Nanofibers conductive polymers

Structure The polymers are produced as powders or as films on the electrodes. Most conductive polymers have a fibrous structure, each fiber consisting of hundreds of strands of polymer molecules. Techniques exist to control fiber preparation so as to obtain nanofibers expected to be particularly useful as catalyst substrates and in electronic applications (MacDiannid, 2000). 

At present a few studies of nanofibers and nanombes are focused on CNS drug delivery. One study evaluated electrospun nanofibers of a degradable polymer, PLGA, loaded with antiinflammatory agent, dexamethasone, for neural prosthetic applications (Abidian and Martin, 2005). A conducting polymer, poly(3,4-ethylenedioxythiophene), was deposited to the nano-fiber surface and the coated nanofibers were then mounted on the microfabricated neural microelectrodes, which were implanted into brain. The drug was released by electrical stimulation that induced a local dilation of the coat and increased permeability. 

Conductive Polymers. EFTEM was used to follow the distribution of ions inside me polymer and me ion-exchange processes as well as to study me elemental distributions in the polymer nanofibers [124], me distribution of lithium ions in solid copolymer electrolytes for limium batteries [125] and me particle morphology of copolymers [116]. 

Electrospun Nanofibers from Other Conductive Polymers... 

Electrospun nanofibers with electrical and electro-optical activities have received a great deal of interest in recent years because of their potential applications in nanoscale electronic and optoelectronic devices, for example nanowires, LEDs, photocells etc. Besides, one-dimensional (1-D) nanostmctures are the smallest dimensional stmctures for efficient transport of electrons and optical excitations. One of the potential future apphcations of conducting polymer nanofibers is as molecular wires, which are required to connect molecular devices to electrodes. For molecular devices, it is necessary to make nanowires with diameters in the order of the size of the molecular device. 

M. Wei, J. Lee, B. Kang, and J. Mead, Preparation of core-sheath nanofibers from conducting polymer blends, Macromolec. Rapid Commun., 26, 1127-1132 (2005). 

S. Chuangchote, T. Sagawa, and S. Yoshikawa, Fabrication and optical properties of electro-spun conductive polymer nanofibers from blended polymer solution, Jap. J. Appl. Phys., 47, 787-793 (2008). 

M. Kotaki, X-M. Liu, and C. He, Optical properties of electrospun nanofibers of conducting polymer-based blends, J. Nanosci. NanotechnoL, 6, 3997-4000 (2006). 

In the nanotechnology field, carbon-based materials and associated composites have received special attention both for fundamental and applicative research. In the first kind, carbon compounds may be included, often taking the form of a hollow spheres, ellipsoids, or mbes. Spherical and ellipsoidal carbon nanomaterials are referred to as fullerenes, while cylindrical ones are called nanombes and nanofibers. In the second class, one includes composite materials that combine carbon nanoparticles with other nanoparticles, or nanoparticles with large bulk-type materials. The unique properties of these various types of nanomaterials provide novel electrical, catalytic, magnetic, mechanical, thermal, and other features that are desirable for applications in commercial, medical, military, and enviromnental sectors. This is the case for conducting polymers (CPs) and carbon nanombes (CNTs) [1-5]. 

Figure 10.43 Current-voltage characteristics of individual polyacetylene nanofibers. (Reprinted with permission from Synthetic Metals, Current-voltage characteristics of conducting polymers and carbon nanotubes by A. B. Kaiser and Y. W. Park, 152, 1-3. Copyright (2005)...

Nanocable chemosensors have been formed in which an inner core fiber filament is further modified by polymerization of the conducting polymer on its surface. This was first described for sensing by Zhang et al. in which a carbon fiber was used as the template for the electrochemical polymerization of a thin film of PANI [27]. The resulting nanoelectrode sensor was used to detect changes in pH resulting from the level of protonation in the polymer backbone. PPy nanofibers have been formed by the electrospinning of nylon fibers. 

Figure 14.6 Sensing ofHCI and NH3 using PPy/carbon nanofiber composites (a) SEM image of the nanofiber mat and (b) TEM of a single composite nanofibers (c) responses of the composite nanocables (a and b) and bulk PPy (c and d) to NHj (a and c) and HC (b and d) (Reprinted with permission from Sensors and Actuators B Chemical, CO gas sensing from ultrathin nano-composite conducting polymer film byM. K. Ram, O. Yavuz, f. Lahsangah and M. Aldissi, 106, 2, 750-757. Copyright (2005) Elsevier Ltd)...

Another strategy for synthesizing conducting-polymer nanofiber arrays based on a two-phase system has also been reported by Li et al [165]. This system ensures a very low concentration of monomer, for instance pyrrole, in the polymerization process (Figure 16.17). 

For aU the above electrochemical synthetic techniques, the electrolysis time for the synthesis of nanostructured conducting polymers must be controlled, depending on the experimental methods and conditions, as the sizes of the conducting polymers, such as nanoparticles, nanorods, nanofibers, and nanotubes, will continuously grow with time. 

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