Visualization of Flow-Induced Strain Using Structural Color in Channel-Free Polydimethylsiloxane Devices

Biomimetic Photonic Elastomer Exhibiting Stress/Moisture Reconfigurable Wrinkle-Lattice for Reversible Deformation Information Storage

Photonic elastomers, capable of converting imperceptible deformations into visible colors, show significant potential in smart materials. However, instantaneous deformation is arduous to record accurately due to the disappearance of optical information after deformation recovery. Herein, inspired by the folding structures of iridocytes in cephalopods, a stress- and moisture-triggered wrinkling and erasure effect is proposed to be introduced in the construction of a photonic elastomer. Implemented in a dual-network polymer framework with modulatable locking, it allows for reversible deformation storage. The photonic elastomer comprises a surface one-dimensional photonic crystal (1DPC) and a poly(dimethylsiloxane) (PDMS) substrate. The deformed 1DPC lattice transforms into a wrinkled state due to a substrate deformation mismatch, preserving strain-induced structural color information through interchain hydrogen bonding and crystalline shape-locking in dual-network polymers. Reading the color provides multidimensional information about the instantaneous deformation degree and distribution. Moreover, the moisture-induced shape-memory feature of the 1DPC can be triggered with a minute amount of water, like fingertip perspiration or humidity change (35% to 80%), to restore the original color. This stress/moisture-responsive photonic elastomer, with its dynamically reconfigurable wrinkle-lattice, holds great promise for applications in mechanical sensing, inkless writing, and anticounterfeiting, significantly enhancing the versatility of photonic materials.

Multifaceted Structurally Coloured Materials: Diffraction and Total Internal Reflection (TIR) from Nanoscale Surface Wrinkling

We investigate the combined effects of surface diffraction and total internal reflection (TIR) in the design of 3-dimensional materials exhibiting distinct structural colour on various facets. We employ mechanical wrinkling to introduce surface diffraction gratings (from the nano to the micron scales) on one face of an elastomeric rectangular parallelepiped-shaped slab and explore the roles, in the perceived colours, of wrinkling pattern, wavelength, the directionality of incident light and observation angles. We propose a simple model that satisfactorily accounts for all experimental observations. Employing polydimethylsiloxane (PDMS), which readily swells in the presence of various liquids and gases, we demonstrate that such multifaceted colours can respond to their environment. By coupling a right angle triangular prism with a surface grating, we demonstrate the straightforward fabrication of a so-called GRISM (GRating + prISM). Finally, using a range of examples, we outline possibilities for a predictive material design using multi-axial wrinkling patterns and more complex polyhedra.