Structure And Properties Of Conjugated Polymer Thin Films And Nanofibers PDF Download

Conjugated polymers are electronically and ionically active organic materials. These polymers are widely used in biomedical interfaces, chemical sensors and organic photovoltaics for their reasonably high conductivity and relatively “soft” mechanical properties. However, despite the wide applications, the structure-property relationship of these materials remains poorly understood. Here we presented a study on the structural characterization and property analysis of conjugated polymer thin films and nanofibers. ☐ Electrochemical polymerization is a convenient method for fabricating polymer thin films. We reported a novel electrochemical deposition of highly crystalline bromine functionalized thiophene monomer, which is a precursor for solid-state polymerized poly(3,4-ethylene dioxythiophene) (PEDOT). We investigated the electrochemical process in detail by altering conditions and carefully monitoring the reaction. The morphology, structure and properties of both the EDOT-Br monomer and PEDOT polymer were characterized. ☐ Despite the wide application of electrochemical polymerization, a detailed, quantitative understanding of nucleation and growth mechanisms has remained elusive. We have studied the electrochemical deposition of PEDOT from an aqueous solution of EDOT monomer using an in-situ Transmission Electron Microscopy (TEM) liquid flow cell. It was found that PEDOT deposition began preferentially at the edge of the glassy carbon anodes at the beginning of the reaction. Fluctuating clusters of liquid-like oligomers were observed to form near the electrode surfaces. As the reaction continued both the nucleation of new domains as well as the growth of pre-existing PEDOT deposits were observed, leading to systematic increases in film thickness and roughness. ☐ Conjugated polymer nanofibers are of particular interest for their high surface-to-volume ratios, and have been considered for applications such as field-effect transistors, biomedical devices and sensors. Electrospinning is a well-developed method for the solution processing of polymers into nanometer to micrometer-sized fibers. We quantitatively studied the relationship between molecular orientation and fiber diameter within single electrospun fibers using low dose electron microscopy and diffraction techniques. It was confirmed that for electrospun fibers with decreasing fiber diameters, the molecular orientation increased. To facilitate the solution processing of the otherwise dilute and low viscosity conducting polymers, another relatively easy-to-process supporting polymer was introduced into the fabrication. Poly(3-hexylthiophene-2,5-diyl) (P3HT) + polycaprolactone (PCL) core-shell nanofibers were prepared via a coaxial electrospinning method. Morphological results from electron microscopy confirmed that P3HT conjugated polymer nanofibers were obtained after solvent removal of the PCL supporting polymer. Molecular orientation studies revealed that polymer chains were oriented parallel to fiber axes in the PCL polymer shell, while perpendicular to fiber axes in the P3HT core. The electrical and mechanical properties of the core-shell polymer nanofibers were investigated at the single fiber level using a specialized stage in the chamber of a Focused Ion Beam – Scanning Electron Microscope (FIB-SEM).