Rattle-type colloidal crystals composed of spherical hollow particles containing an anisotropic, movable core

Controls over the position and orientation of anisotropic particles in their assemblies are intriguing issues for functional colloidal crystals that are switchable with external fields such as electric and magnetic fields. We propose a novel approach for the fabrication of rattle-type colloidal crystals containing an anisotropic, movable core surrounded by a void space that allows rearrangement of the anisotropic core in the assembly. In the fabrication, multilayered core-shell particles composed of a titania core, polystyrene shell, and silica shell were prepared and then heated at 500 °C for 4 h to selectively remove the middle layer of polystyrene. The heating treatment induced deformation of spherical titania cores in the compartment of silica shells, while the void space required for the orientation and relocation of anisotropic core was generated. The rattle particles fabricated were self-assembled by a simple dip-coating to form an arrangement of the spherical yolk/shell particles incorporating an anisotropic core. Brownian motion of the anisotropic cores observed with an optical microscope showed that the assembly of rattle-type particles had the potential to control location and orientation of the anisotropic cores in the shell compartment by application of external fields.