Electro-de-wetting (EDW) effect of ionic surfactant aqueous solution under low-voltage electrostatic field

Abstract

Active control of surface wettability is vital for the development of smart interfaces and fluidic systems. Conventional electrowetting (EW) enhances wetting under high-voltage electric fields but faces limitations in applications requiring reduced adhesion or operating at low voltages. This study focuses on a thoroughly inverse electro-de-wetting (EDW) effect in dilute ionic surfactant solutions under low-voltage electrostatic field (≤4 V) at neutral pH (≈6.5), which significantly reduces wettability in a reversible manner. Though systematic variation of surfactant concentration and applied voltage, it was demonstrated that EDW increases the droplet contact angle (CA) by up to 56.9 %, in stark contrast to the classical EW. A generalized modified Young-Lippmann equation is proposed to quantitatively describe the EDW effect. Temporal evaluation of CA reveals distinct wetting-state transitions driven by electrokinetic migration and adsorption of surfactant molecules at the solid-liquid interface. This process is synergistically enhanced by interfacial charge redistribution and localized tension gradient, leading to increased surface hydrophobicity. The low-energy, tunable EDW mechanism offers a novel paradigm for manipulating wetting dynamics, with promising applications in microfluidics, adaptive coatings, and interfacial transport processes.

Keywords: Contact angle (CA); Electro-de-wetting (EDW); Electrostatic field; Interfacial migration; Surface wettability; Surfactant.