Printing Convertible Microstructures into Elastomer Matrix for Multiliquids Adaptive Information Encryption

Abstract

displaying is: no optical contrast in the dry state but significant optical contrasts by wetting to show invisible cryptographic patterns, which are composed of switchable microstructures. For information encoding, the patterning of microstructure arrays according to the design in a reliable and reproducible manner is the essential procedure. Various strategies for microstructures patterning have been reported, from evaporation-induced colloidal self-assembly, [23][24][25] top-down lithographic techniques [26,27] to model-assisted casting [28] and inkjet printing. [29,30] However, most of these current technologies suffer from some issues, such as limited pattern variants, low throughput, expensive fabrication, and time-consuming and complicated steps, etc. Few of them simultaneously satisfy the requirements for varied commercial applications. As one of the most promising methods for customizable patterning, 3D printing is a manufacturing process in which material is laid down, layer by layer, to form a three-dimensional object. [9,31,32] The critical advantage of 3D printing is the ability to turn arbitrary digital files data into physical objects, which largely extend the scope of the patterning of the microstructures and have higher throughput and printing resolution through more facile processes. However, currently reported 3D printing of optical material mainly focuses on the static system, especially in the printing of the periodic-ordered photonic crystal. [32][33][34][35][36] For dynamic optical materials based on amorphous microstructures, the 3D printing technology is less involved. As known, periodic-ordered structures are highly angle-dependent, which is a major challenge in wide-viewing angles. Instead, with less angle dependency, adaptive amorphous photonic structures show larger potential in covert-overt displaying. [26] Besides, the random morphological feature makes it possible to nondeterministically encode the information. [37] Herein, we report the direct 3D printing of mixture ink of water droplets and polydimethylsiloxane (PDMS) precursor as the customizable encrypted graphics. Lines and faces are directly written by a 3D dispenser, where the water droplets arrangement is set to be an amorphous array. During the curing of the printed graphics, water vapor evaporates from the microdroplets, accompanied by the in-situ formation of dynamic microcreases in the elastomer matrix of the covert graphics (Figure 1). When exposed to varied liquids, the dynamic Adaptive optical performance based on convertible microstructures is very useful for information encryption. However, the facile patterning of microstructures in reliable manner and the unclonable coding are still major challenges. The direct 3D printing of water droplets is reported as templates to polydimethylsiloxane (PDMS) precursor, followed by water evaporation in curing, which introduces convertible microcrease in the elastomeric matrix. The samples show optical response to liquids with the conversion of inner creases to ponds or cavities...

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