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NANO POLYMERS

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INTRODUCTION

The important development due to advancements in Polymer technologies are the production of Nano polymers.
Particles having sizes less than 100nm are generally called Nanoparticles. These have strikingly different properties due to their small sizes and thus are found useful in many applications.
Nanopolymers in simple words are nanostructured polymers. The nanostructure determines important modifications in the intrinsic properties
Polymers are produced by the process of polymerisation.

PROPERTIES OF NANO POLYMERS

The flow induced alignment of nanotubes in a polymer matrix can lead to preferential orientation of the tubes, into either ribbion fibres. Raman spectroscopy is able to determine the degree of shear orientation and the polarization direction of the nanotubes.
The nanofilms show considerable reinforcement when subjected to small deformations, where as at high elongations, the rheology approaches that of the pure nanolatex form.

Vapour condensation process

This process is used to make the metal oxide ceramic nanopolymers.
It involves Vapouration of solid metal followed by rapid condensation to form nano-sized clusters.
Various approaches to Vapourize the metal can be used and variation of the medium in which the Vapour is released affects the size of the particles.
Inert gases are used to avoid oxygen while creating nanopolymers, where as the reactive oxygen is used to produce metal oxide ceramic products.

Electro-spinning method

PRINCIPLE: In the electro-spinning process, the fibres are spun under a high voltage electrical field. A polymer solution is contained in a syringe, which is equipped with a piston and a stainless steel capillary serving as an electrode. A grounded counter electrode (round metal plate at the bottom) is placed down the capillary and a high voltage is applied between the capillary and the counter electrode.

Nanopolymers

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Polymer nanocomposites (PNC) is a polymer or copolymer having dispersed in its nanoparticles. These may be of different shape (e.g., platelets, fibers, spheroids), but at least one dimension must be in the range of 1 to 50 nm. These PNC's belong to the category of multi-phase systems (MPS, viz. blends, composites, and foams) that consume nearly 95% of plastics production. These systems require controlled mixing/compounding, stabilization of the achieved dispersion, orientation of the dispersed phase, and the compounding strategies for all MPS, including PNC, are similar.
The transition from micro- to nano-particles lead to change in its physical as well as chemical properties. Two of the major factors in this are the increase in the ratio of the surface area to volume, and the size of the particle. The increase in surface area-to-volume ratio, which increases as the particles get smaller, leads to an increasing dominance of the behavior of atoms on the surface area of particle over that of those interior of the particle. This affects the properties of the particles when they are reacting with other particles. Because of the higher surface area of the nano-particles, the interaction with the other particles within the mixture is more and this increases the strength, heat resistance, etc and many factors do change for the mixture.
An example of a nanopolymer is silicon nanospheres which show quite different characteristics; their size is 40 – 100 nm and they are much harder than silicon, their hardness being between that of sapphire and diamond.

Bio-hybrid polymer nanofibers

Many technical applications of biological objects like proteins, viruses or bacteria such as chromatography, optical information technology, sensorics, catalysis and drug delivery require their immobilization. Carbon nanotubes, gold particles and synthetic polymers are used for this purpose. This immobilization has been achieved predominantly by adsorption or by chemical binding and to a lesser extent by incorporating these objects as guests in host matrices. In the guest host systems, an ideal method for the immobilization of biological objects and their integration into hierarchical architectures should be structured on a nanoscale to facilitate the interactions of biological nano-objects with their environment. Due to the large number of natural or synthetic polymers available and the advanced techniques developed to process such systems to nanofibres, rods, tubes etc make polymers a good platform for the immobilization of biological objects.[1]

Bio-hybrid nanofibres by electrospinning

Polymer fibers are, in general, produced on a technical scale by extrusion, i.e., a polymer melt or a polymer solution is pumped through cylindrical dies and spun/drawn by a take-up device. The resulting fibers have diameters typically on the 10-µm scale or above. To come down in diameter into the range of several hundreds of nanometers or even down to a few nanometers, electrospinning is today still the leading polymer processing technique available. A strong electric field of the order of 103 V/cm is applied to the polymer solution droplets emerging from a cylindrical die. The electric charges, which are accumulated on the surface of the droplet, cause droplet deformation along the field direction, even though the surface tension counteracts droplet evolution. In supercritical electric fields, the field strength overbears the surface tension and a fluid jet emanates from the droplet tip. The jet is accelerated towards the counter electrode. During this transport phase, the jet is subjected to strong electrically driven circular bending motions that cause a strong elongation and thinning of the jet, a solvent evaporation until, finally, the solid nanofibre is deposited on the counter electrode.

Bio-hybrid polymer nanotubes by wetting

Electro spinning, co-electrospinning, and the template methods based on nanofibres yield nano-objects which are, in principle, infinitively long. For a broad range of applications including catalysis, tissue engineering, and surface modification of implants this infinite length is an advantage. But in some applications like inhalation therapy or systemic drug delivery, a well-defined length is required. The template method to be described in the following has the advantage such that it allows the preparation of nanotubes and nanorods with very high precision. The method is based on the use of well defined porous templates, such as porous aluminum or silicon. The basic concept of this method is to exploit wetting processes. A polymer melt or solution is brought into contact with the pores located in materials characterized by high energy surfaces such as aluminum or silicon. Wetting sets in and covers the walls of the pores with a thin film with a thickness of the order of a few tens of nanometers. Gravity does not play a role, as it is obvious from the fact that wetting takes place independent of the orientation of the pores relative to the direction of gravity. The exact process is still not understood theoretically in detail but its known from experiments that low molar mass systems tend to fill the pores completely, whereas polymers of sufficient chain length just cover the walls. This process happens typically within a minute for temperatures about 50 K above the melting temperature or glass transition temperature, even for highly viscous polymers, such as, for instance, polytetrafluoroethylene, and this holds even for pores with an aspect ratio as large as 10,000. The complete filling, on the other hand, takes days. To obtain nanotubes, the polymer/template system is cooled down to room temperature or the solvent is evaporated, yielding pores covered with solid layers. The resulting tubes can be removed by mechanical forces for tubes up to 10 µm in length, i.e., by just drawing them out from the pores or by selectively dissolving the template. The diameter of the nanotubes, the distribution of the diameter, the homogeneity along the tubes, and the lengths can be controlled.

Applications
The nanofibres, hollow nanofibres, core-shell nanofibres, and nanorods or nanotubes produced have a great potential for a broad range of applications including homogeneous and heterogeneous catalysis, sensorics, filter applications, and optoelectronics. Here we will just consider a limited set of applications related to life science.