Colorful detection of organic solvents based on responsive organic/inorganic hybrid one-dimensional photonic crystals

Solvent sensitive organic/inorganic hybrid one-dimensional photonic crystals (1DPCs) were prepared through alternating thin films of poly methyl methacrylate-co-hydroxyethyl methacrylate-co-ethylene glycol dimethacrylate (PMMA-co-PHEMA-co-PEGDMA) and titania nanoparticle sol by spincoating. Since the titania layer has a higher refractive index compared with the polymer layer, an obvious photonic stop band (PSB) can be easily obtained in several layers. Meanwhile, the materials take on evident color as the PSB falls into the visible region. The PSB can be reversibly tuned by introducing or removing organic solvents. Due to different interactions between the polymer and solvent molecules, the PSB can be shifted to different positions when introducing different solvents. At the same time, the 1DPCs present different colors, and the solvents used can be differentiated by the naked eye through color change. The solvent responsive process is very quick and the solvent sensitivity is very high. Almost all common solvents can be distinguished in this way. As well as pure solvents, mixtures can also be detected through the changes of optical properties. The shift of the PSB and the response speed can be modulated by changing the thickness of the polymer layer, while the thickness of the titania layer has little influence on them.