Characteristic numbers of polymers in dilute solution : a universal description of the cross-over effects

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Abstract
The viscosimetric behaviour of eleven polymer-solvent systems is analysed in order to determine the characteristic numbers in the beginning and in the end of the cross-over region. In the beginning we have a cross-over between Gaussian and excluded volume behaviour and in the end a cross-over between partial excluded-volume and complete excluded-volume behaviour (in the second cross-over the chain exhibits an excluded volume statistics on a macroscopic scale and starts the linearity between log [η ] and log M). We show that in the beginning and in the end of the cross-over region the characteristic molecular weight or the characteristic number of monomers is different for different polymers and the second is related to the stiffness of the chain. In the contrary, the characteristic number of statistical segments in the beginning and in the end of the cross-over region are about the same for all the polymers, and this result confirms the validity of a universal description of polymer solutions