(564d) Orientational Dynamics of Polydiacetylene Monolayers

Polydiacetylenes (PDA) have gained popularity recently as unique materials with interesting electronic properties such as high non-linear optical susceptibility, ultrafast optical response, strong structural anisotropy and the chromogenic transitions arising from its fully p-conjugated system induced by a host of external stimuli such as heat, stress, pH and specific binding to biological targets. These features make them attractive for nanostructured devices in various applications such as chemical and biomolecular sensors. When properly oriented, diacetylene groups can undergo UV-induced photopolymerization to form an ene-yne alternating semiconducting polymer chain, resulting in highly ordered structures. The orientation of the polymer chains is critical to the properties of the film. In this study, monolayers of different PDA derivatives were photopolymerized and placed under extensional flow using rheological techniques such as the four-roll mill. Linear dichroism and Brewster angle microscopy (BAM) were used to explore the orientational dynamics of the different cross-linked polymers as the flow conditions were changed. The temperature and the surface pressure of the film at which polymerization occurs were also varied to observe the effects on film quality and domain formation. The monolayer was then deposited on a solid substrate using the conventional Langmuir-Blodgett transfer technique and the film morphology studied.