Dynamic transmission-reflection dichroism based on humidity-responsive metal-hydrogel-metal nanocavities

Abstract

“Lycurgus cup” effect, referring dichroism between reflection and transmission modes of the same structures, is a peculiar phenomenon of multi-faceted display in structural color. Beyond the static dichrotic display, the realization of dynamic dichroism desires active materials and tunable structures, and owns the great demand from smart display, anti-counterfeiting and environmental sensing. We hereby propose a metal-hydrogel-metal (MHM) nanocavity for dynamic dichrotic display. This structure includes thin silver layers to induce the partial transmission with the existing reflection, and a polyvinyl alcohol (PVA) hydrogel layer owning the swelling/deswelling deformability to humidity change. The following experimental measurements and theoretical analysis prove that the reflection and transmission modes exist at distinct wavelengths, and the swelling hydrogel layer by humidity change between 10 and 90% RH can dynamically modulate the dichrotic resonance with the wavelength shift over 100 nm. Such environmental-sensitive and real-time tunable dichroism with hydrogel-based structural color is then verified for multi-color printing, resolution test, and cycling test.

Configurable swellability of hydrogel microstructure for structural-color-based imaging concealment/encryption

“…41 Polyvinyl alcohol (PVA), as a typical hydrogel material, is well studied as a negative resist in G-EBL, by which multi-stage 3D micro-/nanostructures can be patterned for humidity-driven dynamic structural color. 42–44 In this work, we found that the electron-beam exposure dose can vary the thickness of hydrogel micro-/nanostructures and have a prominent effect on the swelling ratio. Fig.…”

Dynamic control of reflection from a metasurface with distinct modulating mechanisms

“…These static working modes will suffer from some limitations when facing the modern radar detection technology. Consequently, various tunable materials or devices, such as liquid crystal [4][5][6][7], graphene [8][9][10][11], diode elements [12][13][14], and hydrogel [15], have been used to design the tunable * Author to whom any correspondence should be addressed. absorbers to dynamically control the reflection efficiency and/or the absorption frequency.…”