Berlin 2008 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 16: SYMPOSIUM Driven Soft Matter I
CPP 16.8: Vortrag
Dienstag, 26. Februar 2008, 12:15–12:30, C 130
Slip and shear-banding in hard-sphere colloidal glasses — •Rut Besseling1, Pierre Ballesta1, Lucio Isa1, George Petekidis2, and Wilson Poon1 — 1School of Physics, University of Edinburgh, Scotland, UK — 2Inst. Elec. Structure and Laser-FORTH, Heraklion, Crete, Greece
We study slip and flow of colloidal hard-sphere glasses by cone-plate rheometry and simultaneous confocal microscopy, both for microscopically smooth shearing surfaces and for surfaces with particle scale roughness. For smooth walls, the global rheology shows a crossover from Bingham-like slip behaviour at small applied shear rates to a Herschel-Bulkley response at large rate. The velocity profiles show that the *slip to shear* transition is position dependent and we present a phenomenological model that quantifies both local and global rheology. We show that Bingham-type slip is directly connected with the onset of yield stress and that it is generic for hard-sphere glasses at smooth, non-sticky walls.
For rough boundaries, we find global Herschel-Bulkley flow curves, but the associated velocity profiles show marked non-linearity's, developing into strong localization (coexistence of solid and sheared regions) just above the yield stress. This localization has its onset at the glass transition -i.e. flow is uniform for the colloidal fluid- and becomes more pronounced at larger densities. We discuss the possible role of microscopic stress fluctuations as origin for the shear localization.