Disappearing and reappearing of structure order in colloidal photonic crystals

Mechanoresponsive colloidal photonic crystals embedded in elastic solid matrices exhibit tunable optical properties under mechanical force, showing great potential for various applications. However, the response of colloidal crystals embedded in a liquid matrix remains largely unexplored. In this study, we investigate the structural and optical transitions of colloidal crystals composed of particles suspended in a liquid oligomer under pressing and shear forces. We observe that pressing induces a transition from an ordered to a disordered particle arrangement, while subsequent bending shear, such as simple hand-flipping, restores the ordered structure. This reversible transition produces press-induced optical traces that can be erased by subsequent shear, making this material a promising candidate for applications in reversible direct-writing photonic paper and anti-counterfeiting technologies. Our work provides new insights into the structural dynamics of liquid colloidal photonic crystals under mechanical force and highlights their potential for mechanoresponsive applications.