Turbidity and Molecular Weight of Polymer

The light scattering of solutions may now be related to the solute molecular weight by substituting idTL/dc)T into Eq. (4.74). Representing the osmotic pressure for a monodisperse (i.e., single molecular weight) solute by a virial equation [cf. Eq. (4.41)] in the form 

It is also customary to define another optical constant K such that with sub-stutution from Eq. (4.80) one obtains (Rudin, 1982)  

Hence M and A2 can be determined from a plot of KeJR g against e (see Problem 4.12) in the same way as from the plot of Hejr versus e using Eq. (4.79). 

The molecular weight obtained by application of Eq. (4.82) to a poly disperse polymer will be some average over the molecular weight distribution characteristic of the polymer. It can be easily shown that the molecular weight determined from light scattering measurement is Mw (see Problem 4.13). 

Problem 4.10 Given below are typical light scattering data for solutions of polystyrene in benzene ho = 1.5010) with A = 4358 A at 20°C  

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