Viscometric study of mixtures of neutral and charged polymers in aqueous solution

The viscosity behaviour of aqueous mixtures formed by a polyelectrolyte (A) and a neutral polymer (B) such as polystyrene sulfonate (PSS)-polyvinylpyrrolidone (PVP) and polylysine (PLL)-PVP has been studied at 25 degrees C. The intrinsic viscosity and viscosity interaction parameter of each polymer in water have been determined and have served us to estimate the compatibility of the different mixtures according to two different methodologies: (i) mixtures of two polymers in water as solvent and (ii) mixtures of either polymer A or B in a solvent formed by either polymer B or A in water ("polymer solvent method"). By comparing the experimental and theoretical viscosity data it is clearly seen that: mixtures of both polymers in water do not depict any kind of thermodynamic interaction; whereas mixtures formed by a polyelectrolyte in water + neutral polymer as solvent exhibit incompatibility and, on the other hand, ternary systems formed by the neutral polymer (PVP) in a polyelectrolyte solvent show compatibility. The viscosity results show that the compatibility behaviour depends on the concentration ratio of both polymers in the mixture. Finally, an attempt to establish reference systems has been made. (C) 1997 Elsevier Science Ltd.