Electrospinning Nanofiber Preparation, Assembly And Performance

The design, preparation and controlled assembly of functional one-dimensional (1D) nanostructure has attracted considerable attention because of their unique electrical, optical and magnetic properties different from that of bulk and nanoparticles as well as their potential applications in optics, optoelectronics, catalysis and sensors. Nanowires or nanofibers offer the opportunity to investigate electrical and mechanical properties in size-confined systems, with the possibility of providing a deep understanding of physics at the nano-scale. The main challenge in this area is how to precisely control the sizes, dimensionalities, compositions and orientations of nanowires, which may serve as a powerful tool for the tailoring of physical/chemical properties of materials in a controllable way. In this dissertation, valuable explorations have been carried out on the new synthetic and assembly of functional nanofibers via electrospinning. The physical properties and practical applications of these nanostructures have also been investigated.Cermic NanofibersWe fabricated semiconductive oxide and nitrate nanofibers using a simple electrospinning method combined with sol-gel processing and post heat treatment. The synthesized nanofibers have diameters below 100 nm, and length over 1 cm. The morphologies of the oxide nanofibers, including diameters and surface roughness, can be tuned easily. Highly oriented ceramic nanofibers with a length of several centimeters are fabricated using a newly modified electrospinning method.The optical and electrical transport properties of these semiconductive nanofibers were investigated. Functional devices, including p-type and n-type field-effect transistors, p-n junction diodes and high sensitive UV light detectors had been assembled from oriented cermic nanofibers. The mechanical properties of oxide nanofibers were studied. We found novel super-elastic properties in TiO2 nanofibers. The mechanisms in this interesting phenomenon were discussed.Metallic Nanofibers and NanotubesA general synthetic method had been developed to fabricate and assemble ferromagnetic transition metal nanofibers. By employing the novel electrospinning technique followed by subsequent heat treatment, we have successfully prepared uniform nanofibers of Cu, Fe, Co, Ni and Ag/NiO with diameters of-25 nm and lengths longer than 100μm. The electrical transport properties of Cu and Ag/NiO nanofibers, as well as the magnetic properties of Fe, Co and Ni nanofibers were studied.Uniform metallic nanotubes with high aspect ratio and controllable morphologies and orientations were synthesized employing electrospun nanofibers as template. These metal nanotubes show very high SERS activities.Polymer NanofibersFast and easy construction of biomimetic surfaces with controlled wettability was accomplished through electrospinning. The topography and wetting properties of biosurfaces including lotus leaves, bamboo leaves, goose feathers and water strider's legs were mimicked with different patterns of electrospun polymer nanofibers. Surfaces with anisotropic wetting in two or three directions, as well as artificial water strider's legs with maximal supporting force of more than 200 dynes cm-1 were facilely fabricated based on an electrospinning technique combined with aborative designed nanofiber collectors. We believe these polymer nanofiber patterns will help the design of smart, fluid-controllable interfaces that may be applied in novel microfluidic devices and directional, easy-cleaning coatings.