Superadiabatic torques and forces in anisotropic colloidal systems

• Applicant: Professor Dr. Daniel de las Heras
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 447925252

This project aims at unraveling the role of superadiabatic effects in the dynamics ofanisotropic many-body colloidal systems. Colloids are nano- to micron-sized particles suspended in a continuous phase such as a liquid. The interaction between colloidal particles can be highly anisotropic due to the shape of the particles or the addition of interaction sites on the surface of the particle. Recent breakthroughs in colloidal synthesis have made it possible to control with high precision the shape and the surface properties of colloidal particles.The equilibrium phase behaviour of anisotropic colloidal particles is interesting from both fundamental and technological points of view. For example, several liquid crystalline phases such as nematic, columnar, and smectic phases can be stabilized in bulk. The confinement of anisotropic colloidal particles induces the formation of topological defects. Patchy colloids (colloidal particles decorated with patches on the surface) exhibit unexpected properties such as the formation of empty liquids and equilibrium gels.In contrast to equilibrium, the dynamical properties of anisotropic many-body Brownian systems are largely unexplored. Moreover, the most frequently used theoretical approach to describe such systems, dynamical density functional theory, is based on an adiabatic approximation. The adiabatic approximation assumes that the correlations between particles can be well described by those in an equilibrium system. This approximation has a severe impact on the prediction of the dynamics. In this project we will go beyond the adiabatic approximation developing the first power functional theory for anisotropic systems.Power functional theory (PFT) is based on an exact variational approach for nonequilibrium situations, and it goes beyond the adiabatic approximation by incorporating superadiabatic effects via a functional of both the density and the current fields. Despite being a recent theory, PFT was shown to appropriately describe the dynamics of isotropic colloidal systems. Examples include shear migration, lane formation, and phase separation in active particles. In this proposal we will use Brownian dynamics simulations to measure both the superadiabatic torques and superadiabatic forces in simple systems. Next, we will formulate a PFT to explain the observed superadiabatic torques and forces. Finally, we will apply the theory to study superadiabatic effects in bulk and confined lyotropic liquid crystals as well as in patchy particles.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Matthias Schmidt