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Author: Wagner, B. × WGL Institute: WIAS ×

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Now showing 1 - 5 of 5
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    Anisotropic solid-liquid interface kinetics in silicon: An atomistically informed phase-field model
    (Bristol : IOP Publ., 2017) Bergmann, S.; Albe, K.; Flege, E.; Barragan-Yani, D.A.; Wagner, B.
    We present an atomistically informed parametrization of a phase-field model for describing the anisotropic mobility of liquid–solid interfaces in silicon. The model is derived from a consistent set of atomistic data and thus allows to directly link molecular dynamics and phase field simulations. Expressions for the free energy density, the interfacial energy and the temperature and orientation dependent interface mobility are systematically fitted to data from molecular dynamics simulations based on the Stillinger–Weber interatomic potential. The temperature-dependent interface velocity follows a Vogel–Fulcher type behavior and allows to properly account for the dynamics in the undercooled melt.
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    A thin film model for corotational Jeffreys fluids under strong slip
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2006) Münch, Andreas; Wagner, B.; Rauscher, M.; Blossey, R.
    We derive a thin film model for viscoelastic liquids under strong slip which obey the stress tensor dynamics of corotational Jeffreys fluids.
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    Quantifying hydrodynamic slip : a comprehensive analysis of dewetting profiles
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2007) Fetzer, Renate; Münch, A.; Wagner, B.; Rauscher, M.; Jacoobs, K.
    To characterize non-trivial boundary conditions of a liquid flowing past a solid, the slip length is commonly used as a measure. From the profile of a retracting liquid front as measured, e.g., with atomic force microscopy, the slip length as well as the capillary number can be extracted by the help of the Stokes model for a thin liquid film dewetting from a solid substrate. Specifically, we use a lubrication model derived from the Stokes model for strong slippage and linearize the film profile around the flat, unperturbed film, and, for small slip lengths a Taylor approximation of the linearisation for the full Stokes model. Furthermore, from the capillary number and the knowledge of the liquid front velocity and the surface tension, we can obtain the viscosity of the fluid film. We compare theoretical and experimental results, test the consistency and the validity of the models/approximations, and give an easy-to-follow manual of how they can be used to analyze experiments.
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    Slip-controlled thin film dynamics
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2006) Fetzer, Renate; Rauscher, M.; Münch, A.; Wagner, B.; Jacobs, K.
    In this study, we present a novel method to assess the slip length and the viscosity of thin films of highly viscous Newtonian liquids. We quantitatively analyse dewetting fronts of low molecular weight polystyrene melts on Octadecyl- (OTS) and Dodecyltrichlorosilane (DTS) polymer brushes. Using a thin film (lubrication) model derived in the limit of large slip lengths, we can extract slip length and viscosity. We study polymer films with thicknesses between 50 nm and 230 nm and various temperatures above the glass transition. We find slip lengths from 100 nm up to 1 $mu$m on OTS and between 300 nm and 10 $mu$m on DTS covered silicon wafers. The slip length decreases with temperature. The obtained values for the viscosity are consistent with independent measurements.
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    Stationary solutions of driven fourth- and sixth-order Cahn-Hilliard type equations
    (Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2007) Korzec, Maciek D.; Evans, P.L.; Münch, A.; Wagner, B.
    New types of stationary solutions of a one-dimensional driven sixth-order Cahn-Hilliard type equation that arises as a model for epitaxially growing nano-structures such as quantum dots, are derived by an extension of the method of matched asymptotic expansions that retains exponentially small terms. This method yields analytical expressions for far-field behavior as well as the widths of the humps of these spatially non-monotone solutions in the limit of small driving force strength which is the deposition rate in case of epitaxial growth. These solutions extend the family of the monotone kink and antikink solutions. The hump spacing is related to solutions of the Lambert $W$ function. Using phase space analysis for the corresponding fifth-order dynamical system, we use a numerical technique that enables the efficient and accurate tracking of the solution branches, where the asymptotic solutions are used as initial input. Additionally, our approach is first demonstrated for the related but simpler driven fourth-order Cahn-Hilliard equation, also known as the convective Cahn-Hilliard equation.