(604j) Humidity-Responsive Patternable Multilayer Nanofilms with Fast Tunable Colors

Smart surfaces that can dynamically respond to environmental stimuli have demonstrated great promise in wearable electronics, catalytic substrates, optical detectors, and biosensors. Herein, we report a photo-patternable nanolayered polymeric filmthat can reversibly display and hide structural colors in visible range in response to relative humidity (RH) changes. This film was fabricated on a silicon substrate using layer-by-layer assembly of chitosan and photoreactive carboxymethyl cellulose-azido derivative, which can be selectively cross-linked through UV irradiation from a photomask. Comparing to cross-linked regions, un-cross-linked ones swell greater and result in a larger thickness at high RH; as a result, those two regions show distinguishable color difference. The chemical composition and surface morphology of the films were systematically characterized by FT-IR, ¹H NMR, UV-Vis spectrometry, SEM and AFM. The correlation of displayed-color with film thickness at various RH was plotted in a CIEchromaticity diagram. It is demonstrated that the structural color patterns on the film can be hided and displayed spontaneously by contacting with humid air simply from human breath. This humidity-triggered color change is fast, fine resolution, highly reversible, and compatible with most silicon-based devices. This film is low-cost, chemically and mechanically stable under ambient conditions, and ready to be applied to large surface area, which will provide a versatile platform for potential applications in anti-counterfeiting, humidity sensors, and optical color filters.