Dokument: Dynamically asymmetric colloids under external constraints

Titel:	Dynamically asymmetric colloids under external constraints
URL für Lesezeichen:	https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=37012
URN (NBN):	urn:nbn:de:hbz:061-20160128-150718-6
Kollektion:	Dissertationen
Sprache:	Englisch
Dokumententyp:	Wissenschaftliche Abschlussarbeiten » Dissertation
Medientyp:	Text
Autor:	Sentjabrskaja, Tatjana [Autor]
Dateien:	[Dateien anzeigen] Adobe PDF [Details] 14,10 MB in einer Datei [ZIP-Datei erzeugen] Dateien vom 28.01.2016 / geändert 28.01.2016
Beitragende:	Prof. Dr. Egelhaaf, U. Stefan [Gutachter] Prof. Dr. Horbach, Jürgen [Gutachter]
Stichwörter:	colloids, microscopy, rheology, differential dynamic microscopy
Dewey Dezimal-Klassifikation:	500 Naturwissenschaften und Mathematik » 530 Physik
Beschreibung:	Colloids are particles in a solvent which, due to their size in the nano- to micrometer range, undergo Brownian motion and are very susceptible to external forces. Their size is comparable to the wavelength of light, which allows us to follow individual particle under the optical microscope. Because they behave like large atoms, colloidal dispersions have evolved into fascinating model systems to study fundamental physical problems. Furthermore, they are found in many industrial and natural products giving them a vast industrial and technological importance. At very high packing fractions, colloidal hard spheres enter a non-equilibrium glass state, which is characterized by arrested dynamics. Despite the simplicity of this system, many facets of the nature of the glass transition have eluded a satisfactory explanation so far. In particular, a detailed microscopic picture of the arrest mechanism, which is expected to be governed by \glqq caging\grqq{} through neighboring particles, and how these cages can be broken and ergodicity restored still has to be explored. Here we follow two strategies to investigate glassy dynamics. We use binary hard-sphere mixtures with large dynamical asymmetry, which allow us to experimentally explore and contrast different caging mechanisms: for example, the large particles can be caged by large or small particles. Furthermore, we expose these mixtures to strong external constraints, namely shear, to push the systems far from their quiescent state and observe the shear-induced enhancement of the dynamics. The recently developed rheoscopy enables us to follow the particles in situ by confocal microscopy while they are exposed to external shear. We find that different caging mechanisms can lead to different glass states that have very distinct properties, like structure, dynamics or viscoelastic moduli. These caging mechanisms, together with the short- and long-time single particle dynamics as well as dynamical heterogeneities, are also responsible for the different yielding behaviors, i.e. transitions to flow. Finally, we have investigated the dynamics of dilute small particles confined by dense large spheres. Very small tracer particles can pass through the narrow channels between large spheres, whereas larger tracers become increasingly localized. Due to the motion of the large particles, however, localization is never perfect and results in slow anomalous dynamics of the tracers. The competition between localization and diffusion has been found to result in a logarithmic decay of the intermediate scattering function of the tracer particles. The dynamics of the tracer particles could only be determined thanks to a novel combination of fluorescent labeling methods, confocal microscopy and differential dynamic microscopy, which was combined during this PhD.
Lizenz:	Urheberrechtsschutz
Fachbereich / Einrichtung:	Mathematisch- Naturwissenschaftliche Fakultät » WE Physik » Physik der kondensierten Materie
Dokument erstellt am:	28.01.2016
Dateien geändert am:	28.01.2016
Promotionsantrag am:	15.09.2015
Datum der Promotion:	02.11.2015