Advanced Manufacturing Choices ENG 165-265 Spring 2014, Dr. Giulia Canton Electrospinning 4/21/2017

Content Electrospinning Near-Field Electrospinning Electrospinning Setup Working Principle Parameters Modified Electrospinning Setups Near-Field Electrospinning Electro-Mechanical Spinning 4/21/2017

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

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

Electrospinning Setup 3 3 3 3 3 3 4 4 4 3 3

Electrospinning - Working Principle 3 3 3 3 3 3 4 4 4 3 3

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

Electrospinning – Bending Instabilities z 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), 4531-. 3 3 3 3 3 4 4 4 3 3 3

Electrospinning – Bending Instabilities Longitudinal stress in the rectilinear part of the jet and the longitudinal force. 3 3 3 3 3 3 4 4 4 3 3

Electrospinning – Bending Instabilities Illustration of the instability mechanism. Perturbed polymer jet C B A l1 B* θ l FBC FAB FT δ Coulombic forces , idealized nodes representation. 3 3 3 3 3 3 4 4 4 3 3

Electrospinning – Model 3 3 3 3 3 3 4 4 4 3 3

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, and distribution. 10kV 15kV 20kV 3 3 3 3 3 4 4 4 3 3 3

Large Scale Electrospinning 3 3 3 3 3 3 4 4 4 3 3

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

Modified Electrospinning Setups - Forcespinning http://fiberiotech.com 3 3 3 3 3 3 4 4 4 3 3

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

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

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. 3 3 3 3 3 3 4 4 4 3 3

Near Field Electrospinning 3 3 3 3 3 3 4 4 4 3 3

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

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

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

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

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

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

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

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

Electro-Mechanical Spinning Suspended Carbon Nanofibers 3 3 3 3 3 3 4 4 4 3 3

Applications

Questions? Thank You! 3 3 3 3 3 3 4 4 4 3 3