Rheological properties of aqueous solution of new exopolysaccharide secreted by a deep-sea mesophilic bacterium

The rheological properties, such as shear flow behavior, thixotropy and viscoelasticity, of aqueous solution of a new type of exopolysaccharide (SM-A87 EPS) secreted by a deep-sea mesophilic bacterium were investigated using shear flow and dynamic rheological measurements. For the SM-A87 EPS solutions, the overlapping concentration C* and crossover concentration C** were confirmed to be 0.95 g/L and 4.99 g/L respectively by the concentration-dependences of rheological parameters, such as equilibrium viscosity, thixotropic strength, static and dynamic stress, critical shear rate, and storage modulus in the linear viscoelastic region besides the zero-shear viscosity of solutions. At concentrations higher than C*, the solutions exhibited a static stress, a dominant elastic behavior and a stronger absolute positive thixotropic strength. Otherwise, at concentrations lower than C*, no static stress, a dominant viscous behavior and a weaker absolute positive thixotropic strength were exhibited. The SM-A87 EPS solutions may be used as enhanced oil recovery system.