Role of Zn2Â + ion on the formation of reversible thermochromic polydiacetylene/zinc oxide nanocomposites

Polydiacetylene (PDA)/zinc oxide (ZnO) nanocomposite is a class of materials that exhibit reversible thermochromism with controllable color-transition temperature. The nanocomposite also changes color upon exposure to various types of acids and bases. In our continuing efforts to develop this material, we obtain evidences that reveal true nature of the nanocomposite formation. X-ray diffraction (XRD) technique detects a significant increase of the interlamellar distance within the nanocomposite comparing to that of the pure constituent PDA. The investigation of the nanocomposite systems prepared from 10,12-tricosadiynoic acid and 10,12-pentacosadiynoic acid provides consistent results. This indicates an intercalation of the Zn2 + ions, leaking out of the ZnO nanoparticles, between the PDA layers. An atomic absorption spectroscopy confirms the existence of Zn2 + ions in the aqueous solution. The XRD result also shows that using only Zn2 + ions to prepare the nanocomposite can provide the intercalated PDA/Zn2 + structure. However, the enhanced inter- and intrachain interactions within this system is not sufficient to provide reversible thermochromism. An infrared spectroscopy detects the variation of vibrational frequencies of carboxylate head groups within the systems of PDA/ZnO nanocomposite and PDA/Zn2 + assemblies, corresponding to different types of interactions. Therefore, the strong interfacial interaction between PDA head groups and ZnO nanoparticle is essential for obtaining the reversible thermochromism. We also attempt to prepare the nanocomposites by using a combination of Zn2 + ions and various types of substrates including TiO2, SiO2 and Al2O3 nanoparticles.