Polymer nanofiber films

Nafion-115, Nafion-112, and Nafion-212 which have thickness of 175 pm, 125 pm, 50 pm, and 50 pm, respectively. These thiimer composite PEMs contain significantly less amounts of the expensive Nafion resin than the thicker neat Nafion membranes. Thus, another advantage of Nafion/PTFE composite PEMs is the fact that they are inexpensive. Besides porous PTFE films, porous films such as polyethylene (PE) [21, 22] and electro-sptm polymer nanofiber films such as those of poly(vinyhdene fluoride) (PVdF) [23, 24], poly(vinyhdene fluoride-co-hexafluoropropylene) (PVdF-co-HFP) [25], and poly(vinyl alcohol) (PVA) [26-31] have also been used as supporting films for impregnating Nafion ionomer solutions to prepare Nafion/fiber composite PEMs for PEMFC and DMFC applications. 

A concentration of the platinum loading close to the electrolyte interface via Pt-covered polymer nanofibers has been proposed by 3 M [31]. The concentration of the platinum catalyst coated onto nanofibers within approximately 300 nm distances from the electrolyte membrane surface, however, is leading to specific operation characteristics. While high power densities can be achieved under comparatively dry operating conditions even at elevated temperatures, the thin catalyst layers show a tendency for flooding under wet conditions at low temperatures. A summary of the behavior of this type of catalyst layers under specific operating conditions is given in [56]. The low temperature behavior has been improved by addition of a conventional catalyst layer on to this thin film catalyst layer [57]. 

The chitin has limited applications besides such traditional purposes. Therefore, considerable efforts have been still devoted to compatibilization of chitin with synthetic polymers to provide cMtin-based new functional materials. As one of the possible applications of the present chitin nanofiber film, therefore, attempts were made to prepare the chitin nanoilber composite materials with synthetic polymers. Two kinds of approaches, that is, physical and chemical approaches have been considered to yield the polysaccharide-synthetic polymer composite materials (Figure 8). In former case, the polysaccharide and synthetic polymer chains construct material components by physical interaction in the composites, whereas the latter approach results in the formation covalent linkages between two polymer chains in the composites. 

FIGURE 7.24 Schematic diagram of a conducting polymer thin film (left) and nanofibers (right) exposed to gas molecules (arrows). Compared to a thin film, nanofibers have a much higher fi-action of exposed surface (black), and much shorter penetration depth (gray) for gas molecules. (Reproduced fi-om Huang, J.X., Virji, S., Weiller, B.H., and Kaner, R.B., Cherrt. Eur. /., 10, 1314—1319, 2004. With permission.)... 

Polymer composites reinforced with electrospun polymer nanofibers have so far been developed mainly for providing some outstanding physical e.g., optical and electrical) and chemical properties [20,21], Most of the applications at present focus on very small quantity usage for instance, reinforcement of dental resins, thin films, or in the case of large scale composites parts, only as additional ply interface reinforcement between composite laminates [21], As mentioned before, the biggest issues remain fiber alignment and collection at reasonable production rates. Therefore, large scale production (both quantity and size) of SPCs may benefit more from the methods described in Sections 19,2.3 and 19.4.1. 

Both molecular and transition dipole moment orientation can be probed within the solid state samples, especially upon combining structural information with polarized absorption measurements. Small-area electron diffraction experiments are also effective since they allow the orientation of crystalline regions within polymer nanofibers to be probed. Most of these techniques are already well established from the study of polymer alignment in thin-films. Improved analysis methods, which make use of combined polarized Raman spectroscopy and UV-visible absorption data, are especially worthwhile to be mentioned as valuable tools to investigate the orientational properties of light-emitting polymer systems. We will come back in depth to optical properties of polymer nanofibers in Chapter 5. 

---