Volume 199, 2017

Spontaneous electrification of fluoropolymer–water interfaces probed by electrowetting

Abstract

Fluoropolymers are widely used as coatings for their robustness, water-repellence, and chemical inertness. In contact with water, they are known to 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 surfaces of Teflon AF and Cytop, two of the most common fluoropolymer materials, 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 −0.2 mC m−2 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 the 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.

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
28 Nov 2016
Accepted
12 Dec 2016
First published
10 Jan 2017

Faraday Discuss., 2017,199, 29-47

Spontaneous electrification of fluoropolymer–water interfaces probed by electrowetting

A. G. Banpurkar, Y. Sawane, S. M. Wadhai, C. U. Murade, I. Siretanu, D. van den Ende and F. Mugele, Faraday Discuss., 2017, 199, 29 DOI: 10.1039/C6FD00245E

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