Electrospinning of nanofibers 2

As defined by the Non – woven industry, nanofiber is any fiber that has a diameter of less than 1 micron (<1000 nm) (Hegde, R.R. et al, 2005).,[object Object]

NANOFIBERS Figure 2. Entrapped pollen spore on nanofiber web [1].

NANOFIBERS Figure 3. Comparison of red blood cell with nanofibers web [1].

NANOFIBERS Figure 4. Ultra – Web® Nanofiber Filter Media used commercially. (taken from Grafe, 2003)

First nanofibers produced in the Material Science Lab, IMSP, UPLB Figure 5.Polycaprolactonenanofiber (a) and (b) has fiber diameters between 273 nm to 547 nm. SEM taken with 10,000X magnification. (J.I.Zerrudo, E.A.Florido, 2008)

First nanofibers produced in the Material Science Lab, IMSP, UPLB Figure 6. 75:25 Polycaprolactone(PCL)/Polyethylene Oxide (PEO) blend nano10,000X magnification. (J.I.Zerrudo, E.A.Florido, SPP Physics Congress, October 2008)

First nanofibers produced in the Material Science Lab, IMSP, UPLB Figure 7. SEM Micrograph of Poly(DL-lactide-co-glycolide) nanofibers With diameter range of 59nm-126 nm. (J.Clarito, E.A.Florido, October 2008)

First nanofibers produced in the Material Science Lab, IMSP, UPLB Figure 8. SEM Micrograph of Poly(DL-lactide-co-glycolide) nanofibers with diameters of 86 nm, 194 nm, 201 nm. (J.Clarito, E.A.Florido, October 2008)

First nanofibers produced in the Material Science Lab, IMSP, UPLB Figure 9. SEM Micrograph of Poly(DL-lactide-co-glycolide) nanofiber mesh. (J.Clarito, E.A.Florido, October 2008)

First nanofibers produced in the Material Science Lab, IMSP, UPLB Figure 10. SEM Micrograph of Polyvinyl chloride nanofiber with at least 76 nm diameter. (J.Garcia, E.A.Florido, February 2009)

First nanofibers produced in the Material Science Lab, IMSP, UPLB Figure 11. 22 nm-diameter polyvinyl chloride nanofiber with a porous microfiber in the background. (J.Garcia, E.A.Florido, February 2009)

Applications of Nanofibers ,[object Object]

Tissue and Organ Implants (RAMAKRISHNA, S.M., et al. 2004)‏

Extra Cellular Matrix (QUEEN, 2006)‏,[object Object]

ELECTROSPINNING ,[object Object]

The high voltage produces an electrically charged jet of polymer solution or melt, which dries or solidifies leaving a polymer fiber

the process was patented in 1934 by Formhals [2-4],[object Object]

ELECTROSPINNING Figure 13 The distribution of charge in the fiber changes as the fiber dries out during flight

Figure 14. Electrospinning set-up in the IMSP Physics Division Materials Science Laboratory. J.I.Zerrudo, E.A. Florido

was described by Sir Geoffrey Ingram Taylor in 1964 before electrospray was "discovered“

to form a perfect cone required a semi-vertical angle of 49.3° (a whole angle of 98.6°) , the shape of such a cone approached the theoretical shape just before jet formation – Taylor Angle,[object Object]

Taylor Cone Potential Equipotential surface The zero of the Legendre polynomial between 0 and pi is 130.70990 which is the complement (supplement) of the Taylor angle.

Taylor Cone When a sufficiently high voltage is applied to a liquid droplet, the body of the liquid becomes charged, and electrostatic repulsion counteracts the surface tension and droplet is stretched, at a critical point a stream of liquid erupts from the surface. This point of eruption is known as the Taylor cone

Classical liquid jet  0.1mm Orifice – 0.1mm Primary jet diameter ~ 0.2mm Micro-jet diameter ~ 0.005mm ,[object Object]

electrostatic pulling limited to

l/d ~ 1000 by capillary instability ,[object Object]

draw ratio ~106 !NANOFIBRES T. A. Kowalewski, A. L. Yarin & S. Błoński, EFMC 2003, Toulouse

Taylor Cone. J.T.Garcia, E.A. Florido

Electrospinning v=0.1m/s moving charges e bending force on charge e E ~ 105V/m viscoelastic and surface tension resistance Moving charges (ions) interacting with electrostatic field amplify bending instability, surface tension and viscoelasticity counteract these forces NANOFIBRES T. A. Kowalewski, A. L. Yarin & S. Błoński, EFMC 2003, Toulouse

Electro-spinning Simple model for elongating viscoelastic thread Stress balance:  - viscosity, G – elastic modulus stress,  stress tensor, dl/dt – thread elongation Momentum balance: Vo – voltage, e – charge, a – thread radius, h- distance pipette-collector Kinematic condition for thread velocity v Non-dimensional length of the thread as a function of electrostatic potential NANOFIBRES T. A. Kowalewski, A. L. Yarin & S. Błoński, EFMC 2003, Toulouse

Electro-spinning bending instability of electro-spun jet charges moving along spiralling path E ~ 105V/m Bending instability enormously increases path of the jet, allowing to solve problem: how to decrease jet diameter 1000 times or more without increasing distance to tenths of kilometres NANOFIBRES T. A. Kowalewski, A. L. Yarin & S. Błoński, EFMC 2003, Toulouse

Parameters Molecular Weight, Molecular-Weight Distribution and Architecture (branched, linear etc.) of the polymer Solution properties (viscosity, conductivity & and surface tension) Electric potential, Flow rate & Concentration Distance between the capillary and collection screen Ambient parameters (temperature, humidity and air velocity in the chamber) Motion of target screen (collector)

Fibers produced during electrospinning. J.I.Zerrudo, E.A. Florido

PVC Fibers produced during electrospinning. J.T.Garcia, E.A. Florido

Electrospinning of nanofibers 2

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