Photopatternable Nanolayered Polymeric Films with Fast Tunable Color Responses Triggered by Humidity

Abstract

Smart surfaces that can dynamically respond to environmental stimuli have demonstrated great promise in wearable electronics and optical detectors. Herein, a photopatternable nanolayered polymeric film that can reversibly display and hide structural colors in the visible range in response to relative humidity (RH) changes is reported. This film is fabricated on a silicon substrate using layer-by-layer assembly of chitosan and photoreactive carboxymethyl cellulose-azido derivative, and selectively crosslinked through UV irradiation from a photomask. Compared to crosslinked regions, un-crosslinked ones swell more and result in a larger thickness at high RH; as a result, those two regions show distinguishable color differences. The correlation of displayed color with film thickness at various RHs is plotted in an International Commission on Illumination (CIE) chromaticity diagram, which is in good agreement with the results obtained from modeling based on the interference theory. It is demonstrated that the structural color patterns on the film can be hidden and displayed spontaneously by contact with humid air, including human breath.This humidity-triggered color change is fast, of fine resolution, highly reversible, and compatible with most silicon-based devices. This film is low-cost, stable, and ready to be applied to large surface areas for potential applications in anticounterfeiting, humidity sensors, and optical color filters.

Structural Color Materials for Optical Anticounterfeiting

“…Gan and co‐workers reported a photopatternable crosslinking strategy for invisible encryption based on a hydrogel interferometer of photoreactive carboxymethyl cellulose‐azido derivative. [ 98 ] The Bragg reflector was formed via layer‐by‐layer assembly of chitosan and a photoreactive cellulose. A masked UV irradiation led to crosslinked regions.…”

Bio-inspired photonic crystal patterns

“…[31][32][33][34] PCs, as dielectric materials with a periodic modulation for manipulating photons, have demonstrated great success and showed the potential for anti-counterfeiting applications. 272,[274][275][276][277][278][279][280][281] In this case, PC patterns were constructed by responsive materials, which could display two or multiple images by changing their colours and transforming between their appearance/disappearance in the background. Patterned PCs provide a new avenue for developing information security devices.…”

“…18F). 277 Wang et al showed a novel anti-forgery pattern by a combination of the ''tricolourfluorescence'' property of carbon dots (CDs) and the unique microstructures constructed via a structured Si template or thermal treatment. Therefore, precisely assembled letter-shaped CD inverse opals (SiCDIOs) could be generated accordingly.…”

“…copyright 2017 Royal Society of Chemistry. (F) Humidity-triggered photopatternable nanolayered polymeric films with a fast tuneable colour response 277. Reproduced with permission from ref 277,.…”

“…(F) Humidity-triggered photopatternable nanolayered polymeric films with a fast tuneable colour response 277. Reproduced with permission from ref 277,. copyright 2019 John Wiley and Sons.…”