Properties of Electrospinning Jets
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Properties of Electrospinning Jets Darrell H. Reneker, Yu Xin, Hyungjin Lee, Yinan Lin, Kaiyi Liu, Zhenxin Zhong Department of Polymer Science, The University of Akron, OH 44325, U.S.A ABSTRACT Measurement of elongational stresses, stereographic images of jet paths, innovative collection of fluid jets, and utilization of elongational flow for assembly or disassembly of particulate structures, the electron microscopic views inside nanofibers, and the morphological and crystallographic changes that occur during heating of the metastable electrospun fibers illuminate the growing versatility of the electrospinning process. INTRODUCTION As more ways are found to observe and control the electrospinning jet, and as new morphological, mechanical, and thermal properties of the fibers produced by electrospinning are measured and characterized, new ways for creating sophisticated structures and systems becomes feasible. Important innovations may emerge in fields as different as the fashion industry, filtration, clinical medicine, energy conversion, and large structures in interplanetary space. The interest in electrospinning technology and polymer nanofibers has grown rapidly in the past two decades, and is now ramifying in interesting and promising ways. It is essential to learn how to characterize the electrospinning process in many new ways to control the important process variables. New experimental ways to gather the data needed for this purpose are needed. The physical properties of the fluids being electrospun change rapidly, often by several orders of magnitude during the electrospinning process. The viscoelastic properties change from those of a polymer solution in which the molecules are slightly entangled to the properties of a solid fiber with most segments of the molecules aligned with the axis of fibers. Optical observations are very helpful for gathering the needed data, but the observation of the details of the evolving path and the electric charge it carries is quite complex. Optical observations are aided by diagrams that show the three dimensional arrangements of cameras, beams of light, the locations of broad sources of diffuse light, and the locations of intense flashes that are short enough to record the instantaneous position of the jet. Intense glints of light, specularly reflected by segments of the jet that have a tangent plane that is oriented in a mirror-like relationship with a light source and a camera, provide most of the visual information about the jet. The difficult problems of exposition are made much more manageable by the globe-like model described below. The ability of an electrospinning jet to incorporate, package, or sequester atoms, molecules, organelles, or sub-millimeter scale particles of almost any composition, and spanning many scales from the nanoscale diameters to the kilometer scale lengths that are easily created, into a fiber, yarn, non-woven mat or the like, opens a wide vista of possibilities for making structures and compositions useful in materials science, c
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