A.A.T.N.Athauda H.H.S. Chamara S.M. Abeyweera A.C. Darshana M. Amalan

This presentation basically gives about how the nano fiber can be manufactured using Electro spinning process and their readily available applications. Especially about the carbon nano tubes and the polymeric nano fiber structures are discussed along with the nano structure applications.

"The science of small" is truly an interdisciplinary science, in which material scientist, biologists, chemists and Physics share knowledge to extend the Nano-scale boundaries. One billionth of a meter (l0 -9 m) about 80,000 times smaller than a human hair The nano-scale also marks the grey zone where classical laws and quantum - mechanical laws meet each other.

Nano fibers are defined as fibers with diameters on the order of 100 nanometers. Nano fibers have fiber diameters of nanometer (nm) scales that are 5~10 times smaller than smallest melt blown fiber available (AFD <500nm) Nano fibers have several amazing characteristics, such as very large surface area to volume ratio (~1000 m 2 /g).

They can be produced by – Interfacial polymerization – Drawing – Template Synthesis – Phase Separation – Self-Assembly – Electro spinning

Interfacial polymerization is an alternative to bulk polymerization of condensation polymers which would require high temperatures. Two immiscible solvents are used, with monomer in one solvent reacting with monomer in the other solvent. Higher molecular weights are obtained because monomer is more likely to encounter a growing chain than the opposing monomer See Figure

The drawing is a process similar to dry spinning in fiber industry, which can make one-by-one very long single nano fibers. However, only a visco-elastic material that can undergo strong deformations while being cohesive enough to support the stresses developed during pulling can be made into nano fibers through drawing.

The template synthesis, uses a nano porous membrane as a template to make nano fibers of solid (a fibril) or hollow (a tubule) shape. The most important feature of this method may lie in that nanometer tubules and fibrils of various raw materials such as electronically conducting polymers, metals, semiconductors, and carbons can be fabricated. On the other hand, the method cannot make one-by-one continuous nano fibers.

The phase separation consists of dissolution, gelation, extraction using a different solvent, freezing, and drying resulting in a nano scale porous foam. The process takes relatively long period of time to transfer the solid polymer into the nano-porous foam.

The self-assembly is a process in which individual, pre-existing components organize themselves into desired patterns and functions. However, similarly to the phase separation the self-assembly is time-consuming in processing continuous polymer nano fibers.

Electro spinning is the process of using electrostatic forces to distort a pendant droplet of polymer solution into a fine filament to be deposited onto a substrate. Electro spinning shares characteristics of both Electro Spaying (Electro hydrodynamic Atomization) and conventional solution dry spinning of fibers.

Electro spinning is the process of using electrostatic forces to distort a pendant droplet of polymer solution into a fine filament to be deposited onto a substrate. Electro spinning shares characteristics of both Electro Spaying (Electro hydrodynamic Atomization) and conventional solution dry spinning of fibers.

Photograph of a fiber being electro spun from a Taylor cone.

Electrospinning is one of the basic methods for producing fibres with nanometric diameters. It relies on electrostatic forces to produce fibers in the nanometer scale. Under the influence of the electrostatic field, a pendant droplet of the polymer solution at the spinneret is deformed into a conical shape. If the voltage surpasses a threshold value, electrostatic forces overcome the surface tension and a fine charged jet is ejected. See Figure

Photograph of a fiber being electro spun from a Taylor cone

As these electric forces increase, the jet will elongate, accelerate by the electric forces and the solvent evaporates. Splaying occurs in a region in which the radical forces from the electrical charges carried by the jet, become larger than the cohesive forces within the jet, and the single jet divides into many fibers and deposits on a substrate as a random nano fiber mat. See Figure

When a strong electrostatic force is applied to the capillary containing a polymer solution, the solution is ejected from the capillary and deposited as a nonwoven fibrous mat on a template serving as the ground for electric charges

Basic four components 1)High voltage DC power supply 2)Metallic spinneret or pipette 3)Positive displacement syringe pump 4)Collector plate

Realistic View Realistic View

Very large surface area to volume ratio (this ratio for a Nano fiber can be as large as 103 times of that of a microfiber) High porosity Ultra-thin and light weight material Membrane-like textile Possibility of mixture with other Soft touch Superior mechanical performance (stiffness and tensile strength)

A cylinder collector with high rotating speed An auxiliary electrode An auxiliary electrical field A thin wheel with sharp edge A frame collector Oscillating a grounded multi frame collector Multiple field technique

Electro spun nano fibers could be oriented circumferentially. Fiber alignment Speed Cylinder Rotation Speed ~ ~

The auxiliary electrode (grid) made of a plurality of connected aluminum foil strips in 5 mm width, 30 mm long, and 5 mm apart, was placed 8 cm away from the collection mandrel and charged to -8 kV

Electro spun ultrafine fibers with larger diameter

Before reaching the electrically grounded target the nano fibers retain sufficient residual charges to repel each other. Once a nano fiber is attached to the wheel tip, it exerts a repulsive force on the next fiber attracted to the tip. This repulsion from one another results in a separation.

Control the deposition of electro spun polymer nano fibers and even collects nicely aligned fiber yarns.

Ability to produce novel synthetic fibers of unusually small diameter and good mechanical properties. This leads to fiber mats with high surface area to volume ratio and the ability to control pore size. Potential applications for nanometer-diameter polymer filaments including separation membranes, wound dressing materials, artificial organs, nano-composites, and protective clothing

It provides three important advantages over other solvent spinning methods. – Solvent cost will be cancelled. – Does not include any toxic content hence being Environmental friendly. – Solvent can be thought as loss for productivity. Polymer melt will completely electrospun, but solvent will evaporate during solution based electrospinning. No need to prepare solution for thermoplastic fibres.

Viscosity is one of the basic parameters of electrospinning. Polymer melts generally have higher viscosity values than solutions. Heat insulation is compulsory for holding viscosity smaller For melting the polymer, metallic ion parts must be used. That causes electrical discharges more frequently. Many scientists changed polarity to overcome that problem. By changing polarity productivity will decrease and nanofiber diameter will increase

Formation of beads Thick place in a nano fibre Act as a disadvantage when it comes a to the alignment When the viscosity is decreased, the surface tension of the solution is increased, then the inter molecular forces is increased hence forming thick places in the fibre. Beads

Uneven cross section of the fiber surface with pore structure At high temperature, the porosity is less due to the reduction of viscosity in the solution

Military protective clothing Life seeking applications Cosmetic applications Biomedical applications Structural elements in artificial organs Nano-composites Filtering applications Porous membrane Nano sensors

Polymer Nano Fiber Military Protective Clothing  Anti Bio Chemical gases  Minimal impedance to air  Efficiency in trapping aerosol particles Application in Life Seeking  Drug delivery carrier  Wound Dressing  Haemostatic devices Nano Sensors  Thermal sensor  Piezoelectric sensor  Biochemical sensor Tissue Engineering  Porous membrane skin  Tubular shapes for blood vessels and nerves  3D Scaffolds for bone regenerations Cosmetic Skin Mask  Skin Healing  Skin Cleansing  Skin therapy Filter Media  Liquid Filtration  Gas Filtration  Molecular Filtration Other Applications  Micro electronic devices  Electrostatic Dissipation  Electromagnetic shielding

At day 1, the cells were elongated At day 3, there was an increase in cell densities across cell types compared to day 1 At day 7, the cells increase in their numbers significantly and almost reach confluence on the nano fiber mesh

Bio molecular vascular Substitute Wound Dressing

Reference -

Nylon – Nylon 4,6 as nano fiber reinforcement Textile Composites Acetate – Antimicrobial ultrafine cellulose PE – Poly ethylene Glycol Antimicrobial ultrafine cellulose – Poly ethylene oxide [PEO] Carbon Nano tubes Viscose

Polymer specific production. Unable to cover overall applications in textiles due to this. Low production speeds collaborates with higher production cost. Unable to produce a continuous fiber (only fiber webs in tiny lengths) Too fragile to be handled

Continuous fiber yarn made out of electro spun nano fibers (Suit for Textiles) 75m/min production rate (viable in industry) Ease of forming nano fiber made out of different polymer mixtures Ability to mix different fibers composed of different polymer Functionalizing of electro spun fiber is possible Fabrication of ceramic nano fiber through secondary processes

Tube with 100nm of inner diameter and 200nm of outer diameter Having high modulus and tensile strength Has several walls to surround the inner tubes made by poly ethylene oxide [PEO] Diameters are controlled by using an inner liquor (Mineral Oil) 200nm 100nm

In many regions of the electro spun nano fibers the embedded nano tubes appeared to be well-oriented along the fiber axis. Polymer nano fibers reinforced by an embedded oriented system of carbon nano tubes will allow development of advanced materials possessing ultimate tensile strength.

Drug release systems Microelectronics Telecommunications Solar energy conversion Improve electrical properties of fibres Improve thermal properties of textile materials such as silk.

Is there any controlling parameter above or below which the polymer solution is no longer spinnable? How to control or even eliminate defects such as beads and pores Obtain nano fibers with consistent diameter Collecting continuous single nano fibers. Fabrication of nano fibers of other kinds of materials such as metals and ceramics.

 Subbiah, T.; Bhat, G. S.; Tock, R. W.; Parameswaran, S.; Ramkumar, S. S., Electrospinning of Nanofibers. Journal of Applied Polymer Science 2005, 96  esearch.html.      