Viscometric evidence of critical concentration in dilute polymer solution

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Abstract
Two viscometric methods have been developed for detecting the “critical concentration” (the concentration at which individual polymer molecules interfere with each other) of a dilute solution of a high polymer, B. In the first of these, the intrinsic viscosity, [η], of another polymer, A, is measured in a series of mixed solvents, each consisting of a solution of Polymer B in the solvent S, and each differing from the others only in the concentration of B (CB). For a number of polymer‐polymer‐solvent systems, data are presented which show that [η] is essentially independent of CB, except over a small range where its value changes fairly abruptly. This change marks the critical concentration. The second method is much faster but probably less reliable than the first. Nevertheless, the two gave values in good agreement. A method of calculating the critical concentration, based on the Flory‐Fox theory of intrinsic viscosity, is described. Critical concentrations calculated for the several systems investigated agreed well with those obtained experimentally. The critical concentration was shown to be inversely proportional to the intrinsic viscosity of the Polymer B in experiments in which [η]B was varied by changing the molecular weight of the polymer and by changing the solvent. The effects observed are explained as resulting from interactions of the two polymer species in the solutions.