Advanced Manufacturing Choices

1. Advanced Manufacturing Choices ENG 165-265 Spring 2016, Sunny Holmberg Electrospinning

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

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”.

4. Electrospinning - Working Principle

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.

6. Electrospinning Setup

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.

8. Electrospinning – Bending Instabilities z Polymer Source h A 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. l V0: applied voltage : cross section radius Stress pulling B back to A (Maxwell fluid) E: elastic modulus μ: viscosity B Momentum balance of bead B Grounded Substrate Velocity of bead B 0 • Reneker, D H. (2000). Bending instability of electrically charged liquid jets of polymer solutions in electrospinning. Journal of applied physics, 87(9), 4531-.

9. Electrospinning – Model

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

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.

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):3702-3706, 2007.

13. Modified Electrospinning Setups - Forcespinning http://fiberiotech.com

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

15. Large Scale Electrospinning

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

17. Near Field Electrospinning

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-.

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.

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 Needle Needle OR Jet Jet Example of pattern made with NFES Substrate Substrate Copper Plate Copper Plate

21. Distinguishing EMS from NFES ROA < ROP 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 Needle SEM Jet Example of pattern made with EMS Substrate Copper Plate

22. Electro-Mechanical Spinning • Jet Initiation

23. Electrostatic Initiation Video: From the Side

24. Electrostatic Initiation

25. Electro-Mechanical Spinning • Voltage Control 600 V 300 V

26. Electro-Mechanical Spinning • Voltage Control 300V 200V 1μm 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

27. Electro-Mechanical Spinning • Stage Speed Control 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

28. Electro-Mechanical Spinning • Other results 20nm range nanofibers Suspendednanofibers

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

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!

33. sholmber@uci.edu