Viscoelastic Properties of Dilute Aqueous Solutions of Carbohydrate

Abstract

The viscoelastic properties of dilute aqueous solutions of sodium alginate at ultrasonic frequencies were investigated by means of a torsional method with crystal resonators. The new type resonators such as a huge crystal resonator and a jointed resonator used in this study enabled us to cover the frequency range from 26KHz to 131KHz.In order to examine the configuration of carbohydrate in an aqueous solution, the complex intrinsic rigidity which was obtained from the present data by extrapolation to zero concentration was quantitatively compared with those obtainable from the existing molecular theories at infinite dilution. In this study, the concentration dependence of the normalized loss shear moduli was found to be non-linear, so that Fuoss-Strauss equation was used to obtain the intrinsic values.In an aqueous solution of sodium alginate which is assumed to take a "stringlike" configuration, the measured values and their frequency dependences could not be predicted by any of the existing theories. However, with the addition of NaCl, the experimental values approached the theoretical curves given by the Kirkwood's theory for "rodlike" polymer. It was supposed that some electrostatic structures, which can be dissociated with the addition of urea, were formed in the presence of NaCl.