Dual colorimetric response of polydiacetylene/Zinc oxide nanocomposites to low and high pH

This contribution presents our continuation work on the color-transition behaviors of polydiacetylene(PDA)/ZnO nanocomposites prepared by using three types of monomers, 5,7-hexadecadiynoic acid (HDDA), 10,12-tricosadiynoic acid (TCDA) and 10,12-pentacosadiynoic acid (PCDA). The color-transition behaviors of these nanocomposites upon exposure to acid and base are investigated by utilizing UV/vis absorption spectroscopy. We have found that these PDA/ZnO nanocomposites exhibit colorimetric response at both low and high pH regions. The addition of acid causes the poly(HDDA)/ZnO, poly(TCDA)/ZnO and poly(PCDA)/ZnO nanocomposites to change color from blue to red at pH. ~. 5, 3.5 and 2, respectively. The color of pure PDA vesicles, on the other hand, is hardly affected at this pH range. At high pH region, the pure poly(TCDA) vesicles change color at pH. ~. 8 while it requires much higher pH to induce color transition of the PDA/ZnO nanocomposites. The mechanism responsible for color transition of the PDA/ZnO nanocomposites is explored by various techniques including infrared spectroscopy, zeta potential analyzer and light scattering. Our result provides a new approach for controlling the colorimetric response to pH of PDA-based materials.