The effect of solvent and ions on the structure and rheological propertiesof guar solutions

We study the effect of isopropyl alcohol (IPA) and various salts (sodium ch loride, sodium thiocyanate, sodium carbonate, and urea) on the rheological behavior and the conformation of aqueous guar solutions. Ultralow angle lig ht scattering, conventional light scattering, and neutron scattering are us ed to probe the structure of guar over length scales spanning 5 decades, fr om a few angstroms to several tens of microns. Although both IPA and salts worsen solvent conditions, their effect is very different. Isopropyl alcoho l promotes the formation of a network of large-scale structures via intermo lecular associations, thus increasing dramatically the elastic response of guar solutions. Salts. on the contrary, affects guar on a local scale, lead ing to a more collapsed chain configuration, thus to a lower effective volu me fraction and to reduced viscosity.