Nanofiber core-shell

Fig. 14.6). A key is that in many cases solution processing can lead to new structures that are difficult or impossible to attain by other means. This can include, for example, nanofiber arrays, core-shell structures, nanopods, and nanoribbons.30 32 These structures can lead to a variety of new functionalities—from 3D prototyping, to third-generation PV structures, to electronic paper, to a new class of non linear optics, to the ability to order nanostructures at very small length scales and maybe even to the holy grail of the energy field, artificial photosynthesis. Below we briefly discuss how some of these concepts are beginning to be realized.

In order to improve the properties and the spinnability, fibroin sometimes has been electrospun together with other natural or synthetic polymers (Jin et al., 2002 Park et al., 2004, 2006 Wang et al., 2004, 2006). For instance, Jin et al. (2002) developed an aqueous process for silk electrospinning in combination with PEO. More recently, Cao (2008) used PVA/Silk Fibroin (SF), Gelatin/SF, and Hydroxyapatite (HAP)/SF to produce double-layered (core-shell) nanofibers (mats) by coelectrospinning. 

PF nanofibers are a second example of a top-down nanostructure. These fibers are conveniently prepared by electrospinning [143,144], a technique applied to PFs in work by Chen et al. [145] and Jenekhe et al. [146]. An example of PF8 nanofibers is shown in Fig. 34. In this study various different PFs were blended with PMMA and depending on the molar ratio and mother solution used, either uniform or core-shell structures were obtained. PF ag-... 

Fig. 1 Nanofibrous architectures created by electrospinning (a) random nanofibers, (b) porous nanofibers, (c) core-shell nanofibers, (d) aligned nanofibers (e) nano-yam, (f) hollow nanotubes...

Sun ZC et al (2003) Compound core-shell polymer nanofibers by co-electrospinning. Adv Mater 15(22) 1929-1932... 

Zhang YZ et al (2004) Preparation of core-shell structured PCL-r-gelatin Bi-component nanofibers by coaxial electrospinning. Chem Mater 16(18) 3406-3409... 

Figure 4.3 Schematic Illustration of the set-up used to coelectrospin compound core-shell nanofibers. It involves the use of a spinneret consisting of two coaxial capillaries through which two polymer solutions can simultaneously be ejected to form a compound jet. (Reprinted with permission from Advanced Materials, Compound Core-Shell Polymer Nanofibers by Co-Electrospinning by Z. Sun, E. Zussman, A. L. Yarin eta ., 15, 22, 1929-1932. Copyright (2003) Wiley-VCH)...

Figure 4.12 Schematic illustration of the mechanism for preparing core-shell nanostructured conductive PPy composites. (Reprinted with permission from Materials Letters, Fabrication of Polyacrylonitrile/polypyrrole (PAN/Ppy) composite nanofibers and nanospheres with core shell structures by electrospinning by X. Li, X. Hao, H. Yu and H. Na, 62, 1155-1158.

Poly[2-methoxy-5-(2 -ethyl-hexyloxy)-l,4-phenylene vinylene] (MEH-PPV) is an excellent conjugated polymer and broadly used in polymer photoelectron devices, but is difficult to electronspin directly. In the work by Zhao et al, core-shell structured nanofibers were fabricated by coaxial electrospinning MEH-PPV (shell) in chlorobenzene and PVP (core) in 1,2-dichloroethane [64]. MEH-PPV was soluble in the above two solvents, which prevented the precipitation of MEH-PPV and enhanced the adhering action between the two polymers in the coaxial electrospinning process. It should be noted that this is an unusual example of core-shell nanofibers where (a nonprocessable) PPV was spun as the shell and not in the core. These uniform core/shell PVP/MEH-PPV nanofibers with a highly fluorescent property can have potential applications in the fabrication of polymer nanophotoelectron devices. 

S. Nair, E. Hsiao, and S. H. Kim Fabrication of electrically-conducting nonwoven porous mats of polystyrene-polypyrrole core-shell nanofibers via electrospinning and vapor phase polymerization, J. Mater. Chem., 18, 5155-5161 (2008). 

Conducting polymers are promising basic backbones to construct flexible electrodes for LIBs because of their high flexibility, conformability, and versatility. Furthermore, the other active materials can be incorporated into the conducting polymers to form high-performance flexible electrodes. For example, a novel three-dimensional nanoarchitecture composed of PPy-Si core-shell nanofibers was achieved by the deposition of Si onto the electropolymerized PPy nanofibers. This core-shell structure indicated a high cyclic stability after repeated lithium insertion and extraction (Du et al., 2012). 

Yarin, A. L. Zussman, E. Wendorff, J. H. Greiner, A. Material encapsulation in core-shell micro/nanofibers, polymer and carbon nanotubes and micro/nanochannels. J. Mater. Chem. 17, 2585-2599 (2007). 

PANI-Coated Core/Shell-Structured Nanofibers... 

There is a range of applied voltage values where a stable jet is obtained for PEO solutions. For example, in solutions at 6 wt.%, a stable jet is formed between 5 and 15 KV, with a working distance of about 12.5 cm. It is also possible to obtain poly[acrylonitrile-co-vinylacetate [P[AN-co-VAc]] nanofibers embedded with magnetic Fe203 nanoparticles by the use of P[AN-co-VAc]/Fe203 core-shell nanocapsules applying 15 kV with the feed rate of 0.6 mL/h and the distance of 15 cm. [Fig. 1.11]. ... 

The electrically charged part and coaxial jet shown in Fig. 1.17 allow to obtain core-shell nanofibers (nanochannels and nanocapsules) by coaxial electrospinning. ... 

Figure 1.17 Common setup and electrically charged part for coaxial jet for electrospinning and core-shell nanofibers nanochannel and capsule by coaxial electrospinning. Reprinted from Ref. 45, Copyright 2010, Fengyu Li, Yong Zhao, and Yanlin Song.

Figure 8.5 Possible structure and SEM image of core shell nanoparticles and SEM image of nanofibers of P [AN-co-VAc] [above scale bar is 1 micron], P [AN-co-VAc]/PPy, 0.045 mole% Py [below scale bar is 2 micron]. Reprinted from Ref 229, Copyright 2014 by authors and Scientific Research Publishing Inc.

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