Rheological Properties of Concentrated Solutions of a Branched Polysaccharide Dextran in an Ionic Liquid

Abstract

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 (G_N⁰) 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.