Colloidal dispersions of rod-like particles are widely accepted as convenient model systems
to study the phase behavior of liquid-crystal forming systems, commonly found in LCDs. This
is due to the fact that colloidal rods exhibit analogous phase behavior to that of elongated
molecules, while they can be directly observed by optical microscopy. More recently, there
has also been a burst of interest in the liquid crystalline behaviour of so-called bent-core, or
banana-shaped, molecules, which have been predicted to form exotic biaxial nematic
phases such as the twist-bend and splay-bent nematic phase. These may be of particular
interest due to their fast switching response in LCDs. While there have been claims of the
observation of these biaxial nematic phases in molecular bent-core systems, no colloidal
bananas have been reported in which these the structure and dynamics of these phases
could be imaged at the particle level.
Here, we have developed an entirely new family of colloidal SU-8 polymer particles, with
shapes ranging from rods, sphero-cylinders, spheres and bananas with tuneable length,
diameter and curvature that are stable in both aqueous and apolar solvent mixtures. Our
colloidal SU-8 polymer particles are produced in bulk and by varying the composition of the
solvent mixture, both the difference in refractive index and mass density between the
particles and the solvent can be independently controlled. This, for example, enables the use
of colloidal SU-8 rods in both 3D confocal microscopy and optical trapping experiments, and
even in experiments combining both techniques, while the effect of gravity can be carefully
tuned. Particularly exciting is that we can tune the curvature of the bananas, which is a key
parameter in their phase behaviour. This is demonstrated by our observations of the exotic
structures formed by differently curved bananas, including isotropic, anti-ferromagnetic
smectic and even the elusive splay-bend nematic ordering and a completely new `colloidal
vortex liquid'.