Aqueous solutions of amphiphilic polysaccharides: Concentration and temperature effect on viscosity

Amphiphilic polymers have been prepared by chemical modification of a neutral bacterial polysaccharide, dextran, consisting of α-1,6 linked glucose units. Various amounts of aliphatic hydrocarbon groups with six carbon atoms are attached along the dextran chains by ether links. The viscosities of their aqueous solutions in the dilute domain and in the beginning of the semi-dilute domain are considered with particular interest for the variation with temperature and polymer concentration. The equations of Fedors and Martin are shown to conveniently depict the effect of polymer concentration over the whole investigated range. A semi-empirical equation is established between the critical concentration deduced from Fedors equation and both the Huggins coefficient and the intrinsic viscosity (parameters deduced from the results in the dilute domain). The variation of solution viscosity with temperature is also examined. Andrade equation, combined with Martin or Fedors equation, is shown to account for the temperature effect. Particularly, the variation of the activation energy with polymer concentration is conveniently depicted. The validity of the derived semi-empirical equations is extended to other polymer solutions using literature data.