Shear-induced structure in enzymatically-synthesized dextran solutions

Abstract

A number of dextran derivatives and low molecular weight dextrans have found outlets in different fields such as fine chemistry and pharmaceutical industry, whereas only a few native (high molecular weight) dextrans have found applications. Thus, theoretical studies have scarcely concerned the rheological properties of native dextran solutions. Among the different synthesis processes, only the enzymaticin vitro synthesis produces a pure dextran, thereby allowing the rheological behavior of dextran solutions to be interpreted in terms of molecular considerations.

The shear viscosity curve reveals an irreversible threshold-type shear thickening at a specific critical shear rate$\dot \gamma *$. The value of$\dot \gamma *$ depends on the temperature of experiments and on the dextran concentration. Transient experiments give a description of the shear-thickening as a function of time and allows us to study the effect of several parameters (temperature, solvents, etc.). The shear stress growth, during the structure formation, is made of two different kinetics: the first one depends strongly on the molecular conformation; the second one is the result of intermolecular interactions of the hydrogen-type bonds.