Rheology of Tightly Entangled DNA Aqueous Solutions

抄録

The viscoelastic properties of entangled DNA solutions covering the loosely to the tightly entangled region were investigated. Dynamic birefringence measurements found that the stress-optical rule held for the solutions with c < 15 mg/ mL while above this concentration, the rule did not. This result indicates that the curvature mode contributes to the rubbery plateau modulus at high concentrations, which is characteristic of a tightly entangled system where the entanglement length becomes smaller than the Kuhn length. The nonlinear viscoelasticity of the tightly entangled system was also discussed. In the loosely entangled region, the steady-state viscosity follows the Cox-Merz rule. In contrast, the shear rate dependence of the steady-state viscosity became more significant in the tightly entangled region, and the nonlinearity increased with increasing concentration. Stress overshoot was commonly observed in the viscosity growth function at high shear rates. The maximum strain, γ_m, determined from the shear stress maximum, was observed at γ_m = 2 in the loosely entangled system, according to the behavior of ordinary flexible polymers. On the other hand, in the tightly entangled region, γ_m became smaller as the concentration increased.