Polystyrene@poly(methyl methacrylate-butyl acrylate) Core-Shell Nanoparticles for Fabricating Multifunctional Photonic Crystal Films as Mechanochromic and Solvatochromic Sensors

Responsive photonic crystals (PCs) with a nano-scale band gap assembled by colloidal nanospheres have been increasingly utilized in detection and sensing devices owing to their attractive ability to change color in response to external conditions. However, most of the reported works have been dedicated to single-functional PCs, which can only be used as sensors or detectors in a specific situation. Thus, producing a multi-functional PC for various industrial applications remains a challenge. In this work, multi-functional soft PC films (SPCFs) with a brilliant structural color and a robust structure are fabricated by using polystyrene@poly(methyl methacrylate-butyl acrylate) [PS@P(MMA-BA)] nanospheres with size in the range of 200-350 nm as building blocks. The SPCFs possess both the mechanochromic and solvatochromic properties owing to the adjustable photonic band gap under stress and polar solvent conditions. The mechanochromic effect of the SPCF under stretching results in a blue shift of the structural color due to the decrease in lattice spacing. In contrast, the solvatochromic mechanism of the SPCF is that it can be swollen by polar solvents, resulting in the increase in the lattice spacing of PCs and a red shift of the structural color. Meanwhile, the SPCF can keep its original structural color while stretched for 20 cycles or when the organic solvent is completely evaporated. Therefore, robust multi-functional SPCFs fabricated by the self-assembly of PS@P(MMA-BA) nanospheres under gravity sedimentation can respond to stress and organic solvents, showing great potential for use in sensors and detectors.