Nanotech 2011

On the mechanical properties of polymeric nanofibers and their nonwoven membranes (invited presentation)

C-L. Pai, M.C. Boyce, G.C. Rutledge
Massachusetts Institute of Technology, US

Keywords: electrostatic fiber

Abstract:

Electrostatic fiber formation (aka “electrospinning”) has emerged in recent years as one of the simplest and most promising methods for producing long, continuous fibers with diameters less than 1 micron, from a wide variety of materials. Membranes comprised of such fibers are remarkable for their ease of formation, high surface area, and small pore sizes. As a result, these materials have enjoyed considerable attention in both academia and industry for potential commercial applications in areas ranging from biomedical to energy and the environment. The mechanical performance of the nonwoven membranes is essential to commercial viability in any of these areas. Remarkably, the Young’s modulus of individual electrospun fibers has been found to exhibit values in excess of the isotropic bulk value, and to increase with decreasing fiber diameter for fibers with diameter less than roughly 500 nm. Meanwhile, the stiffnesses of nonwoven mats show no such improvement with decreasing diameter. Using poly(trimethyl hexamethylene terephthalamide) (PA 6(3)T) as a case study, we demonstrate how the trend in individual fiber mechanical properties correlates with increasing molecular level orientation within the fibers with decreasing fiber diameter. For the nonwoven fabric, the increase in single fiber properties is compensated by increased curvature and reduced bending stiffness of the smaller diameter fibers. Both of these effects are captured using physically-motivated microstructural models, which provide guidance for the improvement of mechanical properties of nonwoven membranes.
 

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