1. Advanced Manufacturing Choices
ENG
Spring 2016, Sunny Holmberg
Electrospinning
2/19/2018

2. Content Electrospinning Near-Field Electrospinning
Electrospinning Setup
Working Principle
Parameters
Modified Electrospinning Setups
Near-Field Electrospinning
Electro-Mechanical Spinning
2/19/2018

3. Electrospinning
Electrospinning is a cost-effective method to produce novel fibers with diameters from less than 3 nm to over 1 mm.
Common electrospinning setups require only a small amount of investment, often as low as $2,000.
To set-up a lab-scale electrospinning unit there is no need of special laboratory facilities and the space needed is only of the order of 10ft2.
Numbers of scientific publications on electrospinning from 1995 with keywords
"electrospinning" or "electrospun”. 3 3 3 3 3 3 4 4 4 3 3

4. Electrospinning - Working Principle3 3 3 3 3 3 4 4 4 3 3

5. Electrospinning Setup
A high voltage power supply (normally working in a range between 10 and 30kV);
A polymer reservoir that can maintain a constant flow rate of solution, commonly a syringe connected to either a mechanical or a pneumatic syringe pump;
A conductive dispensing needle as polymer source connected to the high voltage power supply;
4. A conductive substrate, normally grounded, which serves as a collector for the electrospun fibers. 3 3 3 3 3 3 4 4 4 3 3

6. Electrospinning Setup3 3 3 3 3 3 4 4 4 3 3

7. Electrospinning – Taylor cone
Sequence of pictures of the evolution of the shape of a fluid drop with high electric field applied. The time zero was taken to be the frame in which the jet first appeared. The electrical potential was applied for a little more than 28 ms earlier.
D. H. Reneker and A. L. Yarin. Electrospinning jets and polymer nanofibers. Polymer, 49(10):2387{2425, 2008. 3 3 3 3 3 3 4 4 4 3 3

8. Electrospinning – Bending Instabilitiesz h A B l
Polymer Source
Grounded Substrate
The jet is considered to be a series of electrically charged beads (“computational beads”), with each bead carrying the same mass of fluid and excess charge.
Stress pulling B back to A (Maxwell fluid)
E: elastic modulus
μ: viscosity
Momentum balance of bead B
V0: applied voltage
: cross section radius
Velocity of bead B
Reneker, D H. (2000). Bending instability of electrically charged liquid jets of polymer solutions in electrospinning. Journal of applied physics, 87(9), 3 3 3 3 3 4 4 4 3 3 3

9. Electrospinning – Model3 3 3 3 3 3 4 4 4 3 3

10. Modified Electrospinning Setups – Aligned fibers
Rotating Drum
Standard Collector
Rotating Drum 3 3 3 3 3 3 4 4 4 3 3

11. Modified Electrospinning Setups – Aligned fibers
Electric Field Manipulation
D. Li, Y. Wang, and Y. Xia. Electrospinning of polymeric and ceramic nanofibers as uniaxially aligned arrays. Nano letters, 3(8):1167{1171, 2003. 3 3 3 3 3 3 4 4 4 3 3

12. Modified Electrospinning Setups – Aligned fibers
Magnetic Field Manipulation
D. Yang, B. Lu, Y. Zhao, and X. Jiang. Fabrication of aligned fibrous arrays by magnetic electrospinning. Advanced materials, 19(21): , 2007. 3 3 3 3 3 3 4 4 4 3 3

13. Modified Electrospinning Setups - Forcespinning 3 3 3 3 3 3 4 4 4 3 3

14. Electrospinning – Parameters
Polymer precursor material.
Solvent and solution additives.
Polymer concentration.
Needle-to-collector distance.
Voltage.
Flow rate.
To optimize material properties, fibers thickness, homogeneity, density, distribution…
10kV
15kV
20kV 3 3 3 3 3 4 4 4 3 3 3

15. Large Scale Electrospinning3 3 3 3 3 3 4 4 4 3 3

16. FFES applications
*S. Ramakrishna MaterialsToday 9(3), 40 (2006)

17. Near Field Electrospinning3 3 3 3 3 3 4 4 4 3 3

18. Near Field Electrospinning
Needle-substrate distance : < 1cm
Voltage : 1-5 kV
Slower yield of nanofibers
Control individual fibers patterning
Challenge:
make the fiber thinner while maintaining the patterning control.
Sun, D. (2006). Near-field electrospinning. Nano letters, 6(4), 839-. 3 3 3 3 3 3 4 4 4 3 3

19. Electro-Mechanical Spinning
Solution:
Minimize instabilities lowering the voltage and combine the use of electrical forces with mechanical pulling to thin the fiber: Electro- Mechanical Spinning (EMS)
This requires:
Jet initiation step.
Optimization of the viscoelastic properties of the polymer solution.
Control of voltage and stage speed. 3 3 3 3 3 3 4 4 4 3 3

20. Distinguishing EMS from NFES
NFES: ROA ≥ ROP
ROA: Rate of Attraction – rate at which the electric field draws the fibrous jet from the polymer meniscus
ROP: Rate of Pull – rate at which stage mechanically pulls at the fiber
ROA > ROP
ROA = ROP
Copper Plate
Needle
Jet
Substrate
Needle OR
Jet
Example of pattern made with NFES
Substrate
Copper Plate

21. Distinguishing EMS from NFES
NFES: ROA < ROP
ROA: Rate of Attraction – rate at which the electric field draws the fibrous jet from the polymer meniscus
ROP: Rate of Pull – rate at which stage mechanically pulls at the fiber
ROA < ROP
SEM
Copper Plate
Needle
Jet
Substrate
Example of pattern made with EMS

22. Electro-Mechanical Spinning
Jet Initiation 3 3 3 3 3 3 4 4 4 3 3

23. Electrostatic Initiation Video: From the Side

24. Electrostatic Initiation
Method
Diameter (nm)
Manual initiation
936.4 ± 431.4
Electrostatic initiation
492.6 ± 296.8
Reduction
47 ± 31%

25. Electro-Mechanical Spinning
Voltage Control
600 V
300 V 3 3 3 3 3 3 4 4 4 3 3

26. Electro-Mechanical Spinning
Voltage Control
1μm
300V
200V
Bisht GB, Canton G, Mirsepassi A, Kulinsky L, Oh S, Dunn-Rankin D, Madou MJ. Controlled Continuous Patterning of Polymeric Nanofibers on 3D Substrates Using Low-Voltage Near-Field Electrospinning, Nanoletters, 2011; 11 (4): pp 1831–1837 3 3 3 3 3 3 4 4 4 3 3

27. Electro-Mechanical Spinning
Stage Speed Control
Stage speed
(mm s-1)
Diameter
(nm) 20
422 40
365 60
204 80
185
Bisht GB, Canton G, Mirsepassi A, Kulinsky L, Oh S, Dunn-Rankin D, Madou MJ. Controlled Continuous Patterning of Polymeric Nanofibers on 3D Substrates Using Low-Voltage Near-Field Electrospinning, Nanoletters, 2011; 11 (4): pp 1831–1837 3 3 3 3 3 3 4 4 4 3 3

28. Electro-Mechanical Spinning
Other results
20nm range nanofibers
Suspended nanofibers 3 3 3 3 3 3 4 4 4 3 3

29. Electro-Mechanical Spinning
Suspended Carbon Nanofibers
20μm
Probing pads
Carbon walls
Carbon wall
Suspended Fibers 3 3 3 3 3 3 4 4 4 3 3

30. Applications

31. Nanogap electrodes based on C-MEMS & electromechanical spun carbon nanofibers
C-MEMS/EMS
Pyrolysis
Breakdown by
Joule heating
Platforms for the electrical characterization at the nanometric or molecular scale.

32. Questions?
Thank You! 3 3 3 3 3 3 4 4 4 3 3

33. 3 3 3 3 3 3 4 4 4 3 3