Reversible Light-, Thermo-, and Mechano-Responsive Elastomeric Polymer Opal Films

A new strategy to achieve easily scalable triple stimuli-responsive elastomeric opal films for applications as stretch-tunable photonic band gap materials is reported. Novel monodisperse highly functional core-interlayer-shell beads are obtained by semicontinuous emulsion polymerization featuring a temperature-sensitive fluorescent rhodamine dye either locally restricted in the core or the shell of prepared beads. After extrusion and compression molding, homogeneous elastomeric opal films with fascinating stretch-tunable and temperature-dependent fluorescent properties can be obtained. Applying strains of only a few percent lead to significant blue shift of the reflected colors making these films excellent candidates for applications as deformation sensors. Higher strains up to 90% lead to a tremendous Bragg reflection color change caused by transition from the (111) to the (200) lattice plane. The well-ordered opaline structure with its stop band at the emission frequency of the incorporated fluorescent dye shows remarkable angle-dependent fluorescence suppression. Herein described elastomeric opal films can be valuable in a wide range of applications such as rewritable 3D optical data storage, tunable laser action, and sensing materials.