Regensburg 2007 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 14: Fluid dynamics II

DY 14.6: Hauptvortrag

Dienstag, 27. März 2007, 12:30–13:00, H2

Instabilities and pattern formation in phase-separating fluids — •Jürgen Vollmer — Fachbereich Physik, Philipps Universität, Renthof 6, 35032 Marburg, Germany

The thermodynamic equilibrium of fluid mixtures and their isothermal relaxation to equilibrium after a rapid temperature quench are well understood due to extensive experimental, numerical and theoretical studies in the past decades. In many technological and natural processes one is however confronted with phase-separating systems where the temperature is slowly drifting. In this case it is of interest to follow the evolution of the local composition also while the temperature is evolving. A simple estimate shows that even for very small drift the composition cannot quasi-statically (in the sense of local thermodynamic equilibrium) follow the change of temperature. The temporal evolution of the composition consequently becomes a problem of pattern formation: For small temperature drift convection arises, and a large drift induces repeated waves of precipitation.

We derive a phase diagram accounting for the cross-over between the quasi-static, convective and oscillatory regimes, and present a minimal theoretical model addressing the parameter dependence of the oscillations. The latter agrees well with recent experimental data of D. Vollmer and G.K. Auernhammer (MPI Polymer Research, Mainz).