Osmometry and Scattering Methods

Measurements performed to determine the molar masses of polymers yield as a valuable byproduct information on the pair interaction between the macromolecules [30]. The composition dependence of the osmotic pressure Ttosm observed via membrane osmometry is directly related to the chemical potential of the solvent [cf. (14) of Sect. 2] and provides the second osmotic virial coefficient A2, from which Xo the Flory Huggins interaction parameter in the limit of high dilution becomes accessible [cf. (15)]. Such data are particularly valuable because they can be measured with higher accuracy than the x values for concentrated polymer solutions and because they represent a solid starting point for the sometimes very complex function x( p)- In principle, membrane osmometry can also be operated with polymer solutions of different composition in the two chambers (differential osmometry) to gain data for higher polymer concentrations however, little use is made of this option. 

Scattering methods represent another route to A2 and Xm these experiments do not monitor the chemical potential itself but its composition dependence. Light scattering like osmosis can in principle also yield information for polymer solutions beyond the range of pair interaction, but correspcMiding reports are seldom. In contrast, small 

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