Origins of polysaccharide conformation and viscoelasticity in miscible heterogeneous solvent

Abstract

Polysaccharide polymers constitute the fundamental building blocks of life and display a diverse set of conformational states which results in complex viscoelastic behaviour of their solutions; the origins of which needs further understanding. Utilising a model high molecular weight, high Trouton ratio ‘pectin’ polysaccharide extracted from okra (Abelmoschus esculentus) mucilage, we combine computer simulations and experimental data to unveil the underlying microscopic hydrodynamic origins of polysaccharide conformation. In miscible heterogenous solvents of water and glycerol, the polysaccharide chain undergoes a conformational transition from swelled-to-collapsed configurations, resulting in marked viscoelastic response. The conformational transition is entropy driven. Molecularly adsorbed water molecules have increased presence within ca. 0.40 nm of the chain surface with increase of glycerol in the solvent composition, thus indicating the emergence of preferential solvation. This preferential solvation elicits an entropically unfavourable dynamic solvent heterogeneity, which is lessened by swelling and collapse of polysaccharide chains. Altering the preferential solvation layer by adjusting solvent composition allows for precise control of chain conformation and viscoelastic parameters. Our results provide an essential missing piece of the puzzle that is inaccessible through mean-field assumptions and offer new fundamental insights applicable in biological, biomedical, and engineering applications, including microrheological flows, microfluidics, bio-inkjet printing, as well as in pharmacological and food formulations.