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.
