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INSTABILITY MECHANISMS of ELECTRICALLY CHARGED LIQUID JETS in ELECTROSPINNING vs. ELECTROSPRAYING

INSTABILITY MECHANISMS of ELECTRICALLY CHARGED LIQUID JETS in ELECTROSPINNING vs. ELECTROSPRAYING. A.L. Yarin Department of Mechanical Eng. UIC, Chicago. Acknowledgement. D.H. Reneker E. Zussman A.Theron S.N. Reznik A.V. Bazilevsky C.M. Megaridis R. Srikar, S.Sinha Ray

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INSTABILITY MECHANISMS of ELECTRICALLY CHARGED LIQUID JETS in ELECTROSPINNING vs. ELECTROSPRAYING

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  1. INSTABILITY MECHANISMS of ELECTRICALLY CHARGED LIQUID JETS in ELECTROSPINNING vs. ELECTROSPRAYING A.L. Yarin Department of Mechanical Eng. UIC, Chicago

  2. Acknowledgement • D.H. Reneker • E. Zussman • A.Theron • S.N. Reznik • A.V. Bazilevsky • C.M. Megaridis • R. Srikar, S.Sinha Ray • Israel Science Foundation, Volkswagen Stiftung-Germany, National Science Foundation through grants NSF-NIRT CBET 0609062 and NSF-NER-CBET 0708711-U.S.A.

  3. Outline 1. Basic physics of the process: bending 2. Branching 3. Multiple jets 4. Needleless electrospinnning 5. Buckling 6. Self-assembly: Nanoropes and crossbars 7. CNT-containing nanofibers 8. Co-electrospinning: nanotubes&nanofluidics

  4. Queen Elizabeth I was interested in electricity

  5. William Gilbert made experiments for the Queen

  6. In 1600 Gilbert published a book on his experiments

  7. Modern Reproduction

  8. Modern reproduction

  9. Modern reproduction

  10. G.I.Taylor’s Experiments with Glycerin

  11. Electrospraying

  12. Modern reproduction

  13. Modern reproduction Splaying

  14. Nanofibers (Definition)

  15. Basic Physics of Electrospinning 30,000 Volt

  16. Electrospinning Setup

  17. Process Initiation: Taylor Cone Yarin A L, Reneker D H, Kombhongse S, J. App. Phys. 90, 2001

  18. Theoretical Model of Jet Initiation

  19. Theoretical Modelof Jet Initiation

  20. Theoretical Modelof Jet Initiation

  21. Experimenton Jet Initiation

  22. Experimenton Jet Initiation # 1 # 3 # 2

  23. 2.0 10 10 9 9 8 7 8 1.5 6 7 6 5 5 4 4 z 3 1.0 3 2 2 1 1 0.5 0 1.0 0.5 -1.0 -0.5 0 r Experiment vs. Theory

  24. Experimentvs. Theory

  25. Theoretical Modelof Jet Initiation The Reynolds number The electrical Bond number The initial contact angle

  26. 1.5 2 1.0 1 z 0.5 1.5 2.0 0.5 1.0 0 r Theoretical Model of JetInitiation z

  27. Theoretical Modelof Jet Initiation

  28. Theoretical Modelof Jet Initiation

  29. Theoretical Modelof Jet Initiation

  30. Theoretical Modelof Jet Initiation

  31. Theoretical Modelof Jet Initiation

  32. Theoretical Modelof Jet Initiation

  33. Theoretical Modelof Jet Initiation 1 – radial velocity at the surface 2 – vertical velocity at the surface

  34. Theoretical Modelof Jet Initiation Critical electric Bond number vs. static contact angle

  35. Theoretical Modelof Jet Initiation Predicted electric current vs. applied voltage

  36. Theoretical Modelof Jet Initiation Predicted convective and conductive parts of the electric current

  37. Electrically-driven bending instability The “Taylor cone” droplet A collection of point charges cannot be maintained at equilibrium: Earnshaw theorem Jet initiation The Electrospinning Mechanism – Dielectric constant  – Electric conductivity  – Surface tension a0– Droplet diameter – Viscosity – Mass density V0– Characteristic fluid velocity in droplet V*– Characteristic velocity in jet l– Characteristic length scale H– Hydrodynamic characteristic time C– Characteristic charge relaxation time Re – Reynolds number • Reneker D H, Yarin A L, Fong H, Koombhongse S, J. App. Phys. 87, 2000 • Reznik S N, Yarin A L, Theron A, Zussman E, J. Fluid Mech. 516, 2004

  38. Modern reproduction

  39. Modern reproduction

  40. Basic Equations: Discretized Quasi-one-dimensional Equations

  41. Electrically-driven Bending Instability time time time i =1 i = 101 i =2 i= N i =1 F0 ~ q.E Fc ~ coulomb force Fve ~ velocity difference i+ 1 Fcap ~ surface tension effects from local curvature and cross section i d i + 1 i - 1 i i - 1 i = 1 i = 1

  42. Electrospinning of Polymer Solutions Reneker D H, Yarin A L, Fong H, Koombhongse S, J. App. Phys. 87, 2000 Yarin A L, Koombhongse S, Reneker D H, J. App. Phys. 89, 2001

  43. Electrospinning of Polymer Solutions Reneker, Yarin, Fong, Koombhogse

  44. Electrospinning of Polymer Solutions Reneker, Yarin, Fong, Koombhongse

  45. 16.5 ms 18 ms 0 ms 22 ms 31.5 ms 32 ms 24.5 ms 30.5 ms Reneker D H, Yarin A L, Fong H, Koombhongse S, J. App. Phys. 87, 2000 38.5 ms 37.5 ms

  46. Nanofiber Garlands Electrospinning of PCL photographed at 2000fps (playback speed = 30fps) Reneker D H, Kataphinan W, Theron A, Zussman E, Yarin A L, Polymer 43, 2002

  47. As-spun Polymer Nanofibers Polyacrylic acid PEO Siloxane 8m 1m 1m PPV PCL PVA 20m 2m 200nm

  48. Branching in PCL Electrospinning Yarin A L, W. Kataphinan, D.H. Reneker J. Appl. Phys. 98, 064501 (2005)

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