Effect of surface properties on adhesion and friction of particle systems

粉末状颗粒物质在过程工程及其邻近的各个领域有着广泛的应用。粒子系统的宏观性质由单个粒子的微观性质决定。粒子相互作用的基本机制仍不完全清楚。特别是，在小颗粒距离(几纳米)下的许多物理和化学机制及其对接触力学的影响仍然未知。该项目的重点是更好地了解颗粒系统接触领域的机制。利用专门开发的原位技术研究了单个颗粒的机械、摩擦学和粘合性能，从而对颗粒之间的接触机理有了独特的见解。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，以及它们的粘结和摩擦学行为随材料和系统参数的变化。这些结果可以控制颗粒加工过程中的粘附力和摩擦力。在之前的资助期间，已经开发出独特的原位技术，并用于表征微颗粒(具有高度统计意义)和自组装单分子膜在机械应力下的微观机械行为。对颗粒接触的粘附性和摩擦学机理的新见解已经提高了基本理解，并使微观机械颗粒特性的量化成为可能。在最后的资助期，我们将主要集中在液体阶段的研究。在前几个供资期间调查的系统将转移到液态，以便研究摩擦学和粘附性的变化以及液体电解液在接触区的行为。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：一方面将通过仔细控制接触对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来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.