EPJ Appl. Metamat. 9, 18 (2022)
https://doi.org/10.1051/epjam/2022016

Research Article

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

¹ International Research Center for EM Metamaterials and Institute of Advanced Magnetic Materials, College of Materials and Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018, PR China
² State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou 310027, PR China

^* e-mail:jianzhang@hdu.edu.cn
^a Dandan Wang and Qiang Li contributed equally to this work.

Received: 22 September 2022
Accepted: 9 November 2022
Published online: 7 December 2022

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.