Geometrical modulation of electrokinetic streaming potential when electrolyte flows over liquid-filled surfaces*

Electrokinetic flow, which can generate electrical voltage through the flow of an electrolyte over a charged surface, may be used for energy transduction. However, the yielded low streaming potential of electrokinetic flow on flat surface limited its practical applications. We have found that enhanced streaming potential could be obtained through the flow of salt water on liquid-filled surfaces that are infiltrated with a lower dielectric constant liquid, such as oil, to harness both of the electrolyte slip and associated surface charges. The geometrical factors of liquid-filled surfaces will influence the effective zeta potential of liquid-filled surface through influencing the fluid slip and contribution of liquid-oil interface to zeta potential. The geometrical factors can be well controlled during the slippery liquid-filled surface fabrication process. Thus, there is a large space of control parameters in modulating streaming potential, and it is important to study the effects of these geometrical parameters on streaming potential. Then the new obtained knowledge will be useful to optimize the geometry of liquid-filled surface for substantial streaming potential or streaming current generation. We have systematically investigated the effects of groove depth, groove width and groove fraction on streaming potential experimentally. Besides, we also derived the theoretical effective channel zeta potential. And a good comparison between the experimental results and theoretical channel zeta potential was found. These results lay the basis for innovative surface charge engineering methodology for the study of electrokinetic phenomena at the microscale, with possible application in new electrical power sources, and yield insights into understanding geometrical effects in electrolyte flows with implications to the establishment of local electric fields, energy generation, and biological separations.