Electrospinning Technique

by

Assistant ProfessorDr. Akram R. Jabur

Dept. of Materials Eng.University of Technology

Electrospinning

• Uses an electrical charge to draw very fine fibres from a liquid.

•This method ensures that no solvent can be carried over into the final product.

•Ability to produce novel synthetic fibers of small diameter and good mechanical properties.

Advantages

Inexpensive and simple

method

Capable of producing nanofibers

positive terminal

negative terminal

Taylor Conerefers to the cone observed in electrospinning,

electrospraying and hydrodynamic spray processes from which a jet of charged particles emanates above a threshold voltage

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

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

ELECTROSPINNING

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

ning Technique

Advantages

•Able to make very thin fibers easily, since the viscosity of many polymer solutions is very

low .

•The lower viscosity of sample makes an elongational deformation easily.

Disadvantages•The instability of

elongational deformation increases with growing deformation of low viscosity

polymer solutions .

•Beads are more easily formed as the fiber diameter decreases. Beads formation decreases the surface area of fabrics

Process

•Electrospinning:–A high voltage is passed

through a polymer solution inducing an electrostatic repulsion force

–The polymer is pumped through an insulin syringe, the repulsion force results in the formation of a thin jet

–This jet is directed toward a grounded collection plate, the solvent evaporates before hitting the collection plate and results in the formation of a polymer scaffold

Fiber dimension and morphology

•The diameter of a fiber produced by electrospinning primarily depends on the spinning parameters.

•An increase in solution concentration results in fibers with larger diameters.

Parameters

•With increasing concentration of the fiber content, increase in mechanical properties. But further increasing it, mechanical properties drops.

•With increasing electric potential the fiber diameter decreases, and the fiber diameter distribution becomes increasing broader.

Parameters•1 .Molecular Weight of the polymer

2. Solution properties (viscosity, conductivity and surface tension)3. Electric potential, flow rate and concentration4. Distance between the capillary and collection screen5. Ambient parameters (temperature, humidity and air velocity in the chamber)6. Motion of target screen (collector)

2 main Properties of fibers produced

•A very high surface to volume ratio

•Defect free structure at the molecular level

Model of Surface-to-Volume Comparisons…

•Neglecting spaces between the smaller boxes, the volumes of the box on the left and the boxes on the right are the same but the surface area of the smaller boxes added together is much greater than the single box.

Single Box Ratio6 m2

1 m3 = 6 m2/m3

Smaller Boxes Ratio12 m2

1 m3 = 12 m2/m3

Interconnected structure

(Source: Ramakrishna, S., et.al, 2005)

Nanofiber Structures

Filtration

Fiber Type Fiber size, in micrometer

Fiber surface area per mass of fiber material

m2/gPolymeric Nanofibers 0.05 80

Spunbond fiber 20 0.2

Melt blown fiber 2.0 2

Polymeric nanofibers have significant applications in the area of filtration since their surface area is substantially greater and have smaller micropores than any other fibers like spun bond and melt blown (MB) webs.

Potential Applications

Cosmetics- Higher utilization- Higher transfer rate

Drug delivery- Increased dissolution rate- Drug-nanofiber interlace

Electrical conductors- Ultra small devices

Filter media- Higher filter efficiency

Haemostatic devices- Higher efficiency in

fluid absorption

Wound dressing- Prevents scar- Bacterial shielding

Protective clothing- Breathable fabric that

blocks chemicals

Optical applications- Liquid crystal optical

shutters

Sensor devices- Higher sensitivity- For cells, arteries and veins

Material reinforcement- Higher fracture toughness- Higher delamination resistance

Tissue engineering scaffolds- Adjustable biodegradation rate- Better cell attachment- Controllable cell directional growth

Medical prostheses- Lower stress concentration- Higher fracture strength

Polymer Nanofiber

NANOFIBERS

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

NANOFIBERS

  Entrapped pollen spore on nanofiber web [1].