MICROVISCOSITY OF AQUEOUS DEXTRAN SOLUTIONS INVESTIGATED BY SQUARE-WAVE POLAROGRAPHY

The polarographic method of measuring microviscosity in aqueous solutions of polymers was applied to dextran solutions (MW 20 000 to 150 000). The diffusing species - T1+ ions, have already been shown to be an excellent microviscosity probe in the investigation of polyethyleneglycol solutions. At low concentrations of dextrans, the microviscosity is much lower than the macroviscosity measured conventionally. The polarographically measured microviscosities, when compared to the macroviscosity, were used to determine several characteristics of the state of dextran molecules of different molecular weight, and their variation with concentration of the polymer. Values of characteristic concentrations, marking dramatic changes of the structure of the solution as well as coil parameters of dextran were thus determined. The experimental critical concentration, limiting the zone of microviscosity, was found to be close to the theoretical value. This, and other parameters not previously available by experiment, contribute to the better understanding of the structure of polymer solutions and permit comparisons between different polymers. © 1979.