Synthesis of color-responsive polydiacetylene assemblies and polydiacetylene/zinc(II) ion/zinc oxide nanocomposites in water, toluene and mixed solvents: Toward large-scale production

Polydiacetylenes (PDAs) are well-known materials that can be utilized as colorimetric sensors of various stimuli. PDA-based materials are normally synthesized via a self-assembly in an aqueous medium. In this study, we explored important experimental parameters including concentration, incubating temperature, and solvent media, that affected the self-assembly of monocarboxylic PDA and reversible thermochromic PDA/Zn²⁺/ZnO nanocomposites. The critical concentration (C*), the lowest concentration for topotactic photopolymerization in each system, was determined. We achieved, for the first time, direct synthesis of PDA/Zn²⁺/ZnO nanocomposites in toluene. Furthermore, it was possible to synthesize the nanocomposites at ambient conditions, simplifying the process for large-scale production. The addition of co-solvent, ethanol, resulted in a significant increase in blue-phase concentration. The presence of ethanol in the solvent medium also caused the morphological change from sheet-like to ribbon-like structures. The ability to synthesize the nanocomposite in nonpolar media allowed the fabrication of solid-state sensors by mixing with various polymers such as polyethylene, polystyrene, poly(methyl methacrylate), and poly(4-vinylpyridine). Reversible thermochromic smart inks were prepared by simple mixing with acrylic paint. Our study extends the utilization of PDA-based materials as colorimetric sensors.