04/21/2304/21/23

Advanced Manufacturing

Choices ENG 165-265

Spring 2014, Dr. Giulia CantonElectrospinning

04/21/23

• Electrospinning – Electrospinning Setup– Working Principle– Parameters – Modified Electrospinning Setups

• Near-Field Electrospinning• Electro-Mechanical Spinning

Content

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”.

Electrospinning Setup

1. A high voltage power supply (normally working in a range between 10 and 30kV);

2. 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;

3. 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.

Electrospinning Setup

Electrospinning - Working Principle

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.

Electrospinning – Bending

Instabilities

Stress pulling B back to A (Maxwell fluid)

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.

Momentum balance of bead B

Velocity of bead B

E: elastic modulusμ: viscosity

• Reneker, D H. (2000). Bending instability of electrically charged liquid jets of polymer solutions in electrospinning. Journal of applied physics, 87(9), 4531-.

z

h

0

A

B

l

Polymer Source

Grounded Substrate

V0: applied voltage

: cross section radius

Electrospinning – Bending

InstabilitiesLongitudinal stress in the rectilinear part of the jet and the longitudinal force.

Electrospinning – Bending

InstabilitiesIllustration of the instability mechanism.

Perturbedpolymer jet

C

B

A

l1

l1

A

B B*

C

θ

l

l

FBC

FAB

FT

δ

Coulombic forces , idealized nodes representation.

Electrospinning – Model

Electrospinning – Parameters

Polymer precursor material. Solvent and solution additives. Polymer concentration. Needle-to-collector distance. Voltage. Flow rate.

10kV 15kV 20kV

To optimize material properties, fibers thickness, homogeneity, density, and distribution.

Large Scale Electrospinning

FFES applications

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

Modified Electrospinning Setups - Forcespinning

http://fiberiotech.com

Modified Electrospinning Setups – Aligned fibers

• Rotating Drum

Standard Collector

Rotating Drum

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.

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.

Near Field Electrospinning

Near Field Electrospinning

• Needle-substrate

distance : < 1cm• Voltage : 1-5 kV• Slower yield of

nanofibers• Control individual fibers

patterningChallenge:make the fiber thinner while maintaining the patterning control.

Sun, D. (2006). Near-field electrospinning. Nano letters, 6(4), 839-.

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.

Electro-Mechanical Spinning

• Jet Initiation

Electro-Mechanical Spinning

• Voltage Control

600 V 300 V

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

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

Stage speed

(mm s-1)

Diameter(nm)

20 422

40 365

60 204

80 185

Electro-Mechanical Spinning

• Other results

Suspended nanofibers20nm range nanofibers

Electro-Mechanical Spinning

• Suspended Carbon Nanofibers

20μm

Probing pads

Carbon walls

Carbon wall

Carbon wall

Suspended Fibers

Electro-Mechanical Spinning

• Suspended Carbon Nanofibers

Applications

Questions?

Thank You!