Scaling Laws in Polysaccharide Rheology: Comparative Analysis of Water and Ionic Liquid Systems

This study investigates the rheological behavior of two plant-based polysaccharides, with different degrees of hydrophilicity, agar (highly hydrophilic) and guar gum (hydrophilic), in water and 1-ethyl-3-methylimidazolium acetate (EMImAc). The rheological response of these polymers is highly dependent on the solvent's ability to disrupt intermolecular associations. In water, agar forms hydrogels, while guar gum behaves as a viscoelastic liquid with slow modes. The plateau modulus (G_N⁰) scales with polymer concentration (c) as G_N⁰ ∼ c³, consistent with other natural polymers. In EMImAc, both polysaccharides form viscoelastic liquids, exhibiting G_N⁰ ∼ c^2.3, as expected for semiflexible polymer solutions. However, the terminal relaxation time, τ_D, and the specific viscosity, η_sp, scale as τ_D ∼ c^5.3 and η_sp ∼ c^7.6, indicative of intermolecular chain-chain associations. Despite the solvent or polysaccharide, the fractional viscosity overshoot and the shear strain at the maximum stress show a terminal Weissenberg number dependence similar to other synthetic polymers.