Abstract
AbstractInteractive materials capable of changing appearance upon exposure to external stimuli, such as photonic inks, are generally difficult to achieve on a large scale as they often require self‐assembly processes that are difficult to control macroscopically. Here this problem is overcome by preparing arrays of cellulose nanocrystal (CNC) microfilms from discrete nanoliter sessile droplets. The obtained microfilms show extremely uniform and intense color, enabling exceptional consistency in optical appearance across the entire array. The color can be controlled through the initial ink formulation, enabling the printing of polychromatic dot‐matrix images. Moreover, the high surface‐to‐volume ratio of the microfilms and the intrinsic hydrophilicity of the natural building block allow for a dramatic real‐time colorimetric response to changes in relative humidity. The printed CNC microfilm arrays overcome the existing issues of scalability, optical uniformity, and material efficiency, which have held back the adoption of CNC‐based photonic materials in cosmetics, interactive‐pigments, or anticounterfeit applications.
Highlights
cellulose nanocrystals (CNCs)-based photonic materials, but it remains challenging to stringently control the organization and alignment of the Cellulose is one of the most abundant natural substances and cholesteric phase.[9,10,11] To overcome this challenge, various has played a crucial role in human history, with uses ranging approaches have been proposed to improve the long-range from cotton clothing to paper manufacture
Results and Discussion building blocks and using only self-assembly techniques, it is possible to achieve a wide variety of different functionalities Inspired by the offset printing technique,[14] here we report a method to produce homogeneous centimeter-scale arrays of monochromatic CNC microfilms
Complex dot matrix images were designed by controlling the size and location of individual CNC microfilms via micropatterning of the substrate
Summary
CNC-based photonic materials, but it remains challenging to stringently control the organization and alignment of the Cellulose is one of the most abundant natural substances and cholesteric phase.[9,10,11] To overcome this challenge, various has played a crucial role in human history, with uses ranging approaches have been proposed to improve the long-range from cotton clothing to paper manufacture. To explore the responsivity of the CNC film array to large changes in relative humidity (0% ↔ 100% RH), the local environment was rapidly alternated six times between saturated and dry atmospheres over a period of 90 s (Figure 7b; Movie S2, Supporting Information), during which the peak wavelength reversibly and repeatedly shifted by ≈300 nm. This much greater peak shift corresponds to an increasing rate of water uptake for CNC films at higher RH, as previously demonstrated by the weight increase of dish-cast CNC films in a humid environment.[20] the thin CNC microfilms have complete water penetration and require only minimal water uptake for instantaneous color shifts (
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