Patterning of Polydiacetylene Supramolecules using Micromolding in Capillaries

Abstract

Polydiacetylenes (PDAs), a family of conjugated polymers that have alternating ene-yne backbone structures, are intriguing substances in several respects. First, PDAs are produced by radiation (UV or γ-ray)-induced polymerization of molecularly-assembled diacetylene monomers in the absence of chemical initiators or catalysts. Second, in general the resultant polymer displays an intense blue color which has a maximum absorption wavelength at around 640 nm. Lastly, the blue-colored PDAs undergo a color transition to form a red phase in response to a variety of environmental stimulations, such as heat, solvent, mechanical stress, and molecular recognition. Owing to their blue-to-red chromic transition and nonlinear optical properties, PDAs have been extensively investigated as potential chemosensors and photonic materials. In this research, we present the results of studies that have led to a new, straightforward strategy for the fabrication of patterned PDA images based on a micromolding in capillaries (MIMIC) technology. Micron-sized polydiacetylene (PDA) supramolecule patterns on titanium substrates have been successfully fabricated by using the MIMIC technique. The shape and width of the PDA patterns are well matched with PDMS molds used in the MIMIC process. However, the thicknesses of the patterned films are less than the depths of the PDMS molds, which may be a consequence of the poor water wettability of the PDMS and/or low concentrations of the PDA solutions. Heat- or UV-treatment of the solid substrate, immobilized with blue-phase PDAs, induces a blue-to-red-phase transition and results in the formation of patterned fluorescence images. The PDA vesicles were found to fill microchannels driven by capillary force and remain on the solid substrates after removal of solvent and the polydimethylsiloxane (PDMS) mold. This enabled generation of patterned PDA images on the solid substrate. Owing to the intriguing optical property of PDAs, patterned PDA images should find great utility in chip-based sensor systems.