Structure and properties of polymers in semidilute solution

Long-chain molecules in dilute solution influence a region of space large with respect to the sum of the volumes of the individual mers. This cc ept was expressed in terms of the pervaded volume, Vp = (4jt/3) R, in Chapter 5. When the sum of the pervaded volumes of the solute macromolecules equals the macroscopic solution volume, the solution can no longer be considered dilute. It is convenient to define a crossover concentration (c ) to the semidilute regime as  

It will be shown that many of the properties of polymer solutions in the semidilute regime depend in a detailed way on the value of the crossover concentration, c.  

This phenomenon is explained in detail in Section 6.3. Many properties of polymer solutions in the semidilute regime are observed to be described by power-law relationships, and the scaling symbol, reflects this mathematical fact. 

The van t Hoff Law for osmotic pressure (Equation 5.19) depends explicitly on the molecular weight of the solute. One of the most remarkable properties of semidilute solutions is that the osmotic pressure is observed to be independent of the molecular weight of the macromolecules. Another property fliat is observed to be independent of molecular weight in semidilute solution is the mutual-diffusion coefficient, DJ c). These phenomena are discussed in Section 6.2 and explained in more detail in Section 6.3. 

The universal behavior of many properties in semidilute solution has been explained by deGennes. He propos that there is a universal length in this concentration range that depends only on the polymer concentration and the nature of the polymer-solvent interactions. The deGennes theory of semidilute solutions is presented in Section 6.3 and used to explain many observed features of these systems. 

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Chapter six Structure and properties of polymers in semidilute solution 77... 

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