Polymer Solutions in Good Solvent Excluded Volume Effect

The relation (1 10) leads to a number of interesting consequences. In a theta solvent, in which the shape of the chain is described by the random flight model, S2 is proportional to M2, so that the intrinsic viscosity should be proportional to M /2. And this prediction has been applied and verified. In solvent media better than 0-solvents, the theory of Flory [11,46] predicts that the linear expansion factor a increases for any polymer - homologous series with chain length. Thus the exponent v in the empirical equation should be larger than 0.50. 

2 Polymer Solutions in Good Solvent Excluded Volume Effect 

If we suppose a very dilute gas of random flight chains. As a result of thermal rotation of chain segments each chain will take up a great number of conformations, with a very short interval of time being spent for the passage from one conformation to another. In so doing, it automatically avoids taking those conformations in which 

In a good solvent, the segment - solvent interaction tends to pull a pair of segments apart, so that the solvent - mediated force F should be repulsive as is F. On the other hand, F should be attractive in poor solvents. Hence, as the solvent is made poorer by changing either solvent species or temperature, the situation should be reached in which the attractive F cancels or suppresses the repulsive F so that the net force F + F becomes zero or even negative. 

What it is concerned with in the physics of polymer systems is not their physical properties for individual polymer conformations but those averaged over the ensemble n of such conformations under given conditions of polymer and solvent. For flexible polymers the averages depend primarily on the strength of the net interaction force F + F and the number of segments contained in the chain. Knowledge of F and F is essential for the understanding of polymers in solution. 

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