Self assembly of anisotropic colloidal particles



Colloidal particles have been successfully used as ''model atoms'', as
their behavior can be more directly studied than that of atoms or
molecules by direct imaging in a confocal microscope. Most studies have
focussed on spherical particles with isotropic interactions. However, a
range of interesting materials such as many supramolecular polymers or
biopolymers exhibit highly directional interactions. To capture their
behavior in colloidal model systems, particles with anisotropic
interactions are clearly required. Here we use a colloidal system of
nonspherical colloids, where highly directional interactions can be
induced via depletion. By biaxially stretching spherical PMMA particles
we create oblate spheroidal particles. We induce attractive interactions
between these particles by adding a non-adsorbing polymer to the
background liquid. The resulting depletion interaction is stronger along
the minor axis of the oblate spheroids. We study the phase behavior of
these materials as a function of the ellipsoid aspect ratio, the
strength of the depletion interactions, and the particle concentration.
The resulting morphologies are qualitatively different from those
observed with spherical particles. This can be exploited for creating
new materials with tailored structures.

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