Fundamental Parameters Affecting Electrospinning of PAN Nanofibers as Uniaxially Aligned Fibers Rouhollah Jalili, Mohammad Morshed, Seyed Abdolkarim Hosseini Ravandi The Center of Excellence in Environmental Nanotechnology, Isfahan University of Technology, P.O. Box 84156/83111, Isfahan, I.R. Iran Received 13 July 2005; accepted 12 February 2006 DOI 10.1002/app.24290 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Electrospinning with a collector consisting of two pieces of electrically conductive substrates separated by a gap has been used to prepare uniaxially aligned PAN nanofibers. Solution of 15 wt % of PAN/DMF was used tentatively for electrospinning. The effects of width of the gap and applied voltage on degree of alignment were inves- tigated using image-processing technique by Fourier power spectrum method. The electrospinning conditions that gave the best alignment of nanofibers for 10 –15 wt % solution concentrations were experimentally obtained. Bundles like multifilament yarns of uniaxially aligned nanofibers were prepared using a new simple method. After-treatments of these bundles were carried out in boiling water under ten- sion. A comparison was made between the crystallinity and mechanical behavior of posttreated and untreated bundles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4350 – 4357, 2006 Key words: electrospinning; polyacrylonitrile; aligned nano- fibers; bundle; INTRODUCTION Electrospinning is a straightforward method that re- lies on electrostatic forces to produce fibers with sub- micron diameter from polymer solutions or melts. In a typical process, an electrical potential is applied be- tween a droplet of polymer solution, or melt, held through a syringe needle and a grounded target. Elec- trostatic charging of the droplet results in the forma- tion of the well-known Taylor cone. When the electric forces overcome the surface tension of the droplet from the apex of the cone, a charged fluid jet is eject- ed. 1 The jet exhibits bending instabilities due to repul- sive forces between the surface charges, which is car- ried with the jet, and follows a looping and spiraling path. 2,3 The electrical forces elongate the jet thousands of times and the jet becomes very thin. Ultimately, the solvent evaporates, or the melt solidifies and very long nanofibers are collected on the grounded target. 1 The fiber morphology is controlled by the experimental design and is dependent on solution conductivity, 4,5 solvent polarity, 5 solution concentration, 4 polymer molecular weight, 6 viscosity 4 and applied voltage. 7 Because of the chaotic oscillation of the electrospin- ning jet the nanofibers are obtained in nonwoven form, which are used in many applications such as filtration, 8 tissue scaffolds, 9 wound dressing, 10 and drug delivery. 11 Some applications (e.g., carbon nano- fibers from electrospun PAN nanofibers precursor) require well-aligned and highly ordered nanofibers. To prepare carbon nanofibers, the precursor PAN nanofibers need to undergo a series of heat treatments. The PAN precursor nanofibers are initially oxidized under tension and then carbonized in an inert atmo- sphere. The electrospun webs are difficult to handle (webs are very delicate, randomly aligned, and are amorphous) and it is difficult to keep the nanofibers in this form under tension during stabilization. As a result carbon nanofibers with poor mechanical prop- erties are expected from these precursor nanofibers. Also in general, higher degree of molecular orienta- tion in the original PAN precursor fiber results in carbon fibers with better mechanical properties partic- ularly the tensile modulus. 12 If one can prepare well- aligned and highly ordered PAN nanofibers precur- sor, then that could lead to higher molecular orienta- tion and degree of crystallinity and as a result better mechanical properties during after-treatment of nano- fibers. Fennessey and Farris prepared tows of unidirection- ally and molecularly oriented PAN nanofibers using a high speed, rotating take-up wheel. The aligned tows were twisted into yarns, and the mechanical proper- ties of the yarns were determined as a function of twist angle. Their yarn with twist angle of 11° had initial modulus and ultimate strength of about 5.8 GPa and 163 MPa, respectively. 12 Deitzel et al. have obtained yarns of aligned poly(ethylene oxide) nanofibers by introducing an electrostatic lens element to stabilize Correspondence to: M. Morshed (morshed@cc.iut.ac.ir). Journal of Applied Polymer Science, Vol. 101, 4350 – 4357 (2006) © 2006 Wiley Periodicals, Inc.