Physical principles of nanofiber production 1 Needleless electrospinning

Physical principles of nanofiber production 1. Needle-less electrospinning D. Lukáš 2010 1

3. 6. Self-organisation of electrospinning jets on free liquid surfaces 2

Needle electrospinning: Self-organisation of the fluid in electrospinning is the underlying cause behind formation of the Taylor cone, the stable jet part, the whipping zone and evaporation of solvent. Now, it will be shown that the self-organising potential of electrospinning is even more forcerful since it has a power to organize : individual jets on free liquid surfaces without any need to use needless / capillaries to create them. This finding is enormously attractive regarding the recent effort to elevate electrospinning technology to industrial level because it opens a chance to design simple as well as highly productive lines for nanofibrous layer production. 3

A rode instead of a needle E=0 d=1 cm + 1 + + 2 E = Ec + + + + 3 Stationary wave 4 Epoxy resin E Ec F. Sanetrník no. 1 2 3 4 5 6 5 Sandra Torres 6 4

Dynamic phenomenon: field strength increment can lead to unlimited growth of a wave amplitude. A. Sarkar Wave vector Amplitude Angular frequency Growth factor 5

Stable amplitude Growing amplitude Dispersion law Lukas D Sarkar A Pokorny P, SELF ORGANIZATION OF JETS IN ELECTROSPINNING FROM FREE LIQUID SURFACE - A GENERALIZED APPROACH, ACCEPTED FOR PUBLICATION, Journal of Applied Physics, 103 (2008), 309 -316. Clemson University Electrospinning - X-rays 6

D. Lukas, A. Sarkar, and P. Pokorny, Journal of Applied Physics, 103 (2008) 7

Euler equation Velocity potential Elektrostatic forces gravitation Surface tension Equation of continuity dispersion law Needleless Electrospinning Prague 2007 8

Tonks-Frenkel instability E Stable waves of various wave numbers and angular frequencies. Various field strengths E Fastest forming instability The only wave Clemson University Electrospinning - X-rays 9

Capillary waves Electrospinning Relaxation time Growth factor 10

Quadratic equation with the only solution Critical field strength 11

capillary length 12

Dimensionless electrospinning number 13

Minimal and negative square values of the angular frequency correspond to the maximal growth factors, q’s, inherently connected with the self-organisation caused by the mechanism of the fastest forming instability. + 14

dimensionless intra-jet distance 15

L Clemson University Electrospinning - X-rays 16

b 32 k. V 43 k. V Linear clefts emit polymeric jets. Linear clefts in (a) and (b) emit polymeric (polyvinyl alcohol) jets at the voltages, 32 k. V and 43 k. V, respectively. The inter-jet distance / wavelength is l. The distance between the cleft and the collector was adjusted on 802 mm. Clemson University Electrospinning - X-rays 17

Technology Jirsák, O. Sanetrník, F. Lukáš, D. Kotek, V. Marinová, L. Chaloupek, J. (2005) WO 2005024101 A Method of Nanofibres Production from A Polymer Solution Using Electrostatic Spinning and A Device for Carrying out The Method. www. elmarco. com Clemson University Electrospinning - X-rays 18