流动和介电泳力可以直接在用于电化学检测的微电极上生成，因为电极的高频交流极化不会干扰分析信号的采集。