From Disordered to Quasi-Ordered Structures: Bioinspired Non-Iridescent Structural Colors from Phase-Separated Polymer Blend Films

Structural colors, have gained lot of prominence in the recent years, owing to their vibrancy, durability and environment friendliness with special emphasis on angle-independent (non-iridescent) colors. Numerous studies on using colloids and block copolymers for fabricating angle-independent colors have been reported in literature. We demonstrate temperature-induced phase-separation in polymer blend films as a strategy to achieve angle-independent colors closely mimicking colors in nature (blue colors of barbs in Eastern bluebird and white color of beetle scales). We have employed PS/PMMA blend system as a model system of study. Morphology of the films ranging from disordered to quasi-ordered to ordered structures with varying length scales were fabricated by controlling the thermodynamics of polymer blend phase-separation in terms of composition, thermal quench depth and film thickness. Characterization of the films using SEM, USAXS and UV-Visible spectroscopy revealed that the resultant color of the films arose from disordered and quasi-ordered structures based on incoherent and coherent scattering respectively. The strategy employed is thus compatible via a roll-to-roll assembly enabling us to fabricate these colors on a large-scale.