Thickness-dependent wrinkling of PDMS films for programmable mechanochromic responses

We report a remarkable thickness-dependent wrinkling behavior of oxygen plasma-treated polydimethylsiloxane(PDMS)flms,in which an energy barrier separates the wrinkling mechanics into two regimes.For thick films,the film wrinkles with a constant periodicity which can be precisely predicted by the classic nonlinear finite mechanics.Reducing the film thickness below 1 mm leads to nonuniform wrinkles with an increasing periodicity which gives rise to random scattering and transparency changes under mechanical strains.By tuning the flm thickness,we were able to control both the quality and size of the periodic wrinkles and further design mechanochromic devices featuring briliant structural colors and programmable colorimetric responses.This work sheds light on the fundamental understanding of the wrinkling mechanics of bilayer systems and their intriguing mechanochromic applications.