Complex Fluids

Non-equilibrium phase diagram of colloidal rods in shear flow

Collaboration with Pavlik Lettinga and Jan Dhont, Research Center Julich and Jan Vermant, KU Leuven

Figure 1

We study the influence of shear flow on the isotropic-nematic phase transition found in colloidal rods. Applying shear flow creates an inherently non-equilibrium system. The fundamental question we seek to answer is what determines the coexistence between these non-equilibrium isotropic and nematic phases. Experimentally we observe flow instabilities on a macroscopic and microscopic scale when a sample is prepared in the two-phase region. We are currently mapping a non-equilibrium phase diagram of these instabilities. In addition, we study the rheology of pure nematic phase of colloidal liquid crystals and observe signatures of tumbling and flow-aligning of rods in the nematic phase.

Figure 1 is an image of flow instability observed when a rod-like suspension at isotropic-nematic coexistence is subject to shear in a cylindrical cell. The bands are up to few millimeters in size and the image is taken between crossed polarizers.