elastic conducting polymer composite nanofibers milroy ca 1, ellison c 1, schmidt ce 1,2 1 dept. of...
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Elastic conducting polymer composite nanofibers
Milroy CA1, Ellison C1, Schmidt CE1,2 1Dept. of Chemical Engineering, UT Austin
2Dept. of Biomedical Engineering, UT Austin
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Nanofiber applications
Intelligent Textiles (UK) Centre for Defence Enterprise (CDE)
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Tissue regeneration
• Nanofibers enhance biomaterial interface:
– Mechanical :
– Chemical:
– Electrical:
pyrrole, pTS, FeCl3
pyrrole , pyrrole-COOH,
pTS, FeCl3
COOH
COOH
COOH
EDC, NHS
NGF
PLGA PPyPLGA PPy(COOH)PLGA NGF-PPyPLGA
NH
O
NH
O
NH
O
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Conducting polymerInsulators: <10-8 S/cmSemiconductors: 10-8 – 103 S/cmConductors: >103 S/cmPolypyrrole: 40-200 S/cm S = Siemens (inverse ohms)
Skotheim TA Handbookof Conducting Polym. (1998)
HN -e
HN
NH
HN *
*
X-
X = anion,(e.g. Cl-, ClO4-, etc)
Electroconductive
Biocompatible in vivo
Capable of delivering active compounds
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Conductive nanofibers
Lee, Schmidt (Py-PLGA); Liu, Wallace (Py-SIBS);
Martin (PEDOT-PLGA); Srivastava, Thorsen (Py-PVP)
PLGA nanofibers (electrospun by Dr Aaron Goldstein at Virginia Tech)
HN -e
HN
NH
HN *
*
X-PPy polymerization
Conductive
Nano-fibrous PPy-coated PLGA nanofibers
PLGA: poly(lactic acid-co-glycolic acid)
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Conductive elastomer
Polypyrrole (PPy) Polyurethane (PU)
Carbothane® TPU PC-3585A (Lubrizol)
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Synthesis of PPyPU
Dissolve PU in chloroform
(CHCl3)
add pyrrole, surfactant
(SDS)
30 minutes stir time
add aqueous initiator (FeCl3) dropwise via
syringe
3 hours of vigorous
stirring
Precipitate product
(pure ethanol)
• Films• Foams• FIBERS
Broda, Lee. JBMR-A, 2011.
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Emulsion polymerizationPyrrole
Fe3+ Fe2+
Polypyrrole
- --
--- Micelle
HN
HN
NH
HN*
n
X-
-
-
--
-
monomer
polymer
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Methods
Electrical conductivity Mechanical properties• ASTM 412D (tensile
testing of elastomers)• INSTRON™ 3345• 10N, 50N loadcell• rectangular strips• vice grips• 5 mm/min
Rs = R*W/D
W
D
Electrospinning parameters:• raw material: 5:1 (PU:Py) dissolve to 8 wt% PyPU in CHCl3
• configuration: 10 cm collection distance, 12 kV voltage, 3 mL/hr flow rate
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Nanofiber dimensions
PPyPU composite fibers:0.771 µm (mean)0.372 µm (std. dev)
Polyurethane fibers: 2.407 µm (mean) 1.097 µm (std. dev)
2 µm 2 µm
2 µm 2 µm
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Elastic PPyPU nanofibers
Young’s Modulus: ~ 0.616 Mpa
Load at maximum tensile strain: ~ 0.76 N
Tensile strain (mm/mm)
Tens
ile s
tres
s (M
pa)
light
peel
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Conductive PPyPU nanofibersRs values
PPyPU fibers:
Front:38.24 kΩ/sq(δ = 24.57)
Back:29.96 kΩ/sq(δ = 44.73)
Ppy-PLGA:
64 kΩ/sq(δ = 44.73)
2 µm
2µm
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PPy nanoparticles
80 keV, carbon formvar slot grid (imaged by Dwight Romanowicz)
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Future research
• Gordon Wallace collaboration (Wollongong)
1. Commercial electrospinner
2. Controlled polymerization, Py-functionalized CNT
3. Probe sonication, self-assembly
• Additional PU formulations to tune mechanical properties
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Acknowledgements
Dr. Dwight Romanovicz(UT Austin)
Dr. John Hardy(UT Austin)Ben Harrison(Wake Forest)
Willson lab(UT Austin)
Ellison lab(UT Austin)
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Questions?
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Supplemental slides
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Conductive nanofibers
2 µm2 µm200 nm
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Conductive nanofibers
2 µm2 µm
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Rayleigh Instability (revisited)
Governing Equations:• Conservation of Mass (Continuity)• Conservation of Momentum
(Navier-Stokes)
Consider a sinusoidal perturbation to an axisymmetric cylindrical jet:
k : wavenumber ( ) ω : growth rate of perturbation ω > 0 instability grows
ω < 0 instability decaysω = 0 standing wave
Dispersion Relationship
aη
Hohman 01
ω
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Electrospinning Jet Stability
Governing Equations:
R = R(z)
• Jet modeled as a perturbation from a cylinder with dR/dz <<1
• “Leaky Dielectric” Model• Sufficiently Dielectric to
maintain a field tangential to fluid surface
• Poorly conductive, free charge only at surface
• Conservation of Mass • Conservation of Charge
• Momentum Balance (Navier Stokes)
• Effective Electric Field at centerline of jet
Hohman, 2001
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Linear Stability Analysis of JetDispersion Relation:• Apply similar perturbations
• Equation is cubic, thus three branches
• Two destabilizing branches:• Rayleigh mode – is
suppressed as electric field is increased
• Conducting mode – is enhanced as electric field is increased.
• Destabilizing if Re ω > 0
Dispersion relations when > 0
Hohman 01
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Methods (fiber optimization) Parameter Setpoints____ solvent type CHCl3, THF, HFIP polymer wt.% 8wt%, 10wt%, 12wt% E-field strength 12 kV, 15 kV polymer flow rate 3 mL/hr, 5 mL/hr collection distance 8 cm, 10 cm
** Normal spinning time: 30 minutes
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SEM from Xia 04
Methods (electrospinning)
Taylor Cone
Stable Jet
Bending Instability
Diagram adapted from Bhardwaj 2010
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Thermogravimetric Analysis
Polyurethane Polypyrrole - polyurethane composite(5:1 ratio, PU:Py)