Abstract

Complex fluids respond sensitively to external perturbations, typically leading to anisotropic macroscopic properties. On a microscopic level, soft matter systems are successfully described by interacting many-particle models obeying Hamiltonian dynamics for translational and rotational degrees of freedom. In order to capture the long-time, large-length scale behavior, coarse-grained descriptions of the orientational ordering and dynamics are urgently needed. Here, we discuss a general method based on projection operators and nonequilibrium statistical thermodynamics in order to systematically and consistently connect microscopic and coarse-grained levels of description. We demonstrate the method for the example of nematic liquid crystals and show its benefits and limitations.