Seeding effects in phase transitions quenched far from of equilibrium

• Applicant: Dr. Peter Keim
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: from 2013 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 237282255

The investigation of phase transitions and the corresponding symmetry breaking mechanism is a fascinating research topic in physic since long. It has been an enormous achievement in statistical physics to classify quite different systems into universality classes depending on their symmetries and the symmetries of the respective order parameters. For Example, the melting scenarios in 3D and 2D systems are very unequal. A prerequisite for the successful statistical description was, that the systems are in thermodynamic equilibrium. One famos example for a system falling out of equilibrium is the glass transition yet another is crystallization with extremely large cooling rates where systems are far out of thermodynamic equilibrium. For 2D system we were able to show, that the mechanism of freezing in equilibrium and out of equilibrium are quite different. Here we would like quantify crystallization far from equilibrium on a microscopic level, while a nucleation seed is offered during a temperature quench.The system consists of super-paramagnetic colloidal particles confined at an absolutely flat liquid/air interface constituting a 2D monolayer. Since the dynamics of the particles is slow enough to be resolved by digital image processing the full phase-space information is available and can be compared to theoretical models. Using an outer magnetic field, the ratio between repulsive interaction of the particles and thermal energy can be varied, controlling the system temperature as function of time. This way the system can be cooled on time scales 10-4-times shorter compared to intrinsic time scales - a unique feasibility in our experiment.Since the out of equilibrium phase transition can not be described with classical nucleation theory as we showed previously we want to investigate the influence of fluctuations of the local order parameters. Therefore we want to impose a seed (small crystalline structures or walls) using holographic optical tweezers during the time of quench. The effect of such a crystalline seed during the quench (where we avoid to name it heterogeneous nucleation) will be studied thoroughly in this project by varying different parameters including the size of the seed and its geometry, quench rate and depth. We will finally compare the results with predictions of Brownian dynamic simulations, dynamic density functional theory, and phase field theory calculations to get deeper insight in this out of equilibrium process of self organization

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Georg Maret