Synthesis and application of functional polymeric nanofibers

The central objectives of this thesis are to develop engineering based approaches for the synthesis of functional (conducting) nanofibers and biocatalytic nanofibers; and to exploit the use of biocatalytic nanofibers for enzyme based applications. Despite several advances in template synthesis, the release and re-capture of nanomaterials produced within the template still remains a critical issue. This difficulty may be avoided if one can produce and transfer nanomaterials directly to the target substrate while they are produced from an ordered array of nano-scale reactors without disintegrating the reactor array. The first part of this thesis aims at developing a nano-manufacturing technique for the continuous synthesis and extrusion of ordered arrays of polymeric nanofibers from nanoporous templates. As a proof of concept the synthesis and extrusion of polyethylene nanofibers by heterogeneous Ziegler-Natta polymerization within nanochannels of robust anodized aluminum oxide membranes is described.;The second part of this thesis aims at the development of nano-manufacturing techniques for the synthesis of conducting polymer composite nanofibers. Conducting polymers such as polypyrrole and poly (3, 4-ethylenedioxythiophene) have a great potential in the field of flexible electronics, nano-electronics and bio-sensing. However, despite its superior thermal and environmental stability it suffers from being intractable. Conducting polymers such as polypyrrole is insoluble and infusible in almost all solvents---a limitation that prevents it from being processed into useful devices, especially at the nanoscale. Due to the same reason, nanofibers of these polymers cannot be directly fabricated by convenient methods such as electrospinning. To address this issue, electrically conducting composite nanofibers are produced by a two step process. First, electrospinning is used to synthesize template fibers loaded with suitable oxidants. Second, the template fibers are exposed to the monomer vapors which diffuse into the templates and are oxidized to form the conducting polymer. Electrically conducting polypyrrole-polyethylene-oxide (PPy-PEO) nanofibers, polypyrrole shell-polystyrene core (PPy-PS) nanofibers and poly (3, 4-ethylenedioxythiophene) shell-polystyrene core (PEDOT-PS) nanofibers were synthesized in this way. The effect of two different oxidants---ferric chloride and ferric toluene-sulfonate, on the polymerization process was also investigated. The nonwoven mat of nanofibers was also exploited for gas sensing applications.;The third part of this thesis focuses on the fabrication of nanofibers for enzyme based biocatalytic applications. Fabrication of highly stable enzyme coatings on the nanofibers is described. To improve the enzyme loading onto electrospun nanofibers an alcohol dispersion technique has been formulated. The dispersed nanofibers containing covalently attached enzymes or crosslinked enzyme coatings have been exploited as continuous flow reactors. Stability of the enzyme coatings in highly reactive environments has been investigated.