Dextran–rare earth ion interactions. I. Dynamics in aqueous solutions



The interaction of light-lanthanoid cations (La3+, Ce3+, and Nd3+) with dextran in aqueous solutions was studied by viscosimetric, turbidimetric, and conductimetric methods. The effects of the type of the cation and the concentration of the cation on the interaction mechanism were investigated. Viscosity behavior of the solutions was interpreted using the Huggins and Kraemer equations; intrinsic viscosities and the slopes were calculated. The results found from the Huggins and Kraemer approaches accorded well. The order of interaction was determined as La3+ > Ce3+ > Nd3+. In all experimental methods applied, a critical concentration of the Ln3+ ion (≈0.08 mol Ln3+/L) was noted at which the observed property showed a significant change. Up to this critical concentration, viscosities of the dextran/Ln3+ solutions decreased and after making an outstanding turn at this point increased toward higher concentrations. Turbidimetric and precipitation experiments gave opposite results as expected but the same order for the cation and the same value of critical concentration. The results obtained from the application of a mathematical model to the precipitation data verified the conclusions attained by viscosimetry and conductimetry. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 323–329, 2001