Hydrophobically ethoxylated modified urethane (HEUR) form the flower micelles and transient network structures through the aggregation of end groups depending on the polymer concentration. The HEUR networks show the viscoelastic relaxation which is described by the Maxwell model. Although there have been many attempts to understand and predict the molecular mechanism, the full understanding remains incomplete. To understand the relaxation mechanism of associative polymers, we measured the linear viscoelasticity and the diffusibility using the fluorescence recovery after photobleaching method. With increasing the polymer concentration, the self-diffusion coefficient decreased, while the relaxation time increased, suggesting that the viscoelastic relaxation is correlated with the diffusion of the polymers. The calculated diffusion distance of the HEUR chains within the viscoelastic relaxation time is 100 times larger than the size of a HEUR chain. This significant deviation suggests that some of the HEUR chains diffuse quickly through the unimer and flower micelles at low concentrations and through the recombination process of the network strands at high concentrations.
The overdamped (inertialess) dumbbell model is widely utilized to study rheological properties of polymers or other soft matters. In most cases, the effect of inertia is merely neglected because the momentum relaxation is much faster than the bond relaxation. We theoretically analyze the effect of inertia on the linear viscoelasticity of the harmonic dumbbell model. We show that the momentum and bond relaxation modes are kinetically coupled and the inertia can affect the bond relaxation if the momentum relaxation is not sufficiently fast. We derive an overdamped Langevin equation for the dumbbell model, which incorporates the weak inertia effect. Our model predicts the bond relaxation dynamics with the weak inertia effect correctly. We discuss how the weak inertia affects the linear viscoelasticity of a simple harmonic dumbbell model and the Rouse model.
Rheological properties of dextran solutions in 1-butyl-3-methylimidazolium acetate were examined up to the concentration (c) of 4.1 × 102 kgm−3. A high molecular weight (≈ 2 × 106) dextran with a degree of divergence of 4 % was used. The zero-shear viscosity estimated from the flow behavior indicated that dextran chains in the solutions entangle each other at c ≥ 1.7 × 102 kgm−3. In fact the plateau modulus (GN0) was obtained from the G′ and G″ curves for c ≥ 2.6 × 102 kgm−3. However, the anomalous results were obtained regarding entanglement of dextran chains: The molecular weight between entanglements was constant against c at 2.3 × 104, so that a large number of entanglements per chain was expected in spite of the subtle rubbery plateau that was actually observed. It was proposed that the dextran has the main structure of long branches and each branch is densely sub-branched.