Elastic conducting polymer composite nanofibers

Milroy CA1, Ellison C1, Schmidt CE1,2 1Dept. of Chemical Engineering, UT Austin

2Dept. of Biomedical Engineering, UT Austin

Nanofiber applications

Intelligent Textiles (UK) Centre for Defence Enterprise (CDE)

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

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

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)

Conductive elastomer

Polypyrrole (PPy) Polyurethane (PU)

Carbothane® TPU PC-3585A (Lubrizol)

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.

Emulsion polymerizationPyrrole

Fe3+ Fe2+

Polypyrrole

- --

--- Micelle

HN

HN

NH

HN*

n

X-

-

-

--

-

monomer

polymer

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

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

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

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

PPy nanoparticles

80 keV, carbon formvar slot grid (imaged by Dwight Romanowicz)

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

Acknowledgements

Dr. Dwight Romanovicz(UT Austin)

Dr. John Hardy(UT Austin)Ben Harrison(Wake Forest)

Willson lab(UT Austin)

Ellison lab(UT Austin)

Questions?

Supplemental slides

Conductive nanofibers

2 µm2 µm200 nm

Conductive nanofibers

2 µm2 µm

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

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

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

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

SEM from Xia 04

Methods (electrospinning)

Taylor Cone

Stable Jet

Bending Instability

Diagram adapted from Bhardwaj 2010

Thermogravimetric Analysis

Polyurethane Polypyrrole - polyurethane composite(5:1 ratio, PU:Py)