Mertens, Stijn F. L., Hemmi, Adrian, Muff, Stefan, Gröning, Oliver, De Feyter, Steven, Osterwalder, Jürg, and Greber, Thomas
Switching of static friction and adhesion of a liquid drop on a corrugated solid boron nitride surface is linked to the intercalation of hydrogen, which changes the electric field of in-plane dipole rings and thus reduces the adsorption energy. Stiction versus adhesion in a single liquid drop Stiction, or static friction, is the force required to persuade an object to start sliding across a surface. It is technologically important in devices with moving parts in contact, but is not well understood. Stijn Mertens et al. describe an inorganic model system for the study of the relationships between surface wetting, stiction, adhesion and lubrication. The system is a hexagonal boron nitride monolayer that can be electrochemically switched by intercalation of hydrogen between a corrugated and a flat morphology. The change in the surface structure of the boron nitride alters the adhesion and its balance with stiction of an aqueous drop sliding across the monolayer. The work of adhesion increases in going from the flat to the corrugated surface, whereas the stiction threshold does not change significantly. Thus the authors make a quantitative connection between the macroscopic properties of stiction and adhesion as a result of structural control at the atomic scale. 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.sup.1. 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.sup.2. Here we show how stiction and adhesion are related for a liquid drop on a hexagonal boron nitride monolayer on rhodium.sup.3, 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.sup.4, because it cannot be explained by the change in surface roughness known from the Wenzel model.sup.5. Although the change in adhesion can be calculated for the system we study.sup.6, 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., Author(s): Stijn F. L. Mertens [sup.1] [sup.2] , Adrian Hemmi [sup.3] , Stefan Muff [sup.3] , Oliver Gröning [sup.4] , Steven De Feyter [sup.1] , Jürg Osterwalder [sup.3] , Thomas [...]