Effect of surface properties on adhesion and friction of particle systems

粉末状颗粒物质在过程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然没有完全理解。特别是，在小颗粒距离（几纳米）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颗粒系统接触领域机制的认识。通过专门开发的原位技术研究单个颗粒的机械、摩擦学和粘附性能，从而对颗粒之间的接触力学有独特的见解。研究了单个微米和纳米颗粒在机械应力作用下的弹塑性变形行为以及它们的粘附和摩擦学行为与材料和系统参数的关系。这些结果允许在颗粒加工过程中控制粘附力和摩擦力。在以前的资助期间，已经开发出独特的原位技术，并用于表征机械应力下微粒（具有高统计显著性）和自组装单分子膜的微观力学行为。对接触中颗粒的粘附和摩擦学机制的新见解已经提高了基本的理解，并允许量化微观机械颗粒特性。在最后的资助期内，我们将主要集中在液相中的研究。在之前的资助期间研究的系统将被转移到液相，以研究摩擦学和粘合性能的变化以及接触区域中液体电解质的行为。我们将通过两种不同的方法来探索极低摩擦（超润滑性）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性货车德瓦尔斯力的影响，另一方面，将研究两个接触体表面上的吸附层的影响。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的原位技术揭示超润滑性的基本机制。

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.