Confining blue phase colloids to thin layers

Colloidal assembly in strongly confined cholesteric structures is demonstrated using phenomenological modelling. Particle trapping sites and trapping potentials, which are intrinsically imposed by the strongly anisotropic orientational profile of the confined blue phases, are calculated. Locations of the trapping sites and profiles of the trapping potentials are shown to depend importantly on the particle size, and the array of trapping sites can even change symmetry. Trapping sites provide robust binding of various colloidal structures with binding energy of similar to 100kT for similar to 100 nm particles. Maximising the filling of the trapping sites by particles proves to lower the full free energy of the system, offering means for thermodynamic stabilisation of confined blue phases. Finally, we present formation of disclination cages, formed as a three-dimensional closed network of defect lines surrounding sufficiently large particles with strong homeotropic anchoring.