Surface Morphing of Azopolymers toward Advanced Anticounterfeiting Enabled by a Two-Step Method: Light Writing and Then Reading in Liquid

Abstract

Surface morphing of organic materials is necessary for advances in semiconductor processing, optical gratings, anticounterfeiting etc., but it is still challenging, especially for its fundamental explanation and further applications like advanced anticounterfeiting. Here, we report one strategy to acquire surface deformation of the liquid-crystalline azopolymer film using a two-step method: selective photoisomerization of azopolymers and then solvent development. In the first step, surface tension of the polymer film can be patterned by the selective photoisomerization of azopolymers, and then in the second step, the flowing solvent drags the underlying polymer to transport, leading to the formation of surface deformation. Interestingly, the direction of mass transport is opposite to the traditional Marangoni flow, and the principle of solvents’ choice is the matching of surface tensions between the azopolymer and the solvent. The two-step method shows characteristics of efficient surface morphing, which could be applied in advanced anticounterfeiting by the way of photomask-assistant information writing or microscale direct writing, and then reading in a specific liquid environment. This paves a new way for understanding the mechanism of mass transport toward numerous unprecedented applications using various photoresponsive materials.

Assembly‐Induced Dynamic Structural Color in a Host‐Guest System for Time‐Dependent Anticounterfeiting and Double‐Lock Encryption

“…Continuing heating at 100 °C until 300 s, the assembly of original trans‐azo groups was completed, but that of the recovered azo moieties was not, because original trans‐azo groups began to assemble at the beginning of heating, while recovered azo moieties had to undergo cis‐to‐trans back‐isomerization first and then become assembled, so it took longer to complete the assembly. As we reported earlier, the surface energy of well‐assembled sample is smaller than that of sample without assembly [20] . Therefore, the difference in the time required for accomplishing the assembly process will cause the reproduction of surface‐energy gradient, and the occurrence of Marangoni flow in film.…”

Steerable mass transport in a photoresponsive system for advanced anticounterfeiting

“… 39 , 40 , 41 Since liquid prefers to flow from the high surface-energy region to the low surface-energy region and the flowing solvent can drag the underlying polymer to transport, thus providing a flow in the opposite direction of the thermally induced Marangoni flow for the polymer, which has been reported in our latest work. 42 , 43 However, T g of that azopolymer is too high, so the Marangoni flow of azopolymer itself is unable to happen at room temperature and heat is required to trigger the flow. In this paper, we report one concise strategy to achieve well-controlled bidirectional mass transport on one film surface in solvent vapor at room temperature.…”

Responsive Liquid Crystal Network Microstructures with Customized Shapes and Predetermined Morphing for Adaptive Soft Micro-Optics

“…For the VP-based 4D printing technique, high-resolution 3D microstructures can be achieved by direct laser writing with two-photon polymerization (DLW-TPP), but they often require additional assistance from alignment techniques, and face difficulties in achieving large-area production. 55−57 Several innovative methods have been proposed, incorporating approaches such as material design with unique properties, 59 special treatments, 60,61 and advanced processing technology. 62 Broer et al introduced a method for fabricating fingerprint surface topography using chiral-nematic polymer coatings.…”

“…Several innovative methods have been proposed, incorporating approaches such as material design with unique properties, special treatments, , and advanced processing technology . Broer et al introduced a method for fabricating fingerprint surface topography using chiral-nematic polymer coatings .…”