Dynamics in dense mixtures: Kinetics versus thermodynamics in non-equilibrium fluctuations, phase separation and structure formation

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Non-equilibrium relaxation is an important phenomenon of fundamental interest in experimental and theoretical physics. This is especially so for dense multi-component mixtures, which are ubiquitous in nature -- in biological fluids such as the cytoplasm -- as well as in soft matter -- for example in colloidal suspensions. Already at equilibrium such mixtures exhibit complex phase behaviour due to fractionation, where particles of different type partition themselves unevenly between phases. Non-equilibrium processes such as phase separation after a quench inherit all of this thermodynamic complexity but contain kinetic effects as a further important ingredient. These kinetic effects, which are described by mobilities in continuum approaches, carry significant structure in dense systems because e.g. movement of different particle species in opposite directions can be much slower or faster than collective particle motion. This can lead to novel phenomena like the emergence of multiple timescales and long-lived non-equilibrium structures in phase separation, which have only begun to be explored.This project will study the dynamics of dense mixtures theoretically to address the many open challenges in this area. Its main novelty lies in connecting the limiting cases of colloidal and biological mixtures with their rather different thermodynamics, and in studying the non-trivial kinetics that can occur in dense, slow mixtures. In this way the project aims to achieve a step change in our understanding of the physics of dense mixtures, by tackling a number of key open questions, while at the same time developing new methodologies for e.g. the systematic derivations of mobilities that will open the way for a broad range of future work. The ambitious research plan requires, and is designed explicitly to exploit, the unique combination of expertise that the two PIs bring to the project. These include coarse-graining techniques and continuum approaches for non-equilibrium liquids (M. Krüger) and projection methods for phase separation in large mixtures (P. Sollich).