Studies of the blue to red phase transition in polydiacetylene nanocomposites and blends

The conjugated polymeric backbone of polydiacetylenes (PDAs), comprising of alternating eneyne groups, undergo intriguing stress-, chemical- or temperature-induced chromatic phase transitions associated with the disruption of the backbone structure and shortening of the conjugation length. PDAs, such as polymerized 10. 12 pentacosadiynoic acids (PCDA), when incorporated with inorganic oxides form nanocomposites and uniform blends with polymers. Blends of poly-PCDA with polymers, such as polyvinyl alcohol, polyvinylidene fluoride and cellulose increase the blue to red transition temperature without affecting the irreversibility of the red phase. However, the addition of zinc oxide to pure poly-PCDA makes the red phase highly reversible and substantially increases the blue to red transition temperature. The addition of TiO₂ to poly-PCDA on the other hand does not affect the irreversibility of the red phase and the chromatic transition temperature. In order to understand the atomic scale interactions associated with these changes in the chromatic transitions, we have investigated both the nanocomposites and polymer blends using Raman and Fourier-transform infrared spectroscopy, and extended X-ray absorption fine structure (EXAFS) measurements.