Measurement of rotation of individual spherical particles in cohesive granulates
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ORIGINAL PAPER
Measurement of rotation of individual spherical particles in cohesive granulates Jennifer Wenzl · Ryohei Seto · Marcel Roth · Hans-Jürgen Butt · Günter K. Auernhammer
Received: 10 August 2012 / Published online: 20 November 2012 © Springer-Verlag Berlin Heidelberg 2012
Abstract To explore dynamical processes in granular matter, we use a combination of 3D imaging and mechanical testing. We analyze structural changes using confocal microscopy while applying a compression load simultaneously. Fluorescently labeled polydisperse silica particles were hydrophobized with long alkyl chains and dispersed in an index-matching liquid. The particles show a weak attraction. Photobleaching the central plane of individual particles generates an optical anisotropy without changing particle interaction. In a series of 3D images, we follow trajectories and rotation of single particles. We focus on particle translation and rotation in dependency of the local volume fraction. During compression, restructuring happens predominantly in regions of low packing density. We show that rotation plays an important role and is hence a key parameter for explaining dynamical processes in granular systems. Keywords Confocal microscopy · Particle tracking · Granular matter · Rotation · Photobleaching 1 Introduction Granular matter is present in many industrial applications and daily life, e.g. pharmaceutics or food processing. When handling granular matter, its mechanical and flow properties are essential. Due to the high relevance of the question, numerous ways of characterizing the mechanical properties J. Wenzl (B)· R. Seto · M. Roth · H.-J. Butt · G. K. Auernhammer Experimental Physics of Interfaces, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany e-mail: [email protected] R. Seto Benjamin Levich Institute for Physico-Chemical Hydrodynamics, City College of New York, New York, NY 10031, USA
have been developed. Microscopic and macroscopic views have been explored. When applying a mechanical stress, granular systems show a complex response, which depends on the type and strength of the applied load. Classical rheometry [1] provides various possibilities probing the rheology of bulky colloidal and granulate systems. For industrial processing, knowing the macroscopic mechanical properties is essential. This is achieved by a wide a range of shear devices [2]. One approach for studying elasticity and plasticity of bulky systems is indentation. Being originally developed for atomic systems, it is now also used for probing granular systems. Here Young’s modulus, strain tensor and other quantities of colloidal crystalline [3], semicrystalline[4] and amorphous structures [5] have been investigated. In the granular field, Murthy et al. [6] used indentation for studying the deformation field of sand. When exposed to high mechanical stress, many granular systems behave no longer elastically, but start to flow [7,8]. McDowell et al. [9] recapitulate this yielding behavior for different types of granula
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