| Formation of polymer nanocomposites is becoming an increasingly attractive and facile means by which to combine the desirable properties of metals and metal oxides (e.g., electrical, magnetic, optical, and thermal) with those of polymers (e.g., flexible, lightweight and tough). Incorporation of nanoscale objects such as spheroidal nanoparticles or elongated nanorods into electrospun polymer nano/microfibers measuring from 50 nm to 1 mum in diameter yields functional nanomaterials that can be used in various applications ranging from data storage and conductive nanowires to nonwoven sensors, magnetic filters and drug delivery patches. By aligning nanoscale objects in one-dimensional constructs, we expect that desirable attributes arising from highly anisotropic electronic, optical, thermal, magnetic, and catalytic properties can be realized. The objective of this study is to gain a better fundamental understanding of how to controllably align and position nanoparticles and nanorods within polymer nano/microfibers to generate unique properties. To achieve this objective, we focus on four specific process strategies. In the first, superparamagnetic iron oxide nanoparticles (SPIONs) are aligned into one-dimensional nanoarrays through the use of magnetic field-assisted electrospinning. In this case, an electromagnet is positioned near the Taylor cone of the suspension to be electrospun so that the magnetic field is oriented perpendicular to the electric field. Transmission electron microscopy (TEM) is utilized to ascertain the morphology of the resultant nanocomposite fibers and reveals that the SPION nanoarrays persist intact beyond 1 mum. Since the magnetic field can be pulsed, the length of the nanoarrays can be judiciously controlled. Magnetization hysteresis curves measured on a superconducting quantum interference device yield saturation magnetization and mean magnetic moment values. Secondly, gold nanorods (GNRs) varying in aspect ratio have been flow-aligned in electrospun fibers, and the fibers have likewise been aligned to permit longrange orientation order at both the nanoscale and macroscale. This is an important consideration in the fabrication of devices spanning multiple size scales. The GNRs within nano/microfibers exhibit excellent alignment with their longitudinal axis parallel to the fiber axis. Optical absorbance spectroscopy measurements reveal that the longitudinal surface plasmon resonance bands of the aligned GNRs are highly anisotropic, depending on polarization angle, and that maximum absorption occurs when polarization is parallel to the fiber axis. Lastly, blends of hydrophobic and hydrophilic polymers have been prepared to control the spatial position of SPIONs within electrospun fibers on the basis of thermodynamic compatibility. In this case, TEM confirms that a core-sheath nanostructure naturally forms due to polymer-polymer phase separation and that the hydrophobic nanoparticles are sequestered in one preferred phase. Lastly, a nanocomposite fiber is created using only one entity, the organometallic polymer poly(ferrocenylsilane) (PFS)and its crystalline structure is probed alone and in the presence of SPIONs. Block copolymer cylindrical micelles of PFS-b-poly(isoprene) (PI) are crosslinked within an elastomeric matrix of poly (vinylmethoxysilane) (PVMS) and found to maintain their crystalline structure with the target application being nanowires in soft electronics. |
