Dresden 2017 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 62: Fluids and Interfaces III

CPP 62.10: Vortrag

Donnerstag, 23. März 2017, 17:30–17:45, ZEU 255

Spontaneous electrification of fluoropolymer-water interfaces probed by electrowetting — Arun Banpurkar^{1, 2}, Yogesh Sawane¹, Sandip Wadhai^{1, 2}, Chandra Murade², Igor Siretanu², Dirk van den Ende², and •Frieder Mugele² — ¹Pune University, Pune, India — ²Univ. of Twente, Enschede, The Netherlands

Fluoropolymers are widely used as coatings for their robustness, water-repellence, and chemical inertness. In contact with water, they assume a negative surface charge, which is commonly attributed to adsorbed hydroxyl ions. Here, we demonstrate that a small fraction of these ions permanently sticks to Teflon AF and Cytop surfaces upon prolonged exposure to water. Electrowetting measurements carried out after aging in water are used to quantify the density of trapped charge. Values up to -0.07 and -0.2mC/m² are found for Teflon AF and for Cytop, respectively, at elevated pH. A similar charge trapping process is also observed upon aging in various non-aqueous polar liquids and in humid air. A careful analysis highlights the complementary nature of electrowetting and streaming potential measurements in quantifying interfacial energy and charge density. We discuss possible mechanism of charge trapping and highlight the relevance of molecular scale processes for the long term stability and performance of fluoropolymer materials for applications in electrowetting and elsewhere.