Diffusion Coefficient for Non-Theta Solutions

In a good solvent, polymer coils expand, increasing the effective molecular radius, which results in a lowering of the diffusion coefficient. Coil expansion is usually expressed as follows [see Eq. (8.6.14)]  

Because dilute polymer solutions are encountered more frequently than infinitely dilute solutions, we need to be able to predict the diflusivity of dilute solutions as well. The diffusion coefficient in a solution having a mass concentration of polymer equal to p can be written in series form as follows [42]  

In the preceding discussion, b, and u can be obtained from density measurements, A2 is available in the literature for many polymer-solvent pairs, and can be estimated by the procedines suggested by Vrentas and Ehida [42]. 

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