Large tuning in the electrowetting behaviour on ferroelectric PVDF-HFP/Teflon AF bilayer

Wadhai, Sandip M.; Sawane, Yogesh B.; Limaye, Abhay. V.; Banpurkar, Arun G.

Electrowetting (EW) response on a dielectric depends on its permittivity value, Young contact angle and voltage amplitude. We present a large change in EW contact angle, from 163° to 80°, on the bilayer dielectric made up of ferroelectric PVDF-HFP with a thin layer of fluoropolymer. The thickness values of both layers were separately optimized for high effective capacitance essential for the large EW response. It reveals that the bilayer with ~ 500 nm thick PVDF-HFP layer and ~ 50 nm thin layer of Teflon results in the maximum value of effective dielectric constant, ε ≈ 8. Besides this gain, dc-voltage EW response exhibits hysteresis mainly due to polarization in the ferroelectric layer such that, hysteretic offset voltage was found to depend on the applied voltage amplitude and thickness of the dielectrics. Finally, bilayer was subjected to ac-voltage EW in silicone oil for ambient temperature ranging from − 25 to 70 °C. The consistent EW response in this ambient without any degradation/delamination of polymer surface confirmed the durability of the bilayer on the transparent ITO electrodes. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10853-021-06308-z.