Micropatterning of aligned polydiacetylene fibers using micromolding in capillaries (MIMIC)

Abstract

Among the many existing conjugated polymers with diverse physical, chemical and optical functionalities, polydiacetylenes (PDAs) are classified as a unique group of polymers with well-aligned and closely packed conjugated backbones decorated with designated pendant side groups and terminal functionalities. Besides the ease of preparation through photopolymerization by UV or γ-light irradiation of diacetylene (DA) monomers, PDAs are very promising in terms of stress-induced colorimetric and fluorogenic transitions. Though colourless in the monomer state, upon polymerization, PDAs display a characteristic absorption peak of blue at around 640 nm. Upon exposure to environmental stimulus, a chromatic shift occurs resulting in blueto-red colour transition as well as an induction of fluorescence. Recently, fabrication of one dimensional PDA structures has been a topic of great interest. Certain DA monomers which possess the appropriate functional moieties such as hydrogen bondable amide/urea groups, aromatic π stacking, electrostatic interactions, and hydrophobic long alkyl chains favour the formation of one-dimensional nanostructures under a self-assembling environment. For instance, the DA monomer 5-pentacosa-10,12-diynamidoisophthalic acid (PCDA-IPA) (Figure 1) derived from 10,12-pentacosadiynoic acid (PCDA) and aminoisophthalic acid was observed to form nanofibers when a warm aqueous ethanolic solution is cooled to room temperature. UV irradiation of the nanofibers resulted in the generation of blue-colour PDA nanofibers. The micromolding in capillaries (MIMIC) technique has been actively utilized to control the morphology of selfassembling materials in the designed polydimethylsiloxane (PDMS) micro-channels. We have recently reported fabrication of patterned PDA images using the MIMIC technology. The selective immobilization of PDA vesicles was achieved by applying a PDA solution at one end PDMS microchannel. The PDA solution was found to move into the channels by the action of capillary force. After evaporation of the solvent, the PDMS mold was removed to leave PDA vesicles on the solid substrate. We were curious if the combination of the MIMIC method and the facile nanofiber forming property of PCDA-IPA would allow fabrication of aligned PDA nanostructures. Although one dimensional PDAs have been obtained by employing the self-assembly, templating, electrospinning, and wet-spinning methods, the tailor-made controlling of one dimensional PDA structures has been a challenging task. Accordingly, if the fiber favoring PCDA-IPA could be aligned from the self-assembly in the microchannel, the simple strategy should find great utility for the generation of aligned PDA fibers.