Poly(meta-phenylene isophthalamide) nanofibers: Coating and post processing
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Matthew Graham and Edward A. Evans Department of Chemical Engineering, The University of Akron, Ohio 44325-3909
Darrell H. Reneker Maurice Morton Institute of Polymer Science, The University of Akron, Ohio 44325-3909 (Received 3 July 2002; accepted 26 September 2002)
Electrospun nanofibers have applications in the areas of filtration, composites, biomaterials, and electronics. Controlling the surface properties of these nanofibers is important for many applications. Nanofibers can also be used as unique substrates for observing the growth of deposited films and creating nanoscale structures. In this work, electrospun poly(meta-phenylene isophthalamide) (MPD-I) nanofibers were used as substrates for creating nanoscale structures out of carbon-based materials and metals. MPD-I was used because it can be electrospun into nanofibers with diameters smaller than 10 nm and it has good thermal stability. MPD-I nanofibers were coated with carbon, copper, and aluminum using plasma enhanced chemical vapor deposition and physical vapor deposition methods. Some of the aluminum-coated nanofibers were then converted into nanotubes. Transmission electron microscopy was used to determine the thickness, uniformity, and grain size of the coatings on the fibers and the nanotubes.
I. INTRODUCTION
Nanoscale materials have attracted great academic and industrial interest in recent years.1–3 Electrospinning is a straightforward method for producing fibers with diameters in the nanometer range.4–6 Since the 1990s, research efforts in electrospinning have focused on the mechanism of fiber formation,4–10 the physical properties of nanofibers,11–15 and the application of nanofibers in the areas of filtration,16 composites,17–20 biomedicine,21–23 and electronics. High-performance nanofiber materials with improved and controlled surface properties are required for further development of these applications. Control over the surface of the nanofibers, achieved by coating the nanofibers, will lead to novel devices and structures. Recently, Greiner’s group has shown that fibers can be coated by both sol-gel and thermally activated vapor deposition techniques.24–25 Coating by chemical vapor deposition (CVD) or physical vapor deposition (PVD) offers an effective way to modify the surface properties of nanofibers. Subnanometer-thick coatings with high purity can be deposited by CVD and PVD techniques. Coatings with an average thickness smaller than 1 nm can be deposited. Bognizki et al., for example, reported that 3206
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J. Mater. Res., Vol. 17, No. 12, Dec 2002 Downloaded: 14 Mar 2015
electrospun poly(L-lactide) fibers could be coated with a variety of materials using thermally activated CVD and PVD techniques. These coated fibers were then used to form tubes by selectively removing the polymer fiber core.26 The synthesis of high-quality nanostructured ceramic materials by either CVD or PVD techniques normally requires high deposition temperatures (>200 °C). The nanofiber used as a substrate and/or template must be
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