Andreja Zupančič and Miha Žumer
University of Ljubljana, Faculty of Chemistry and Chemical Technology, Aškerčeva 5, 1001 Ljubljana, Slovenia
Rheological characterization of polymer solutions and polymer dispersions deals with wide range of mechanical responses. Flow behaviour and especially the viscoelastic properties of aqueous dispersions of hydrophilic bio-polymers: welan, gellan, and carboxymethyl cellulose were examined at low polymer concentrations. Different types of rheological responses were achieved by varying polymer concentration and by preparing different mixtures of the polymers at various mutual ratios. Dispersions of polymer blends were prepared at constant overall polymer concentration. These systems were prepared in order to study the influence of different structural conditions of the samples on rheological properties. The transition from sol-to-gel behaviour was achieved by changing the polymer concentration, or by changing the composition at constant polymer concentration. The viscoelastic properties of the systems were measured under non-destructive shear conditions of oscillatory shear, by using the controlled stress rheometer. The analysis of experimental data was performed by using the generalized Maxwell model and the Friedrich - Braun model for describing the mechanical spectra in linear viscoelastic regime.