The effect of ionic strength on the viscosity of sodium alginate solution

The viscosities of aqueous sodium alginate solutions were measured in different NaCl concentrations (Q,) at 298 K. Based on the Odijk-Skolnick-Fixman theories, the electrostatic persistence lengths were calculated for various ionic strengths. The intrinsic persistence length of sodium alginate in solution was determined to be 125 by the method suggested by Odijk. In the region of C-S(-1/2) > 6.5, the increase in intrinsic viscosity, [eta], for sodium alginate on decreasing the C-s is due to the larger contribution of electrostatic persistence length to the total persistence length, and the departure Of [eta](calc) from is attributed to the variation of the Flory Phi constant with ionic strength. A peak was observed in the plot of reduced viscosity v. sodium alginate concentration at a constant low ionic strength. As in the treatment of Rinaudo et al., this maximum in reduced viscosity is attributed to a preferential intermolecular distance. The roles of electrostatic persistence length, the critical inter-rod spacing and the effect of added salt concentration on this maximum are discussed. Copyright (C) 2001 John Wiley Sons, Ltd.