Binary Mixtures

In the frame work of the DFG-Project BL555-3, we investigate the special properties of binary mixtures in complex plasmas. So far, complex plasma studies concentrated on monodisperse micro-particles which turned out to be an excellent model system for strong coupling. Systems with two different particle species (i.e. with different charge) are called binary mixtures. In complex plasmas all experiments so far show that the two particle species instantaneously demix. Our recent experiments however show that it is possible to create binary mixtures. This opens unique opportunities to study structural and dynamical phenomena in strongly coupled systems. Normal modes, waves, phase transitions, transport processes and heat conduction are just a few examples which can be addressed for the first time in binary mixture experiments. Therefore, this project aims at a systematic characterization of the structural and dynamical properties of binary mixtures in complex plasmas.

  • Frank Wieben and Dietmar Block, Photophoretic force measurement on microparticles in binary complex plasmas, Physics of Plasmas 25, 123705 (2018);

  • Frank Wieben, Jan Schablinski, and Dietmar Block, Generation of two-dimensional binary mixtures in complex plasmas, Physics of Plasmas 24, 033707 (2017);

Bild vom Lasersystem und der Plasmakammer

Recently, we managed to explore basic thermodynamic properties of complex plasmas and especially binary mixtures. In the Dezember 2019 issue of PRL ( we reported on successful direct measurements of entropy and its change during heating and cooling. Although entropy is one of the most fundamental quantities in thermodynamics, its direct measurement is impossible in most systems. Using two-dimensional plasma crystals, a sophisticated laser heating mechanism to heat these crystals without melting and high precision particle tracking to measure the full phase space allowed to study the change of entropy in a heating and cooling experiment. It turned out that these systems strictly follow the laws of thermodynamics even if mixtures of different particles are used. The results show on the one hand side that complex plasmas are a model system for strongly coupled systems even with respect to thermodynamic properties and on the other hand side that fundamental studies of systems with non-Maxwellian distributions should be feasible.