This paper describes an elastic colloidal crystal, soft opal, with tunable stop band and its potential application for mechanical strain sensing. A poly-dimethylsiloxane, PDMS, rubber sheet was coated with a thin layer of the soft opal. In the layer, polystyrene, PS, submicron particles were cubic-closely packed, CCP, and among the particles filled with PDMS elastomer. We design the array of CCP (111) planes selectively diffracts light in visible wavelength. The wavelength, i.e. photonic stop band, was reversibly tuned by tensile strain. As the PDMS sheet was stretched in horizontal direction, the film becomes compress in vertical direction. As a result, the lattice distance of CCP (111) planes decreased and the stop band shifted to shorter wavelengths. As released the mechanical strain on the PDMS sheet, the stop band completely returned to the initial wavelength. The PDMS sheet also displays reversible change of the structural color during elastic deformation. The potential application is a simple stress sensor enables visual judgment of the intensity of tensioning.
|