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

该项目的首要目标是在分子尺度上使附着力合理化，即在带电和电化学活性的软物质|固体界面上发生吸引人的相互作用。有趣的是，我们在理解单分子相互作用方面的最新进展表明，宏观粘合失效不能完全基于化学和/或物理吸附事件的相互作用自由能来合理化。相反，必须同时考虑相互作用自由能和特定结合单一官能团的解离途径，或者换句话说，分子键断裂的动力学，以便在宏观尺度上理解粘合失效的分子起源。从这个意义上说，理解宏观粘合失效依赖于找到分子尺度上能量景观方面最薄弱的环节，而不是简单地通过评估相互作用自由能差；这一方面在粘合科学领域基本上被忽视和探索。在这里，我们建议使用表面力装置(SFA)和原子力显微镜(AFM)作为补充工具，将宏观粘接失效的测量与单分子水平上的单分子解离景观的直接测量结合起来。我们将特别关注两个官能团，胺和电活性3，4-二羟基苯丙氨酸(DOPA)片段，从电活性模型金属(金)和氧化物表面(氧化铝)解离。独特的电化学SFA(EC-SFA)和最新设计的电化学AFM(EC-AFM)池允许我们同时测量相互作用力和电化学操作相互作用的表面。这提供了通过直接操纵表面的电子性质以及双电层性质和Van der Waals相互作用来改变表面电位从而改变电极、溶液和软物质界面处的结合能景观的手段。这项工作的预期成果可能在许多领域具有广泛的适用性，因为相互作用力、分子粘合和解离途径与材料、设备甚至生物的结构、性能和降解有关。

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.