Dissertation/Thesis Abstract

Colloids in Non-Equilibrium: From One-Dimensional Transport to Pattern Formation at Surfaces
by Lichtner, Ken, Dr.Nat., Technische Universitaet Berlin (Germany), 2014, 153; 10695428
Abstract (Summary)

In this thesis, we investigate the collective behavior of colloidal suspensions at the mesoscale level in equilibrium as well as in non-equilibrium. Related to recent experiments, we focus in the first part of the thesis on the transport behavior of suspensions of purely repulsive "soft" particles in narrow, spatially modulated channels. Based on the modern dynamical density functional theory (DDFT) we investigate for the first time the impact of external control loops with time delay on colloidal dynamics in non-equilibrium. For different control targets which are also accessible in experiments we demonstrate that the manipulation of the global particle behavior is possible, including the reversal of the particle current and the stabilization of spatiotemporal oscillations. By adding magnetic particles with classical spins of Heisenberg type in the second part of the thesis, we find spontaneous pattern formation with magnetic and non-magnetic domains. Depending on the particle density and concentration we find a first-order demixing transition and a second-order phase transition for the magnetization at fixed magnetic coupling. Based on classical and dynamical density functional approaches we calculate the fluid-fluid interface in equilibrium as well as the domain growth in non-equilibrium. We find two distinct demixing regions for the equilibrium phase diagram, namely spinodal decomposition and nucleation where the latter is an activated growth process. Based on DDFT we show that the domain growth within spinodal decomposition grows systematically with a power law exponent that corresponds to predictions from classical theories. For the nucleation process in non-equilibrium we show new results for the physical pathway towards equilibrium where we choose the energy barrier and particle excess number as coordinates. In the last part of the thesis we demonstrate that the pattern formation in non-equilibrium can be altered in a controlled way by using time-dependent external surface fields. For a novel dynamical instability where stripes against the symmetry of the external potential form, we show that the underlying mechanism is based on an interplay between the intrinsic spinodal decomposition and time-dependent external forces. Moreover, we find that this structural transition is accompanied by directed particle transport which is tuneable by changing external parameters.

Indexing (document details)
Advisor: Klapp, Sabine
School: Technische Universitaet Berlin (Germany)
School Location: Germany
Source: DAI-C 81/1(E), Dissertation Abstracts International
Subjects: Theoretical physics, Electromagnetics, Physical chemistry
Keywords: Colloidal suspensions, Spinoidal decomposition
Publication Number: 10695428
ISBN: 9781392571576
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