Fundamentals of molecular adhesion for the prediction of macroscopic adhesion at electrified interfaces

• Applicant: Professor Dr. Markus Valtiner
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Solid State and Surface Chemistry, Material Synthesis
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 290813605

The overarching goal of this project is the molecular-scale rationalization of adhesion i.e. attractive interactions at electrified and electrochemically active softmatter|solid interfaces in aqueous electrolytes. Interestingly, our recent advances in understanding single molecule interactions suggest that macroscopic adhesive failures cannot be rationalized exclusively based on interaction free energies of chemi- and/or physisorption events. Rather, it is imperative to consider both interaction free energies and unbinding pathways of specifically binding single functionalities, or in other word the kinetics of molecular bond breaking, in order to understand the molecular origin of an adhesive failure at the macroscopic scale. In this sense, understanding macroscopic adhesive failure relies on finding the weakest link on the molecular scale in terms of energy landscapes rather than simply by evaluating interaction free energy differences; an aspect that is largely ignored and unexplored in the field of adhesion science. Here, we propose to combine the measurement of macroscopic adhesive failures with the direct measurement of single molecule unbinding landscapes on the single molecular level using the Surface Forces Apparatus (SFA) and Atomic Force Microscope (AFM) as complementary tools. We will focus in particular on the unbinding of two functional groups, amines and electro-active 3,4-dihydroxyphenylalanine (DOPA) fragments, from electro active model metal (gold) and oxide surfaces (aluminum oxide). The unique electrochemical SFA (EC-SFA) and a newly designed electrochemical AFM (EC-AFM) cell simultaneously allow us both, to measure interaction forces and to electrochemically manipulate interacting surfaces. This provides means to variation of surface potentials and thereby change of the binding energy landscapes at electrode|solution|softmatter interfaces through a direct manipulation of the electronic properties of the surfaces as well as electric double layer properties and Van der Waals interactions. The envisioned outcome of the proposed work potentially has wide range applicability in many fields were interaction forces, molecular adhesion and unbinding pathways are relevant to structure, properties and degradation of materials, devices and even living matter.

• DFG Programme: Research Grants