title: Switching stiction and adhesion of a liquid on a solid.
abstract: When a gecko moves on a ceiling it makes use of adhesion and stiction. Stiction--static friction--is experienced on microscopic and macroscopic scales and is related to adhesion and sliding friction. Although important for most locomotive processes, the concepts of adhesion, stiction and sliding friction are often only empirically correlated. A more detailed understanding of these concepts will, for example, help to improve the design of increasingly smaller devices such as micro- and nanoelectromechanical switches. Here we show how stiction and adhesion are related for a liquid drop on a hexagonal boron nitride monolayer on rhodium, by measuring dynamic contact angles in two distinct states of the solid-liquid interface: a corrugated state in the absence of hydrogen intercalation and an intercalation-induced flat state. Stiction and adhesion can be reversibly switched by applying different electrochemical potentials to the sample, causing atomic hydrogen to be intercalated or not. We ascribe the change in adhesion to a change in lateral electric field of in-plane two-nanometre dipole rings, because it cannot be explained by the change in surface roughness known from the Wenzel model. Although the change in adhesion can be calculated for the system we study, it is not yet possible to determine the stiction at such a solid-liquid interface using ab initio methods. The inorganic hybrid of hexagonal boron nitride and rhodium is very stable and represents a new class of switchable surfaces with the potential for application in the study of adhesion, friction and lubrication.
authors.affiliation: Department of Chemistry, KU Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium.|Institut für Angewandte Physik, Technische Universität Wien, Wiedner Hauptstrasse 8-10/E134, 1040 Wien, Austria.
authors.forename: Stijn F L
authors.initials: SF
authors.lastname: Mertens
authors.affiliation: Physik-Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
authors.forename: Adrian
authors.initials: A
authors.lastname: Hemmi
authors.affiliation: Physik-Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Muff
authors.affiliation: Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland.
authors.forename: Oliver
authors.initials: O
authors.lastname: Gröning
authors.affiliation: Department of Chemistry, KU Leuven, Celestijnenlaan 200F, 3001 Leuven, Belgium.
authors.forename: Steven
authors.initials: S
authors.lastname: De Feyter
authors.affiliation: Physik-Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
authors.forename: Jürg
authors.initials: J
authors.lastname: Osterwalder
authors.affiliation: Physik-Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Greber
mesh_terms: D000268:Adhesiveness; D000818:Animals; D001896:Boron Compounds / Q000737:chemistry*; D004560:Electricity; D017276:Friction; D006859:Hydrogen / Q000737:chemistry; D008124:Locomotion; D008153:Lubrication; D012238:Rhodium / Q000737:chemistry*; D017155:Wettability
chemical_list: D001896:Boron Compounds; C017282:boron nitride; D006859:Hydrogen; D012238:Rhodium