Solution properties of sodium alginate

Abstract

Abstract Sodium alginate fractions derived from three different sources— Laminaria hyperboria (75% guluronate), Fucus vesicularus (95% mannuronate), and Azotobacter vinelandii (85% mannuronate)—were investigated in aqueous solution over a wide range of ionic strength and pH using the techniques of light scattering, viscometry, and osmometry. Light‐scattering data extrapolated to infinite ionic strength yielded b 0 = 4.7 ± 0.3 and 3.0 ± 0.2 nm for the unperturbed effective bond lengths of the guluronate‐ and mannuronate‐rich samples, respectively. These values are in the same ratio as predicted by conformational analysis, although lower by a factor of 0.7, probably due, in part at least, to the fact that measurements cannot be made on pure homopolymers. A comparison of the light‐scattering and the viscosity data indicated that Φ in the Flory‐Fox equation is lower than for more flexible polymers and increases with molecular weight, probably due to decreasing hydrodynamic permeability. Mark‐Houwink exponents obtained from data extrapolated to infinite ionic strength were found to be considerably greater than 0.5, and we attribute this entirely to a variation in Φ. Comparison of the results obtained for the two mannuronate‐rich samples indicated that the value of Φ and its variation with molecular weight can, in the case of alginates, differ markedly for chains, which, although having chemical differences, have similar chain statistics.