Dokument: Microswimmers: dynamical density functional theory and discrete particle models
| Titel: | Microswimmers: dynamical density functional theory and discrete particle models | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=51465 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20191106-115920-1 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Hoell, Christian [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Löwen, Hartmut [Gutachter] Priv.-Doz. Dr. Menzel, Andreas [Gutachter] [im Online-Personal- und -Vorlesungsverzeichnis LSF anzeigen] | |||||||
| Stichwörter: | Active matter, Microswimmers, DDFT, Dynamical density functional theory | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 530 Physik | |||||||
| Beschreibung: | The study of active matter concerns physical systems that take up energy from their environment and use it to drive themselves out of equilibrium. Here, we focus on active microswimmers, i.e., force- and torque-free particles that are suspended in a viscous fluid and induce fluid flows in order to propel themselves. We describe microswimmers that self-propel along straight or circular trajectories, involving mutual far-field hydrodynamic interactions at low Reynolds numbers.
Our microswimmer models are taken as an input for statistical descriptions of corresponding (semi)dilute suspensions via dynamical density functional theory (DDFT). The theory includes the influences of self-propulsion, external potentials, and thermal noise, as well as pairwise steric and hydrodynamic interactions between the swimmers. It is applied to characterize the behavior of swimmers in a spherically symmetric external trapping potential, reproducing results of previous particle-based computer simulations. Namely, the swimmers propel against the trapping force and can form high-density ring structures. In this configuration, hydrodynamic interactions can induce a spontaneous symmetry breaking, assembling the swimmers effectively on a high-density spot. Our numerical evaluations showed a further instability of this pumping state. In contrast to that, for circle swimmers, a sufficiently strong curvature of their trajectories leads to localizations near the center of the trap. Additionally, we adapt Percus' equilibrium test-particle method and combine it with our DDFT to calculate, for non-trapped planar systems of self-propelled particles, corresponding pair distribution functions. They serve as an input to determine, from a linear stability analysis of our DDFT, the possible onset of collective orientational order due to hydrodynamic interactions. We derive a quantitative criterion whether such order can develop, which again agrees qualitatively with the results from existing particle-based computer simulations. Furthermore, an extension of our statistical framework to describe binary mixtures of microswimmers is presented and then applied to again analyze the effect of a trapping potential, to the question of orientational ordering, and to the situation of a circular shear cell. In contrast to the above DDFT, we further perform discrete particle modeling for specific physical setups. First, we discuss the behavior of an individual three-sphere swimmer near one rigid wall, and confined in a channel comprised of two parallel rigid walls. Depending on its initial position and orientation, the swimmer can show a variety of different types of behavior, including trapped and gliding states. Second, interactions of (active) particles with elastic interfaces are studied. We introduce a simple model membrane and discuss, e.g., under which circumstances it can keep an approaching particle from breaking through it. Furthermore, the interplay between hydrodynamic interactions and the elastic response of an interface is discussed for a driven passive point-like particle in a non-axisymmetric setup inside an elastic spherical cavity and for the lowest modes of ow induced by a general microswimmer near an infinitely-extended planar elastic interface, using a force multipole expansion. | |||||||
| Lizenz: |  Urheberrechtsschutz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Physik » Theoretische Physik | |||||||
| Dokument erstellt am: | 06.11.2019 | |||||||
| Dateien geändert am: | 06.11.2019 | |||||||
| Promotionsantrag am: | 17.09.2019 | |||||||
| Datum der Promotion: | 25.10.2019 |
