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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 4: Colloidal Fluids

CPP 4.7: Vortrag

Montag, 25. Februar 2008, 16:15–16:30, C 264

Structural Rearrangements of Colloidal Gels under Shear — •Laurati Marco¹, Petekidis George², Koumakis Nikos², and Egelhaaf Stefan¹ — ¹Soft Matter Laboratory, HHU Duesseldorf, 40225 Duesseldorf, Germany — ²Polymer and Colloid Group, IESL, FORTH, 71110 Heraklion, Greece

The experimental system investigated in this work are short-ranged attractive colloids obtained from mixtures of PMMA colloidal spheres and PS chains dispersed in cis-decalin. The colloid volume fraction is 40%, the polymer concentration is increased from the fluid to the gel phase. Structural rearrangements of gels under oscillatory shear are investigated by non-linear Rheology and Echo-Diffusing Wave Spectroscopy (Echo-DWS). Rheology allowed us to estimate yield strains and stresses of the gels. Echo-DWS allowed us to determine the characteristic times of the rearrangements and the mean square displacement. The amount and characteristic times of structural rearrangements depend on strain, polymer concentration and frequency of oscillation in a fashion which can be rationalized on the basis of a recently proposed simple model of structural rearrangements driven by breaking of two-particles depletion bonds (Smith,PRE,2007). Additionally, rheological measurements indicate interesting connections with the yielding mechanisms of attractive glasses (Pham,EPL,2006). Two distinct yielding points are observed: one, at strains comparable to the range of the interaction potential, corresponds to the strain at which bonds between particles are broken; the second, at larger strains, corresponds to irreversible rearrangement of the gel structure.