Angle-independent responsive organogel retroreflective structural color film for colorimetric sensing of humidity and organic vapors

The angle dependence of photonic crystals (PCs) dramatically limits their practical applications in the colorimetrical sensing of humidity and volatile organic compound (VOC) vapors. In addition, it is challenging for inverse opal PCs to colorimetrically distinguish between vapors with similar refractive indices. Different from the mechanism of PC-based sensors, here, we report an angle-independent polyacrylamide (PAAm) organogel structural color film based on the mechanisms of retroreflection, total internal reflection (TIR) and interference with a shape similar to a single-sided egg waffle. During the process of responding to humidity and VOC vapors, the color of the film remains angle-independent in the normal angle range of 0 degrees to 45 degrees under coaxial illumination and observation conditions. At the same time, the film can colorimetrically distinguish between vapors with similar refractive indices, such as methanol and ethanol, which is mainly due to the differences in their polarity and solubility parameters. The film shows good stability, reversibility and selectivity when exposed to vapors. A colorimetric sensor with a new response mechanism is proposed and has the potential to effectively distinguish between vapors with similar refractive indices. Furthermore, this responsive retroreflective structural color film (RRSCF) provides a universal strategy to develop targeted angle-independent structural color sensors by selecting optimized materials. (C) 2021 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.

Automated summary

This study presents an angle-independent polyacrylamide organogel structural color film that can maintain angle-independence during the response to humidity and VOC vapors, while also being able to distinguish between vapors with similar refractive indices. The film shows good stability, reversibility, and selectivity in vapor exposure.