Uncovering the effect of molecular structure on the rheology of welan gum by viscoelastic characterization, density functional theory and molecular dynamics simulation

The heteropolysaccharide of welan gum has been widely utilized as a rheological modifier in various industrial fields due to its high viscosity and robust tolerance towards shear, temperature, pH, and salinity. However, the research on its solution rheology is inadequate, particularly regarding the impact of its chemical structure on solution properties. Herein, we investigate the rheology of three welan samples with different substitution patterns at concentrations ranging from 0.5% to 2.0%. The impact of side group type, content, and molecular size on flow behavior, dynamic viscoelasticity, thixotropy, and yield behavior is elucidated. Welan gum with mannose side groups exhibits characteristics of a thixotropic yield stress fluid with the highest viscosity, viscoelasticity, thixotropy, and yield stress. In contrast, the other two welan gums lacking mannose substituents display only weak thixotropy and low yield stress at higher concentrations. The creep and stress bifurcation tests have demonstrated that the solid-liquid transition of welan gum with mannose side groups depends on the magnitude and duration of applied stress, which can be interpreted through two critical stress values. The rheological properties of welan gum are influenced by its fine structure and molecular size in combination. In addition, density functional theory calculations and molecular dynamics simulations have further provided insight into the fine structure-function relationship of welan gum, indicating that monosaccharide side groups increase molecular polarity and enhance hydrogen bonding. This work provides a fundamental understanding of the structure-function relationship of welan gum for tailoring its versatile applications.