Influence of Ion Exchange on Size and Shape of Chain-like Polyelectrolyte Molecules

Abstract

ON conversion of the sodium salt of alginic acid (poly-d-manuronic acid) into the magnesium salt, a marked alteration of molecular weight and viscosity properties takes place, as shown by the figures in Table 1. The molecular weights were determined by light scattering and refractivity measurements (λ = 536 and 446 mµ, angular scattering dependence, in some tests, between 135 and 25°, 19 angles), and the viscosities were measured in Flory and Couette viscometers, the rate of shear being varied from 0.4 to 2,500 sec.⁻¹. In most experiments the solvent was an unbuffered aqueous solution of, respectively, 0.100 M sodium chloride and 0.0200 M magnesium chloride, pH about 5, but some of the viscosity tests were also made in solutions of different ionic strength and in the presence of sodium or magnesium veronal buffers, pH = 7.43.