Structure of the Scleroglucan Biopolymer in Aqueous Solutions of Inorganic Salts and Ionic Liquids

The effect of inorganic salts and ionic liquids (ILs) on the solution properties of scleroglucan (SG), an increasingly used and researched natural biopolymer, is reported here. Various rheological, electrophoretic, and small-angle X-ray scattering experiments were carried out to assess rheological and charge-related features, as well as the characteristic transitions in terms of the system's viscoelastic and structural features were unambiguously determined. The SG solution shows pseudoplastic properties at moderate polymer concentrations. Multivalent metal ions tend to stabilize the strong elastic character of the pseudoplastic SG solutions even at elevated salt concentrations relevant to many SG applications due to the specific interactions with the polymer chains. The affinity of the metal ions to the SG chains followed the calcium-(II) > magnesium-(II) > sodium-(I) order, which was reflected in different charge values at the same salt concentrations. The coherent structure of the SG was interrupted at high monovalent salt concentrations and was recovered by adding imidazolium-based ILs (C2-mimCl and C4-mimCl) of different alkyl chain lengths. These results shed light on the importance of chemical additives to alter the pseudoplastic and viscoelastic features of the studied SG solutions, which makes such biopolymers promising candidates in applications where high-viscosity samples with distinct viscoelastic character are needed.