SFB TR6 - TP C4 Effect of modulated boundaries on structure formation near the liquid-solid transition in equilibrium and under shear"

Beschreibung

In this project the investigation of the effects of modulated boundaries (walls, light fields) on the structure formation in colloidal fluids near the fluid-solid transition are scheduled by experiments (video microscopy) and computer simulations (Monte Carlo and Brownian Dynamics). Systems in two and three dimensions are explored in equilibrium and in non-equilibrium situations. In detail we explore the structure formation of magnetic colloids in front of structured surfaces, in light fields and in magnetic fields, where interesting competing effects modify the growth from line-shaped structures to bulk-structures. Capillary crystallization is explored for charged colloids and for colloidal mixtures in fields between two parallel walls at various distances. The effect of shearing of parallel walls on the diffusion of defects in the ordered colloidal systems shall be investigated as well as the layering and laning effect of external forces on mixtures between walls.

Teilnehmer
Institutionen
  • FB Physik
  • AG Nielaba (Theoretische Physik mit Schwerpunkt Statistische Physik)
  • AG Maret (Experimentalphysik mit Schwerpunkt Weiche kondensierte Materie)
Publikationen
    Deutschländer, Sven; Franzrahe, Kerstin; Heinze, Birte; Henseler, Peter; Keim, Peter; Schwierz, Nadine; Siems, Ullrich; Virnau, Peter; Wilms, Dorothea; Binder, Kurt; Maret, Georg; Nielaba, Peter (2013): Effects of boundaries on structure formation in low-dimensional colloid model systems near the liquid-solid-transition in equilibrium and in external fields and under shear The European Physical Journal Special Topics. 2013, 222(11), pp. 2973-2993. ISSN 1951-6355. eISSN 1951-6401. Available under: doi: 10.1140/epjst/e2013-02070-3

Effects of boundaries on structure formation in low-dimensional colloid model systems near the liquid-solid-transition in equilibrium and in external fields and under shear

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A brief review focusing on low-dimensional colloidal model systems is given describing both simulation studies and complementary experiments, elucidating the interplay between phase behavior, geometric structures, and transport phenomena. These studies address the response of these very soft colloidal systems to perturbations such as uniform or uniaxial compression, laser fields, randomly quenched disorder, and shear deformation caused by moving boundaries.
Binary hard-disk mixtures are studied by Monte Carlo simulation, to investigate ordering on surfaces or in monolayers, modeling the effect of a substrate by an external potential. By weak external laser fields the miscibility of the mixture can be controlled, and the underlying mechanism (laser-induced demixing) is clarified. The stability of various space-filling structures is discussed only for the case where no laser fields are present.Hard spheres interacting with repulsive screened Coulomb or dipolar interaction confined in 2D and 3D narrow constrictions are investigated by Brownian Dynamics simulation. With respect to the structural behavior, it is found that layers or planes throughout the microchannel are formed. The arrangement of the particles is disturbed by diffusion, and can also be modified by an external driving force causing a density gradient along the channel. Then the number of layers or planes gets reduced, adjusting to the density gradient, and this self-organized change of order also shows up in the particle velocities.
The experimental work that is reviewed here addresses dipolar colloidal particles confined by gravity on a solid substrate on which a set of pinning sites has been randomly distributed. The dynamics of the system is studied by tracking the trajectories of individual particles, and it is found that the mean square displacements of particles that are nearest neighbors of pinned particles are strongly affected by these defects. The influence of the pinning sites on the order and microscopic mechanism of phase transitions in two dimensions is investigated.

Forschungszusammenhang (Projekte)

Mittelgeber
Name Finanzierungstyp Kategorie Kennziffer
Deutsche Forschungsgemeinschaft Drittmittel Forschungsförderprogramm 52960802
Weitere Informationen
Laufzeit: 01.07.2009 – 30.06.2013