Abstract

The results presented in this work show for the first time that an electric field used to macroscopically align polymer nanofibers can also align polymer chains parallel to the fiber axis. This important result indicates that anisotropic structural properties (mechanical, electrical, etc.) can be induced in polymer nanofibers during the electrospinning process. Such uniaxially oriented nanofibers exhibit a variety of potential applications in biomedicine, microelectronics and optics. A simple technique of vertical electrospinning with electric field induced, stationary collection was employed to obtain the molecular orientation in polymer nanofibers. This thesis describes the orientation process and verifies this molecular orientation in the polymer nanofibers using three independent methods: polarized Fourier transform infrared spectroscopy, polarized Raman scattering and X-Ray diffraction. The results are analyzed and the orientation mechanism is discussed in detail.

It becomes very intriguing to understand the effect of molecular orientation on specific properties of electrospun nanofibers. For example, the effect of molecular orientation on the photoluminescence of electroactive polymers was studied and it was found that the electrospinning of 8 wt% PEO in MPS-PPV solution Poly[5-methoxy-2-(3-propyloxysulfonate)-1,4-phenylenevinylene] potassium salt solution (0.25% in water) (C₁₂H₁₃KO₅S) _n into uniaxially oriented nanofibers produced an oriented guest polymer (MPS-PPV) in an oriented host polymer (PEO). This macroscopic alignment of PEO+MPS-PPV nanofibers was characterized using confocal florescence microscopy, while the polymer chain orientation of PEO+MPS-PPV was observed using polarized resonance Raman spectroscopy. The effect of this molecular orientation within the macroscopically aligned PEO+MPS-PPV nanofibers on its photoluminescence was determined by using Photoluminescence spectroscopy. It was observed that the photoluminescence of electrospun MPS-PPV fibers was reduced as a result of molecular orientation within the fibers. Possible mechanisms to explain this observation are discussed.