Polyelectrolyte behaviour of dilute xanthan solutions: Salt effects on extensional rheology

The flow behaviour of xanthan, a biological polyelectrolyte, has widely been reported to be complex, and unlike that of synthetic polyelectrolytes. Most studies have been confined to xanthan concentrations above 0.02% w/w. Using a highly sensitive opposed-jets technique, we have now measured salt concentration effects on the extensional flow behaviour of xanthan in aqueous solution at a concentration of 0.01% w/w. At this low concentration xanthan behaves precisely as expected for a 'normal' polyelectrolyte, collapsing from an extended worm-like conformation to a more compact coil. We suggest that the behaviour at higher xanthan concentrations arises from a disorder-order transition due to intermolecular effects. Copyright (C) 1996 Elsevier Science Ltd.