title: Ultra-low voltage electrowetting using graphite surfaces.
abstract: The control of wetting behaviour underpins a variety of important applications from lubrication to microdroplet manipulation. Electrowetting is a powerful method to achieve external wetting control, by exploiting the potential-dependence of the liquid contact angle with respect to a solid substrate. Addition of a dielectric film to the surface of the substrate, which insulates the electrode from the liquid thereby suppressing electrolysis, has led to technological advances such as variable focal-length liquid lenses, electronic paper and the actuation of droplets in lab-on-a-chip devices. The presence of the dielectric, however, necessitates the use of large bias voltages (frequently in the 10-100 V range). Here we describe a simple, dielectric-free approach to electrowetting using the basal plane of graphite as the conducting substrate: unprecedented changes in contact angle for ultra-low voltages are seen below the electrolysis threshold (50° with 1 V for a droplet in air, and 100° with 1.5 V for a droplet immersed in hexadecane), which are shown to be reproducible, stable over 100 s of cycles and free of hysteresis. Our results dispel conventional wisdom that reversible, hysteresis-free electrowetting can only be achieved on solid substrates with the use of a dielectric. This work paves the way for the development of a new generation of efficient electrowetting devices using advanced materials such as graphene and monolayer MoS2.
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. robert.dryfe@manchester.ac.uk.
authors.forename: Deborah J
authors.initials: DJ
authors.lastname: Lomax
authors.affiliation: MCND and School of Physics & Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Pallav
authors.initials: P
authors.lastname: Kant
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. robert.dryfe@manchester.ac.uk.
authors.forename: Aled T
authors.initials: AT
authors.lastname: Williams
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. robert.dryfe@manchester.ac.uk.
authors.forename: Hollie V
authors.initials: HV
authors.lastname: Patten
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. robert.dryfe@manchester.ac.uk.
authors.forename: Yuqin
authors.initials: Y
authors.lastname: Zou
authors.affiliation: MCND and School of Physics & Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Anne
authors.identifier: http://orcid.org/0000-0003-3342-7388
authors.initials: A
authors.lastname: Juel
authors.affiliation: School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK. robert.dryfe@manchester.ac.uk.
authors.forename: Robert A W
authors.initials: RA
authors.lastname: Dryfe