Dresden 2009 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 20: Focused Session: Pattern formation in colloidal and granular systems

DY 20.6: Topical Talk

Donnerstag, 26. März 2009, 12:15–12:45, HÜL 386

Pattern Formation in Colloids Induced by Shear Flow and Electric Fields. — •Jan Dhont, Kyongok Kang, and Pavlik Lettinga — Forschungszentrum Juelich

Shear flow and electric fields are shown to induced non-patterned states in suspensions of colloidal rods (fd-virus particles). In part of the two-phase, paranematic-nematic region in the non-equilibrium phase diagram of colloidal rods under flow, regularly bands are formed that extend along the vorticity direction. Experiments indicate that the possible mechanism for the vorticity-banding instability is due to non-uniform elastic deformation of inhomogeneities that are formed during the initial stages of phase separation. This is similar to the Weissenberg effect in polymeric systems, where hoop stresses give rise to rolling flow as a result of the non-uniform deformation of polymer chains. Vorticity banidng is thus proposed to be similar to the Weissenberg effect, where the role of polymers is now played by inhomogeneities. The non-equilibrium phase/state behaviour of charged colloidal rods in electrric fields will be discussed, where the frequency is sufficiently low to polarize double layers. The polarized double layer around each of the rods interact with eachother, giving rise to a number of phases and dynamical states depending on the electric field amplitude and the frequency.