Nisanart Traiphol

Stable polydiacetylene/ZnO nanocomposites with two-steps reversible and irreversible thermochromism: The influence of strong surface anchoring

This contribution introduces a versatile method to prepare a new class of polydiacetylene(PDA)-based material. ZnO nanoparticle is used as a nano-substrate for spontaneous assembling of diacetylene monomer, 10,12-pentacosadiynoic acid, on its surface. An irradiation of the organized assemblies by UV light results in PDA/ZnO nanocomposites with deep blue color. Strong ionic interaction and hydrogen bonding at the ZnO surface restrict the dynamics of alkyl side chains and promote the PDA ordering, which in turn drastically affects its thermochromic behaviors. We have found that the PDA/ZnO nanocomposite exhibits two-steps color transition upon increasing temperature. The first transition of the nanocomposite in aqueous suspension, causing the color change from blue to purple, occurs reversibly at ∼90°C. The transition temperature shifts to ∼100°C when the nanocomposite is embedded in polyvinyl alcohol matrix. Further increasing temperature to 145°C induces the second transition, which causes irreversible color change from purple to red.

Controlling the reversible thermochromism of polydiacetylene/zinc oxide nanocomposites by varying alkyl chain length.

In this work, polydiacetylene (PDA)/ZnO nanocomposites are successfully fabricated by using three types of monomers with different alkyl chain length, 5,7-hexadecadiynoic acid, 10,12-tricosadiynoic acid, and 10,12-pentacosadiynoic acid. The monomers dispersed in aqueous medium spontaneously assemble onto the surface of ZnO nanoparticles, promoted by strong interfacial interactions. The PDA/ZnO nanocomposites obtained via photopolymerization process are characterized by scanning electron microscopy, laser light scattering, infrared spectroscopy, and uv/vis absorption spectroscopy. The strength of interfacial interactions and morphologies of the nanocomposites are found to vary with alkyl chain length of the monomers. The PDA/ZnO nanocomposites also exhibit rather different thermochromic behaviors compared to their pure PDA counterparts. All nanocomposites show reversible blue/purple color transition upon multiple heating/cooling cycles, while the irreversible blue/red color transition is observed in the systems of pure PDAs. The shortening of alkyl side chain in PDA/ZnO nanocomposites leads to a systematic decrease in their color-transition temperatures. Colors of the nanocomposites at elevated temperature also vary with the alkyl chain length. Our results provide a simple route for controlling the reversible thermochromism of PDA-based materials, allowing their utilization in a wider range of applications.

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.

Fine tuning the color-transition temperature of thermoreversible polydiacetylene/zinc oxide nanocomposites: The effect of photopolymerization time.

An ability to control the thermochromic behaviors of polydiacetylene (PDA)-based materials is very important for their utilization. Recently, our group has developed the PDA/zinc oxide (ZnO) nanocomposites, which exhibit reversible thermochromism (Traiphol et al., 2011). In this study, we present our continuation work demonstrating a rather simple method for fine tuning their color-transition temperature. The PDA/ZnO nanocomposites are prepared by varying photopolymerization time, which in turn affects the length of PDA conjugated backbone. We have found that the increase of photopolymerization time from 1 to 120min results in systematically decrease of the color-transition temperature from about 85 to 40°C. These PDA/ZnO nanocomposites still exhibit reversible thermochromism. The PDA/ZnO nanocomposites embedded in polyvinyl alcohol films show two-step color-transition processes, the reversible blue to purple and then irreversible purple to orange. Interestingly, the increase of photopolymerization time causes an increase of the irreversible color-transition temperature. Our method is quite simple and cheap, which can provide a library of PDA-based materials with controllable color-transition temperature.