Electrowetting‐Assisted Generation of Ultrastable High Charge Densities in Composite Silicon Oxide–Fluoropolymer Electret Samples for Electric Nanogenerators

Niels Mendel, Hao Wu, Frieder Mugele*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

4 Citations (Scopus)
25 Downloads (Pure)

Abstract

Electric nanogenerators that directly convert the energy of moving drops into electrical signals require hydrophobic substrates with a high density of static electric charge that is stable in “harsh environments” created by continued exposure to potentially saline water. The recently proposed charge‐trapping electric generators (CTEGs) that rely on stacked inorganic oxide–fluoropolymer (FP) composite electrets charged by homogeneous electrowetting‐assisted charge injection (h‐EWCI) seem to solve both problems, yet the reasons for this success have remained elusive. Here, systematic measurements at variable oxide and FP thickness, charging voltage, and charging time and thermal annealing up to 230 °C are reported, leading to a consistent model of the charging process. It is found to be controlled by an energy barrier at the water‐FP interface, followed by trapping at the FP‐oxide interface. Protection by the FP layer prevents charge densities up to −1.7 mC m−2 from degrading and the dielectric strength of SiO2 enables charge decay times up to 48 h at 230 °C, suggesting lifetimes against thermally activated discharging of thousands of years at room temperature. Combining high dielectric strength oxides and weaker FP top coatings with electrically controlled charging provides a new paradigm for developing ultrastable electrets for applications in energy harvesting and beyond.
Original languageEnglish
Article number2007872
JournalAdvanced functional materials
Volume31
Issue number11
Early online date4 Jan 2021
DOIs
Publication statusPublished - 10 Mar 2021

Keywords

  • UT-Hybrid-D
  • charge injection
  • electrowetting
  • droplets
  • electrets
  • nanogenerators

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