ELECTROSPINNING Presented by

A.Akila II yr M.Tech

Nanoscience & TechnologyAnna university-BIT campus

Trichirappalli

Electrospinning uses an electrical charge to draw very fine (typically on the micro or nano scale) fibres from a liquid.

It is a technique for electrostatic fiber formation which utilizes electrical forces to produce polymer fibers with diameters ranging from 2 nm to several micrometers using polymer solutions of both natural and synthetic polymers.

Electrospinning shares characteristics of both electrospraying and conventional solution dry spinning of fibers.

This makes the process particularly suited to the production of fibers using large and complex molecules.

Introduction

This process offers unique capabilities for producing novel natural nanofibers and fabrics with controllable pore structure.

This process of electrospinning has gained much attention not only due to its versatility in spinning a wide variety of polymeric fibers but also due to its ability to consistently produce fibers in the submicron range consistently that is otherwise difficult to achieve by using standard mechanical fiber-spinning technologies techniques

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

Nanofibers (Definition)

High tensile strength stronger than steel (on weight basis )

High extensibility comparable to rubber (elasticity)

Spun Nanofibers Also Offer Several Advantages Such As, An extremely high surface-to-volume ratio Tuneable porosity Malleability to conform to a wide variety of sizes and shapes The ability to control the nanofiber composition to achieve

the desired results from its properties and functionality.

Strong mutual electrical repulsive forces overcome weaker forces of surface tension in the charged polymer liquid.

Principle

Process

It uses an electrostatic forces to produce a fine fibers from polymer solutions or melts and the fibers thus produced have a thinner diameter and a larger surface area than those obtained from conventional spinning processes

Electrospinning is conducted at room temperature with atmosphere conditions.

A DC voltage in the range of several tens of kVs is necessary to generate the electrospinning.

Basically, an electrospinning system consists of three major components:

A high voltage power supply, A spinneret and A grounded collecting plate.

Also it utilizes a high voltage source to inject charge of a certain polarity into a polymer solution or melt, which is then accelerated towards a collector of opposite polarity.

Most of the polymers are dissolved in some solvents before electrospinning.

The polymer fluid is then introduced into the capillary tube .

Capillary tube is subjected to an electric field and an electric charge is induced on the liquid surface due to this field.

When the electric field applied reaches a critical value , the repulsive electrical forces overcome the surface tension forces.

A charged jet of the solution is ejected from the tip of the Taylor cone.

A rapid whipping of the jet occurs in the space between the capillary tip and collector which leads to evaporation of the solvent, leaving a polymer behind.

The jet is only stable at the tip of the spinneret and after that instability starts.

Thus, the electrospinning process offers a simplified technique for fiber formation.

Electrospun nanofibers have been reported as being from various synthetic polymers, natural polymers or a blend of both including proteins , nucleic acids and even polysaccharides.

Typical natural polymers include collagen, chitosan, gelatin , casein, cellulose acetate, silk protein, chitin , fibrinogen etc. Scaffolds fabricated from natural polymers promise better clinical functionality.

Polymers used in this process

Electrospinning with copolymers offers property enhancement of polymeric materials, including tailoring of thermal stability, mechanical strength and barrier properties.

Therefore it has been often pursued for engineering structural applications through methods as copolymerization.

Copolymers

The solvent used in preparing polymer solutions has a significant influence on its spinnability.

Solvents should have some properties such as, good volatility, vapour pressure, boiling point and should maintain the integrity of the polymer solution.

The intermolecular interaction in a polymer–solvent system is either attractive or repulsive which depends solely on the type of solvent.

Solvents used for electrospinning

solvent vapour pressure plays a critical role in determining the evaporation rate and the drying time.

Solvent volatility also plays a significant role in the formation of nanostructures as it influences the phase separation process.

The properties of solvents have a profound effect on fiber diameter.

Different properties of solvents such as surface tension, dielectric constant and boiling point that should be kept in mind during selection for electrospinning process.

Electrospinning process is solely governed by , Solution parameter. Process parameter. Ambient parameter.

Solution parameters includes, viscosity, conductivity, molecular weight, and surface tension and

Effects of various parameters on electrospinning

Process parameters includes, applied electric field, tip to collector distance and feeding or flow rate.

Each of these parameters significantly affect the fibers morphology obtained as a result of electrospinning.

Ambient parameters includes, the humidity and temperature of the surroundings.

This also plays a significant role in determining the morphology and diameter of electrospun nanofiber.

The characterization of fibers produced by the electrospinning process remains one of the most difficult tasks as the chances of getting single fibers are rare.

Generally in electrospinning, the spun fibres are characterized into three distinct categories:

Geometrical characterizations Chemical characterizations. Mechanical characterization .

Characterizations of electrospun nanofibers

Geometrical characterizations Geometric properties of nanofibers include fiber diameter,

diameter distribution , fiber orientation, and fiber morphology. For the characterization of geometric properties, techniques such

as scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) are used.

Chemical characterizations By using this ,Not only the structure of the two materials can be

detected but the intermolecular interaction can be determined by the use of these methods

The characterization of the molecular structure of a nanofiber can be done by Fourier transform infra red (FTIR) and nuclear magnetic resonance (NMR) techniques.

Mechanical characterizations Precise measurement of mechanical properties of the nanofibrous

matrix is crucial, especially for biomedical applications. Mechanical characterization is achieved by applying tensile test

loads to specimens prepared from the electrospun process. mechanical characterization of nanofibers can be done by

nanoindentation, bending tests, resonance frequency measurements, and microscale tension tests.

High surface to volume ratio

Very high porosity Enhanced physico-mechanical properties

Manipulation of the solution and process parameters can be easily done to get the desired fiber morphology and mechanical strength.

Advantages

Applications

Electrospinning is a simple, versatile, and cost-effective technology which generates non-woven fibers with high surface area to volume ratio, porosity and tunable porosity.

Melt electrospinning, an alternative means of electrospinning , apart from solution, is also available that is done with polymer melts, which alleviates the requirement of solvents.

Despite of several advantages and success of electrospinning there are some critical limitations in this process such as small pore size and lack of proper cellular infiltration inside the fibers.

In general, the electrospinning process shows excellent promise for tissue engineering and regenerative medicine.

Conclusion