  The relaxation dynamics of a model fluid of platelike colloidal particles is
investigated by means of a phenomenological dynamic density functional theory.
The model fluid approximates the particles within the Zwanzig model of
restricted orientations. The driving force for time-dependence is expressed
completely by gradients of the local chemical potential which in turn is
derived from a density functional -- hydrodynamic interactions are not taken
into account. These approximations are expected to lead to qualitatively
reliable results for low densities as those within the isotropic-nematic
two-phase region. The formalism is applied to model an initially spatially
homogeneous stable or metastable isotropic fluid which is perturbed by
switching a two-dimensional array of Gaussian laser beams. Switching on the
laser beams leads to an accumulation of colloidal particles in the beam
centers. If the initial chemical potential and the laser power are large enough
a preferred orientation of particles occurs breaking the symmetry of the laser
potential. After switching off the laser beams again the system can follow
different relaxation paths: It either relaxes back to the homogeneous isotropic
state or it forms an approximately elliptical high-density core which is
elongated perpendicular to the dominating orientation in order to minimize the
surface free energy. For large supersaturations of the initial isotropic fluid
the high-density cores of neighboring laser beams of the two-dimensional array
merge into complex superstructures.
