Crossover from Asymmetric to Symmetric Electrowetting Linked to Double-Layer Restructuring

Abstract

Voltage-controlled wetting at solid–liquid interfaces is central to the performance of a range of electrochemical and microfluidic technologies, yet the molecular basis of polarity-dependent electrowetting remains unresolved. Classical electrocapillarity predicts a symmetric dependence of contact angle on applied potential, but experiments and simulations frequently exhibit pronounced asymmetry. Here, combining electrowetting measurements with atomistic simulations, we show that asymmetric wetting at aqueous carbon interfaces arises from the structure of the electrical double layer. By investigating aqueous KF and LiCl electrolytes at graphitic interfaces across lower concentration and water-in-salt regimes, we identify a crossover from strongly asymmetric electrowetting at lower concentration to a symmetric response at high concentration for KF, while LiCl retains a pronounced asymmetry. This transition is accompanied by corresponding changes in the solid–liquid interfacial tension, demonstrating that polarity-dependent wetting can arise from voltage-dependent molecular restructuring of the interfacial liquid, which modifies the interfacial thermodynamics, without invoking faradaic processes. We introduce interfacial connectivity, defined by the network of intermolecular interactions within the first adsorption layer, as a molecular descriptor linking double-layer structure to macroscopic wetting behavior. These results demonstrate that electrolyte-controlled electrowetting can recover the symmetric electrocapillary limit under appropriate conditions and establish a unified framework connecting double-layer structure, interfacial free energy, and voltage-dependent wetting.