Low‐Powered E‐Switching Block Copolymer Structural Color Display with Organohydrogel Humidity Controller. Issue 8 (29th April 2022) - Lee, Chang Eun
Abstract: Soft‐solid photonic crystals (PCs) based on periodically ordered block copolymer (BCP) nanostructures demonstrate stimuli‐adaptive structural colors (SCs) and desirable mechanical properties suitable for reflective‐mode electric‐switching (E‐switching) displays. However, the low electrochemical stability and humidity‐dependent E‐switching performance of hygroscopic ionic salts, often employed for E‐field‐adaptive structural alteration, limit their applications. In this study, a low‐powered capacitive E‐switching BCP SC display with an organohydrogel (OH) humidity controller is proposed, where a bilayer of a BCP and a polymer blend with hygroscopic E‐field‐adaptive ionic salts is sandwiched between Au electrodes. The display reliably exhibits reversible full‐color E‐switching (100 on/off cycles) at operating voltages of +2.5 to −2 V within the ionic salts' electrochemical window at ≈50% humidity. A patchable and reusable OH serves as a water reservoir (with optimized geometries and dimensions) to improve the display's humidity tolerance, providing a target humidity (≈50%). The proposed display performs at ambient humidity lower than 60% for over 10 days because of the long water retention and mechanical integrity properties of OH. Additionally, the topologically micropatterned BCP PC allows lateral diffusion of ionic salts through the sides of the patterned domain under E‐field, facilitating E‐switching speeds of ≈30 s. Abstract : Humidity‐tolerant and electrochemically stable block copolymer (BCP) structural color (SC) display is demonstrated, based on 1D BCP photonic crystal with self‐assembled periodic nanostructures and an organohydrogel (OH) acting as humidity controller. The long water retention and mechanical integrity of OH allow the reliable full‐color operation of the BCP SC display, making it suitable for emerging reflective‐mode interactive display.