Effect of surface properties on adhesion and friction of particle systems

粉体形式的颗粒物质在工艺工程及相关领域有着广泛的应用。粒子系统的宏观性质是由单个粒子的微观性质决定的。粒子相互作用的基本机制仍未完全了解。特别是，在小颗粒距离（几纳米）上的许多物理和化学机制及其对接触力学的影响仍然未知。该项目的重点是提高对微粒系统接触区域机制的理解。单颗粒的机械，摩擦学和粘接性能研究与特别开发的原位技术提供了独特的见解颗粒之间的接触力学。研究了单粒微粒子和纳米粒子在机械应力作用下的弹塑性变形行为，以及它们的黏附和摩擦学行为与材料和系统参数的关系。结果允许在颗粒加工过程中控制附着力和摩擦力。在之前的资助期内，独特的原位技术已被开发并用于表征微颗粒（具有高统计显著性）和自组装单层在机械应力下的微观力学行为。对接触颗粒的粘附和摩擦学机制的新见解已经改善了基本的理解，并允许对微机械颗粒特性进行量化。在最后的资助期，我们将主要集中于液相的研究。在之前的资助期内所研究的系统将转移到液相，以研究摩擦学和粘合性能的变化以及液体电解质在接触区域的行为。我们将通过两种不同的方法探索超低摩擦（超润滑）的可能性：一方面，通过仔细控制接触伙伴的介电性质来研究排斥范德华力的影响，另一方面，将研究两个接触体表面吸附层的影响。这将使我们能够识别超润滑颗粒系统，并通过应用我们的新型原位技术揭示超润滑的基本机制。

Granular matter in form of powders has widespread application in process engineering and various adjacent fields. The macroscopic properties of the particle systems are determined by the microscopic properties of the single particles. Fundamental mechanisms of particle interactions are still not fully understood. In particular, many physical and chemical mechanisms at small particle distances (of a few nm) and their effect on the contact mechanics are still unknown. The project focuses on an improved understanding of mechanisms in the contact area of particulate systems. The mechanical, tribological and adhesive properties of single particles are studied with specially developed in-situ techniques giving unique insight into the contact mechanics between particles. The elastic-plastic deformation behavior of single micro- and nanoparticles under mechanical stress as well as their adhesive and tribological behavior as a function of material and system parameters are investigated. The results allow the control of adhesion and friction forces during particle processing.Within the previous funding periods unique in-situ techniques have been developed and used for the characterization of the micro-mechanical behavior of microparticles (with high statistical significance) and self-assembled monolayers under mechanical stress. Novel insights into the adhesive and tribological mechanisms of particles in contact already improved the fundamental understanding and allowed the quantification of micro-mechanical particle properties.In the final funding period we will focus mainly on studies in the liquid phase. The systems investigated in the previous funding periods will be transferred to the liquid phase in order to study variations in tribological and adhesive properties as well as the behavior of liquid electrolytes in the contact area. We will explore the possibilities of extremely low friction (superlubricity) by two different approaches: On the one hand the effect of repulsive van der Waals forces will be studied by careful control of the dielectric properties of the contact partners, on the other hand the effect of adsorbate layers on the surfaces of the two contacting bodies will be investigated. This will enable us to identify superlubricating particle systems and reveal basic mechanisms of superlubricity by application of our novel in-situ techniques.