Transport Processes in Melts under External Fields


Both in the materials design from the melt, and to understand the complex flow behaviour of many colloidal suspensions known from daily application (such as paint), the effect of external forces and/or external flow fields on the solidification behaviour of dense, viscous liquids plays a major role. In this project, we study such externally induced changes by means of theoretical physics modelling and molecular-dynamics computer simulation, with a main focus on glass-forming liquids and suspensions. In particular, we study how the generic aspects (those applicable over a wide variety of different systems) of transport processes on the microscopic scale change under the influence of external forces and fields, and how this transcedes to the material properties observed on the macroscale.

  • Department of Physics
  Voigtmann, Thomas (2008): Idealized glass transitions under pressure : Dynamics versus thermodynamics Physical Review Letters. 2008, 101(9). ISSN 0031-9007. Available under: doi: 10.1103/PhysRevLett.101.095701

Idealized glass transitions under pressure : Dynamics versus thermodynamics


The interplay of slow dynamics and thermodynamic features of dense liquids is studied by examining how the glass transition changes depending on the presence or absence of Lennard-Jones-like attractions. Quite different thermodynamic behavior leaves the dynamics unchanged, with important consequences for high-pressure experiments on glassy liquids. Numerical results are obtained within mode-coupling theory (MCT), but the qualitative features are argued to hold more generally. A simple square-well model can be used to explain generic features found in experiment.

Origin (projects)

    Zausch, Jochen; Horbach, Jürgen; Laurati, Marco; Egelhaaf, Stefan Ulrich; Brader, Joseph M.; Voigtmann, Thomas; Fuchs, Matthias (2008): From equilibrium to steady state : the transient dynamics of colloidal liquids under shear Journal of Physics : Condensed Matter. 2008, 20, 404210. Available under: doi: 10.1088/0953-8984/20/40/404210

From equilibrium to steady state : the transient dynamics of colloidal liquids under shear


We investigate stresses and particle motion during the start-up of flow in a colloidal dispersion close to arrest into a glassy state. A combination of molecular dynamics simulation, mode-coupling theory and confocal microscopy experiments is used to investigate the origins of the widely observed stress overshoot and (previously not reported) super-diffusive motion in the transient dynamics. A link between the macro-rheological stress versus strain curves and the microscopic particle motion is established. Negative correlations in the transient auto-correlation function of the potential stresses are found responsible for both phenomena, and arise even for homogeneous flows and almost Gaussian particle displacements.

Origin (projects)

Funding sources
Name Finanzierungstyp Kategorie Project no.
Exzellenzinitiative third-party funds research funding program 842/09
Further information
Period: 01.07.2008 – 30.06.2013