Biomimetic Tunable Disordered Photonic Structures via Programmable Polymer Blend Phase-Separation

Biopolymers such as proteins undergo self-assembly resulting in complex hierarchical structures with well-defined structure and fascinating multi-functional properties. For example, disordered photonic structures in avian birds are responsible for white and blue non-iridescent colors. These structures are thought to arise from phase-separation between β-keratin and cytoplasm during cell growth and the degree of disorder determines coloration. We utilized temperature-induced phase-separation in polymer blends as an approach to attain multi-functional non-iridescent structural colors similar to nature. We further examined the dynamics of phase-separation to gain insights into the molecular self-assembly process and understand the temporal-evolution of structural and optical disorder. Our results indicate that structural disorder scales with domain-size as well as phase-separation time and a strong direct correlation between structural and optical disorder is observed. Tunable disordered photonics can also be obtained simply by tuning the molecular weight of the polymer blend components. In future photonic designs, it is important to exercise good control on structural disorder at multiple length scales in order to obtain tunable visible colors with multi-functionality.