Influences of structural mismatch on morphology, phase transition temperature, segmental dynamics and color-transition behaviors of polydiacetylene vesicles

In this contribution, we report a systematic study of polydiacetylene (PDA) vesicles fabricated by mixing two types of monomers, 10,12-tricosadiynoic acid (TCDA) and 10,12-pentacosadiynoic acid (PCDA). These diacetylene (DA) monomers constitute the same head group but different alkyl chain length, which in turn causes structural mismatch within the PDA layers. The PCDA:TCDA ratios are 100, 75, 50, 25 and 0 mol%. Morphologies and properties of these PDA vesicles are explored by utilizing laser light scattering, transmission electron microscopy, differential scanning calorimetry, temperature-dependent nuclear magnetic resonance spectroscopy (NMR) and spin-lattice relaxation time (T-1) measurements. An increase in DA mole ratio to 50 mol% leads to significant increase in particle size. The mixed PDA vesicles also exhibit irregular shape with rather rough surface. The mismatch of alkyl side chain causes the drop of phase transition temperature. For the system of mixed poly(PCDA50:TCDA50), its transition temperature is lower than those of the pure PDAs. The NMR line shape analysis detects an abrupt change of proton signal adjacent to the PDA head group during the blue/red color-transition process. The T-1 measurements also reveal different local environments of PDA alkyl side chains in the blue and red phases. The mismatch of PDA side chains causes significant drop of the color-transition temperature. (C) 2014 Elsevier Inc. All rights reserved.