A Versatile Strategy for Transparent Stimuli-Responsive Interference Coloration

Abstract

The bioinspired stimuli-responsive structural coloration offers a wide variety of potential applications, ranging from sensing to camouflage to intelligent textiles. Because of its design simplicity, which does not require multilayers of materials with alternative refractive indices or micro- and nanostructures, thin film interference represents a promising solution toward scalable and affordable manufacturing of high-quality responsive structural coloration systems. However, thin films of polymers with appropriate thickness generally do not exhibit visible structural colors if they are directly deposited on transparent substrates such as glass. In this work, a versatile new strategy that enables transparent stimuli-responsive interference coloration (RIC) in the polymer–metal–substrate system is presented. The key concept is to use an ultrathin metal layer as an optical filter instead of high refractive index substrate or highly reflective substrate. Such an optical filter layer allows tuning of the degree of transparency, the constructive interference reflection light, and complementary destructive interference transmission light via changing the metal layer thickness. Real-time, continuous, colorimetric RIC sensors for humidity, organic vapor, and temperature are demonstrated by using different stimuli-responsive polymers. The transparent RIC film on glass shows strong coupling of constructive interference reflected colors and complementary destructive interference transmitted colors on opposite sides of the film. Such transparent RIC film allows for the proof-of-concept demonstration of a self-reporting, humidity-sensing window.

Self‐Powered Humidity Sensor Using Chitosan‐Based Plasmonic Metal–Hydrogel–Metal Filters

“…The simplest structural coloration mechanism consists of planar multilayered arrangements 13–17. In particular, the metal–insulator–metal (MIM) configuration based on a Fabry–Pérot resonator has a high quality factor efficient band‐pass filtering with scalability and cost‐effective fabrication 18–20. However, conventional planar MIM resonators lack tunable function, because the resonance depends only on the geometry and optical parameters of the insulating layer.…”

High-Performance Colorimetric Humidity Sensors Based on Konjac Glucomannan

“…The ultrathin metal layer acts as an optical filter, which can dramatically enhance the interference color intensity by simultaneously optimizing both the constructive interference reflection light and complementary destructive interference transmission light. Without the ultrathin metal layer, thin films of polymers with an appropriate thickness generally do not exhibit visible structural colors on low-cost substrates such as glass …”

Multi‐stimuli‐responsive and Multi‐functional Smart Windows

“…Hygroscopic cholesteric liquid crystal polymers altered their optical spectra and transparency owing to structural changes induced by water absorption (which causes swelling) at high humidity and dehydration at high temperatures [157] . Windows based on polymer‐metal substrates changed color because of humidity‐induced changes in interference [158] . Optical changes have been also achieved as a result of humidity‐induced conformational changes of cellulose crystals in the hydroscopic matrix [159–161] and wrinkling‐stretching switching of a multilayer polymer composite films [162,163] .…”

“…[157] Windows based on polymer-metal substrates changed color because of humidity-induced changes in interference. [158] Optical changes have been also achieved as a result of humidityinduced conformational changes of cellulose crystals in the hydroscopic matrix [159][160][161] and wrinkling-stretching switching of a multilayer polymer composite films. [162,163] A hybrid film material with porous structure containing hygroscopic and deliquescent materials was also suggested as a humiditysensitive smart window material.…”