Bifunction-Integrated Dielectric Nanolayers of Fluoropolymers with Electrowetting Effects

Abstract

Fluoropolymers play an essential role in electrowetting (EW) systems. However, no fluoropolymer possesses the desirable properties of both hydrophobicity and dielectric strength. In this study, for the first time, we report the integration of two representative fluoropolymers—namely, Teflon AF (AF 1600X) and Cytop (Cytop 809A)—into one bifunctionalized dielectric nanolayer. Within this nanolayer, both the superior hydrophobicity of Teflon AF and the excellent dielectric strength of Cytop were able to be retained. Each composed of a 0.5 μm Cytop bottom layer and a 0.06 μm Teflon AF top layer, the fabricated composite nanolayers showed a high withstand voltage of ~70 V (a dielectric strength of 125 V/μm) and a high water contact angle of ~120°. The electrowetting and dielectric properties of various film thicknesses were also systemically investigated. Through detailed study, it was observed that the thicker Teflon AF top layers produced no obvious enhancement of the Cytop/Teflon AF stack.

Charge Trapping‐Based Electricity Generator (CTEG): An Ultrarobust and High Efficiency Nanogenerator for Energy Harvesting from Water Droplets

“…In a previous report, charge densities up to 0.46 mC m −2 have been achieved utilizing the EWCI method. However, these charge densities were highly localized and could not be increased any further due to the finite dielectric strength of fluoropolymer (FP) coatings V µm −1 depending on the preparation process [19][20][21][22] ) in combination with diverging electric fields at the air-water-solid contact. In this work, we therefore develop a new homogeneous electrowetting-assisted charge injection (h-EWCI) method by introducing a SiO 2 layer with much higher electric strength [23] than the polymer layer in combination with a mask to suppress the well-known divergence of the electric fields [17,24] and local dielectric breakdown near the contact line.…”

Electrically Controlled Localized Charge Trapping at Amorphous Fluoropolymer–Electrolyte Interfaces

“…The reliability of any EW applications in microfluidics [20][21] , optofluidics [22][23] , display technology [24][25] , and energy harvesting 26 relies on the reproducibility, performance, and durability of the dielectric layer; thus the stability of AFPs is particularly important [27][28][29][30] . Charge trapping induces the degradation of the electrical response of AFP films, leading to contact angle saturation and failures in EWOD devices 26,[31][32] .…”

“…The reliability of any EW applications in microfluidics, [15,16] optofluidics, [17,18] display technology, [19,20] and energy harvesting [21] relies on the reproducibility, performance, and durability of the dielectric layer, and hence, the stability of AFPs is particularly important. [22][23][24][25] Charge trapping at the dielectric/ electrolyte interfaces is a long-standing problem in EW, leading to the degradation of the electrical response of AFP films, and thus causing the contact angle (CA) saturation and failures in EWOD devices. [21,26,27] While early experiments with composite dielectrics displayed a reversible response and symmetric saturation for positive and negative bias voltage, suggesting substantial mobility of both types of charge carriers upon injection into the AFP films, [28] more recent studies displayed a strongly asymmetric and sometimes irreversible response.…”