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

Rheological properties of dextran solutions in 1-butyl-3-methylimidazolium acetate were examined up to the concentration (c) of 4.1 x 10(2) kgm(-3). A high molecular weight (approximate to 2 x 10(6)) 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 x 10(2) kgm(-3). In fact the plateau modulus (G(N)(0)) was obtained from the G' and G '' curves for c >= 2.6 x 10(2) 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 x 10(4), 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.