Electrocapillary Rise in Nanoporous Media

Capillary flow has been extensively studied due to its broad applications in both engineering and sciences. Detailed studies have shown that capillary rise in hydrophilic microchannels obeys the Lacus-Washburn law, which illustrates a square-root relationship between the imbibition height and the time. The imbibition kinetics depends on the medium structures, liquid viscosity as well as the wetting behavior. These properties are hardly tunable for common porous materials such as rock and paper so as to achieve active control on the imbibition process. In this work, we investigate controllable capillary rise in novel conductive nanoporous materials, i.e., nanoporous gold (NPG) and carbon nanotube (CNT) sponges, by employing the electrocapillary technique to manipulate the wetting property of water on the material surface. Reversible on-off switchable control on the capillary flow in both materials is realized using ultra-low electric voltages. In comparison with NPG, more pronounced flow rate has been obtained in CNT sponges, and, moreover, direct oil recovery can also be realized with the assistance of water-soluble surfactant.