The generation of electrical voltage through the flow of an electrolyte over a charged surface may be used for energy transduction. Here, we show that enhanced electrical potential differences (i.e., streaming potential) may 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 electrolyte slip and associated surface charge. A record-high figure of merit, in terms of the voltage generated per unit applied pressure, of 0.043 mV Pa−1 is obtained through the use of the liquid-filled surfaces. In comparison with air-filled surfaces, the figure of merit associated with the liquid-filled surface increases by a factor of 1.4. 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.

A significant enhancement in the streaming potential (V s ) was obtained in experiments considering the flow of electrolyte over liquid-filled surfaces (LFSs), where the grooves in patterned substrates are filled with electrolyte immiscible oils. Such LFSs yield larger V s (by a factor of 1.5) compared to superhydrophobic surfaces, with air-filled grooves, and offer tunability of electrokinetic flow. It is shown that the density, viscosity, conductivity, as well as the dielectric constant of the filling oil, in the LFS, determine V s . Relating a hydrodynamic slip length to the obtained V s offers insight into flow characteristics, as modulated by the liquid interfaces in the LFS.

The relative influence of the capillary, Marangoni, and hydrophobic forces in mediating the evaporation of water from carbon foam based porous media, in response to incident solar radiation, are investigated. It is indicated that inducing hydrophilic interactions on the surface, through nitric acid treatment of the foams, has a similar effect to reduced pore diameter and the ensuing capillary forces. The efficiency of water evaporation may be parameterized through the Capillary number (Ca), with a lower Ca being preferred. The proposed study is of much relevance to efficient solar energy utilization.

Textured surfaces, comprised of grooves filled with air, e.g., air-filled surfaces (AFS), or with liquid, e.g., liquidfilled surfaces (LFS), significantly influence fluid flows and the related electrokinetic streaming potential (V s ). Here, electroosmotic mobility related tensorial effects on the V s were experimentally investigated. A significant modulation of the V s , as high as 100%, due to transverse pressure gradients, was demonstrated. The study yields insights into understanding geometrical effects in electrolyte flows with implications to the establishment of local electric fields, energy generation, and biological separations.

A significant enhancement of solar irradiation induced evaporation of water, and ethanol-water mixtures, through the use of carbon foam based porous media, is demonstrated. A relationship between the consequent rate of mass loss, with respect to the equilibrium vapor pressure, dynamic viscosity, surface tension, and density, was developed to explain experimental observations. The evaporative heat loss was parametrized through two convective heat transfer coefficients-one related to the surface and another related to the vapor external to the surface. The work promotes a better understanding of thermal processes in binary liquid mixtures with applications ranging from phase separation to distillation and desalination.