Brownian particle transport in periodic structures

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Title: Brownian particle transport in periodic structures
Authors: Antonov, Alexander
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Thesis advisor: Prof. Dr. Philipp Maa√ü
Thesis referee: RNDr. Artem Ryabov, Ph.D.
Abstract: Particle transport in both natural and fabricated systems often takes place in confined geometries under single-file conditions. This means, that particles cannot pass each other, as, for example, when the particles move through membrane pores or microfluidic channels. A generic model describing particle dynamics in such systems is the Brownian asymmetric simple exclusion process (BASEP). It describes the driven Brownian particle motion of hard spheres through a periodic structure under a constant drag force. This model has been introduced as Brownian dynamics variant of the asymmetric simple exclusion process (ASEP), which is a discrete lattice model that has been established to study fundamental aspects of nonequilibrium physics. Current-density relations in the BASEP are characterized by three effects: a barrier reduction effect, a blocking effect and a commensurability effect. These effects dominate the dynamics for different ranges of particle diameters: the barrier reduction effect is dominant when it is likely that a potential well is occupied by more than one particle. The blocking effect prevails when the particle diameter becomes large such that the multiple occupation of a potential well becomes unlikely due to steric reasons. The commensurability effect governs the dynamics when the particle diameter is close to the spatial period of the external structure. One part of this thesis is devoted to the investigation to what extent and how these effects are modified when considering particles with a soft core that can partially penetrate or even pass each other. We develop an effective size method by which the system of soft particles is mapped onto that of the BASEP. This effective size method is well suitable to describe the dynamics of partially penetrating particles. In the main part of the thesis, particle transport in the BASEP is studied with a focus on crowding effects appearing at high densities. The investigation involves both analytical derivations and extensive Brownian dynamics simulations, including the development of novel algorithms. One intriguing crowding effect is the emergence of solitary cluster waves that propagate without dispersion. At low temperatures, these solitons generate measurable particle currents for certain particle diameters even if potential barriers are hundred times larger than the thermal energy. In effectively frustrated systems, where the blocking effect typically inhibits particle motion, solitons can result in high particle currents. The presence of the theoretically predicted solitons has been experimentally verified recently in colloidal particle transport.
Subject Keywords: Statistical physics; Brownian motion; Stochastic processes; Nonequilibrium statistical mechanics; Langevin algorithm; Brownian soliton
Issue Date: 28-Aug-2023
License name: Attribution 3.0 Germany
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Type of publication: Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:FB06 - E-Dissertationen

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