Physics – Condensed Matter – Soft Condensed Matter
Scientific paper
2011-02-21
Physics
Condensed Matter
Soft Condensed Matter
Scientific paper
The mechanical properties of aggregated colloids depend on the mutual interplay of inter-particle potentials, contact forces, aggregate structure and material properties of the bare particles. Owing to this variety of influences experimental results from macroscopic mechanical testings were mostly compared to time-consuming, microscopic simulations rather than to analytical theories. The aim of the present paper was to relate both macroscopic and microscopic mechanical data with each other and simple analytical models. We investigated aggregates made from monodisperse poly-methyl methacrylate (PMMA) particles (diameter: 1.6{\mu}m) via nanoindentation in combination with confocal microscopy. The resulting macroscopic information were complemented by the three dimensional aggregate structure as well as the individual displacements of the constituent particles. Microscopic reorganization processes were identified and the average strain field was calculated. In case of dense amorphous aggregates the strain field was in reasonable agreement with the predictions from analytical continuum theories. In semi-crystalline assemblies heterogeneities and the generation of dislocation defects were observed which was in accordance with the behavior of atomic crystals. As a consequence the measured force-depth curves could be quantitatively analyzed with the theory of Oliver and Pharr that had usually been used for indentation of atomic matter such as metals, ceramics and polymers. The extracted values for hardness and effective elastic modulus represented average values characteristic of the aggregate. Beside to the variation in aggregate structure the influence of particle bonds was verified by alternatively introducing polystyrene (PS) between the particles.
Auernhammer Günter K.
Kwade Arno
Lellig Philipp
Roth Marcel
Schilde Carsten
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