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Elastic conducting polymer composite nanofibers. Milroy CA 1 , Ellison C 1 , Schmidt CE 1,2 1 Dept. of Chemical Engineering, UT Austin 2 Dept . of Biomedical Engineering, UT Austin. Nanofiber applications. Intelligent Textiles (UK) Centre for Defence Enterprise (CDE).
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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
Nanofiber applications Intelligent Textiles (UK) Centre for Defence Enterprise (CDE)
Tissue regeneration • Nanofibers enhance biomaterial interface: • Mechanical : • Chemical: • Electrical:
Conducting polymer Insulators: <10-8 S/cm Semiconductors: 10-8 – 103 S/cm Conductors: >103S/cm Polypyrrole: 40-200 S/cm S = Siemens (inverse ohms) X = anion,(e.g. Cl-, ClO4-, etc) • Electroconductive • Biocompatible in vivo • Capable of delivering active compounds Skotheim TA Handbook of Conducting Polym. (1998)
PPy-coated PLGA nanofibers Conductive nanofibers PLGA nanofibers(electrospun by Dr Aaron Goldstein at Virginia Tech) Lee, Schmidt (Py-PLGA); Liu, Wallace (Py-SIBS); Martin (PEDOT-PLGA); Srivastava, Thorsen (Py-PVP) Nano-fibrous PPy polymerization Conductive PLGA: poly(lactic acid-co-glycolic acid)
Conductive elastomer Polypyrrole (PPy) Polyurethane (PU) Carbothane® TPU PC-3585A (Lubrizol)
Synthesis of PPyPU add aqueous initiator (FeCl3) dropwisevia syringe 30 minutes stir time Dissolve PU in chloroform (CHCl3) add pyrrole, surfactant (SDS) 3 hours of vigorous stirring Precipitate product (pure ethanol) • Films • Foams • FIBERS Broda, Lee. JBMR-A, 2011.
Emulsion polymerization Polypyrrole Pyrrole Fe3+ Fe2+ polymer - - - - - - - Micelle - - - - monomer
Mechanical properties Methods 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 Electrical conductivity ASTM 412D (tensile testing of elastomers) INSTRON™ 3345 10N, 50N loadcell rectangular strips vice grips 5 mm/min Rs = R*W/D W D
Nanofiberdimensions 2 µm 2 µm Polyurethane fibers: 2.407 µm (mean) 1.097 µm (std. dev) PPyPUcomposite fibers: 0.771 µm (mean) 0.372 µm (std. dev) 2 µm 2 µm
Elastic PPyPUnanofibers Young’s Modulus: ~ 0.616 Mpa Load at maximum tensile strain: ~ 0.76 N Tensile stress (Mpa) Tensile strain (mm/mm) light peel
Conductive PPyPUnanofibers Rs 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) 2µm 2 µm
PPy nanoparticles 80 keV, carbon formvar slot grid (imaged by Dwight Romanowicz)
Future research • Gordon Wallace collaboration (Wollongong) • Commercial electrospinner • Controlled polymerization, Py-functionalized CNT • Probe sonication, self-assembly • Additional PU formulations to tune mechanical properties
Acknowledgements Dr. John Hardy (UT Austin) Ben Harrison (Wake Forest) Ellison lab (UT Austin) Dr. Dwight Romanovicz (UT Austin) Willson lab (UT Austin)
Conductive nanofibers 200 nm 2 µm 2 µm
Conductive nanofibers 2 µm 2 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 decays • ω = 0 standing wave • Dispersion Relationship a η ω Hohman 01
Electrospinning Jet Stability • Jet modeled as a perturbation from a cylinder with dR/dz <<1 R = R(z) • “Leaky Dielectric” Model • Sufficiently Dielectric to maintain a field tangential to fluid surface • Poorly conductive, free charge only at surface Governing Equations: • Conservation of Mass • Conservation of Charge • Momentum Balance (Navier Stokes) • Effective Electric Field at centerline of jet Hohman, 2001
Linear Stability Analysis of Jet Dispersion relations when > 0 • Dispersion 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 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
Methods (electrospinning) Taylor Cone Stable Jet Bending Instability SEM from Xia 04 Diagram adapted from Bhardwaj 2010
Thermogravimetric Analysis Polypyrrole - polyurethane composite (5:1 ratio, PU:Py) Polyurethane