Berlin 2015 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 61: Focus: Disordered Systems, Glasses under Shear I (joint session CPP, DY)

CPP 61.1: Hauptvortrag

Donnerstag, 19. März 2015, 09:30–10:00, C 243

Flow instabilities in soft glassy materials — •Suzanne Fielding — Department of Physics, Durham University, UK

Many soft materials, including dense emulsions, microgel suspensions, star polymers, onion surfactants, and textured morphologies of liquid crystals, share underlying glassy features of structural disorder and metastability. These give rise to several notable features in the low frequency rheology of these materials: for example, the existence of a yield stress below which the material behaves like a solid, and above which it flows like a liquid. Experiments have also revealed that these materials often display a phenomenon known as shear banding, in which the flow profile across the shear cell exhibits macroscopic bands of different viscosity. Two distinct classes of yield stress fluid have been identified: those in which the shear bands apparently persist permanently (for as long as the flow is applied), and those in which banding arises only transiently during a process in which a steady flowing state is established out of an initial rest state (eg in shear startup or step stress). After surveying this motivating experimental data, we describe recent progress in addressing it theoretically, using the soft glassy rheology model and a simple fluidity model. Time permitting we shall also discuss failure modes of these "soft glassy materials" in free-surface extensional flows.