Self-Assembled Tetratic Crystals by Orthogonal Colloidal Force

Bonding simple building blocks to create crystalline materials with design has been sophisticated in the molecular world, but this is still very challenging for anisotropic nanoparticles or colloids, because the particle arrangements, including position and orientation, cannot be manipulated as expected. Here biconcave polystyrene (PS) discs to present a shape self-recognition route are used, which can control both the position and orientation of particles during self-assembly by directional colloidal forces. An unusual but very challenging two-dimensional (2D) open superstructure-tetratic crystal (TC)-is achieved. The optical properties of the 2D TCs are studied by the finite difference time domain method, showing that the PS/Ag binary TC can be used to modulate the polarization state of the incident light, for example, converting the linearly polarized light into left-handed or right-handed circularly polarized light. This work paves an important way for self-assembling many unprecedented crystalline materials.