Core-sheath structure

As mentioned above, metal/CPs with core-sheath structure can be prepared by the template method. However, the approach based on the template technique is complicated and non-economical because of the need to remove the templates. In fact, metal/CPs with core-sheath structure can be fabricated via a one-step chemical polymerization [83-87]. Niu and co-workers demonstrated that Au/PANI coaxial nanocables could also be fabricated by the redox reaction between chloroauric acid and aniline in the presence of d-CSA [85]. In that case, CSA acted not only as a dopant, but also as a surfactant or a soft template. In addition to Ag/PPy and Au/PANI nanocables, cable-like Au/poly(3,4-ethylenedioxythiophene) (PEDOT) nanostructures have been synthesized in the absence of any surfactant or stabilizer through one-step interfadal polymerization of EDOT dissolved in dichloromethane solvent and HAuCl dissolved in water [86]. Microscopy studies showed (Figure 13.6) that the outer and inner diameters of Au/PEDOT nanocables were aroimd 50 and 30 nm, respectively. 

Fig. 7 Microbeam X-ray fiber pattern of drawn monofilaments, recorded from the three marked points in the microscope image, and schematic display, revealed by microbeam X-ray diffraction a cold-drawn and two-step-drawn UHMW-P(3HB) monofilaments with core-sheath structure b one-step-drawn P(3HB-co-3HV) monofilaments after isothermal crysteillization with a uniform structure. The arrows indicate a reflection derived from the p-structure. (Reprinted with permission from Iwata 2005. Copyright 2005, Wiley-VCH Verlag GmbH Co)...

Yang, Y., Li, X.H., Cheng, L., He, S.H., Zou, J., Chen, F., and Zhang, Z.B. (2011) Core-sheath structured fibers with pDNA polyplex loadings for the optimal release profile and transfection efficiency as potential tissue engineering scaffolds. Acta Biomater., 7, 2533—2543. 

Wei, M., B. W. Kang, C. M. Sung, and J. Mead (2006a). Core-sheath structure in electrospun nanofibers from polymer blends. Macromolecular Materials and Engineering 291(11) 1307-1314. 

H. Wang, L. Bian, P. Zhou, J. Tang, and W. Tang, Core-sheath structured bacterial cellulose/ polypyrrole nanocomposites with excellent conductivity as supercapacitors. J. Mater. Chem. 

Mitsubishi Rayon Co. has reported the development of heat-storage and electrically conductive acrylic fibres with electrical conductivity > 10 S/cm and clothes for winter clothing and sportswear. These bicomponent fibres comprise a core-sheath structure, a core of P(AN/MA/Sod. methaUyl sulphonate) containing 15-70vol% white electrical conductive ceramic particles (e.g. W-P) and P (acrylonitrile/vinyl acetate) as a sheath. 

Figure 4 shows a series of micro-beam X-ray diffraction patterns of one-step-drawn P(3HB-co-8%-3HV) fiber with isothermal crystallization scanned perpendicular to the fiber axis. All micro-beam X-ray diffraction patterns of one-step-drawn fiber showed the reflections of both a- and )8-forms. These reflections were not changed throughout fiber except for intensities. This result indicates that one-step-drawn P(3HB-co-8%-3HV) fiber with isothermal crystallization has not a core-sheath structure such as cold-drawn and two-step-drawn UHMW-P(3HB) fiber. In the other word, one-step-drawn P(3HB-co-8%-3HV) fibers with isothermal crystallization is an uniform structure throughout fiber consistent with both a- and )8-form crystals. This structure supports the result that one-step-drawn fiber with isothermal crystallization has a high tensile strength in spite of low draw ratio. 

Lyocell fibers consist entirely of cellulose. One fiber is composed of uniformly thick fibrils distributed over the whole cross section. This structure is another difference from the traditional fibers from regenerated cellulose, which is usually characterized by a core-sheath structure. The evolution of this fibrillar structure can be explained by the rapid segregation processes occurring during the regeneration of the cellulose from the spinning solution. This structure (Fig. 2.30) imparts the particular properties of the lyocell fiber. 

Wang et al. [51] used the coaxial technique to fabricate poly(bis[p-methylphe-noxy])phosphazene (PMPPh)/PAN nanofibrous membranes. Under the optimized electrospinning conditions of a 15 wt% concentration and 0.2 mL/h flow rate for both PMPPh and PAN, nanofibers of diameter 150 20 nm and a clear core/sheath structure were obtained. 

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