title: Mechanism for Asymmetric Nanoscale Electrowetting of an Ionic Liquid on Graphene.
abstract: The electrowetting behavior of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) confined between two oppositely charged graphene layers is investigated using molecular dynamics simulations. By introducing charges on the surface, counterions are attracted to the surface and co-ions are repelled from it, leading to the reduction of the solid-liquid interfacial free energy and consequently the contact angle. Recently, we have shown that changes in the contact angle upon charging the surface are asymmetric with respect to surface polarity and opposite to the changes in the solid-liquid interfacial free energy. In this work, the asymmetry of the solid-liquid interfacial free energy is shown to originate from differences in structural organization of the ions at the interface, with positively polarized surfaces inducing a more favorable electrostatic arrangement of the ions. Analysis of the liquid structure in the vicinity of the three phase contact line, however, shows that the ion size asymmetry, together with differences in orientational ordering of the cations on oppositely polarized surfaces, instead leads to enhanced spreading on the negatively polarized surfaces, resulting in a corresponding contact angle asymmetry.
authors.affiliation: Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Straße 10, D-64287 Darmstadt, Germany.
authors.forename: Fereshte
authors.initials: F
authors.lastname: Taherian
authors.affiliation: Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Straße 10, D-64287 Darmstadt, Germany.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Leroy
authors.affiliation: Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Straße 10, D-64287 Darmstadt, Germany.
authors.forename: Lars-Oliver
authors.initials: LO
authors.lastname: Heim
authors.affiliation: Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Straße 10, D-64287 Darmstadt, Germany.
authors.forename: Elmar
authors.initials: E
authors.lastname: Bonaccurso
authors.affiliation: Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Center of Smart Interfaces, Technische Universität Darmstadt , Alarich-Weiss-Straße 10, D-64287 Darmstadt, Germany.
authors.forename: Nico F A
authors.initials: NF
authors.lastname: van der Vegt