Reversible thermochromic polydiacetylene/zinc-aluminium layered double hydroxides nanocomposites for smart paints and colorimetric sensors: The crucial role of zinc ions

Abstract

This work presents our continuing effort to develop PDA-based nanocomposites for reversible thermochromic sensors and smart paints. Here, we demonstrate that an incorporation of zinc-aluminium layered double hydroxides (ZnAl-LDH) into PDA assemblies via a simple mixing process promotes local interactions, yielding reversible thermochromism. The Zn2+ ions, released from ZnAl-LDH particles, play an essential role on achieving this phenomenon. X-ray diffraction and infrared spectroscopy reveal that the Zn2+ ions intercalate with PDA bilayer and strongly interact with carboxylate headgroup. Color-transition temperature of the nanocomposites can be tuned from 50 to 90 °C by varying the alkyl side chain of PDA. Furthermore, the reversible thermochromism persists in various organic solvents, allowing the utilization in smart paints and coating technologies. Compared to the previous studies of other PDA/LDH nanocomposites, our new materials exhibit more distinct color transition. The synthetic method is also much simpler. The new nanocomposites are more stable at low or high pH regions compared to the system of PDA/Zn2+/ZnO nanocomposite, expanding new routes for fabrication and applications in harsh conditions.