Intrinsic viscosities of polyelectrolytes in the absence and in the presence of extra salt: Consequences of the stepwise conversion of dextran into a polycation

Viscosities of dilute polymer solutions were measured in capillary viscometers for samples varying in their fraction f of charged units from 0.00 to 0.90. The dependence of the logarithm of the relative viscosity on polymer concentration c is in all cases reproduced quantitatively by three characteristic parameters: [η], the intrinsic viscosity; B, a viscometric interaction parameter (related to the Huggins constant); [η], a parameter required only for polyelectrolytes at low concentrations of extra salt. In pure water [η] increases more than 80 times as the fraction f rises from zero to 0.90 and [η] starts from zero and goes up to ≈71 mL/g. Upon the addition of NaCl [η] decreases by at least one order of magnitude (depending on the value of f). The observed dependences of log [η] on log csalt can be modeled quantitatively by Boltzmann sigmoids.