Determination of molecular weight by Light scattering method.

Due to big size macromolecules in solution, turbidity is produced. The light rays get scattered, when pass through macromolecule solution due to turbidity. The turbidity T is given by

Where I₀ is the intensity of incident light.
Iₜ is the intensity of transmitted light after passing through a solution of length l.
In case of proteins or higher polymers the turbidity is small and is determine from the intensity of light scattered at 90° to the beam. This can be done by using a simple photometer as shown in figure below.

Turbidity increase with increase in concentration as well as molecular weight. The Turbidity is related to molecular weight by the equation given by Debye.
Hc/T=1/M+2Bc
Where B is second virial coefficient and H is a constant.
If we plot a graph between Hc/T vs c we get a straight line with intercept 1/M. Thus

This curve was plotted by Zimm, so is called Zimm's Curve. Thus the curve is a straight line which is extrapolated to zero concentration gives the intercept equal to 1/M can be calculated.

Limitation

1) This method gives wrong results at molecular weight M above 10,000,00.

2) Dust particles also scattered light , hence it causes problem and gives wrong result. Next

Comments

Difference between organic and inorganic polymers.

Difference between organic and inorganic polymers. Definition Organic polymers are the polymers that essentially contain carbon atom in the backbone. Inorganic polymers are the polymers that have no carbon atom in the backbone. Structure Most organic polymers have simple structures. Almost all inorganic polymers are highly branched and have complex structures. Electrical Conductivity In most of the aqueous solutions, organic polymers are typically poor conductors of electricity and heat. Inorganic polymers in aqueous solutions are good conductors of electricity, this is because they have high ability to ionise and this makes them better conductors. Flammability Organic polymers are flammable whereas inorganic polymers are nonflammable. Effect on nature Organic polymers are environmental friendly as these are biodegradable. Inorganic polymers are not environmental friendly as these are non biodegradable. Examples Organic polymers include polysaccharide...

Determination of molecular weight by osmotic pressure method

Determination of molecular weight by osmotic pressure method. Osmotic pressure method is also called membrane osmometry. This method is widely used to determine the number average molecular weight of polymers. This method is based on the phenomenon of osmosis. If a pure solvent is separated from a solution through a semipermeable membrane, due to concentration (chemical potential) difference between the solvent and solution, the solvent will flow into the solution through semipermeable membrane. The pressure applied on the solution to completely stop the flow of solvent into it through semipermeable membrane is called osmotic pressure. The theory of osmotic pressure also applies to a solution of polymers. Ordinary solution obeys Van't Hoff equation i.e π=cRT/M Where π is osmotic pressure, c is concentration in mass per unit volume, R is gas constant, T is temperature and M is molar mass. The polymer solution are non ideal. Taking into account their deviation and us...

Polypropylene (PP)

Polypropylene (PP). Polypropylene (PP) is also known as polypropene. Polypropylene is made from the polymerisation of propylene gas in the presence of Zeiglar Natta catalyst or metallocene catalyst. Polypropylene. Thus propene (or propylene) is the monomer of polypropylene. Polypropylene is a highly flammable material. It is sensitive to microbial attacks, such as bacteria and mold. It exhibits excellent resistance to diluted and concentrated acids, alcohols and bases. Polypropylene is used to make lunch boxes, margarine containers, yogurt pots, syrup bottles etc. Disposable syringes is the most common medical application of polypropylene. Polypropylene rope and twine are very strong and moisture resistant very suitable for marine applications. Polypropylene, highly colorfast, is widely used in manufacturing carpets, rugs and mats. Uses of Polypropylene. Questions on polypropylene; Q1) What is polypropylene? Ans) Polypropylene is a polymer of propylen...

Polymers

Search This Blog