The rheopectic behavior of sacran aqueous solutions, a natural giant molecular polysaccharide with a molecular weight of 1.6 × 10⁷ g/mol, was investigated. When a low shear was applied to 1.0 wt.% sacran solution, the shear viscosity increased from 7.2 to 34 Pa·s. The increment in the viscosity was enhanced as the shear rate decreased. The shear viscosity was independent of the time at a shear rate of 0.8 s⁻¹; simultaneously, thixotropic behavior was observed at shear rates higher than 1.0 s⁻¹. A crossover was observed at 0.15 wt.% for the concentration dependence of both the viscosity increase and zeta potential, which was the vicinity of the helix transition concentration or gelation concentration. It was clear that the molecular mechanism for the rheopexy was different at lower and higher regions of the crossover concentration.

We have detected second-order nonlinear optical response from an amphoteric mega-saccharides named sacran under a needle/ring electrode stimulus by using an optical second harmonic generation (SHG) microscope. SHG was observed from sacran in the neighborhood of the negatively biased needle electrode below −4.5 V with respect to the outer ring electrode. From the incident light polarization dependence of SHG, this sacran was suggested to be oriented toward the electrode needle. SHG of the sacran polymer was judged to be induced by sacran aggregates with net positive charge.