1 Physical principles of nanofiber production 1.Introduction D.Lukáš 2010

2 Physical principles of electrospinning (Electrospinning as a nano- scale technology of the twenty- first century) D. Lukáš; A. Sarkar; L. Martinová; K. Vodsed'álková; D. Lubasová; J. Chaloupek; P. Pokorný; P. Mikeš; J. Chvojka; M. Komárek Department of Nonwovens, Faculty of Textile Engineering, Technical University of Liberec, Liberec, Czech Republic Physical principles of electrospinning (Electrospinning as a nano-scale technology of the twenty-first century)

3 The monographs: [2] S. Ramakrishna, K. Fujihara, W. Teo, T. Lim, and Z. Ma, An introduction to electrospinning and nanofibres, World Scientific Publishing Co., Singapor, [3] D.H. Reneker and H. Fong, Polymeric nanofibres, Oxford University Press, Washington D.C., [1] Y. Filatov, A. Budyka, and V. Kirichenko, Electrospinning of micro- and nanofibres: fundamentals in separation and filtration processes, Begell House Inc., Redding, [4] D.H. Reneker and A.L. Yarin, Electrospinning jets and polymer nanofibres, Polymer, 49 (2008), pp [89] A.L. Andrady, Science and Technology of Polymer Nanofibres, Wiley, New Jersey, 2008.

4 Figure Schematic diagram of an electrospinning set up: (1) syringe and metering pump (2) needle/capillary serving as the electrode (3) stable part of the jet, (4) whipping/coiling zone, (5) collector, (6) ground, (7) high voltage supply,

5 It has remarkable manifold external morphology: (2) ‘Roots’ evolving from a charged extremely thin surface layer, called as Debye’s layer, of the polymer solution. (3) Stable part of the jet that looks like a ‚tree stem‘. (4) Whipping zone / bending instability of the jet looks out like ‚branches‘ of the tree with lives of the form of jet coil cascades and jet-branching. (5) Eventually, the nanofibres collected on the other electrode, so- called collector, may literally be thought of as the ‘fruits’ of the entire process. Electrospun polymeric jet almost resembles a tree.

Physically, the phenomenon of electrospinning is a consequence of a tug of war between electrostatic and capillary forces. The first of them speaks of charged liquid bodies that disintegrate due to long range repulsive Coulombic forces between ions of the same signs, while the last one causes liquid particles to flock together to minimize the liquid surface area and surface energy, resulting from short distance intermolecular interactions at quantum level. 6

7 Liquid bodies disintegrate in two possible ways, depending on their internal molecular structure: (1) Simple liquids, having small molecules, spray in clouds of small charged droplets with a tendency to break down further until one single elementary charge remains trapped in each of them. (2) Liquids with higher viscosity, particularly, polymer solutions and polymer melts with sufficiently entangled macromolecules disintegrate in long tiny liquid columns while moving from one electrode to the other. The internal pressure of electric nature, caused by an enormous concentration of charged particles of similar nature, forces them to be stretched longitudinally. This stretching tendency, along with jet inertia and rheology, results in a wild lateral jet motion.

Needle Electrospinning Solvent evaporation Whipping Taylor cone Stable jet 1 2 John Zeleny, Physical Review, Vo. III, No. 2, 1914

9 Narrowing down of the jet diameter results in an increased curvature of the jet segments that brings about an associated phenomenon that effectively drives the solvent out from the jet.

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11 The electrospinning process has potential to revolutionise spinning technology. It resembles biological procedures, in some ways, wherein bio- nanofibres like cellulose and collagen are created by self- organization.

12 d =200 nm Polymer solution Self-organized nanofibrous layer s S

13 Unlike a typical classic nonwoven technology, that has a line for production of carded needle-punched nonwovens, the devices and equipments in electrospinning process are free of complex passive or rotating components.

Polymer-to-fabric processes Fibre web directly from polymers Melt of fibre forming polymer Extrusion through a system of spinnerets High velocity current of air Deposition of fibres on conveyor

15 Various physical phenomena play the role of traditional mechanical components when fibre spun under external electric field. So, the magnificence of mechanical engineering is substituted indirectly by external fields in helping in diverse physical self-organization. Hence, a better understanding of its intrinsic physical fundamentals is needed for further technological developments and, so, this review is largely devoted to the physical insight, in an attempt to enlighten the marvellous phenomenon of electrically driven polymeric jets.

16 Electrospinning technology can be divided into two branches. (1)Previously, it was based on less productive needle / capillary spinners with production rates in the order of unit grams per hour. (2) Recently, technologies that are based on highly productive jet creation from free liquid surfaces by self-organization, have been developed. These effective methods may be classified as needleless electrospinning.

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18 These technologies to produce polymeric nanofibrous materials, are of primary interest of various disciplines, like: medicine, biology, chemical, textile and material engineering, nano-porous materials are employed as filters, scaffolds for tissue engineering, protective clothing, drug delivery systems, substrates for catalysis, etc.

19 Chapters: 1. Introduction 2. Historical overview 3. Theoretical evolution of electrospinning 4. Liquid jet in an electric field 5. Special collectors 6. Electrospinning variants 7. Exceptional features of electrospinning 8. Polymeric solutions for electrospinning 9. Nanofibers in a cell 10. „drawing“of nanofibers 11. Force spinning

20 Homework: Draw a scheme of needle electrospinning technology and describe its parts and phases of polymeric jet during the electrospinning proces.