Co-axial electrospinning

Schematic of the voltage dependence of the core-sheath fiber formation in co-axial electrospinning (a) lower voltage (b) critical voltage (c) higher voltage. ... 

In this novel approach using the technique of co-axial electrospinning, it has been shown that the sheath can act as a template and guide the core... 

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. 

Hollow composite nanofibers prepared by co-axial electrospinning technique. Reprinted with permission from reference 66. Copyright 2004 American Chemical Society. 

McCaim et al. recently introduced an approach that combined the process of melt co-axial electrospinning to encapsulate the phase change materials (PCMs) into polymer or composite sheath. PCM can help stabilize the temperature near its melting point as the material changes the state from a solid to liquid or vice versa and the enthalpy of fusion involved can absorb or release thermal energy. The nanofibers produced using such a material can be used in thermal insulation applications. The researchers used three PCMs, octadecane, hexadecane and eicosane, in melt forms as core solutions and demonstrated temperature stabilization at three different points, 17°C, 30°C and 37°C, respectively ... 

Zhang Y, Huang ZM, Xu X, Lim CT and Ramakrishna S, Preparation of coreshell structured PCL-r-Gelatin bi-component nanofibers by co-axial electrospinning , Chem. Mater.,2004,16,3406-3409. 

Moghe AK and Gupta BS, Co-axial electrospinning for nanofiber structures preparation and applications , Polym. Rev., 2008,48(2), 353-377. 

A complex multicomponent system based on PMMA and PA6 was developed and processed as fibers by co-axial electrospinning [153]. The co-axial composite nanofibers with a core-shell stmcture embedded Ti02 nanoparticles, as well MWCNTs. When Ti02 nanoparticles were added to the shell, the fibers exhibited a remarkable ability to absorb UV radiation, but a lower transmittance in the visible light range. Using the Ti02 nanoparticles for the core, the effects were reversed. 

---