When Particles Meet Nanoindentation: A Novel Strategy for Studying Particle Motion and Particle/Surface Interaction
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When Particles Meet Nanoindentation: A Novel Strategy for Studying Particle Motion and Particle/Surface Interaction Regina Fuchs1, Thomas Weinhart2, Jan Meyer1, Hao Zhuang1, Thorsten Staedler1, Xin Jiang1, and Stefan Luding2 1 Institute of Materials Engineering, University of Siegen, Paul-Bonatz-Str. 9-11, 57076 Siegen, Germany 2 Multiscale Mechanics, Department of Mechanical Engineering, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands ABSTRACT A plethora of applications in pharmacy, cosmetics, food industry and other areas are directly linked to the research fields of particle technology and contact mechanics. Here, a typical particle ensemble features particle sizes ranging from the nanometer up to the micrometer regime. In this context we introduce a nanoindentation based approach capable of probing mechanical interaction of micron-sized particles. Basically, the concept of the colloid probe technique, which is well established in the AFM community, is transferred to a nanoindenter. In particular, this setup allows addressing limitations, which are typically associated with AFM based techniques, such as particle weight and accessible load regime. Additionally, we will show the versatility of this approach by presenting simple experimental paths capable of probing sliding, rolling and torsional friction. The potential of such setting is shown by studying rolling friction of silica microspheres featuring radii of about 2.5µm, 10µm, 25 and 50µm in contact with various substrates, respectively. Substrates utilized within the framework of this study are Si surfaces featuring various roughness as well as flat gold films (300nm film thickness). Key aspects of this work include the influence of surface roughness, adhesion force, humidity and the elastic/plastic transition on the rolling contact of the corresponding particles. INTRODUCTION The influence of adhesion, capillary forces (humidity), surface roughness, and plastic deformation on the contact mechanics of particles interacting with a wall/surface plays a crucial role in numerous physical, chemical and biological phenomena. Nevertheless, the characteristics of individual particle contacts as well as the details of the deformation of the corresponding contacting surfaces are still not fully understood. Scanning probe microscopy offers a way to determine particle substrate adhesion [1,2] as well as particle motions [3,4]. Until now, however, all studies of particle substrate contact as well as particle motion either required dedicated homebuilt setups [5,6] or are limited with respect to the weight of the particle and/or the accessible load regime [7]. Nanoindentation offers the potential to address these issues. In the present work, the idea of the colloid probe technique is transferred to a nanoindenter setup which allows for the preparation of larger particle probes, higher maximum normal load and a unique strategy to sample rolling and torsion of individual particles. The capability of this approach to sample sliding, rolling, and torsional
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