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Charge separation behind moving water drops occurs in nature and technology. Yet, the physical mechanism has remained obscure, as charge deposition is energetically unfavorable. Here, we analyze how a part of the electric double layer charge remains on the dewetted surface. At the contact line, the chemical equilibrium of bound surface charge and diffuse charge in the liquid is influenced by the contact angle and fluid flow. We summarize the mechanism in an analytical model that compares well with experiments and simulations. It correctly predicts that charge separation increases with increasing contact angle and decreases with increasing velocity.Received 19 July 2023Revised 12 September 2023Accepted 9 April 2024DOI:https://doi.org/10.1103/PhysRevLett.132.224002© 2024 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasContact line dynamicsDrops & bubblesElectrokinetic flowsElectrostatic interactionsIonic transportStokesian dynamicsWettingFluid DynamicsPolymers & Soft Matter
Ratschow et al. (Fri,) studied this question.