Browsing by Author "Lander, Boris"

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Open Access
Nonequilibrium dynamics of colloids
(2013) Lander, Boris; Seifert, Udo (Prof. Dr.)
This thesis is dedicated to the nonequilibrium dynamics of colloidal systems. Colloids belong to the class of mesoscopic systems at typical length scales ranging from a few nanometers to several micrometers. In addition to colloids, such systems span proteins, molecular motors, up to living organisms such as bacteria. The mesoscopic regime is mainly characterized by two important properties. First, the small length scale typically entails an accordingly small energy scale in the order of the thermal energy. Hence, thermal fluctuations play a prominent role. Second, mesoscopic systems, especially biological ones, occur mostly under far-from-equilibrium conditions. Stochastic thermodynamics eliminates these problems by extending thermodynamic concepts such as work, heat, and entropy to the level of fluctuating trajectories under fairly general nonequilibrium conditions. The cornerstones of this approach, which has been developed over the past decades, are the first law along fluctuating trajectories and the definition of a stochastic entropy. A central quality of this framework is that it merely requires the coupling to an equilibrated heat bath, while the mesoscopic system itself can be situated arbitrarily far from equilibrium. The goal of this thesis is to investigate different aspects of the nonequilibrium dynamics of colloids in the light of this framework. In order to tackle this task, colloidal systems are ideally suited as their complexity can be varied from simple systems comprising only few degrees of freedom up to interacting many-body systems. In order to address the more fundamental questions in this thesis, we start by considering two interacting colloidal particles driven along two separate rings by optical tweezers. We use this experimentally well-controllable system to introduce and test an efficient method to measure the dissipation rate in nonequilibrium steady states and to investigate how a hidden degree of freedom affects the fluctuation theorem for entropy production. In order to study collective phenomena, we employ a colloidal suspension subject to a linear shear flow. For this system, we examine the fluctuation-dissipation theorem and the closely related Einstein relation in connection with an approximate effective temperature. Moreover, we study the effect of a linear shear flow on the dynamics of the crystallization process if the colloidal suspension is prepared in a supersaturated state.