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Electrospinning and Polymer Nanofibers

           The recently fast developing technology “electrospinning” is a unique way to produce novel polymer nanofibers with diameters typically in the range from 50 nm to 500 nm.  Polymer nanofibers can be made from a variety of polymer solutions or melts, and are of substantial scientific and commercial interests including composite, filtration, protective clothing, biomedical and electronic applications.  Carbon nanofibers made from polymeric precursors further expand the list of possible uses for nanofibers.  Polymer nanofibers could have many extraordinarily properties including, small diameter (and the resulting large surface area to mass ratio), highly oriented crystalline structures (and the resulting high strength), etc.  Meanwhile, the non-woven fabrics made of polymer nanofibers offer unique capabilities to control pore size and have been researched to be the novel scaffold for cell growth. 

The followings are two projects in this area.

• Study of the Technology of Electro spinning to Produce Polymer Nanofibers with the Controllable Morphology and Properties.

The process of electrospinning is a complicated combination of polymer science, electronics and fluid mechanics.  Both solution properties and processing variables can significantly affect the electrospinning process.  To date, a fundamental mechanism of the process of electrospinning is still characterized only qualitatively.  The absence of the comprehensive knowledge of electrospinning has resulted in the polymer nanofibers with less controllable morphology and properties, and has significantly affected the polymer nanofibers to be used as a functional material.  It is the purpose of this research to systematically study the process of electrospinning to produce polymer nanofibers with controllable morphology and properties.  Several key objectives are outlines as follows:

1. Design and construct of a comprehensive electrospinning station, for controllable and reproducible electrospinning. 

2. Systematically investigate the process of electrospinning.  The process will be studied based on three stages: jet initiation, jet elongation (bending instability), and nanofiber formation.  For each stage, systematical observations and measurements will be carried out.

3. Clarify of the polymer solution characteristics (viscosity, conductivity, surface tension, etc.) and the process variables (electrostatic field, flow rate, polarity of the power supply, etc.) as well as environment conditions (temperature, pressure, solvent vapor pressure, etc.) on the electrospinning process, and their effects on the morphology and properties of polymer nanofibers.

4. Explore of the effects of the external electro-magnetic field on the morphology and properties of the electrospun polymer fibers.

5. The research will further be expanded to prepare and evaluate (a) novel carbon (and/or graphite) nanofiber nano composites, and (b) high efficiency polymeric photovoltaic devices. 

• Highly oriented crystalline, strong carbon nanofibers and very porous, extremely large surface area carbon nanofibers produced from electrospun precursors

          This research is to study the formation and physical properties of the carbon nanofibers made from the electrospun precursors.

 Two kinds of carbon nanofibers will be produced and studied:

1. Highly graphite-crystalline ordered, strong carbon nanofibers made from mesophase pitch or PAN nanofiber precursors.

2. Very porous carbon nanofibers made from PAN or PVA nanofiber precursors, with extremely large specific surface area.  (Note: Different approaches will be employed to generate micropores.  For PAN based carbon nanofibers, steam and/or CO2 treatment will be used; while for PVA based carbon nanofibers, micropores will be generated in situ with carbonization, through thermal decomposition of (NH4)2HPO4.)

 Further objectives include:

• Study the electrospinning process to make precursor nanofibers with desirable morphological and physical properties.

• Investigate the stabilization, carbonization, graphitization and activation conditions of the nanofiber precursors.

• Prepare (polymer/strong carbon nanofibers) nanocomposite, and evaluate the mechanical properties.

• Explore the advantages of substituting activated carbon black by highly porous carbon nanofiber nonwoven fabrics.

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