Contact electrification efficiency dependence on surface energy at the water-solid interface

Abstract

Liquid-solid contact electrification is a useful mechanism to harvest wasted micromechanical energy. In this study, we investigate how the surface properties of a solid substrate affect contact electrification efficiency. Substrate surfaces were modified from hydrophilic to hydrophobic by changing the density of self-assembled monolayers (SAMs) on a SiO2 surface. A substrate with a partially-covered SAM exhibited superior performance. The partially-covered SAM substrate is hydrophobic enough to induce quick dewetting of water from the surface and sufficiently electronegative to induce a high charge density on the surface. The quick dewetting results from the aliphatic tail groups of the SAM and -OH groups make the SiO2 surface electronegative; these two competing properties can be simultaneously obtained by optimizing the SAM density. Our findings contribute to the understanding of contact electrification in liquid-solid-type energy-harvesting devices and advance the strategies to maximize the electrification efficiency by optimizing surface geometries and properties.

Slide electrification: charging of surfaces by moving water drops

“…7 Other hydrophobic surfaces such as poly(methyl methacrylate) (PMMA) 10 or silicon oxide hydrophobized with monolayers of octadecyltrichlorosilane also induced charging. 43 The fact that charging depends on the chemical nature of the substrate was confirmed by measuring charges of drops flowing out of tubes. 11,37,39 Polycarbonate, 18 nylon, polyethylene, polyvinyl chloride, 11 polystyrene, and even copper or steel tubes 39 have all been observed to release positively charged drops.…”

“…Water drops sliding down a hydrophobic tilted plane often acquire a charge and deposit a surface charge of opposite sign. 18,[43][44][45] In 1994, Yatsuzuka, Mizuno, and Asano introduced the term ''slide electrification'' for this process. 18 They dripped drops of distilled water from a grounded pipette onto a tilted polytetrafluoroethylene (PTFE) plate.…”

Enhancement of the Triboelectrification Using Artificial Surface Charges

“…It is shown in the figure that the brightness of the LEDs with the device that has artificial induced surface charges is greater than that of the pretreated device where there were no induced charges. At the end, a micro water droplet was also used to check the wettability of the sample, ultimately demonstrated the variation in tribocharge density on the polymer surface [36]. Before plasma treatment, the droplet in Fig.…”

Drop race: How electrostatic forces influence drop motion

“…It is known that on bulk Teflon samples, fluorinated insulators, and superhydrophobic surfaces, sliding water drops deposit negative electric charges, while the drops acquire a positive charge 11,12,14,[33][34][35][36][37][38] . Surface charges generate an electric field in the air above the surface.…”