Hollow Nanofibers

Hollow nanofibers also can be prepared using the same coaxial spinneret system, as shown in Fignre 7.13. To obtain the hollow stmcture, the material used for 

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Spiral shaped hollow nanofibers were formed from the reaction of p-aminophenyl-p-D-glucopyranoside and p-dodecanoylaminophenyl-p-o-glucopyranoside with excess tetraethoxysilane. The diameter distributions of these tubes ranged from 1 to 2 nm and from 3 to 7 nm. Metal oxide nanotubes derived from this process displayed excellent hydrogen adsorption and storage capacity for potential use in hydrogen-powered vehicles. 

Li D, Xia YN (2004) Direct fabrication of composite and ceramic hollow nanofibers by electrospinning. Nano Lett 4(5) 933-938... 

Lee, G.H., Song, J.C. and Yoon, K.B. 2010. Controlled wall thickness and porosity of polymeric hollow nanofibers by coaxial electrospinning. Macmmolecjda 18 571—576. 

FIGURE 9 Electro spinning setup and its corresponding nanofiber profile (a) conventional nanofiber] (b) Oriented nanofiber (c) Core-shell nanofiber, (d) Hollow nanofiber. 

Li, D. Xia, Y. Direct Fabrication of Composite and Ceramic Hollow Nanofibers by Electrospinning, Nano Lett, 2004,4(5), 933-938. 

Nanotubes Hollow nanofibers. Carbon nanotubes consist of one or more cylindrical structures or shells, each composed of a single tubular graphitic layer. 

Co-axial electrospinning has also been used to develop hollow nanofibers or nanotubes from ceramic and ceramic-polymer composites that are otherwise commonly prepared using tedious processes, such as self-assembly and template synthesis. The latter are known as bottom-up techniques in nanotechnology,as they require atoms and molecules to be manipulated and assembled in desirable structures that are at least an order of magnitude larger than the molecules themselves. The procedure for making hollow fibers at nano level is, in fact, opposite to that illustrated in Fig. 2.33. In the current case (Fig. 2.34), the core, instead of the sheath, is selectively removed. 

Loscertales IG, Barrero A, M quez M, Spretz R, Velarde-Ortiz R and Larsen G, Electrically forced coaxial nanojets for one-step hollow nanofiber design /. Am. Chem. Soc., 2004,126,5376-5377. 

Li D, McCann JT and Xia Y, Use of electrospinning to directly fabricate hollow nanofibers with fnnctionalized inner and outer surfaces . Small, 2005,1,83-86. 

Choi J-K, Hwang I-S, Kim S-J, Park J-S, Park S-S, Jeong U, Kang YC, Lee J-H (2010) Design of selective gas sensors using electrospun Pd-doped SnO hollow nanofibers. Sens Actuators B 150 191-199 Chung W-Y, Oh S-J (2006) Remote monitoring system with wireless sensors module for room environment. Sens Actuators B 113 64-70... 

Spinneret needle has been modified in some semps to produce nanofibers with new properties. For instance, coaxial spinneret which consists of two capillary spinnerets one inside another has been developed for some certain purposes and applications (Fig. 5a). This modified spinneret is capable of producing hollow nanofibers (Fig. 5b) (Li and Xia 2004). Core-shell nanofibers can also be obtained using this modified coaxial spinneret through spinning two different and immiscible polymer solutions (Zander 2013) (Fig. 5c) or emulsion polymer solution (Fig. 5d). 

Fig. 5 a Coaxial spinneret of a modified electrospinner, b the obtained hollow nanofibers, c spinning of two immiscible polymer solutions in form of core-shell nanofibers using a coaxial spinneret, d spinning of polymer emulsion solution through single nozzle spinneret. Adopted with modification from Pham et al. (2006) and Zander (2013)... 

Li D, Xia Y (2004) Direct fabrication of composite and ceramic hollow nanofibers by electrospinning. Nano Lett 4(5) 933-938. doi 10.1021/nl049590f Li W-J, Laurencin CT, Caterson EJ, Tuan RS, Ko FK (2002) Electrospun nanofibrous structure a noyel scaffold for tissue engineering. J Biomed Mater Res, 60(4) 613-21. http //www.ncbi. nlm.nih.gov/pubmed/11948520... 

Figure 9.7 (a) TEM image of a coaxially spun nanofiber with a shell layer of PEO and a core of poly(dodecylthiophene) (PDT). Both polymers were electrospun from CHCI3 (1-2% solutions). Reprinted with permission from Sun et al. (2003). Copyright 2003. John Wiley Sons, (b) Hollow nanofibers of titania obtained by calcination of PVP (containing titanium isopropoxide) coaxially electrospun with an oil core. Reprinted with permission from Li and Xia (2004). Copyright 2004. American Chemical Society. 

Reddy N, Xu H, Yang Y (2011) Unique natural-protein hollow-nanofiber membrane produced by weaver ants for medical applications. Biotechnol Bioeng 108 1726-1733... 

Fig. 11.3 (a) Gas sensing mechanisms of n-type emd p-type semiconductors and the different connecting configuration between long nanoflbers and nanopaiticles or short nanofibers, (b) Schematic model of the three steps for the sensitization mechanism of the as-prepared nanofiber sensor, (c) Response of Sn02 hollow nanofibers versus thin films serving as a reference (a Reprinted with permission from Yoon et al. [55]. 2012 Elsevier b Reprinted with permission from Zhang et al. [73]. 2010 Elsevier c Reprinted with permission from Cho et al. [74]. 2011 Elsevier)... 

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