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

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

11. Electrospraying

12. Modern reproduction

13. Splaying

14. Nanofibers (Definition)

15. 30,000 Volt Basic Physics of Electrospinning

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

21. Experiment on Jet Initiation

22. # 1 # 2 # 3

23. Experiment vs. Theory -0.50 0.5 1.0 r 2.0 1.5 1.0 0.5 0 z 10 9 8 9 8 7 6 7 6 5 5 4 4 3 2 1 2 1 3

24. Experiment vs. Theory

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

26. Theoretical Model of Jet Initiation 1.5 1.0 0.5 1.0 1.52.0 r 2 1 z 0 z

27. Theoretical Model of Jet Initiation

33. 1 – radial velocity at the surface 2 – vertical velocity at the surface

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

35. Theoretical Model of Jet Initiation Predicted electric current vs. applied voltage

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

37.  – Dielectric constant  – Electric conductivity  – Surface tension a 0 – Droplet diameter  – Viscosity  – Mass density V 0 – 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 Electrically-driven bending instability A collection of point charges cannot be maintained at equilibrium: Earnshaw theorem The Electrospinning Mechanism 1.Reneker D H, Yarin A L, Fong H, Koombhongse S, J. App. Phys. 87, 2000 2.Reznik S N, Yarin A L, Theron A, Zussman E, J. Fluid Mech. 516, 2004 The “ Taylor cone ” droplet Jet initiation

39. Modern reproduction

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

42. Electrically-driven Bending Instability time  i i= N i+ 1 i - 1 i = 1 F 0 ~ q. E F ve ~ velocity difference F c ~ coulomb force i =1 i =2 time i = 1 i = 101 time i + 1 i i - 1 F cap ~ surface tension effects from local curvature and cross section

44. 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

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

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

47. 0 ms 16.5 ms 18 ms 22 ms 24.5 ms 30.5 ms 31.5 ms 32 ms 37.5 ms 38.5 ms Reneker D H, Yarin A L, Fong H, Koombhongse S, J. App. Phys. 87, 2000

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

49. 2m2m 8m8m 200nm 20  m 1m1m 1m1m As-spun Polymer Nanofibers PEO PCL Siloxane Polyacrylic acid PVA PPV

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

51. Branching in PCL Electrospinning

54. Experiment with a 3x3 Setup S.A.Theron, A.L. Yarin, E. Zussman, E. Kroll, Polymer, 46, 2005

55. Experiment with a 9x1 Setup

56. Multiple Jet Electrospinning Multiple Jet Electrospinning

57. Theoretical Model of 3x3 Multiple Jets

58. Theoretical Model of 3X3 Multiple Jets

59. Theoretical Model of 3x3 Multiple Jets

61. Theoretical Model of 9x1 Multiple Jets

64. a b c f d e H Upward Needleless Electrospinning of Multiple Nanofibers a- Layer of magnetic fluid b- Layer of polymer solution Yarin&Zussman Polymer 45, 2977-2980 (2004)

65. Magnetic Fluid Cones

66. Perturbed Outer Surface of Polymer Solution

67. Electrospinning of Multiple Nanofibers

68. As-spun Nanofibers

69. Buckling of Electrified Jets Han,Reneker,Yarin, Polymer 48, 6064-6076 (2007)

70. Buckling of Electrified Jets Han,Reneker,Yarin, Polymer 48, 6064-6076 (2007)

71. Self-assembly: Nanoropes and Crossbars. A Sharpened Wheel – Electrsostatic Lens Experimental setup Plot of the electric field strength in the region of the wheel Tip of the wheel Axis of the wheel Theron A, Zussman E, Yarin A L, Nanotechnology 12, 2001 Tip of wheel Tip of syringe

72. 3D Nano-structures A rotating table on the wheel collector enables collection of multiple nanofiber layers at different angles. Theron A, Zussman E, Yarin A L, Nanotechnology 12, 2001

73. Aligned Nanofibers: 2D Arrays Fiber Diameter: 100nm - 500nm Pitch: 1  m - 1.5  m 2m2m 2m2m

74. Nanoropes 5m5m 2m2m

75. Diameter: 50nm - 100nm Pitch: 2  m - 3  m. 3D Nanocrossbars Theron A, Zussman E, Yarin A L, App. Phys. Lett. 82, 2003

76. 00 180  Sink flow CNT ~200 nm CNTs in Polymer Solution (PEO) CNT Alignment During Electrospinning of Polymer Solutions Dror Y, Salalha W, Khalfin R, CohenY,Yarin A L, Zussman E, Langmuir 19, 2003; Langmuir, 20, 2004.

77. CNTs Embedded and Aligned in Electrospun Nanofibers 50nm Single-wall carbon nanotubes embedded in nanofiber Multi-wall carbon nanotube embedded in nanofiber

78. 1 st CNT 2 st CNT Overlap area

79. Co-electrospinning: Compound Nanofibers Solution: PEO (1e6) 1% in ethanol/water Inner solution contains 2% bromophenol Outer solution contains 0.2% bromophenol Sun Z, Zussman E, Yarin A L, Wendorff J H, Greiner A, Advanced Materials 15, 2003 and Nanotubes

80. Co-electrospinning Zussman E, Yarin A L, Bazilevsky A.V., R. Avrahami, M. Feldman, Advanced Materials 18, 2006 Core: PMMA Shell: PAN

81. Carbonization Core: PMMA Shell: PAN

82. Turbostratic Carbon Nanotubes Core: PMMA Shell: PAN

83. Core Entrainment Problems Core: PMMA Shell: PAN

84. Numerical Simulation: Core-shell Jet (a) (b) S.N. Reznik, A.L. Yarin, E. Zussman, L. Bercovici. Phys. Fluids v. 18, 062101 (2006)

85. Co-electrospinning with Protrusion Zussman E, Yarin A L, Bazilevsky A.V., R. Avrahami, M. Feldman, Advanced Materials v. 18, 348-353 (2006). Stress level at the interface: ~ 5000 dyne/(square cm)

86. Optical appearance of a PMMA/PAN emulsion about 1 day after mixing of a homogeneous blend containing 6 wt% PMMA + 6% PAN in DMF Core-Shell Nanofibers from PMMA-PAN Emulsion A.V.Bazilevsky, A.L. Yarin, C.M. Megaridis Langmuir v.23, 2311-2314 (2007).

87. Experimental set-up and hollow carbon tubes

88. Schematic of the modeled PAN/DMF flow around a spherical PMMA/DMF droplet trapped over the core-shell Taylor cone

89. The Stokes equations in Lubrication approximation

90. Integrating the momentum balance eq using the no-slip&free surface conditions, we find

92. Fine emulsion should result in multi-core fibers

93. Conclusion (i) Sophisticated nanofibers and nanotubes are relatively easily achievable. (ii) In situ self-assembly is possible. (iii) Jet bending is the leading mechanism. Branching is secondary. No splaying. (iv) Modeling is quite reliable for jet initiation and bending stages in both single- and multiple-jets cases. (v) Core-shell nanofibers and hollow nanotubes can be made. (vi) Co-electrospun nanofluidics is possible. (vii) Bio-medical applications are tempting and challenging.