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DY: Dynamik und Statistische Physik

DY 52: Statistical Physics far from Thermal Equilibrium

DY 52.6: Vortrag

Mittwoch, 9. März 2005, 13:45–14:00, TU H3010

Phase separation in binary mixtures: Oscillatory instabilities under continuous cooling or heating — •Doris Vollmer¹, Jürgen Vollmer², and Günter Auernhammer³ — ¹MPI for Polymer Research, Mainz — ²Physics Department, Philipps University, Marburg — ³Laboratoire de Dynamique des Fluides Complexes, Universite Louis Pasteur, Strasbourg, France

The kinetics of phase separation of binary mixtures under slowly ramping the temperature is discussed. For a broad range of compositions and heating rates the mixtures show pronounced oscillations in the turbidity. It hardly matters if phase separation is induced by cooling or heating, and whether the liquids are of low molecular weight or if a polymer solution is investigated. The oscillations in the coexisting liquid phases can be analysed separately. By choosing an appropriate temperature ramp the time averaged flux across the meniscus is kept constant in the experiments. For all investigated systems the oscillations can be observed over a wide temperature range, as far as 25 degrees away from the transition temperature. From simultaneous shadow graph imaging it can be shown that convection is always present, however amazingly, convection hardly influences the period of the oscillations. The oscillations are generic, of thermodynamic origin and caused by repeated cycles of nucleation, coarsening and sedimentation.