# Dresden 2006 – wissenschaftliches Programm

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# SYSS: Structure Formation and Self-Organization in non-equilibrium Systems

## SYSS 1: Structure Formation and Self-Organization in non-equilibrium Systems I

### SYSS 1.5: Vortrag

### Donnerstag, 30. März 2006, 10:30–10:45, BAR Sch\"o

**B****é****nard–convection in colloidal suspensions** — •Björn Huke and Manfred Lücke — Institute for theoretical physics, Saarland University, D-66041 Saarbrücken

Colloidal suspensions differ from molecular binary mixtures like, e.g.,
ethanol-water by the fact that the solutal diffusion time scales are
several orders of magnitudes longer: The Lewis number of the former is
typically of the order of 10^{−3} to 10^{−4}. In addition they can
also exhibit a Soret effect that is several orders of magnitude stronger
leading to separation ratios of the order of 100.

We numerically studied the convection in a such a fluid layer heated from below for these parameters using the Galerkin method. We calculated bifurcation diagrams for roll, square, and crossroll patterns that are known to exist as stable form of convection in molecular mixtures with positive separation ratios. The stability region of these structures was investigated for selected parameter combinations. Oscillatory crossrolls and their transition into the square and stationary crossroll state were studied via a time integration of the mode equations.

Traveling waves that are an important structures in molecular fluids with negative separation ratio were also studied and found to play no role in colloids at moderate heating rates.