Photonic rubber sheets with tunable color by elastic deformation.

This article describes an elastic silicone sheet with reversible tuning structural color. The sheet has a thin layer of cubic close-packed, ccp, colloidal particles embedded in poly(dimethylsiloxane), PDMS, elastomer. The array of ccp (111) planes diffracts light of selective wavelengths according to Bragg's law. This is responsible for the structural color of the PDMS sheet. Because the sheet was stretched in the horizontal direction, it was reduced in size in the vertical direction. As a result, the lattice distance of ccp (111) planes decreased, and the reflected wavelength of light shifted to shorter wavelengths. For example, the peak of reflection was tuned from 589 to 563 nm as a function of sheet elongation. The peak position decreased linearly with deformation when the deformation was within 20% of its elongation. Accordingly, the color of the PDMS sheet changed from red to green. When the mechanical strain on the PDMS sheet was released, the peak returned to its original position, and the color of the PDMS sheet also changed back to red. Tuning the color of the PDMS sheet is a reversible and repeatable process. The novel PDMS sheet has the potential to be applied to mechanical strain sensing.