Tunable Optical Gratings and Mechanochromic surfaces by Wrinkling of Plasma-Oxidised PDMS

We report strain-modulated uni- and multi-axial phase gratings induced by wrinkling of plasma-oxidised polydimethylsiloxane (PDMS). While plasma exposure yields a glassy skin with high modulus contrast compared to bulk PDMS, it inherently results in a gradient conversion profile emanating from the top film interface. We examine and quantitatively model the consequences of this gradient layer on the optical properties of the resulting strain-tuneable phase gratings. We then develop and validate a surface reconstruction methodology based on the grating diffraction pattern, extending to the high deformation regimes and to 2D gratings. The surfaces display structural color and we demonstrate that sub-micron structures can efficiency discretise colors, with tuneable properties depending on strain, skin thickness and viewing angles.