Characterization of Nanofibers and Mats

Science and Technology of Polymer Nanofibers. By Anthony L. Andrady Copyright 2008 John Wiley Sons, Inc. 

In the following sections, selected characterization tests based on several common anticipated uses for nanofiber materials are presented. The assessment of interstitial porosity properties, analysis of fiber dimension by microscopy, and mechanical integrity of fiber mats are the more important metrics in several application areas. Some of these will eventually be adopted as standard test methods in the field — both the American Sodely for Testing Materials (ASTM) and the International Standards Organization (ISO) have initiated efforts to standardize the nomenclature and test methods relating to nanomaterials, including nanofibers. Here, the reader wiU be afforded a flavor of the rather limited research literature on single-fiber measurements. 

Polymer SEM TEM XRD Tensile Properties Raman Spectroscopy FTIR Thermal Methods Other Methods Reference 

Polymer SEM TEM Tensile XRD Properties Raman Spectroscopy Thermal ETIR Methods Other Methods Reference 

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Gouda, M., Hebeish, A.A., Aljafari, A.I., 2014. Synthesis and characterization of novel drug delivery system based on cellulose acetate electrospun nanofiber mats. Journal of Industrial Textiles 43 (3), 319-329. 

Characterization of individual nanofibers is critical to understanding their physics because invariably it is the fiber characteristics that govern the properties of their mats. But, their minute dimensions makes this a daunting task. Nanofibers of particular interest, those with dimensions smaller than the wavelength of light, are especially difficult to isolate or test. It is not practical to extract fiber-level information by manipulation of test data generated from even the best-characterized fiber mats. Several innovative techniques for the direct assessment of mechanical properties of individual nanofibers are being developed and are discussed in this section. 

Figure 19.14 Schematic illustration of the basic setup for electrospinning, (a) The typical SEM image of nonwoven mat of polymer nanofibers, (b) CCD image of the stable con-jet spinning model. Photographs illustrating the instability region of a liquid jet and the capture time was on two different scales (c) 1/250 s and, (d) 18 ns. (Reprinted from Polymer, 42, Y.M. Shin, M.M. Hohman, M.P. Brenner and G.C. Rutledge Experimental characterization of electrospinning The electrically forced jet and instabilities, 9955-9967, 2001, with permission from Elsevier.)...

Seo S-J, Yun S-H, Woo J-J, Park D-W, Kang M-S, Hinsch A, Moon S-H (2011) Preparation and characterization of quasi-soUd-state electrolytes using a brominated poly(2,6-dimethyl-1,4-phenylene oxide) electrospun nanofiber mat for dye-sensitized solar cells. Electrochem Common 13(12) 1391-1394. doi 10.1016/j.elecom.2011.08.018... 

Ji Y, Li B, Ge S, Sokolov JC, Rafailovich MH (2006) Stiucture and nanomechanical characterization of electrospun PS/clay nanocomposite fibers. Langmuir 22 1321-1328 McCuUen SD, Stevens DR, Roberts WA, Ojha SS, Qatke LI, Goiga RE (2007) Morphological, electrical, and mechanical characterization of electrospun nanofiber mats containing multi-walled carbon nanotubes. Macromolecules 40(4) 997-1003... 

Karim, M. R., et al. Preparation and characterization of eleetrospun pullulan/montmorillonite nanofiber mats in aqueous solution. Carbohydrate Polymers. In Press, Accepted Manuscript. 

Vondran, J. L. Fabrication, optimization, and characterization of carboxymethylated chitosan nanofiber mats for cartilage regeneration applications. Materials science and engineering Philadelphia Drexel University. 2007,123. 

The pore size distributions obtained by the mercury intrusion and liquid extrusion techniques are expected to be different. Mercury intrusion allows access to the pores from both sides of the mat and the entire pore volume is likely to be sampled. For pores that have large surface openings, the liquid extrusion generally tends to imderestimate the pore volumes relative to those measured by intrusion porosimetry. Liquid extrusion measurements yield the pressure needed to push the liquid past the most constricted part (or the throat ) of the pore. The pore volume of the channel is estimated based on the throat diameter. This also introduces directionality to the liquid extrusion measurement For a sample where porosity includes converging or diverging channels, the pore volumes (and pore dimensions) obtained from the liquid extrusion method will depend on the direction of the gas flow into the membrane. However, this is not expected to be a serious source of error in routinely characterizing nanofiber mats. 

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