Morphology and Photophysical Properties of Light-Emitting Electrospun Nanofibers Prepared from Poly(p-phenylene vinylene) (PPVs) Derivatives and Polymer Blends
Date Issued
2009
Date
2009
Author(s)
Chen, Hsieh-Chih
Abstract
Conjugated polymers have been extensively studied for diverse electronic and optoelectronic devices due to the excellent electronic and optoelectronic properties. The photophysical properties of conjugated polymers could be tuned through the approaches of copolymers, or blending. However, most of the above studies are based on the thin film devices. Electrospinning (ES) has emerged as a new technique to produce various functional nanofibers because of its advantages of low cost, flexible morphology tuning, and a high-throughput continuous production process. The electrical conductivity, field effect mobility, or photoluminescence of the conjugated polymer ES nanofibers were found to be significantly different from those of spin-cast films due to different geometry confinement. In this dissertation, various ES nanofibers (nonwoven, core-shell type, and aligned) were prepared from poly(p-phenylene vinylene) derivatives and their polymer blends. The morphology and photophysical properties of the prepared ES nanofibers were characterized and correlated with the blend compositions, as summarized below: In Chapter 2, 2,3-dibutoxy-1,4- poly(phenylene vinylene)(DB-PPV) nanofibers were fabricated by coaxial electrospinning DB-PPV (core) in chlorobenzene or chloroform and PVP (shell) in water and ethanol mixture. The diffusion rates of solvents were significantly slower than that in the electrospinning process and thus the core-shell morphology was preserved through the process. After the removal of PVP, the resulting DB-PPV fibers were obtained as a ribbon-like structure aligned with wrinkled surface due to the extraction process. By adjusting the inner flow rates from 0.15 to 0.6 ml/h led to increase the overall average diameter of DB-PPV/PVP nanofibers from ca. 580 to 633 nm, while the core volume fractions also followed the same trend. Also, the fiber diameters studied as a function of various ES parameters could be predicted by the Rayleigh equation and Fowler-Nordheim theory. Different UV-vis absorption peak maxima of DB-PPV nanofibers prepared from CB (λabsmax = 454 nm) and CHCl3 (λabsmax = 458 nm) were observed, which were explained by the polymer solubility in two solvents. The photoluminescence spectra of the ES fibers from the two solvent exhibited a similar trend as the absorption. Moreover, Pure DB-PPV ES fibers prepared from either CB or CHCl3 solvent systems showed a slightly red-shifted as compared to corresponding spin-coated films, which could be due to the better chain alignment and lead to improved
Subjects
electrospinning
conjugated polymers
blends
luminescence
morphology
nanofibers
Type
thesis
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