Digitale Bildverarbeitung schneller Partikelbewegungen in kolloidalen Suspensionen

The structure and short time particle dynamics of electrostatically stabilized colloidal suspensions was examined with a high-speed camera. The particle positions were extracted from the image sequences by means of digital image processing. Correlation functions in space and time could be calculated from the particle distances and displacements. At a time resolution of up to 10exp-3 the short time range of selfdiffusion of unordered, strongly diluted suspensions showed significant deviations from the gaussian behaviour within the first 30ms, which indicates hydrodynamic interactions. The influence of shear stress on the structure of crystalline ordered colloidal suspensions was examined from the two dimensional pair correlation function of sliding layers. It could be shown, that the hexagonal symmetry of crystalline layers at rest is broken by shear stress. In the examined shear rate range the string distances increased, whereas particles within the strings moved together. The illustration of particle trajectories proved, that at lower shear rates particles move on a zig zag path lateral to the flow direction in order to minimize shear resistance. The analysis of the van Hove selfterm and the mean squared displacement revealed a significant periodical change of the particle mobility, like it is to be expected when passing a changing potential. The amplitude of these oscillations decreases with increasing shear rate, which indicates the transition of the lateral zig zag path into a straight forward movement. These results demonstrate, that high speed video microscopy is well suited to examine rheological mechanisms in colloidal suspensions and therefore is an important addition to the established scattering methods.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2002

Author dc:creator

• Bongers, Ulf

Contributors dc:contributor

• Versmold, Heinrich

• info:eu-repo/classification/ddc/530
• Physik

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-119197%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:57129