Stimuli-Responsive Photonic Hydrogels

Abstract

Photonic hydrogel (PHG) is a class of soft material, which possesses periodically arranged photonic crystal (PC) structures in the polymer networks and contains large amounts of water interposed in their network structure. Photonic crystal structures have been observed in nature creatures over the million years of evolution. A wide variety of structural colors, which are found in natural organisms such as insects, birds, fish, plant leaves, and berries, are originated by various spectacular photonic architectures. The bright structural colors of these natural creatures play an important role in their life span to survive in response of various environmental stimuli. The origin of the photonic structure and their tunable behavior under various stimuli have attracted a great amount of interest in the scientific community. The striking photonic structure of these natural creatures have been inspired researchers to dedicate enormous efforts for underlying the hidden mechanisms. Therefore, various fabrication techniques to mimic natural photonic structures for applications as colorimetric sensors have been developed. In this article, we have summarized few spectacular natural photonic creatures with variable structural colors and the origin of these structural colors. Various fabrication techniques of these bio-inspired synthetic photonic materials particularly PHGs and their stimuli-responsive behaviors as colorimetric sensors such as pH, solvent, ionic strength, thermal, mechanical, electric, magnetic, and biological, are also emphasized.