Low-Temperature Reversible Thermochromic Polydiacetylene/Zinc(II)/Zinc Oxide Nanocomposites for Colorimetric Sensing

A series of reversible thermochromic poly-diacetylene/zinc(II) ion/zinc oxide (PDA/Zn2+/ZnO) nano composites have been prepared using seven types of diacetylene monomer. The shortening of the PDA alkyl tail from 12 to 6 methylene units systematically decreases color transition temperature (T-CT) from 90 to 30 degrees C. Increasing the photopolymerization time during the preparation process further reduces the T-CT down to 10 degrees C. The shortening of alkyl segment adjacent to PDA headgroup causes unpredictable changes of T-CT. X-ray diffraction reveals variation of the molecular tilting angle within the bilayer structure of PDA depending on the length of alkyl segment. Infrared and Raman spectroscopies also detect the change of local interactions and backbone conformation within the nanocomposites. Our study provides a guideline for preparing reversible thermochromic materials with T-CT ranging from 10 to 90 degrees C. These nanocomposite materials can be utilized in various applications such as colorimetric sensors, smart labels, and thermochromic inks/paints that change color in the hot, cold, or ambient conditions.