A rheological study of the order-disorder conformational transition of xanthan gum

The rheological properties of a moderately concentrated solution of xanthan gain in both the ordered and the disordered state have been studied. Oscil latory shear, steady shear flow, and extensional flow experiments have been performed at different temperatures, covering the order-disorder transitio n determined by differential scanning calorimetry (DSC). The principle of t ime/temperature superposition iras applied to the xanthan solutions for the different types of flow Although a master curve covering six decades of fr equency could be obtained for the storage modulus over the entire investiga ted temperature range, less agreement was found for the other modulus. This indicates that the order-disorder transition reflects changes on the molec ular scale and slight modification of the physical network structure. To th e authors' knowledge, this is the first tinge that this transition has been observed using these different rheological techniques. (C) 2001 John Wiley & Sons, Inc.