Berlin 2015 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 53: Focus: Disordered Systems/Glasses under Shear (joint session CPP/ DY)

DY 53.1: Invited Talk

Thursday, March 19, 2015, 15:30–16:00, C 243

Microscopic flows of complex suspensions — •Anke Lindner — PMMH-ESPCI, Paris

The flow of complex suspensions is ubiquitous in nature and industrial applications. Their non-Newtonian character is due to flow-induced orientation, rearrangement, or deformation of microscopic objects suspended in simple fluids. These objects can be isotropic or anisotropic, rigid or deformable, active or passive. Linking the microstructure on the particle level to the macroscopic response under flow is one of the fundamental scientific challenges of soft matter physics. Recent micro-fabrication techniques lead to a precise control of even complex particle properties and new microfluidic rheometers show high resolution. Using these new approaches, we present two examples of flows of complex suspensions in chosen microfluidic geometries which allow this link to be established. First, we use a solution of flexible polymers, where normal stresses are known to arise when the polymers are stretched under flow and characterize the onset of elastic flow instability in a serpentine channel as a function of its curvature. The calibrated serpentine channel can then be used as a sensitive rheometer to detect even small normal stresses in unknown suspensions. Second, we employ a Y-channel, a powerful rheometer for measuring shear viscosities, to study the viscosity of active suspensions of e-coli bacteria. In this way we link the activity of the bacteria to the measured non-Newtonian effective viscosity.