instability mechanisms of electrically charged liquid jets in electrospinning vs. electrospraying
DESCRIPTION
INSTABILITY MECHANISMS of ELECTRICALLY CHARGED LIQUID JETS in ELECTROSPINNING vs. ELECTROSPRAYING. A.L. Yarin Department of Mechanical Eng. UIC, Chicago. Acknowledgement. D.H. Reneker E. Zussman A.Theron S.N. Reznik A.V. Bazilevsky C.M. Megaridis R. Srikar, S.Sinha Ray - PowerPoint PPT PresentationTRANSCRIPT
INSTABILITY MECHANISMS of ELECTRICALLY CHARGED LIQUID
JETS in ELECTROSPINNING vs. ELECTROSPRAYING
A.L. Yarin
Department of Mechanical Eng. UIC, Chicago
Acknowledgement
• D.H. Reneker• E. Zussman• A.Theron• S.N. Reznik• A.V. Bazilevsky• C.M. Megaridis• R. Srikar, S.Sinha Ray• Israel Science Foundation, Volkswagen Stiftung-
Germany, National Science Foundation through grants NSF-NIRT CBET 0609062 and NSF-NER-CBET 0708711-U.S.A.
Outline
1. Basic physics of the process: bending 2. Branching 3. Multiple jets 4. Needleless electrospinnning 5. Buckling 6. Self-assembly: Nanoropes and crossbars 7. CNT-containing nanofibers 8. Co-electrospinning: nanotubes&nanofluidics
Queen Elizabeth I was interested in electricity
William Gilbert made experiments for the Queen
In 1600 Gilbert published a book on his experiments
Modern Reproduction
Modern reproduction
Modern reproduction
G.I.Taylor’s Experiments with Glycerin
Electrospraying
Modern reproduction
Modern reproduction
Splaying
Nanofibers (Definition)
30,000 Volt
Basic Physics of Electrospinning
Electrospinning Setup
Process Initiation: Taylor Cone
Yarin A L, Reneker D H, Kombhongse S, J. App. Phys. 90, 2001
Theoretical Model of Theoretical Model of Jet InitiationJet Initiation
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
ExperimentExperimenton Jet Initiationon Jet Initiation
ExperimentExperimenton Jet Initiationon Jet Initiation
# 1
# 2 # 3
Experiment vs. Experiment vs. TheoryTheory
-1.0 -0.5 0 0.5 1.0
r
2.0
1.5
1.0
0.5
0
z
109
8
98
76
7
65
54
43
21
21
10
3
ExperimentExperimentvs. Theoryvs. Theory
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
The Reynolds number
The electrical Bond number
20
E
a EBo
0 0V aRe
The initial contact angle
Theoretical Model of JetTheoretical Model of JetInitiationInitiation
1.5
1.0
0.5
0.5
1.0
1.5
2.0
r
2
1
z
0
z
EBo 5.06
/ 3
The critical semi-angle: Taylor-49.3º,
The analytical model, numerics&experiment-33.5º
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
EBo 5.29
/ 3
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
EBo 3.24
/ 2
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
EBo 2.25
0.8
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
EBo 2.25
0.8
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
EBo 2.25
0.82
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
E
E
E
E
1 Bo 1.1
2 Bo 1.2
3 Bo 1.3
4 Bo 2.25
0.8
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
1 – radial velocity at the surface2 – vertical velocity at the surface
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
Critical electric Bond number vs. static contact angle
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
Predicted electric current vs. applied voltage
Theoretical ModelTheoretical Modelof Jet Initiationof Jet Initiation
Predicted convective and conductiveparts of the electric current
E
E
E
E
1 Bo 5.29
2 Bo 9
3 Bo 16
4 Bo 25
– Dielectric constant
– Electric conductivity
– Surface tension
a0 – Droplet diameter
– Viscosity
– Mass density
V0 – Characteristic fluid velocity in droplet
V* – Characteristic velocity in jet
l – Characteristic length scale
H – Hydrodynamic characteristic time
C – Characteristic charge relaxation time
Re – Reynolds number
Electrically-driven bending instability
A collection of point charges cannot be maintained at equilibrium: Earnshaw theorem
The Electrospinning Mechanism
1. Reneker D H, Yarin A L, Fong H, Koombhongse S, J. App. Phys. 87, 20002. Reznik S N, Yarin A L, Theron A, Zussman E, J. Fluid Mech. 516, 2004
The “Taylor cone” droplet
Jet initiation
Modern reproduction
Modern reproduction
Basic Equations: Discretized Quasi-one-dimensional Equations
Electrically-driven Bending Instability
time
i
i= N
i+ 1
i - 1
i = 1
i =1
F0 ~ q.E
Fve ~ velocity difference
Fc ~ coulomb force
i =1
i =2
time
i = 1
i = 101
time
i + 1i
i - 1
Fcap ~ surface tension effects from local curvature and cross section
Electrospinning of Polymer Solutions
Reneker D H, Yarin A L, Fong H, Koombhongse S, J. App. Phys. 87, 2000
Yarin A L, Koombhongse S, Reneker D H, J. App. Phys. 89, 2001
Electrospinning of Polymer Solutions
Reneker, Yarin, Fong, Koombhogse
Electrospinning of Polymer Solutions
Reneker, Yarin, Fong, Koombhongse
0 ms 16.5 ms 18 ms 22 ms
24.5 ms 30.5 ms 31.5 ms 32 ms
37.5 ms 38.5 ms
Reneker D H, Yarin A L, Fong H, Koombhongse S, J. App. Phys. 87, 2000
Nanofiber Garlands
Reneker D H, Kataphinan W, Theron A, Zussman E, Yarin A L, Polymer 43, 2002
Electrospinning of PCL photographed at 2000fps (playback speed = 30fps)
2m
8m
200nm 20m
1m1m
As-spun Polymer Nanofibers
PEO
PCL
SiloxanePolyacrylic acid
PVA PPV
Branching in PCL Electrospinning
Yarin A L, W. Kataphinan, D.H. Reneker J. Appl. Phys. 98, 064501 (2005)
Branching in PCL Electrospinning
Branching in PCL Electrospinning
Experiment with a 3x3Experiment with a 3x3 SetupSetup
S.A.Theron, A.L. Yarin, E. Zussman, E. Kroll, Polymer, 46, 2005
Experiment with a 9x1 Experiment with a 9x1 SetupSetup
Multiple JetMultiple Jet ElectrospinningElectrospinning
Theoretical ModelTheoretical Modelof 3x3 Multiple Jetsof 3x3 Multiple Jets
Theoretical ModelTheoretical Modelof 3X3 Multiple Jetsof 3X3 Multiple Jets
Theoretical ModelTheoretical Modelof 3x3 Multiple Jetsof 3x3 Multiple Jets
Theoretical ModelTheoretical Modelof 3x3 Multiple Jetsof 3x3 Multiple Jets
Theoretical ModelTheoretical Modelof 9x1 Multiple Jetsof 9x1 Multiple Jets
Theoretical ModelTheoretical Modelof 9x1 Multiple Jetsof 9x1 Multiple Jets
Theoretical ModelTheoretical Modelof 9x1 Multiple Jetsof 9x1 Multiple Jets
a
b
c
f
d
e
H
Upward Needleless Electrospinning of Multiple Nanofibers
a- Layer of magnetic fluidb- Layer of polymer solution
Yarin&Zussman Polymer 45, 2977-2980 (2004)
Magnetic Fluid Cones
Perturbed Outer Surface of Polymer Solution
Electrospinning of Multiple Nanofibers
As-spun Nanofibers
Buckling of Electrified Jets
Han,Reneker,Yarin, Polymer 48, 6064-6076 (2007)
Buckling of Electrified Jets
Han,Reneker,Yarin, Polymer 48, 6064-6076 (2007)
Self-assembly: Nanoropes and Crossbars.A Sharpened Wheel – Electrsostatic Lens
Experimental setup
Plot of the electric field strength in the region of the wheel
Tip of
the wheel
Axis of
the wheel
Theron A, Zussman E, Yarin A L, Nanotechnology 12, 2001
Tip of wheel
Tip of syringe
3D Nano-structuresA rotating table on the wheel collector enables collection of multiple nanofiber layers at different angles.
Theron A, Zussman E, Yarin A L, Nanotechnology 12, 2001
Aligned Nanofibers: 2D Arrays
Fiber Diameter: 100nm - 500nm
Pitch: 1m - 1.5m
2m
2m
Nanoropes
5m
2m
Diameter: 50nm - 100nmPitch: 2 m - 3m.
3D Nanocrossbars
Theron A, Zussman E, Yarin A L, App. Phys. Lett. 82, 2003
0 180
Sink flow
CNT
~200 nm
CNTs in Polymer Solution (PEO)
CNT Alignment During Electrospinning of Polymer Solutions
Dror Y, Salalha W, Khalfin R, CohenY,Yarin A L, Zussman E, Langmuir 19, 2003; Langmuir, 20, 2004.
CNTs Embedded and Aligned in Electrospun Nanofibers
50nm
50nm
Single-wall carbon nanotubes embedded in nanofiber
Multi-wall carbon nanotube
embedded in nanofiber
1st CNT
2st CNT
Overlap area
Co-electrospinning: Compound Nanofibers
Solution: PEO (1e6) 1% in ethanol/water
Inner solution contains 2% bromophenolOuter solution contains 0.2% bromophenol
Sun Z, Zussman E, Yarin A L, Wendorff J H, Greiner A, Advanced Materials 15, 2003
and Nanotubes
Co-electrospinning
Zussman E, Yarin A L, Bazilevsky A.V., R. Avrahami, M. Feldman, Advanced Materials 18, 2006
Core: PMMA
Shell: PAN
Carbonization
Core: PMMA
Shell: PAN
Turbostratic Carbon Nanotubes
Core: PMMA
Shell: PAN
Core Entrainment Problems
Core: PMMA
Shell: PAN
Numerical Simulation: Numerical Simulation: Core-shell JetCore-shell Jet
(a) (b)
S.N. Reznik, A.L. Yarin, E. Zussman, L. Bercovici. Phys. Fluids v. 18, 062101 (2006)
Co-electrospinning with Protrusion
Zussman E, Yarin A L, Bazilevsky A.V., R. Avrahami, M. Feldman, Advanced Materials v. 18, 348-353 (2006).
Stress level at the interface:~ 5000 dyne/(square cm)
Optical appearance of a PMMA/PAN emulsion about 1 dayafter mixing of a homogeneous blend containing 6 wt% PMMA + 6% PAN in DMF
Core-Shell Nanofibers from PMMA-PAN Emulsion
A.V.Bazilevsky,A.L. Yarin,C.M. MegaridisLangmuir v.23,2311-2314 (2007).
Experimental set-up and hollow carbon tubes
Schematic of the modeled PAN/DMF flow around a sphericalPMMA/DMF droplet trapped over the core-shell Taylor cone
2
r
2
2
r
p v0
1 p v0
R
v 1 (v sin )0
R sin
The Stokes equations inLubrication approximation
'
r r
r
R R R, h( ) ecos
From the continuity eq : v O(Rv / ) v
From the momentum eq :[ p / ]/[ p / R ]
v / v / R
Then, p p( )
Integrating the momentum balance eq using the no-slip&free surface conditions, we find
2
2
h dp dpv
R d 2 R d
and the average velocity in the gap is
h dpV
3 R d
Then intergrating the continuity eq over the gap
3
we arrive at the Reynolds eq
d dp[h sin ] 0
d d
3 3
r
Integrating the Reynolds eq, find pressure
3 Qp (p 0)
2 [1 (e / )]
Also, / p O( / R) 1
2
3 1/ 2
The tip is stretched by the traction
and resists elastically :
2G(L / ) P
which yields
L / [( Q) / ]
For Q 1 mL / h, 0.1s, 0.005 cm,
we deduce L / 10.
Fine emulsion should result in multi-core fibers
Conclusion
(i) Sophisticated nanofibers and nanotubes are relatively easily
achievable.
(ii) In situ self-assembly is possible.
(iii) Jet bending is the leading mechanism. Branching is secondary. No splaying.
(iv) Modeling is quite reliable for jet initiation and bending stages in
both single- and multiple-jets cases.
(v) Core-shell nanofibers and hollow nanotubes can be made.
(vi) Co-electrospun nanofluidics is possible.
(vii) Bio-medical applications are tempting and challenging.