Anomalous viscosity behavior of polymer solutions at very low concentrations

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Abstract
Recently, it was reported by many authors that polymer solutions display a peculiar anomaly in their viscosity behavior at very low concentrations. In order to explain this phenomenon, the expansion of the polymer coils with dilution has been taken into account. Krigbaum, in his fine calculation of molecular sizes at finite polymer concentrations, indicated that the unperturbed configuration is rapidly approached as the concentration is increased. His result is utilized in this paper to obtain the theoretical ηsp/c vs. c curve. It is assumed that a modified Huggins' formula is valid for a conveniently defined [η], which varies with concentration in accordance with the Krigbaum theory. The upswing of the ηsp/c vs. c curves, observed frequently at very low concentrations, can be predicted from theory. Moreover, this treatment seems capable of accounting for the influence of molecular weight of the polymer and of the solvent type upon the observed viscosity behavior. Before a conclusion is drawn, however, the experimental difficulties in working with very dilute solutions must be carefully considered. Several points which still require clarification are also discussed briefly.