  Colloidal particles in polymer solutions and functionalized nanoparticles
often exhibit short-range attraction coupled with long-range repulsion (SALR)
leading to the spontaneous formation of symmetric patterns. Chiral
nanostructures formed by thin film of SALR particles have not been reported
yet. In this study, we observe striking topological transitions from a
symmetric pattern of concentric rings to a chiral structure of a spiral shape,
when the system is in hexagonal confinement. We find that the spiral formation
can be induced either by breaking the system symmetry with a wedge, or by
melting of the rings. In the former case, the chirality of the spiral is
determined by orientation of the wedge and thus can be controlled. In the
latter, the spiral rises due to thermally induced defects and is absent in the
average particle distribution that form highly regular hexagonal patterns in
the central part of the system. These hexagonal patterns can be explained by
interference of planar density waves. Thermodynamic considerations indicate
that equilibrium spirals can appear spontaneously in any stripe-forming system
confined in a hexagon with a small wedge, provided that certain conditions are
satisfied by a set of phenomenological parameters.
