D. Lukáš2010

Physical principles of nanofiber production

1. Needle-less electrospinning

1

3.6. Self-organisation of electrospinning jets on free liquid surfaces

2

Needle electrospinning:Self-organisation of the fluid in electrospinning is the underlying cause behind formation of the Taylor cone, the stable jet part, the whipping zone and evaporation of solvent.

Now, it will be shown that the self-organising potential of electrospinning is even more forcerful since it has a power to organize :

individual jets on free liquid surfaces without any need to use needless / capillaries to create them.

This finding is enormously attractive regarding the recent effort to elevate electrospinning technology to industrial level because it opens a chance to design simple as well as highly productive lines for nanofibrous layer production.

3

4

Epoxy resinEE

no.no.

11 22 33 44

66

1 2 3 4 5 61 2 3 4 5 6

E = 0E = 0E = EE = Ecc

EEcc

A rode instead of a A rode instead of a needleneedle

55

d=1cm

+++

++ ++++

++++++++++++ ++ ++

Stationary wave

F. Sanetrník

Sandra Torres

5

Wave vector

Angular frequency Growth factor

Dynamic phenomenon: field strength increment can lead to unlimited growth of a wave amplitude.

A. SarkarA. Sarkar

tkxiAtx exp,

Amplitude

Clemson University Electrospinning - X-rays 6

ikxAetx t exp, Im

cEE Stable amplitudeStable amplitude

GrowingGrowing amplitude amplitudecEE

tkxiAtx exp, 02

02 Lukas D Sarkar A Pokorny P, SELF ORGANIZATION OF JETS IN ELECTROSPINNING FROM FREE LIQUID SURFACE - A GENERALIZED APPROACH, ACCEPTED FOR PUBLICATION, Journal of Applied Physics, 103 (2008), 309-316.

?,2 kfDispersion lawDispersion law

0E

CEE

D. Lukas, A. Sarkar, and P. Pokorny, Journal of Applied Physics, 103 (2008)

timerelaxation

7

Needleless Electrospinning Prague 2007 8

0202

2

0

kE

xg

t z

Euler equation

gravitationSurface tension

Elektrostatic forces

?2 f

kkEkg 2

022 dispersion law

Velocity potential

/2k

tkxiAtx exp,

0Equation of continuity

Clemson University Electrospinning - X-rays 9

kkEkg 222

Stable waves of various wave numbers and angular frequencies.

Fastest forming instability

The only wave

02

02

Various field Various field strengthsstrengths

tAe Im

cEE

cEE

E

E

Tonks-Frenkel instabilityTonks-Frenkel instability

/0teAtA

Capillary waves

Electrospinning

Relaxation time

qteAtA 0Growth factor 10

11

kkEkg 222 02

02

k

42

4

g

Ec

0k022 gkEk

044222 gEacbD c

Quadratic equation with the only solution

02 cbxax

Critical field strength

12

42

4

g

Ec

g

Ec22

gEc 2

2

1

ga

aEc

2

2

1ce pp

capillary length

13

2

20Ea

Dimensionless electrospinning number

aEc

2

2

1

12

2

cEa

1c

14

Minimal and negative square values of the angular frequency correspond to the maximal growth factors, q’s, inherently connected with the self-organisation caused by the mechanism of the fastest forming instability.

0/2 dkd

kkEkg 222

6

122222

020

2,1

gEEk

+

15

k/2

6

122222

020

2,1

gEEk

gEE

1222

1222

020

4/3

32

a

dimensionless intra-jet distance

Clemson University Electrospinning - X-rays 16

4/3

32

Clemson University Electrospinning - X-rays 17

Linear clefts emit polymeric jets. Linear clefts in (a) and (b) emit polymeric (polyvinyl alcohol) jets at the voltages, 32 kV and 43 kV, respectively. The inter-jet distance / wavelength is . The distance between the cleft and the collector was adjusted on 802 mm.

b

ba EE 32 kV 43 kV

Clemson University Electrospinning - X-rays 18

Technology

Jirsák, O. Sanetrník, F. Lukáš, D. Kotek, V. Marinová, L. Chaloupek, J. (2005) WO2005024101 A Method of Nanofibres Production from A Polymer Solution Using Electrostatic Spinning and A Device for Carrying out The Method.

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