[Negative Thixotropic Behavior for Sacran Aqueous Solutions].

We investigated the electric and viscoelastic properties for the aqueous solution of cyanobacterial megamolecules, named sacran. Sacran is an anionic polyelectrolyte that has carboxylate and sulfate groups on the saccharide chain. The electric conductivity and shear viscosity demonstrated three crossover concentrations; overlap concentration at 0.004 wt%, entanglement concentration at 0.02 wt%, and gelation concentration at 0.1 wt%. The decrease in the charge density of the sacran chains reduces the repulsive force between the chains and this would cause transformation from the dilute to condensed states. At extremely low flow rates, sacran demonstrated a behavior called negative thixotropy in which the shear viscosity increased over time. In this review, the conformation of sacran chain in pure water is discussed and its negative thixotropy is briefly described.