Effects of monomer structure and type of metal oxide nanoparticles on colorimetric response of polydiacetylene/metal oxide nanocomposites

Abstract

In this study, a simple route for controlling the colorimetric behaviors of PDA/ZnO nanocomposites is presented by varying monomer structures and polymerization time. Three types of monomers with different alkyl chain length 5,7-hexadecadiynoic acid (HDDA), 10,12-tricosadiynoic acid (TCDA), and 10,12-pentacosadiynoic acid (PCDA) were used for preparing the nanocomposites. All PDA/ZnO nanocomposites exhibit rather different thermochromic behaviors compared to their pure PDA counterparts. All nanocomposites show reversible blue/purple color transition upon multiple heating/cooling cycles. The shortening of alkyl chain length leads to the decrease in color-transition temperature. For the colorimetric response to pH, it is found that all nanocomposites are interestingly sensitive to acidic conditions. However, in basic condition, the color transition takes place at much higher pH compared to that of the pure PDAs. The nanocomposites with shorter alkyl length are found to be more sensitive to pH and alcohols. Moreover,the polymerization time by UV irradiation is also found to affect the colorimetric behaviors of the PDA/ZnO nanocomposites. Long period of irradiation reduces color- transition temperature of the nanocomposites. The complete color reversibility was detected in poly(TCDA)/ZnO irradiated for 60 min and poly(HDDA)/ZnO irradiated for 30 min. Increasing in polymerization time also reduces the magnitude of color changing upon variation of pH or addition of alcohols. In addition, other metal oxide nanoparticles such as SiO₂, TiO₂ and Al₂O₃ are used to prepare the PDA/metal oxide nanocomposites. It is found that their colorimetric behaviors are similar to the pure PDAs.