Simulation of a Hard-Spherocylinder Liquid Crystal with the pe

The pe physics engine is validated through the simulation of a liquid crystal model system consisting of hard spherocylinders. For this purpose we evaluate several characteristic parameters of this system, namely the nematic order parameter, the pressure, and the Frank elastic constants. We compare these to the values reported in literature and find a very good agreement, which demonstrates that the pe physics engine can accurately treat such densely packed particle systems. Simultaneously we are able to examine the influence of finite size effects, especially on the evaluation of the Frank elastic constants, as we are far less restricted in system size than earlier simulations

Simulation kolloidaler Flüssigkristalle

The manipulation of liquid crystals by external potentials, such as electric or magnetic fields, is of great importance in many industrial and research applications. To gain insight into the impact of the different mechanisms in such a complex multi-particle system is a scientific challenge. Interactions between particles and external potential, particle-particle interactions, and, in case of colloidal systems, hydrodynamic interactions lead, in their interplay, to fascinating dynamical states and unusual diffusion behavior. This work presents new insights into the dynamics of colloidal liquid crystals with computer simulations. For this purpose several model systems of increasing complexity are studied. The first model system is the most basic model system possible: a system of hard spherocylinders that only interact via excluded volume. In a next step Brownian motion, the random motion of colloidal particles in a fluid, is included via Langevin Dynamics. Finally, also the impact of hydrodynamic interactions between the particles is studied within a Lattice Boltzmann framework.Die Manipulation von Flüssigkristallen mittels externer Potentiale, in der Form von elektrischen oder magnetischen Feldern, hat große Bedeutung in vielen Industrie- und Forschungsanwendungen. Es ist eine wissenschaftliche Herausforderung den Einfluss der verschiedenen Mechanismen in einem solch komplexen Vielteilchensystem zu verstehen. Die Wechselwirkungen zwischen Teilchen und externen Potentialen, von Teilchen mit anderen Teilchen und, im Falle von Kolloidsystemen, hydrodynamische Wechselwirkungen führen in ihrem Zusammenspiel zu faszinierenden dynamischen Zuständen und außergewöhnlichem Diffusionsverhalten. Diese Arbeit bietet neue Einblicke in die Dynamik kolloidaler Flüssigkristalle durch Computersimulationen. Dabei werden Modellsysteme von zunehmender Komplexität untersucht. Das erste Modellsystem ist das denkbar grundlegendste Modellsystem: ein System harter Sphärozylinder, die nur aufgrund des ausgeschlossenen Volumens miteinander wechselwirken. In einem zweiten Schritt wird das Modell mittels Langevin Dynamik um die Brownsche Bewegung, die ungerichtete Beweging von Kolloidteilchen in einer Flüssigkeit, erweitert. Im letzten Schritt werden innerhalb einer Lattice Boltzmann Simulation zusätzlich die Auswirkungen von hydrodynamischen Wechselwirkungen zwischen den Teilchen untersucht

Dynamical states in driven colloidal liquid crystals

We study a model colloidal liquid crystal consisting of hard spherocylinders under the influence of an external aligning potential by Langevin dynamics simulation. The external field that rotates in a plane acts on the orientation of the individual particles and induces a variety of collective nonequilibrium states. We characterize these states by the time-resolved orientational distribution of the particles and explain their origin using the single particle behavior. By varying the external driving frequency and the packing fraction of the spherocylinders we construct the dynamical state diagram