Electrically Switchable Molecular Adhesion via Self-Assembled Monolayer-Mediated Hydration and Ion Structuring

Abstract

The interplay of specific surface interactions as well as ion and hydration structuring takes on a pivotal role in dictating the intermolecular, intersurface, and colloidal behavior at solid-liquid interfaces. The detailed atomic and molecular structure consequently influences a wide array of surface-mediated functions in technological and biological systems. Ion and hydration structuring at the interface is susceptible to various surface parameters, including surface potential, structural modifications including molecular adsorbents, the charge of specific functional groups, and electrolyte composition. Here, we disclose an electromechanical adhesion switch mechanism and demonstrate, in operation, the impact of molecular surface modification and potential modulation on adhesive and repulsive forces between surfaces. We exemplify these fundamental interactions by measuring the acting intermolecular forces between mica and metal surfaces modified with self-assembled monolayers including mercaptobenzimidazole and cysteamine films, showcasing the potential for tailoring surface interactions via ion adsorption manipulation. Employing an electrochemical surface forces apparatus complemented with molecular dynamics simulation, we present a comprehensive analysis of the specific forces involved in film-mica interactions and the impact of ion ordering under electrochemical modulation on such forces. Our results offer a novel perspective on how hydration and ion adsorption shape solid-solid interactions involving organic thin films and how these interactions provide a flexible route for electromechanical adhesion switches.