Studies of the blue to red phase transition in polydiacetylene nanocomposites and blends
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Studies of the blue to red phase transition in polydiacetylene nanocomposites and blends Anitha Patlolla1, Qi Wang2, Anatoly Frenkel2, James L. Zunino III3, Donald R. Skelton3 and Zafar Iqbal1* 1
Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, NJ 07102 2 Department of Physics, Yeshiva University, New York, NY 10033 and Brookhaven National Laboratory, Upton, NY 11973 3 U.S. Army ARDEC, Picatinny Arsenal, NJ 07806
ABSTRACT 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 Xray absorption fine structure (EXAFS) measurements.
Introduction Polydiacetylenes (PDAs) are a unique class of conjugated polymers which undergo dramatic thermochromic and chemically-induced chromatic transitions [1] due to shortening of the conjugation length of the polymeric backbone [2]. Modification of the polydiacetylenes as nanocomposites integrated into inorganic host matrices can have significant effects on their chromatic transitions [3]. It was also reported that the thermochromic transition temperatures are a function of the nature of the side groups on the polymer backbone and the structure of the substituents [4]. A number of the polydiacetylenes in the form of nanocomposites have been synthesized and their chromatic responses to various stimuli have been demonstrated. Previous studies of the mechanism of the solid state phase transitions in the polydiacetylenes [5] have demonstrated that structural changes occur independently in the polydiacetylene backbone and hydrocarbon side chains of PDAs to give rise to the chromatic transitions. It was also reported that changes do not occur directly in the distribution of electron density along the backbone when chromatic effects are induced [6], but side chain interactions
lead to strain on the diacetylene backbone [7] to give rise to the chromatic transformations. Many of the thermochromic tran
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