Ultrafine Electrospun Polyamide-6 Fibers: Effect of Emitting Electrode Polarity on Morphology and Average Fiber Diameter PITT SUPAPHOL, 1 CHIDCHANOK MIT-UPPATHAM, 2 MANIT NITHITANAKUL 1 1 Technological Center for Electrospun Fibers and The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok 10330, Thailand 2 Department of Materials Technology, Faculty of Science, Ramkhamhaeng University, Bangkok 10240, Thailand Received 10 December 2004; accepted 26 September 2005 DOI: 10.1002/polb.20671 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Electrostatic spinning or electrospinning is now a well-known process for fabricating ultrafine fibers with diameters in the submicrometer down to nanometer range from materials of diverse origins. The polarity of the emitting electrode (i.e., the one that is in contact with the polymer solution or melt) can be either positive or negative. In the present contribution, the effects of emitting electrode polarity and some processing parameters (i.e., polyamide-6 (PA-6) concentration, molecular weight of PA-6, electrostatic field strength, solution temperature, solvent type, and addition of an inorganic salt) on morphological appearance and average size of the as-spun PA-6 fibers were investigated. Scanning electron micrographs showed obvious mor- phological difference between the fibers obtained under positive and negative polarity of the emitting electrode. The main differences were that the cross section of the as- spun PA-6 fibers obtained under the negative electrode polarity was flat, while that of those obtained under the positive one appeared to be round and that the average size of the fibers obtained under the negative electrode polarity was larger than that of those obtained under the positive one. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3699–3712, 2005 Keywords: electrode polarity; electrospinning process; polyamide-6; ultrafine fibers INTRODUCTION Electrostatic spinning or electrospinning is a pro- cess by which ultrafine fibers with diameters in the submicrometer down to nanometer range can be produced. These ultrafine fibers exhibit sev- eral interesting characteristics, which are, for example, large surface area to mass or volume ratio, small pore size between depositing fibers of the electrospun mats, and vast possibility for sur- face functionalization. These unique properties render electrospun ultrafine fibers as excellent candidates for various applications. 1 The basic principles of the electrospinning process concern with the application of a high electrostatic potential from a high-voltage power supply to a polymer solution or melt across a finite distance between a conductive nozzle and a grounded collector. 2 The Coulombic repulsion force between charges of the same polarity being present in the polymer solution or melt destabil- izes the partially-spherical droplet of the polymer solution or melt located at the tip of the nozzle to finally form a droplet of a conical shape (i.e., the Taylor cone). Further increase in the electrostatic Correspondence to: P. Supaphol (E-mail: pitt.s@chula. ac.th) Journal of Polymer Science: Part B: Polymer Physics, Vol. 43, 3699–3712 (2005) V V C 2005 Wiley Periodicals, Inc. 3699