Question

Give an example of a material that is processed using plasma processing and write about the structure of that material

Answer 1

Answer :

One of the material processed by plasma processing is polymers.

Polymers prepared by plasma processing is using technology know as plasma polymerisation .

Plasma polymerization (or glow discharge polymerization) uses plasma sources to generate a gas discharge that provides energy to activate or fragment gaseous or liquid monomer, often containing a vinyl group, in order to initiate polymerization. Polymers formed from this technique are generally highly branched and highly cross-linked, and adhere to solid surfaces well. The biggest advantage to this process is that polymers can be directly attached to a desired surface while the chains are growing, which reduces steps necessary for other coating processes such as grafting. This is very useful for pinhole-free coatings of 100 picometers to 1 micrometre thickness with solvent insoluble polymers.

Following mechanism involved :

Glow discharge:

Plasma consists of a mixture of electrons, ions, radicals, neutrals and photons.Some of these species are in local thermodynamic equilibrium, while others are not. Even for simple gases like argon this mixture can be complex. For plasmas of organic monomers, the complexity can rapidly increase as some components of the plasma fragment, while others interact and form larger species. Glow discharge is a technique in polymerization which forms free electrons which gain energy from an electric field, and then lose energy through collisions with neutral molecules in the gas phase. This leads to many chemically reactive species, which then lead to a plasma polymerization reaction. The electric discharge process for plasma polymerization is the “low-temperature plasma” method, because higher temperatures cause degradation. These plasmas are formed by a direct current, alternating current or radio frequency generator.

Reactors used :

There are a few designs for apparatus used in plasma polymerization, one of which is the Bell (static type), in which monomer gas is put into the reaction chamber, but does not flow through the chamber. It comes in and polymerizes without removal.

Characteristics:

The most significant difference between conventional polymers and plasma polymers is that plasma polymers do not contain regular repeating units. Due to the number of different propagating species present at any one time as discussed above, the resultant polymer chains are highly branched and are randomly terminated with a high degree of cross-linking.An example of a proposed structure for plasma polymerized ethylene demonstrating a large extend of cross-linking and branching.

Applications :

Applications ranging from adhesion, composite materials, protective coatings, printing, membranes, biomedical applications, water purification .