Novel Robust Ion-specific Responsive Photonic Hydrogel Elastomers

Embedded photonic crystal hydrogels and responsive photonic crystal microspheres that can change structural color by external stimuli have shown great prospect in various applications, but their practical applications have been greatly limited due to their low mechanical properties of hydrogel materials and unideal optical at sometimes. Although some achievements have been acquired, it is still a challenge to develop photonic crystal hydrogel materials with desired mechanical properties and structural color. Inspired by the excellent mechanical properties of polyurethane, this article represents a novel smart composite material, which combining of nonionic UV-curable polyurethane and cross-linked polystyrene-co-poly (N-isopropylacrylamide) (PS-co-PNIPAM) microspheres for the first time. This photonic hydrogels perform desired optical and narrow half-width of reflection peak, while the tensile strength of cured elastomers changes between 0.1Mpa and 0.43Mpa when the swelling ratio is changed, the maximum elongation at break can reach 143% and this multifunctional material can recover from deformation to original size quickly. As proof-of-concept, SCN- was selected as target analyte. The hydrogel sensors enable to detect SCN ions quantitatively and selectively in water through ion-specific deswelling behavior of hydrogels (Hofmeister series principle) and corresponding change of the wavelength of the diffraction peak, the limit of detection is 5μM. Our strategy is a straightforward way for designing simple smart materials whose response and mechanical properties can be tuned by judicious choice of the hydrophilic group type and content, which extend the potential application of photonic hydrogels.